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SPONGE AND FAUNAL ASSOCIATION OF THE BRITTLE STAR O PHIOTHRIX SUENONII (ECHINODERMATA) AT CAYOS COCHINOS, HONDURA S AND THE FEEDING POSTURES AND GENERAL BEHAVIORS OF MARIAMETR ID FEATHER STARS (ECHINODERMATA) ( IN VIVO ) BY STEPHANIE SHERMAN A Thesis Submitted to the Division of Natural Sciences New College of Florida In partial fulfillment of the requirements for the degree of Bachelor Arts Under the Sponsorship of Dr. Sandra Gilchrist Sarasota, Florida May 2001
Acknowledgements This research was founded by the New College Resear ch and Travel Grant. I would like to thank my sponsor, Dr. Sandra Gilchrist, for her support and guidance throughout my thesis process, Dr. Leo Demski and Dr Elzie McCord, for their support and criticism, and Dr. David Meyer and Dr. Charles Messing, for their expertise and invaluable help with my many crinoid questions. I would also like to thank my parents, Irene and Mi chael Sherman, for all their support over the years, my New College family, for being an inspirational force unlike any other, and a special thanks to Geoff, for always being the re.
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LIST OF FIGURES % Suspension feeding crinoids and ophiuroids '%': Echinoderm Tree %: Depiction of Ancient Crinoids and Blastoids %: Dense bed of fossilized stalked crinoids *%* The clades of Crinoidea 1%1 Pentacrinoid vs. young feather star of Oxycomanthus japonicas.%.The phylogenetic relationship between extant crinoi d families8%8 A plate drawing of examples of color diversity in comatulid species%3Anatomy of the sea lily, Neocrinus decorus %4: Close up of oral pinnules and ambulacra surroundi ng the mouth of Brown Mariametrid. *%Arm branching of a young feather star during develo pment.%': Diagram of the comatulid mouth and surrounding an atomy8%The crinoid arm, pinnule, and tube feet 8%: Diagram of the pinnule: triad of tube feet, food groove, and lappets3%* a and b: ( a ) A plate drawing of a Mariametrid comatulid exhibi ting the "bull's eye" display and two color variations of L. palmata '%1Amazingly-colored feather stars '%.: Ophiuroid anatomy '%87Photos of Crinoid Associates '8%3a and b: The arrow crab Stenorhynchus seticornis on the Caribbean crinoid, Davidaster rubiginosa, with which it regularly associate and near the Urch in Diadema antillarum '8%'4: Crinoid Clingfish Discotrema crinophilia '3%'C. melops attacking the pinnules of A. bifida in vivo'%''a and b: C. ephippium and L. nebulosus
%'%' C. micans and a diagram depicting an Isocrinid fleeing from a cidaroid urchin *%'*a and b: O. suensonii individuals on C. vaginalis and color variations of O. suenonii .%'1: A. fiordensis on A. constrictum 3%'.: O. cacaotica of similar color on its feather star host, T. catinata%'8: N. grandis exposed and feeding perch during midday%'3: Arm waving and recovery stoke by the crinoid Endoxocrinus parrae1%4: Parallel flow streams around an element *4%: Mechanisms of Particle Capture for Suspension Fee ders*%'a and b: A triad tube feetand a cross-section of th e crinoid pinnule with triad of tube feet *%: Photo of grooves and diagram of Up and Downstream Capture*1%: The postures of comatulid crinoids 14%* a and b.: Arcuate fan exhibited by L. palamata form brachypecha and the radial fan 1%1 a and b: Parabolic fan in Endoxcrinus wyvillethomsoni ; Multi-directional posture of Nemaster grandis 1'%. a and b: 4 Row Pinnular Posture; Davidaster rubiginosa off the islands of Honduras, exhibiting the multi-directional of crypt ic species 1%8: Conical feeding of an aggregation F. serratissima1 *%3: Honduran mainland, Roatan, and the marked Hog Isl ands, or Cayos Cochinos .%4: Cayos Cochinos with cross-hatching indicated the bay of study.1%: Plantation Beach Bay, the research area ..%' a and b: Two tank formats 84% a and b: The Black Sea Rod, Plexaurella homomalla; the Bent Sea Rod, Plexaurella flexuosa with brittle stars clinging to its inner branches8'%a and b: Site 8, a grooved blade sea whip Pterogorgia guadalupensis8'
%* a to d: ( a) Gorgonia sp with three brittle stars, indicated by the arrows Note that the top two cling to Millepora alcicornis, a fire coral commonly associated with such gorgonians ( c and d ) The Pink Vase Sponge, Niphates digitalis8%1 a and b: Knobby Sea Rod, Eunicea spp. with the 5 total brittle stars.8%.: Brittle stars among M illeporta alicornis on a a Callyspongia vaginalis site8*%8 a and b: Comparative densities of brittle stars 8*%3: Brittle Star Count by Site Type 81%*4: a, b, and c: ( a ) Site 17 with the densest aggregation of brittle s tars and known predators. ( b ) The blue-headed T. bifasciatum male with the yellow female pictured below ( c ) Elacatinus spp. next to a C. vaginalis site 34%* a, b, and c: Fishes of O. suenonii sites 34%*'a and b: Gobies of the genus Elacatinus on C. vaginalis site 16, possibly the shark goby, E. evelynae 3%*a and b: ( a ) Elacatinus sp. and an unidentified fish, shown in a close-up ( b ). This fish quite possibly utilizes the sponge as she lter, versus being attracted by the brittle star. 3%*+-Coloration All Sites 3%**: Brittle Star Coloration Sponge Sites 3%*1: Brittle Star Coloration Dark Sites 3*%*.a and b: Brown and unusual moprh of O. suenonii3 1%*8 a and b: Yellow morph with the distinct Ophiothrix banding31%*3a, b, and c: ( a ) Grey Morph; ( b ) Brown and White Morph; (c) Purple and Orange Morph with orange legs and a distinctly purp le disc 3.%14 38%1a. and b: (a ) Unidetified anemone on the cirrus of the Oxymetra sp crinoid, seen as a small protrusion on the cirrus. ( b ) Dried worm on calyx and beginning of division series of L. palmata 4%1': Unidentified hydroid colony around the base of L. palmata form brachypecha 4%1: Close up of Hydroid under microscope, likely fill ed with brine nauplii4%1: Comparison of primary tube feet: Oxymetra sp. and L. palamata41
%1* a to d: L. palmata opening into feeding posture 48%11a and b: Irregular to arcuate fans with (b) showing the importance of strong, unidirectional flow for these organisms as they ori ented themselves immediately in front of the power heads 43%1. a and b: Arcuate fan exhibited by L. palamata form brachypecha; Radial fan exhibited by the unknown Mariametrid %18a and b: Oxymetra sp forming the Radial to Parabolic Fan as a function ally stalked crinoid '%13: Sketch of odd posture and its orientation to curr ent flow.'%.4a to c: Possible tester arms
SPONGE AND FAUNAL ASSOCIATION OF THE BRITTLE STAR O PHIOTHRIX SUENONII (ECHINODERMATA) AT CAYOS COCHINOS, HONDURA S AND THE FEEDING POSTURES AND GENERAL BEHAVIORS OF MARIAMETR ID FEATHER STARS (ECHINODERMATA) ( IN VIVO ) Stephanie M. Sherman New College of Florida, 2011 ABSTRACT Feather stars (Class: Crinoidea) and brittle stars (Class: Ophiuroidea) represent two classes of suspension-feeding echinoderms that are common to the reef environment. All crinoids are limited to suspension feeding, whi le ophiuroid brittle stars are capable of multiple feeding modes, including predation and dep osit feeding. The crinoid filter is composed of an array of arms held in distinct postu res that are dependent upon the species and ambient currents. Feeding postures in r esponse to current flow and general behaviors were observed in laboratory conditions fo r the following Indo-Pacific mariametrid crinoids: Lamprometra palmata (Mller, 1841), Lamprometra palamata (form brachypecha ), Oxymetra sp (Clark, 1909), and one unidentified Mariametrid. Specimens of Ophiothrix suenonii (Ltken, 1856), the sponge-dwelling brittle star, were studied in situ at the reef preserve of Cayos Cochinos, Honduras. The suspension and deposit feeding methods of this brit tle star allow it to inhabit such organisms as gorgonian sea fans, hydrocorals, and s ponges. This species shows a strong preference for the tube sponge, Callyspongia vaginalis (Lamarck, 1814) over all other available fauna. Ophiothrix suenonii occurred most frequently and in highest concentrations on this sponge and than all other su bstrate types occupied by the brittle
< star. The color morphs of O. suenonii were found to contrast their substrate for all sit e types. Dr. Sandra Gilchrist Division on Natural Sciences
nnCrinoids and ophiuroids represent an invaluable lin k in the reef ecosystem as suspension feeders. These echinoderms are capable o f consuming thousands of organisms while feeding. They reduce the trophic levels of co nsumption by directly capturing the minute organisms and particles that would otherwise need to be eaten by successively larger organisms. For the crinoids and ophiuroids, it is suspension feeding that creates the means for their close relationships with organisms of many taxa, such as the organisms to which crinoids play host and the sponges which host ophiuroids. Many aspects of their inter-relatedness are due to the feeding modes of f eeding of these organisms, both of which use suspension feeding. Brittle stars are commonly found on sea sponges (Ch avarro et al., 2004). The spongedwelling of the brittle star, Ophiothrix suensonii (Ltkem, 1856) facilitates this brittle stars methods of feeding. This mutually beneficial relationship between the organisms is promoted by the deposit feeding of the brittle star which clears the sponge surface while gaining its meal. The brittle star additionally ben efits from the elevated position provided by the sponge, exposing the ophiuroid to more ideal currents and an alternative food source for suspension feeding. The adaptability of the crinoid form to changes in current flow make them highly efficient filterers on the reef. Their feeding post ures, which are specialized for particular current flow, can give insight into the crinoid hab itat and ecological niche. Crinoids
' experience close relationships with a variety of ot her organisms, including ophiuroids. Suspension feeding crinoids provide a food source t hat their inhabitants would otherwise find unavailable. Many of these organisms are depen dent on the crinoid and form obligate relationships, some of which have existed for millions of years (Table 1). The overlap of niches of crinoid and brittle stars is well known and is in exhibited in many crinoid photographs, although the presence of accompanying ophiuroids is often unmentioned. Such overlap is illustrated in Fig. 1 a-c, the following photos, in which both crinoids and suspension-feeding ophiuroids exist. r a to c: Suspension feeding crinoids and ophiuroids ( a) An ophiuroid like of the Ophiothrix genus, with its arm extended, possibly for suspens ion feeding, while on a suspension feeding crinoid (Modified from Poppe & Poppe Conc hology, Inc. 1996-2011); ( b ) Suspension feeding white ophiuroid perched atop a gorgonian an d next to a yellow crinoid (Crum, 2008). (c) Ophiuroid clinging to the stalk of a crinoid (Baumi ller, 2008) In the present study, the filtering aspects of the crinoids as well as the filtration feeding aspects of sponges that possibly lend thems elves to the inhabiting by brittle stars are examined. The general aspects of the ecology of Ophiothrix suensonii were recorded in the field, while those of the crinoids were obse rved in the lab. The fact that these echinoderm classes share ecological niches and expe rience an overlap in habitat is
specifically seen with the suspension feeding of th e sympatric species of the feather star Antedon bifida and brittle star Ophiothrix fragilis (Nichols, 1996), which share the intertidal region of the same geographic area. The species covered in the present study include Lamprometra palmata, Oxymetra sp ., an unidentified species of the Mariametrid family (Echinodermata: Crinoidea), and Ophiothrix suensonii (Echinodermata: Ophiuroidea). rnThe two classes concerned with this study are the O phiuroidea and Crinoidea. The suspension feeding and additional ecological simila rities of these two organisms can be explained by their relatedness and shared anatomy. Both brittle stars and crinoids are a part of the larger group known as Echinoderms. The Phylum Echinodermata encompasses approximately 6,000 species (Jeng, 1998 ) belonging to the five extant classes: Asteroidea, Holothuroidea, Echinoidea, Oph iuroidea, and Crinoidea (Hickman, 1967), which are seen in Fig. 2. The Ophiuroids contain those organisms commonly kno wn as brittle stars (the Ophiurida), as well as their perhaps less commonly witnessed sisters, the basket stars and serpent stars (the Eurylida). The class Crinoidea i ncludes the feather stars (known as comatulid or un-stalked crinoids) and the sea lilie s (or stalked crinoids. The stalk of the sea lilies and the generally delicate, flower-like appearance of the crinoids give them their name, meaning lily-form.
r : Echinoderm Tree (Kondo, 2010) Their early evolutionary divergence from the rest o f Echinodermata took place approximately 450-590 million years ago around the Cambrian period (Pawson, 2007). Because the Crinoidea diverged first, their early b ranching makes them more of a sister group to the extant echinoderms and places them mor e closely related to the chordates (Pawson, 2007). r r : Depiction of Ancient Crinoids and Blastoids (Mars hall, 2004) Image from: http://www.marshalls-art.com/images/ipaleo/paleopg1 7/Crinoid_Blastoid.jpg
* The Crinoidea are the least studied of all the echi noderm classes (Rutman and Fishelson, 1984) and are the only extant group of t heir once numerous Subphylum Pelmatozoa. Crinoids are prevalent in the fossil re cord and likely originated in the Precambrian period (Hickman, 1967), however, fossil ized specimens were first noted in the Ordovician (Hess and Ausich, 1999 phide Kitazawa, et al., 2007). A dense bed of fossilized crinoids is shown in Figure 4. Ancient c rinoids are depicted in Figure 3. Impressively the Crinoidea exhibit 5,500-6,000 know n fossilized species (MacGinitie, 1968; Briemer and Lane, 1978); ten times more than that of the living species (Hendler, et al. 1995), all of which belong to the Subclass A rticulata -a group that has existed since the Triassic (Kitazawa, 2007). See Figure 5. The degree of preservation of fossilized crinoids has provided a unique look into the phylogeny of these echinoderms (Guensburg and Sprinkle, 2009) and fossilized crino ids are often compared to modern species to infer more about their form and function r : Dense bed of fossilized stalked crinoids (Gahn an d Baumiller, 2005)
1 Today, there are around 650 extant species of crino ids, the majority of them stalkless with the stalked crinoids numbering about 100 (Pawson, 2007). Overall the stalked crinoids should not be regarded as monophyletic, bu t as belonging to a mixed grouping of crinoids external to the stalk-less comatulids (Rou x, et al. 2002). These stalked orders or suborders include the following orders: Isocrinida, Millericrinida, and Cyrtocrinida, while the stalk-less crinoids are of a monophyletic linea ge, belonging to the Order Comatulida (Hickman, 1967). r The clades of Crinoidea (Ausich and Messing, 1998) Image from: http://tolweb.org/Crinoidea/19232/1998.04.21 The stalk-less, or comatulid, crinoids are the more recently-evolved form of extant crinoids and stem from stalked ancestors not unlike modern sea lilies (Meyer and Macurda, 1977). Aspects of their lineage can be wit nessed in the comatulid development during the pentacrinoid stage, which exhibits a pro nounced stalk that is subsequently lost
. by the end of development (Mladenov and Chia, 1983) Figure 6 b shows the stalked pentacrinoid stage of Hathrometra sarsi ( Duben & Koren, 1846) %1 a to c: ( a ) Pentacrinoid vs. young feather star of Oxycomanthus japonicas ( Mller,1841) (Shibata, 2008) Image from: http://www.coralscience.org/main/articles/developme nt-5/feather-stars ); ( b ) Pentacrinoid development: pentacrinoid, juvenile, a nd young feather star (modified from Holland and Kubota, 1975) Image form: http://picasaweb.google.com/lh/photo/Zu35h1DEBeETat wGNPhMUw ; ( c ) The pentacrinoid of H. sarsi ( 2010) Today there are eight modern crinoid families and t heir phylogeny is illustrated in Fig. 7 taken from McEdward and Miner (2001):
8 r The phylogenetic relationship between extant crinoi d families (McEdward and Miner, 2001) While an extensive record fossil record yields much information on the morphology of the ancient crinoids, knowledge on mo dern species, particularly concerning their ecological aspects and interaction s, is lacking. Limitations to our ability to study these organisms include the inaccessibilit y of deep water species, such as the sea lilies, as well as the fact that crinoids are among st the most difficult of the echinoderms to maintain in aquaria, and thus to study in vivo The delicate nature of crinoids additionally makes research challenging. Even tagging, a helpful method in the field to track crinoid movements pertaining to feeding, has proved difficu lt with their fragility (Vail, 1987). Many of the basic facts about these organisms were uncovered in the past century. Until the 1960s, some of the more elementary aspec ts of crinoids, including the means by which they receive their food particles, was mis understood (Meyer, 1984) by
3 observers. By the 1980s the belief that crinoids m ight be predator-free began to dissipate (Meyer, 1988). While modern research continues to reveal the exten t of their ecological importance, other factors function to further our k nowledge about these organisms. It is their difficult maintenance, delicate nature, and t heir lack of commercial importance (Hendler, et al., 1995) relative to other echinoder ms, or even other organisms, that have been significantly limiting factors to research. Cr inoids are not known as a major food source for organisms on the reef, nor are they part icularly edible to humans. Although beautiful, they are not an easy option for commerci al sale and are kept only by experienced aquarists because of their delicate nat ure in addition to their food and current flow requirements. In contrast to the more easily-k ept sea stars, for example, feather stars are an echinoderm less-readily held by suppliers of the pet and aquarium trades. The commercial importance of feather stars has, how ever, been growing within recent years with a rising interest in the aquarium Their striking appearance has popularized them both in aquaria and photography an d demand for them is on the rise. As comatulids are more regularly shipped to wholesaler s, they are gradually becoming more accessible to the public. Feather stars are frequen tly collected from the wild and transported worldwide for trade, being commonly imp orted from the Indo-Pacific region. Common families in the trade include Mariametridae, which are typically of the genus Lamprometra (Meyer, personal communication 2010). Despite their growing accessibility, feather stars are delicate organisms that are notoriously difficult to transport and the culturin g of feather stars is only a recent and
4 limited development (Shibata, 2008). When under str ess, feather stars will autotomize pinnules and portions of the arms, thus it is not u ncommon for shipments to be in poor shape upon arrival. For this reason, they can be co stly and are considerably lessaccessible than most organisms in the aquarium trad e. In addition to this, feather stars are also notoriously tricky to maintain in home aquaria as so little is known of their culturing conditions. They require specified current conditio ns for their feeding, as well as special foods that can be expensive or tricky to maintain i n ones home. Aquaculture is limited and not yet productive for c rinoids. Long-term culturing is not yet feasible, but success has been seen in the species Oxycomanthus japonicus from Japan. Oxycomanthus has been successfully raised to sexual maturity us ing cultures in a bay to provide the necessary nutrients that are not easy to maintain in aquaria (Shibata, 2008). Perhaps with methods such as this, feather s tars will be cheaper and more common in aquaria and thus more available for research.
r A plate drawing of examples of color diversity in comatulid species (Clark, 1921) !"#$%r&'r(#'$The habitat of living crinoids has an impressive sp an from the shallowest reefs to the deepest ocean floors. Stalked crinoids, once pr evalent in the shallow and ancient waters well before the Mesozoic, are in modern day often exposed to colder and deeper waters than the feather stars. This former crinoid group is restricted to waters deeper than one hundred meters (Oji, 1996) and thrive far deepe r, composing the crinoid species of the abyssal and hadal plains with a reach that exte nds to waters over 8,000 meters in depth (Jorgensen, 1966). When compared to the sea lilies, feather stars are better adapted to shallow-water living (Meyer and Macurda, 1977) and have thus beco me the more prevalent Crinoidea group to inhabit waters less than two hundred meter s (Briemer, 1978). Known worldwide from both deep and polar waters, they are frequentl y found in shallow, tropical waters,
' though rare in intertidal areas (Meyer et al., 1984 ; Nichols, 1994). In the shallow waters of the West Indies, they are common; however they a re composed only of about eight species and with maximum densities of about twenty individuals per square meter (Macurda and Meyer, 1976), far fewer species than t hose of the Indo-Pacific. In the shallow tropical waters of the Indo-Pacific, feathe r stars show a greater diversity and high population densities with around 120 species (Hendl er, et al., 1995) and, in some locales, up to 70 individuals a square meter (Fabricius, 199 4). Owing to the size of the IndoPacific region and inaccessibility of its islands, there is still much research to be done on crinoid species (Zmarzly, 1985). "#(#')The anatomical features of crinoids reveal the mean s by which crinoids perform crucial interactions with their environment. These features explain how parts of the crinoid body lend themselves to occupation by organ isms from numerous phyla or how current flow is manipulated by the crinoid form for ideal feeding conditions: both of which are examples of the intriguing aspects of the Crinoidea researched in the present study. Because of their early evolutionary divergence from the other Echinodermata, their form can be strikingly different from their o ther spiny-skinned cousins. The Crinoidea are the only echinoderms to retain the pr imitive feature of an upwards-facing, centered mouth, directed away from the substrate, ( Breimer, 1978), while sharing with the other echinoderms such characteristics as radia l symmetry. The prominent features of crinoids are illustrated in the below diagram: the arms, pinnules, cirri, and calyx.
Feather stars and sea lilies have much of their ana tomy in common and their differences have allowed us to accurately understan d their divergence from the ancestral echinodermal form (see Figure 9 a. and b.). The maj ority of the crinoid body is devoted to feeding and is predominantly composed of the arm s and pinnules with their respective (not shown) ambulacral systems and tube feet, all o f which composing the crown, or main body, of the crinoid. The ambulacra, which are the feeding tracts of the arms and pinnules, are lined with tube feet and lead to the mouth on the main body. See Figure 12. r* a and b: Anatomy of the sea lily, Neocrinus decorus (Thomson, 1864) (Baumiller, 2008); Comparative general anatomy of a stalked and comatu lid crinoid (Meyer and Macurda, 1977, originally from Clark, 1915 ) In figures 9 a and b the cup and calyx can be c onsidered synonymous All of the afore mentioned features rely on the sup port of the calyx and centrodorsal plate, an evolutionary remnant of the sea lilys stalk, to which it is homologous (Kitazawa et al., 2007). The centrodorsa l plate of feather stars aids in the positioning of the body as the attachment site of t he cirri -the slender, gripping appendages used by the crinoid for attachment to th e substrate. The placement of cirri
differs between comatulids and sea lilies. Cirri ar e seen on the underside of the calyx in the former and along the stalks of the latter. Used by feather stars to attach directly to their substrate, the cirri of sea lilies are genera lly used for anchoring (Baumiller, 2008), including reattachment to a locale after the stalk has been broken (Meyer and Macurda, 1977). It is the modern comatulid centrodorsal and cirri t hat have evolved from the form seen in ancestral stalked crinoids. Over time, cirr i changed with the loss of the stalk and became better suited to direct attachment. Cirri differ in type and length amongst the feather star species (Meyer and Macurda, 1977) and show specialization with respect to preferred environmental conditions, such as certain current and substrate t ypes (Meyer, 1973). Some crinoids have perhaps taken the next evolutionary step in terms o f cirri by lacking them entirely. These species are found on soft bottom substrates and ins tead use their arms to control their position on the substrate (Messing et al., 2006). S ea lilies that experience a loss of their stalk are additionally known to support themselves by use of their arms during periods of stalk re-growth (Nakano, 2002). The basis of the crinoid body is a predominantly ca lcareous endoskeleton. This skeleton is composed of numerous calcareous portion s known as ossicles that provide the basis for the crinoids flexibility (Hickman, 1967) The range of this flexibility is exhibited in their motions of swimming, crawling, a nd posture formation. Numbering and divisions of ossicles are distinct between species and are standard features examined in both taxonomic identification and classification.
* The modern comatulid bodies are based on such a ske leton and have similar basic forms. Their cone-shaped anus is raised higher than the mouth: a position that allows excreted waste to be removed by currents downstream during feeding without contaminating the mouth. Although the position of t he mouth can vary between species, it lies on the same surface as the anus and varies between being centered or marginal (Meyer, 1982). Surrounding the mouth at the bases o f the arms are the five ambulacral tracts, which continue along the arms, branching if the arms do, and extending to the pinnules. Additionally, surrounding the mouth are t he oral pinnules, which can be seen in Figure 10. r+ : Close up of oral pinnules and ambulacra surroundi ng the mouth of Brown Mariametrid (S. Sherman, 2010). In some species, the function of oral pinnules diff ers from those pinnules found further down the arm. In these cases, those lacking ambulacra no longer function to
1 capture particles. Species with elongate and spiny oral pinnules use them to deter fish from nibbling on the viscera of the central body (N ichols, 1996). Long and flexible oral pinnules aid in feeding by moving food from the sur face of the mouth (Roux et al., 2002). Because the arms compose the majority of the crinoi d and are the platform for the feeding structures (the pinnules and tube feet) the y participate greatly in the lifestyle of the crinoid and can be indicative of preferred habi tat. The number of crinoid arms varies by species and maturity. Arms number from five to 1 00s depending on the species (Hendler et al., 1995). Arms also and affect the ov erall filter of the crinoid. All crinoids begin life with five arms, which later branch durin g development, depending upon species, with 10 or more arms. See Figure 11. The l ength of crinoid arms differs. Shorter arm length is associated with cold water (Hickman, 1967). All arms run to the mouth and attach via five bases on the centrodorsal, where th e body and viscera are located.
. %a and b: Arm branching of a young feather star duri ng development (Coral Publications, 2008-2009 and Shibata, 2008) Image from: http://www.coralscience.org/main/articl es/development-5/featherstars While the arms are the main platform for the crinoi d filter, the suspension feeding to which crinoids devote most of their time would n ot be possible without the pinnules and tube feet. The characteristic feathery appearan ce of feather stars (and sea lilies) is due to rows of alternating pinnules that line the arms. Food grooves run from the pinnules and meet with those of the arms, where they run in a zi gzag pattern between the pinnules on their way to the mouth. In crinoids with more than five arms, these grooves merge at each fork of the arms and pinnules, and eventually conso lidate into the five grooves that lead to the mouth.
8 r : Diagram of the comatulid mouth and surrounding an atomy: ( Left ) AN Anus, AR Arm, PI Pinnule, MO Mouth; ( Right ) PI Pinnule, ARArm, TF Tube Foot, PIFGPinn ular Food Groove, ARFG Arm food groove. (Modified from Holland et al., 1987) r a and b: The crinoid arm, pinnule, and tube feet: ( a ) Tube feet just visible along the 2nd pinnule down on the left side (S. Sherman, 2010). ( b ) Diagram of the crinoid arm (Messing, 1987) The pinnular food grooves compose the majority of t he ambulacral system in feather stars and are typically smaller than arm am bulacra to which they lead (Liddell, 1982). For this reason, the pinnular grooves can re strict the ingested particle size. However, the tube feet of the arm ambulacra are cap able of their own particle capture (Holland et al., 1987), possibly allowing for the c apture and transport of larger particles. The form and function of the crinoid tube feet diff er from some of the other echinoderms, such as the Asteroids and Echinoids. I nstead of having large, sticky tube
3 feet for locomotion, crinoids have tube feet that l ack suckers and function solely as a feeding element, leaving locomotion to the movement of the arms, much like the Ophiuroids. In total, an individual crinoid can hav e thousands of tube feet, occurring in groups of three. The minute primary tube feet, long er than the secondary and tertiary members of their group, extend just visibly and boa rder both sides of the pinnules at ninety degrees. These tube feet are seen in Figure 14. %: Diagram of the pinnule: triad of tube feet, food groove, and lappets (Nichols, 1960) Tube feet and the grooves that they neighbor are pr otected by the lappets, which are hard coverings that line the food grooves and a ttach to the secondary tube feet (Byrne and Fontaine, 1983) ( Note: For further description and activities of tube fee t, see Microfeeding Behavior. When disturbed by forceful motion s, these tube feet contract into the
'4 groove, bringing the protective lappets down over t hem to cover both the groove and the neighboring tube feet (Nichols, 1960). While the basic body plan is fairly conserved acros s modern comatulids, colors and patterns are highly variable. Coloration differ s greatly even within species and thus is not an ideal characteristic for species identificat ion (Jeng, 1998), although it can be used to discriminate between species of one locale. The Caribbean comatulid, Davidaster rubiginosa (Pourtals, 1869) is well-documented for its distin ct color variations, some of which are more regio-typical. Conjugated carotenoids (in part) provide the divers e color variability seen across the crinoid species (Hickman, 1967), although multi ple color morphs are not readily witnessed in crinoids living in water deeper than 1 00 m due to the limitations of light (Zmarzly, 1984). Examples of color diversity are se en in Figure 16. The role of crinoid pigmentation is unknown, although one study at Enew etak Atoll showed almost no variance in the polychromatism within cryptic speci es of comatulids. Exposed comatulids often had numerous morphs: six or more per individu al species. This potentially indicates a function, though unknown, of the crinoid colorati on when in a visible habitat. Such color variation within a species is seen with the s pectrum of documented colors for the shallow-water Mariametrid, Lamprometra palmata (J. Mller, 1841), which has been observed with at least 10 color morphs (Suksudej et al., 2001), including green, brown, yellow, red, and purple varieties. This species has also been documented to occur in a dark mixture between brown and purple, with a simil ar color highlighting the articulations on its cream cirri (Zmarzly, 1985). B ands on the arms are exhibited in many
' individuals of this species and form a bulls-eye ring when the arms open into a filtration fan (Meyer and Macurda, 1980). The indiv iduals of L. palmata included in this study were of the green and red varieties, both of which were colored to form such rings during certain feeding postures. r a and b: ( a ) A plate drawing of a Mariametrid comatulid exhibi ting the "bull's eye" display from H.L. Clark's Echinoderm Fauna of the Torres Strait (1921) ; (b) Two color variations of L. palmata a yellow with the green variety used in this stu dy, plus a brittlestar! (Poppe and Poppe, Conchology, Inc, 1996-2010) Image from: http://www. poppe-images.com/?t=17&photoid=915165 %1a b and c.: Amazingly-colored feather star, with b. listed as Comanthus benetti and 2 unidentified crinoid species (McMeins, 2006; Michelini, 2006; IYOR08 Singapore, 2008). Figure 16 a: http://www.flickr.com/photos/95759222@ N00/4044772534/ Figure 16 b: http://www.flickr.com/photos/lorenzomi chelini/2533887772/ Figure 16 c: http://1.bp.blogspot.com/_Vxu_tx5NynY/R7GMufeEqpI/A AAAAAAAEQs/9ZHFXN0y qkI/s400/IMG_0996.jpg
'' "#(#',&')As we have seen the general diversity and the numer ous ecological interactions of the crinoids, we must elaborate on the aspects of t he ophiuroids and their roles in the oceans, particularly on the reefs. Ophiuroids show a greater range of both habitat and feeding methods than their crinoids cousins; qualit ies that are partly be explained by their form. Examination of the ophiuroid anatomy shows th e particular aspects of brittle stars that lend themselves to suspension feeding and inha biting such environments as sponges and gorgonians. The ophiuroids are not limited to life on the reef, but are an extensive and diverse group represented by approximately 2,000 extant spe cies (Pawson, 2007) from sixteen families, with the family of concern in the present study being Ophiothrichidae. Their worldwide range encompasses such environments as es tuaries, bays, sandy beaches (Neves et al., 2007) and almost all depths of the o cean floor (Hickman, 1967). The ophiuroids and crinoids share many ancestral fe atures of the Echinodermata and their members often overlap ecologically. While members of these two classes can occupy similar niches, they can differ significantl y in appearance. Brittle stars, like crinoids, exhibit a pentamorous, radial symmetry, b ut have only five arms -which are typically lined with spines, although many Euryalid brittle stars have smooth and highly branched arms that form a filter not unlike that of crinoids. Distinguishing features of the Ophiothrichidae fami ly include such prominent spines along the arms and that the dental papillae compose the only armor of the oral area (Hendler, 2005). Members of the genus Ophiothrix have modified spines, which function
' as hooks (MacGinitie and MacGinitie, 1968) that are capable of clinging to exposed posts, such as the sponges and gorgonians in the pr esent study. Specialized modifications from the generic Echinode rm form are witnessed in the podia of brittle stars, which are comparable to tho se of crinoids. The tube feet play a minor role, if any, in locomotion. Arms are used to crawl across the substrate and grip platforms, such as sponges, while the tube feet fun ction in particle capture for suspension-feeding species. Such suspension-feeding ophiuroids include most members of Ophiothrix genus (Family: Ophiothrichidae). The ciliary tracts that are typically used for self -cleaning in other echinoderms have been modified in brittle stars to function in feeding (Jorgensen, 1966). The mouth of the brittle stars differs from that of the crinoids in that it is seen in the relatively more modern position of being on the underside of the or ganism. The mouth is located centrally on the oral disc and surrounded by triang ular plates that function as jaws (Hickman, 1967). This centered mouth additionally f unctions as the site of waste removal as brittle stars lack an anus. In the case of depos it feeding, brittle stars are known to sweep their arms across surfaces, including sponges and corals, to collect detritus to be moved along the arms down ciliary tracks to the mou th (MacGinitie and MacGinitie, 1968).
' %.: Ophiuroid anatomy (Boardman et al., 1987) Brittle stars, as with the crinoids, exhibit a grea t diversity in coloration with numerous color morphs occurring in some species. Th e family Ophiothrichidae is an example of a diverse group that inhabits numerous n iches and varies greatly in color, particularly members of the Ophiothrix genus such as Ophiothrix suensonii and its wide variety of color morphs. Members of this genus freq uent warm, shallow waters (Hendler, 2005) and, while showing great diversity in appeara nce; these brittle stars can be easily identified species because of distinct bands along their arms (MacGinitie and MacGinitie, 1968). This attribute is seen with O. suensonii in the shallows of the Caribbean and with the double-banded juveniles of its congener, Ophiothrix lineocaerula (H.L. Clark, 1928), which is found in waters of less than ten meters (J eng, 1998). Parallel characteristics continue between these species with their habitatio n of particular objects. Ophiothrix suensonii is commonly known as the sponge-dwelling brittle st ar because of its frequent
'* association with sponges, while the juveniles of it s congener have been known to inhabit branching corals, such as Pocillopora verrucosa (Ellis and Solander. 1786). ##$-#',#',r$"$It is clear that both the Crinoidea and Ophiuroidea associate with many organisms in rich and diverse ways. However, when it comes to crinoids, much of their relationships remain to be fully explained or identified. Researchers are still identifying interactions betw een crinoids and their environment, particularly those that are diverse on the reef and those that are lesswitnessed, miles beneath the oceans surface. Altho ugh some of these roles may be more minor or indirect trophic interactions, others are more apparent, such as the vast array of organisms that depend on crinoids, whether for food or for shelter and, in some cases, both. nrFor millions of years, feather stars have served as hosts for a wide variety of organisms belonging to many taxa. Faunal associatio ns with crinoid hosts have been observed in the fossil record since the Ordovician with such preserved organisms as ophiuroids, corals, and gastropods (Gahn and Baumil ler, 2005). Modern associations persist with many of the same organisms and commonl y include shrimps, crabs, clingfishes, ophiuroids, and gastropods (Fishelson, 1974). It is estimated that 90% of all extant myzostome worms associate with crinoids, mai ntaining a relationship over 350 million years old (Lanterbecq et al., 2006)
'1 Organism Family Species Proboscidian Myzostomid Myzostomatidae Myzostoma cirriferum Alpheid Shrimp Alpheidae Alpheus sp., Synalpheus sp. Palamonid Shrimp Palaemonidae Laomenes sp. Crinoid Crab/Squat Lobster Galatheidae Allogalathea elegans Arrow Crab Inachidae Stenorhynchus seticornis Ophiuroids Ophiotrichidae Ophiomaza cacaotica;, Ophiothrix purpurea, O. stri Clingfishes Gobiesocidae Discostrema crinophilia Gorgonian Octocorals --./ Examples Modern Associations of Crinoids (Compiled from Fishelson, 1974; Breimer and Lane, 1978; Nichols, 1996; Calfo and Fenner, 2005; Marin, 2009) Diversity is seen in the types of organisms that in teract with crinoids and the relationships that they have. The roles of crinoid occupants and the degree of their dependence on their hosts vary. The relationship ty pes between crinoids as hosts and their fauna are considered to range from commensal to sem i-parasitic and parasitic, with some of these even being considered obligate (Fishelson, 1974). The relationships of associates and their crinoid hosts also vary with their specie s specificity: some associates have only been found on a particular species in an area, whil e others can be found to inhabit many to most comatulid individuals in the same area. At one island locale, more than eighteen species of crinoid associates were found living amo ngst four species of comatulids and, of these, more than half were only found on one spe cies (Zmarzly, 1984). Of the crinoid fauna, shrimps are some of the most common. There a re over 25 known species of
'. pontoniine shrimp that have commensal relationships with feather stars (Marin, 2009) and the list continues to grow. Note: Ophiuroids are common examples of the assoc iates of crinoids and are covered in Associations of Ophiuroidea.
'8 %8a and b: Photos of Crinoid Associates: Shrimp comme nsal with shared coloration of its comatulid crinoid host, a feature common amongst crinoid associates. Image from: http://www.thediveblog.com/2007/11/index.html ( b ) Crinoid clingfish of a greenish color found on a blue and gold feather sta r (Dive Blog, 2007; Hanson, 2005) Image from: http://www.flickr.com/photos/arne/2551606628/in/fav es-jonhanson/ r* a and b: The arrow crab Stenorhynchus seticornis (Herbst, 1788) on the Caribbean crinoid, Davidaster rubiginosa, with which it regularly associate ( a ) and near the Urchin Diadema antillarum (Philippi, 1845) (S. Sherman, 2010) ( b ) shows the echinodermal associations of this crab (S. Sherman, 2010) Among the common crinoid associates are the clingfi sh, such as the species Discotrema crinophilia (Briggs, 1976). Its name describes its affinity for crinoids as well
'3 as the cavity of its adhesive disc (Briggs, 1976), which is used for attachment to the feather stars arms. %'4: Clingfish: Genus and Species Discotrema crinophilia discovered associated with crinoids (Briggs, 1976). Although crinoid fauna can exhibit species-specific ity, multiple types of fauna can occur on an individual comatulid. Fauna that in habit the same crinoid can compete for food and shelter resources. Some even prey upon other crinoid associates. This dynamic is witness with the shrimp that eat copepod s or the clingfish that eat scale worms and myzostomes (Fishelson, 1974). These interactions between the crinoid fauna may pe rhaps benefit the crinoid by minimizing, although still contributing to, the bur den of the crinoid to sustain these organisms. The roles of these associate organisms r equire further examination, particularly their relationships on the species-spe cific level.
4 rrrrMuch of the predation aspects on crinoids are yet t o be fully identified. A relatively recent study on the trophic interactions of the reef environment left out crinoids completely, while considering other echinoderms, un der the reasoning that: No component of the community was found to feed di rectly on crinoids and therefore they were not included in the database(Optiz, 1993) Although for a long time it was unknown what predat ors the modern crinoids had, observations of the last few decades on crinoids ha ve shown that they are preyed upon by both fishes and invertebrates. Most observations on fish predators report that they appear to feed on crinoids infrequently or only on portion s (Meyer, 1985) of the crinoid. Luckily for crinoids, they exhibit remarkable regenerative properties, exceeding those of the other echinoderms. The full extent to which fishes prey o n crinoids remains unknown, but the majority of their predation appears non-lethal and consists of the removal of such regenerative parts as the arms, pinnules, and even viscera (Fishelson, 1974; Nichols, 1996). Crinoid predation by fish is no recent development. It appears to have been an issue for crinoids since ancient times, at least si nce the early radiation of the bony fishes during the late Mesozoic (Romer, 1966 phide Meyer and Macurda, 1977). This explosion of predators is likely one of the major environment al pressures that has caused the depth discrepancies between the two modern groups of crin oids. Predation may have pushed the once shallow-living sea lilies to their current depths of less fish predation (Baumiller, 2008), while allowing the seemingly better-adapted (including more mobile) feather stars to continue to thrive in the shallows.
Evidence of ancient crinoid predation is witnessed as portions of stalked crinoids in the fossilized feces of fishes. Fossilized crino ids additionally reveal potential aspects of predation by fishes in their loss of portions an d, in more finely preserved specimens, examples of re-growth (Gahn and Baumiller, 2005). While feather stars are not necessarily a primary f ood source for modern fishes, they do contribute to their diet, at least in part. Mucus strings bearing lots of food particles are eaten from the ambulacra by fishes (M agnus, 1963 phide Breimer, 1978). Some species of clingfish, including Lepadichthys lineatus (Briggs, 1966), consume multiple pinnules of their host daily (Fishelson, 1 974). Species Common Name Family Balistoides conspicillum Clown Triggerfish Balistidae Chaetodon ephippium Saddled Coralfish Chaetodontidae Lepadicthys lineatus Double-Liner Crinoid Clingfish Gobiesocidae Crenilabrus melops Corkwing Wrasse Labridae Lethrinus nebulosus Spangled Empororfish Lethrinidae Gynmocranius torquata Sea-bream Lethrididae ./ Fish Predators of Crinoids (Compiled from Nichols, 1996, Baumiller, 2008) Since predation is nothing new to crinoids, some ha ve taken preventative measures, such as the feather star Antedon bifida (Pennant, 1777), which has taken an interesting approach to limit severe attacks by fis h. This species compares to the majority of feather stars in that it reproduces only once an nually, yet differs in that, throughout the year, it maintains its reproductive structures (Nic hols, 1994), which are located in the
' pinnules (Shibata, 2008) and subsequently eaten by the corkwing wrasse, Crenilabrus melops (Linnaeus, 1758) (now Symphodus melops ). This fish has not been observed to take the main body and it will also consume the end ozoic fauna near the crinoid (Nichols, 1996) before moving on to eating the genital pinnul es (Nichols, 1994). This feature of A. bifida to maintain its reproductive structures is quite p ossibly to deter fishes so that they will consume these structures rather than the body (Nichols, 1996), thus reducing the severity of fish predation. Vail (1987), on the oth er hand, has highlighted a contrasting method of reproduction that perhaps reinforces the hypothesis of Nichols. Because feather stars do not typically maintain such reprod uctive structures year-round, some more cryptic-living comatulids studied by Vail exhi bited the asymmetrical production of the genital pinnules that favored the more hidden s ide of the crinoid. Stating that such pinnules might be delectable to fish, this sheltere d asymmetry was supposedly to limit the predation by fish on these structures. Because A. bifida is a more exposed species, maintaining these structures year-round in its more exposed habitat likely functions for a non-reproduction purpose, such as deterring lethal predation by fish. r C. melops attacking the pinnules of A. bifida in vivo (Nichols, 1994)
In contrast to the portions of A. bifida ingested by the corkwing wrasse, the Spangled Emperor fish, Lethrinus nebulosus of the family Lethrinidae, frequently consumes whole crinoids. This fish should be consid ered a major predator in that 38% of all those specimens caught (in a study of comatulid s) contained within their guts crinoid portions (Fabricius, 1994), many that would indicat e lethal attacks. This percentage weighs more heavily in that only about half of the specimens of L. nebulosu s caught had eaten recently enough for their contents to be exam ined. Consumption by fish of entire crinoids was also witnessed by Meyer (1985) for the emperorfish Gymnocranius torquatus although attacks on whole crinoids seemed to occu r less frequently than those on only segments. Those attacks by Chaetedon ephippium in contrast were only witnessed as crinoid portions in the mouth of one f ish, raising question as to whether this fish only peruses fauna on or around the crinoid, o r if it attacks the crinoid itself. %''a and b: C. ephippium a species previously witnessed with portions of crinoids in its mouth, whether or not its attack wa s on the crinoid or fauna of the crinoid was not determined (Meyer, 1985) (http://www.eol.or g/pages/1012777). ( a ), L. nebulosus (http://www.eol.org/pages/222438) ( b ) (Modified from Carpenter and Allen, 1989) There are a few invertebrates known to prey on crin oids, some of which provided the first insights into predation on crinoids. Thes e organisms include crabs and even fellow echinoderms, amongst others. Predatory starf ish, including the species Pycnopodia
helianthoides (Brandt) (Mladenov, 1983), are known to induce swi mming in crinoids (a potential sign of their predation on crinoids) (Sha w and Fontaine, 1990 phide Baumliller 2008), while the starfish Luidia ciliaris (Phillipi) is known to consume other echinoderms. Specimens of Luidia have been found to contain remnants of Antedon bifida within their guts (Brun, 1972 phide Nichols, 1994) and it was this latter finding that altered our beliefs on the limitations of pred ation on crinoids. Asteroids are not the only echinoderm predators of crinoids as urchins have been found to prey on stalked crinoids. Such crinoids ha ve composed up to 99% of the gut contents of cidaroid urchins such as Histocidaris nuttingi (Mortensen, 1926) and Calocidaris micans (Mortensen, 1903) (Baumiller, 2008). Species Organism Order Calocidaris micans Cidaroid Urchin Cidaroida Histocidaris nuttingi Cidaroid Urchin Cidaroida Luidia ciliaris Predatory Starfish Paxillosida Pycnopodia helianthoides Predatory Starfish Forcipulatida ./ Invertebrate Predators of Crinoids (Compiled from M ladenov, 1983; Nichols, 1994; Baumiller 2008)
* rr ( Above ) C. micans (Dave Pawson, NMNH) ( Below) Diagram depicting an Isocrinid fleeing from a cidaroid urchin (From Baum iller, 2008) Crabs have additionally been observed to harass fea ther stars, such as the crab Oregonia gracilis (Dana, 1851), and have been witnessed with a portio n of a feather star within its claw (Mladenov, 1983). Other crabs live with echinoderms and may consume mucus as well (Gilchrist, personal communication). nnnAs we expand upon our knowledge of the basic ecolog ical aspects of crinoids, we can better understand the threats, both natural and man-made, that these organisms face on the reef environment. Due to the delicate nature of crinoids, trawling can have a large site-specific impact on their destruction, particul arly in areas where dense groups gather. Due to their limited mobility, crinoids often do no t escape such nets and begin to break into portions from the resultant physical and mecha nical stress. Less direct impacts, such as those on the reef env ironment, certainly have their effects on crinoids, too. These impacts include tho se of the coral-eating crown of thorns starfish, Acanthaster planci (Linnaeus, 1758), which is known for its devastatin g effects on reefs. In such areas, even more than five years after the prevalence and destructive
1 behaviors of the starfish, the numbers of crinoids were minimal, especially compared to reefs unaffected by the starfish (Fabricius, 1994). A number of reef sites in the Atlantic, such as those of Curaao and Bonaire and the Nether lands Antilles, have also shown significantly, if not alarmingly, diminishing numbe rs of their crinoid populations. Possible negative effects on the crinoid numbers of these sites have been speculated to include both temperature increases in the waters of the reefs of Curaao and Bonaire that have caused bleaching of the corals there (CARICOMP 1997 and Nagelkerken 2006 phide Meyer, et al., 2008) as well outbreaks in the Neth erlands Antilles affecting its gorgonian populations (Nugues and Nagelkerken, 2006 phide Meyer, 2008). After such events on these reef sites, decreases in their crin oid populations were seen, although neither of these events should be considered to hav e definitive effects on the crinoid populations. As feather stars are frequently shipped internation ally from the Indo-Pacific, these adult feather stars are removed from their wild hab itats on the reefs to be sold and exported. What impact this has on reef ecosystems i s unknown, but currently the conservation efforts on crinoids are limited. As we continue to realize the wide array of ecological roles feather stars play in the reef env ironment, the more we can comprehend the significance of their removal. nr Brittle stars are often associated, sometimes exclu sively, with other organisms. These organisms include sponges, corals, and even c rinoids amongst others. There are a number of reasons why brittle stars may select thes e organisms and, although their
. associations are not always clearly understood, som e explanations for their associations include both feeding and shelter. Ophiothrix species often associate with gorgonians, fire coral sea grasses, and coral rubble (Henkel and Pawlik, 2005) with O. suensonii commonly associating with Callyspongia vaginalis (Lamark, 1814), its main habitat in the present st udy. The shallow dwelling of O. suensonii its distinct and bright appearance, and great pre valence in waters easily accessed by snorkeling make this spec ies an ideal candidate of study for its curious sponge association. %'*a and b: ( a ) Photo close-up of O. suensonii individuals on C. vaginalis. Note in-current pores scattered along the outsides and broad exurrent openings at the top (S. Sherman, 2009). ( b ) Some color variations of O. suenonii (Chemistry, 2011) (http://chemistry.csudh.edu/faculty/jim/trip%20repo rts/Cocumel%20fix.html) Henkel and Pawlik (2005) looked at the sponge-dwell ing brittle stars of Ophiothrix lineata (Lyman, 1860) and O. suensonii for their sponge preferences These Ophiothrix species only chose the predominating sponges of C. vaginalis C. plicifera (Lamarck, 1814), and Niphates digitalis (Lamarck, 1814) despite the availability of other sponge species with similar refuge capabilities. Ophiothrix suensonii chose the following
8 sponges with the respective percentages: C. vaginalis (79.1%), N. digitalis (19.4%), and C. plicifera (1.5%). Ophiothrix lineata was significantly more exclusive than its congener and chose C. vaginalis ninety-nine percent of the time over N. digitalis (1%), while ignoring all other sponge species (Hendler,1984). T his suggests that their involvement may be linked to species-specific characteristics o f the sponges. Callyspongia vaginalis known as the (yellow) tube sponge (Class: Demospongiae, Order: Haplosclerida, and Family: Cal lyspongiidae), is considered an active suspension feeder as it actively pumps water during its feeding on particulate matter (Trussel et al., 2006). Its water flow consi sts of an ex-current and in-current flow. Ex-current water flows from the broad opening of it s elongate tubes, while the in-current pores cover the surface of these sponges, moving wa ter into the long cavity of the sponge. While O. suensonii often uses this sponge as its habitat, it is not c onsidered an obligate sponge-dweller (Henkel and Pawlik, 2005). In sponges it has been suggested that ophiuroids co uld keep inhalant surfaces of the sponges clear, resulting in better pumping capa bilities for the sponges and a consistent diet for the brittle stars (Hendler, 198 4b; Stewart, 1998). Siltation blocks the out-going current flow of sponges, like the ones on which O. lineata resides. Large particles are cleaned off the sponge indiscriminate ly by the brittle star (Hendler, 1984), potentially benefiting both sponge and brittle star alike. Astrobrachion constrictum (Farquhar, 1900) a Euryalid snake star is a mutualist with the black coral, Antipathes fiordensis (Grange, 1990). In its wiping during deposit feeding, this snake star removes detritus and epizo ic creatures (Stewart, 1998).
3 r0 : A. fiordensis on A. constrictum (Stewart, 1998) As with crinoids, fish are a major predator of brit tle stars. Ophiuroids have been known to compose more than 10% of the diet of reef fishes in certain areas (Hendler, 1984) and up to 100% in some individual fishes (Ran dall, 2004) examined. Sponge habitation may provide protection from predation, a lthough sponge toxicity generally does not protect brittle stars and the sponges of C. vaginalis and N. erecta have been shown not to deter fish nor hermit crab predators ( Waddell and Pawlik, 2000); possibly suggesting that other factors may come into play wh en choosing an object for habitation. nrOphiuroids are known to associate primarily with cr inoids as semi-parasitic commensals (Breimer, 1978). These include such memb ers of the family Ophiotrichidae as Ophiomaza cacaotica, Ophiothrix (Acanthophiotrix) purpurea von Martens (Fishelson, 1974), and O. stri (Hendler, 2005). Both Ophiomaza cacaotica and Ophiothrix purpurea are known from comatulids, frequently occurring on particular species.
4 Ophiothrix purpurea frequently appeared on specimens of Heterometra savignii (Mller, 1841) from waters in the Red Sea region (F ishelson, 1974) and was additionally found on the following comatulids: Tropiometra carinata (Lamark, 1816), Oligometra serripinna (P.H. Carpenter, 1881), and Stephanometra indica (Smith, 1876). This brittle star species commonly extends and wraps its arms ar ound the arms of its associated crinoid (Fishelson, 1974), but the exact associatio n of O. purpurea with feather stars at the time was unclear. More modern studies on other crinoid-brittle star interactions, such as those with such as O. cacoatica perhaps provide explanations for these associatio ns of O. purpurea While the bright coloration of O. suensonii often contrasts those of the hosts it inhabits, the coloration of Ophiomaza cacaotica matches that of its host crinoid, a feature seen in many crinoid commensals (Clark, 1915), alth ough some ophiuroid species do contrast their crinoid host. Individuals of this la tter species have rarely, if ever, been observed elsewhere. Some studies have shown that th is brittle star only lives with feather stars, typically being found on the feather star Tropiometra carinata but also found on other feather star hosts, such as Capillaster sentosa (Carpenter, 1888) and Heterometra reynaudii (James, 1995). These semi-parasitic to parasitic Op hiuroids benefit by channeling the collected food away from the ambulac ra of the feather star and using their host for possible refuge, while limiting the moveme nt of the host with their grip (James, 1995)
r a and b: Photo of O. cacaotica of similar color on its feather star host, T. catinata (Ria, 2010) Image from: wildshores.blogspot.com/2010_03_28_arch ive.html Ophiothrix stri has been associated with the crinoid Comactinia echinoptera (Mller) in multiple Caribbean sites, but it has al so been found alone in crevices. It is thought that this association may incidental and related to a shared preference by both organisms for certain habitats, rather than an inte raction between the species (Hendler, 2005). It is important to note, however, that the w rasse Crenilabrus melops avoids eating the brittle star Ophiothrix sp.? found on the feather star Antedon bifida although additionally this brittle star may not, on its own accord, be appetizing to the wrasse (Nichols, 1995). These specific associations of ophiuroids with othe r organisms show that the ophiuroids benefit from their diverse relations by a number of means. For most cases, these benefits are likely associated with feeding a nd, in some capacity, relief from predatory exposure. The variety of relationships sh ows that ecological interactions of the
' ophiuroids between other organisms are diverse and common on the reef environment, if not clearly understood. '%/1!"#$'!$(#'2# $The crinoids perform a range of functions that, as with many features of the crinoidea, are not all definitively explained. The motives of their motions include deterring the unwanted settling of some of the prev iously mentioned associates, predator avoidance, and seeking preferred feeding sites. As a whole, modern crinoids are capable of a range of movement that can be typically catego rized with the following behaviors: rapid arm movements, crawling, swimming, and the po sture formations of feeding. Sea lilies are less mobile than feather stars and h ave only been observed to crawl; even with the experimental loss of their stalk they have not been observed to swim (Nakano, 2002). Feather stars show a greater flexib ility over their stalked cousins as they are capable of crawling and swimming, both of which appear to be conserved behaviors. The primary reason for crinoid movement is typicall y exhibited as the result of unfavorable conditions (Briemer, 1978), such as avo iding a negative stimulus (i.e. predation) or seeking preferred current flow. It is unknown whether movement occurs without such stimuli as feather stars have been obs erved to crawl and swim, seemingly without apparent provocation (Meyer et al., 1984). Feather star species vary between their levels of exposure on the reef, qualities tha t will be described in more detail in later sections. While they often remain at their perch du ring favorable feeding conditions, nocturnally feeding comatulids have been observed c rawling between their day light hiding places and their nocturnal feeding perches a round crepuscular periods.
This behavior combined with nocturnal feeding is p ossibly to avoid diurnal fish predators (Meyer et al., 1987), but it is important to note that not all comatulid crinoids exhibit this. While these comatulids remain hidden during the day and expose themselves more to feed at night, some species remain more or less in their protected niches at all times, only extending their arms to feed. Other fea ther stars, for example the Caribbean swimming crinoid, Analcidometra caribbea (Clark, 1942) remains stationary and exposed at all time. One individual of this species was documented to feed from its exposed gorgonian perch for up to five years (Meyer 1973a). Many feather stars are nocturnal feeders, hiding wi thin the reef infrastructure during the day. At night these species emerge, some being limited to dwelling amongst the infrastructure, others moving to more advantage ous feeding positions near them on the reef. The reasons for nocturnal feeding habits are not clearly understood, but avoidance of daytime emergence likely eliminates ex posure to diurnal fish predators. This nocturnal feeding behavior could also relate t o the higher levels of some planktonic organisms during the night, thus making night feedi ng preferable over the food availability of the day (Magnus 1963; Meyer and Mac urda, 1977 phide Meyer, 1984). While some feather stars are limited to nocturnal f eeding, other species feed both day and night, remaining partly exposed during the day and emerging fully at night. Others still, such as the previously mentioned N. grandis appear to feed continuously.
r : The non-cryptic species of N. grandis in its exposed feeding perch during midday (S. Sherman, 2010) Crawling by feather stars is performed by attaching the gripping ends of the pinnules to the substrate and contracting the arms (Hickman, 1967). These anchored arms allow for a motion that pulls the main body in the direction of the extended, but contracting, arm. Crawling, but not swimming, is a behavior additionally observed in the less-mobile stalked crinoids. Recent footage of a c rawling sea lily has caused questioning of the range of motion in sea lilies (Knight, 2005) which are now considered to be able to flee such predators as cidaroid urchins (Baumill er, 2008). Swimming is common in comatulids, but is not exhibi ted in all species (Meyer, et al., 1987). Limitations of the stalked crinoid move ments are seen in their inability to swim, even without their stalks (Kitazawa et al., 2 007). Feather stars are capable of horizontal and vertical swimming (Shaw and Fontaine 1989), but the degree of swimming capabilities also varies among species. Du ring swimming all of the arms work
* together, moving alternately in upward and downward strokes (Moore, 1924). This range of motion likely helps comatulids to escape predato rs and possibly has contributed to their success in shallow waters over the sea lilies which remain restricted to the deeper waters today (Meyer and Macurda, 1977). One of the general behaviors of the Crinoidea inclu des autotomy, a process by which crinoids drop off sections such as the arms, pinnules, or cirri. This loss of portions in crinoids is the result of the breakdown of the f ibers of the ligaments that hold together the ossicles (Breimer, 1978). This behavior is seen during periods of high and potentially abnormal stress, such as excessive temperatures. Rapid Arms Movements The rapid arm movements of crinoids concern the qui ck motions of the arms in the direction of the mouth and are typically follow ed with a slower return or recovery stroke. They have been documented in deep sea crino ids for the stalked family of Isocrinidae and witnessed in comatulids suggesting a response to physical disturbance. Individual arms have been observed to flex from con tact by small crustaceans, potentially preventing their unwanted settling. The rapid movem ent of multiple arms has been observed to during such experimental observations a s dripping sand particles over the crinoid Endoxocrinus parrae (Gervais, 1845). This study additionally showed th at small levels of fine silt did not elicit dramatic respons es from the crinoids observed in terms of arm movement.
1 r* : Arm waving and recovery stoke by the crinoid Endoxocrinus parrae, (A-C) Arm waving, (D) Maximum extension, (E-F) Recovery stoke. (Young and Emson, 1995) Lamprometra palamata has been found to be a nocturnal crinoid species ( Meyer and Macurda, 1980), being fully exposed at night to feed (Zmarlzly, 1985; Wilson, 2005). Found in the Indo-Pacific region, this species can occur in high densities during feeding periods. At night Fishelson (1974) observed around 12,000 comatulids, composed of three species, predominantly the conger of L. palmata conenger, Lamprometra klunzingeri (Hautlaub). During the day this species hides with in the reef infrastructure, sometimes in clusters of two-five individuals, occa sionally moving to exposed areas during cloudy weather (Putchakarn et al., 2001), al though it has been witnessed to be fully emerged during the day (Kirkendale and Messin g, 2003) Once exposed, the typical perches of L. palmata can vary, but are typically of rocky or coral substrates. Substrates for L. palmata have been known to include corals, rock (Meyer, 1979), and rocks with algal coverings (Kirkendale and Messing, 2003).
. Lamprometra palmata form brachypecha has been witnessed in surroundings of grass beds, branching corals, and macro algae (Messing, 2 007). At sites located on the Marshall Islands, L. palmata was found on the reef flats that faced seaward dur ing the day (Zmarlzly, 1985). nnnnn To comprehend the roles of crinoids and the brittl e star O. suenonii on the reef environment, it is important to understand the mech anics of suspension feeding, a method highly important to both brittle stars and crinoids alike. It is the primary means of food collection for crinoids, which devote the majority of their body and time to it. Much of the ecological niche of the crinoid revolves around this one capability; without this mode of feeding, these creatures could not support some of the various organisms that they host. Even those relationships that are parasitic i n nature to the crinoid, such as those organisms that consume its mucus-embedded food, non etheless provide a fine-tuned, inter-species dynamic that is made possible by the suspension feeding of the crinoid. Suspension feeding by brittle stars, on the other hand, does not occur in all species. It is often used in conjunction with other feeding methods to varying degrees, depending on the species. Many brittle stars do not always use filtration feeding as their primary method, but as an opportunistic alternative depending on external conditions. In such brittle stars as O. suensonii this method could quite possibly be used in combi nation with other feeding methods, such as deposit feeding from the surface of their sponges. Although this method of feeding is important to bot h echinoderms, the basics of such a method will be discussed with a more specific appli cation to crinoids.
8 The dynamics of suspension feeding and the structu re and function of filter apparatuses, such as the tube feet, are crucial in the abilities in these echinoderms to feed. Such filter elements are designed to feed in a visc ous medium and their structures reveal what particular factors must be combated to feed ef fectively in the marine environment. Suspension feeders, by definition, are those that r emove particles from their suspension in a form of media (Jorgensen, 1966), su ch as the liquid medium of the marine environment. All suspension feeders rely on the content of the water to bring their food particles and are subdivided into active and p assive suspension feeders. Active suspension feeders, such as bivalves and acorn barn acles, must actively move water over their structures by using metabolic energy to creat e currents (Jorgensen, 1966 phide LaBarbera, 1982). Because feather and brittle stars do not make their own currents, they are categorized as passive suspension feeders, mean ing they require the movement of the surrounding water to flow over their filter-feeding apparatuses (Messing, 1997). The delineation between active and passive suspension f eeders is not always clear as some opportunistic organisms are capable of both feeding methods (LaBarbera, 1984). Those organisms capable of both methods will often passiv ely feed during periods of preferred current flow, while switching to active feeding whe n current flow is limited. Suspension feeding, whether active or passive, occu rs by means of a series of basic steps described by LaBarbera (1984). First water fl ows over the feeding apparatuses. Next the particles are removed from the surrounding fluid by capture (via the tube feet in the case of ophiuroids and crinoids). Finally the c aptured items must then travel toward the mouth to be consumed, or down the ambulacra in the case of crinoids. While these
3 steps are the basic format of such capture, there a re multiple mechanisms by which particles are captured by a filtering element. Suspension feeding occurs by a variety of mechanism s that use porous media to remove and keep particles from a fluid (Rubenstein and Koehl, 1977), based on their form and size (Jorgensen, 1966). Methods for partic le capture fall into either sieving or aerosol filtration mechanisms. Sieving mechanisms f ilter out and retain those particles that are larger in size than the gaps of the filter while permitting those particles smaller than the gaps to pass (LaBarbera, 1978). Compared t o aerosol filtration mechanisms, sieving is likely the least utilized method of part icle capture by suspension feeders (Baumiller, 2007). Aerosol filtration, by its nature, is capable of ca pturing particles of a greater size range than sieving mechanisms. The distinguishing f eature of an aerosol (or in the case of a watery medium, hydrosol) filter is that it captur es particles via an adhesive filtering element. This feature allows for the capture of par ticles that are larger than the filter gaps as well as those that stick to it, including those smaller than the filter gaps. The aerosol filter is typical of many suspension-feeding marine organisms, including crinoids, which use their tightly-spaced, mucus-covered tube feet a s an adhesive filter. Although stickiness aids in capture, other factors determine what types of particles are brought to the filter in the first place, such as those that c oncern the particles movement in water. These factors are explained by the aerosol filtrati on mechanisms which, depending on the interactions of the particles with the filterin g implement, are divided into five groups: direct interception, inertial impaction, gravitatio nal deposition, motile-particle (or
*4 diffusion) deposition, and electrostatic attraction (Rubenstein and Koehl, 1977; LaBabera, 1984). These methods can be understood wi th the basic motion of flow around the filtering element. The fluid flows to the eleme nt, around it, and rejoins on the other side, assumingly unaffected by the motion of the (i deally round) particles it brings to the elements (Rubenstein and Koehl, 1977). r+ : Parallel flow streams around an element (Rubenste in and Koehl, 1977) The crinoid filter functions as a baffle to slow ar riving currents to the filtering elements for better aid in particle capture (Meyer, 1973b). As a whole, it consists of the arms, pinnules, and tube feet (Leonard et al., 1988 ) and its effectiveness can be adjusted by the crinoid by changing in the arm posture and p innular orientation in response to ambient currents (Note: See Section on Macro-Feedin g ). The efficiency of a filter was originally defined b y Rubenstein and Koehl (1977) as the number of particles that strike the element (or tube foot), but was later redefined for crinoids by Leonard (1989). Leonard equated the eff iciency of the crinoid filter for Antedon mediterranea (Lamarck, 1816) not as a function of the rate at which particles approach the filter but as the ambient particle c oncentration and current speed (Davoult and Gounin, 1994).
* The five mechanisms of the aerosol filtration theor y have varying effectiveness according to the velocity of the surrounding waters (Meyer, 1973b phide Rubenstein and Koehl, 1977). Since feather stars generally have pr eferred current niches, different mechanisms are employed for particular types of amb ient current and thus by certain species. Meyer (1982) notes that, concerning the aerosol fil tration theory, the methods for particle capture at higher rates of flow are motile -particle deposition and gravitational settling. Lower flow speeds witness capture via ine rtial impaction and direct interception. Variations on the crinoid filter, such as the numbe r of arms or the length and spacing of tube feet, affect the flow around the elements and determine what current types are ideal for particle capture (Meyer, 1979) and thus the mec hanism employed. r : Mechanisms of Particle Capture for Suspension Fee ders (Baumiller, 1997)
*' The first two mechanisms, gravitational deposition and diffusion deposition, both occur at lower flow velocities according to the aer osol filtration theory (Meyer, 1982) and are more applicable to those comatulids exposed to slower current flow. Gravitational deposition concerns particles that are inclined to sink due to their greater density than the surrounding medium. When these particles cross the streamlines flowing around the element, they are more likely to fall, hit the elem ent (Rubenstein and Koehl, 1977), and subsequently be captured by the tube feet (LaBarber a, 1984). This method, in terms of impaction with the element, is more efficient for l arger and heavier particles, which have greater tendency to sink when not being propelled b y the velocity of faster current flow. Motile particle or diffusion deposition come into p lay when suspended particles in a watery medium exhibit what only appear to be random displays of movement, deemed Brownian motion. This motion is applied to miniscul e particles that, when they bump into one another, can send a particle close enough into the streamlines flowing around an element to be captured by it (Rubenstein and Koehl, 1977); a process more prevalent for slower or medium flow. At higher current speeds, crinoids capture particle s more efficiently by direct interception and inertial impaction (Meyer, 1982). Direct interception simply concerns the motion of a particle that is brought directly t o the filtering element and its sticky coating with the flow of the media. Of all suspensi on feeding mechanisms used by marine organisms, direct interception is perhaps th e most common method and is used by both crinoids and ophiuroids alike (Meyer, 1973; Da voult and Gounin, 1995; Baumiller, 1997). Inertial impaction, on the other hand, conce rns the movement of a particle that
* differs in density than the surrounding medium. Whe n such a particle is brought within a radius of its own size to the element, rather than flowing around the element with the moving media, its inertia instead brings it to the tube foot, where it then impacts it (Rubenstein and Koehl, 1977). Although Rubenstein and Koehl (1977) indicated that electrostatic deposition was a potentially ineffective mechanism in sea water, a s tudy by LaBarbera (1978) seemed to indicate otherwise. LaBarbera suggested that the pr imary method of capture in the brittle star Ophiopholis aculeata (Linnaeus, 1767) was direct interception. He obser ved potential electrostatic attraction as a method of c apture in that charged particles were three times more likely to be captured by the britt le star than neutrally charged ones. Considering both that the mucus of this species mai ntains a negative charge in sea water and that particles in sea water usually have an ove rall charge, this method of capture would potentially be quite useful to marine suspens ion feeders. 13(r'!Aspects of feeding at the level of the tube feet ar e considered small-scale in comparison to posture formation. These micro-feedi ng behaviors pertain to the physical capture and transport of particles during feeding and thus determine the particles that will compose the diet of a species. It is thei r dimensions that influence what feeding postures are formed by the arms for efficient captu re and what available particles compose the diet. Despite differing opinions on tube feet, their main function is capturing food -an activity requiring both sensory capabilities and a method of transfer (Nichols, 1960).
* Occurring in groups of three, the tube feet run alo ng the grooves of the pinnules and arm ambulacra. Each group, or triad, of tube feet consi sts of a long (primary), medium (secondary), and small (tertiary) tube foot (Meyer, 1979 ) each type with a varying and cooperative role for particle capture and transport The tube feet of crinoids and ophiuroids are cylind rical in shape, a common feature seen the filtering elements of suspension feeders, including the setae in barnacles (LaBarbera, 1984). %'a and b: ( a ) A triad of a primary, secondary, and tertiary tub e feet. Note (L) the lappet and (P) the papillae along the tub e feet. (Modified from Byrne and Fontaine, 1983) ( b) Cross-section of the crinoid pinnule with triad of tube feet. (Note current and particle flow in relation to pinnule) (Brower, 2006) On the tube feet are solid, perpendicular projectio ns known as papillae. These structures are a main producer of mucus in feather stars (Nichols, 1960) and are thus an
** essential contributor to particle capture, despite their small size relative to other structures pertaining to feeding. Particle capture is almost a lways performed by the primary tube feet (Brower, 2007). The primary tube feet catch dr ifting particles in the currents and promptly bend downstream towards the groove. The fo od particles stick to the mucus and are moved by the primary tube feet to the secondary and then to the tertiary, tube feet of the triad. The tertiary tube feet are the most flex ible of the tube feet and bend into the food groove to deposit food particles. At this leve l of feeding, podia actions do vary between species. For instance the secondary tube fe et of some feather stars may not interact with the primary tube feet (Byrne and Font aine, 1981). No matter the differences, once in the pinnular grooves, mucus-embedded partic les make their way to arm ambulacra and eventually the mouth (Rutman and Fish elson, 1969) via ciliary action (Meyer, 1982). A study by Holland and colleagues (1986) showed how objects are captured by single tube feet by Oligometra serripinna These tube feet bend into food grooves when makin g contact with particles 20 m and smaller. Sensory c ells in the epithelium of tube feet likely function as mechanoreceptors to cause bendin g after the stimulus. Contact with particles larger than this induced the tube feet to work with neighboring and adjacent tube feet along the groove in a coordinated flick to h andle these larger particles. Although the majority of crinoids orient their ambu lacra downstream for downstream particle capture, some crinoids, such as Oligometra serripinna are capable of upstream capture to take advantage of shift in c urrent as well as slack currents. The occurrence of upstream capture in feather stars lik ely varies in performance across
*1 species and may be even more efficient in other spe cies, but further examination on a species-specific level is required. While upstream capture does occur, it is at most ha lf efficient (Holland et al. 1987) when compared to downstream capture. This may be due to the filter shape being more structured for capture downstream, but the fac t that upstream capture occurs at all shows the ability of feather stars to feed in varyi ng conditions such as temporary shift in current flow. r : Photo of grooves and diagram of Up and Downstream Capture: PIFG Pinnular Food Groove, PI Pinnule, TFTube foot, DSC Downstre am, USC Upstream (Modified from Holland, et al., 1987) 13r'!"4$#$4/, ## #'"(#/-Particle capture at the micro-feeding level can be greatly influenced by aspects of the large-scale, or macro, feeding behaviors, whi ch concern the feeding actions performed beyond the level of the tube feet. These actions primarily concern the orientation to flow of the arms and pinnules, which are held in positions that manipulate and slow currents to maximize particle capture for the available flow.
*. Overall the crinoid filter acts as a baffle to slow given currents and individuals are known to overlap filtration fans as this behavior m ay increase the effectiveness of the baffle and each individuals ability to both captur e and retain particles (Meyer, 1973b). In the field, for example, mariametrid crinoids share perches with other mariametrid and non-mariametrid feather stars (Wilson, 2003) while forming their postures for feeding. While different postures and their associated curre nts are well-documented for crinoids, it has been only since the latter-half of the past century that this information has even been determined. Initial reasoning, going as f ar as about the mid-sixties, described postures simply as functioning as collecting bowls to catch the downward-drifting detritus (Macurda and Meyer, 1974). This view great ly contrasts our current perception of feather stars as actively manipulating currents with their postures for more efficient passive suspension feeding. While this mode is the primary feeding method of the great majority of living crinoids, it is important to not e that there is evidence to suggest that some of the deep sea species (in waters more than a kilometer deep) do feed by methods of gravitational deposition (Eleaume, 2002). Because crinoids use the surrounding currents, they do not use their energy to create current flow as do active suspension feeders but instead use the energy they expend during feeding to maintain the postures and placement of their structures during flow, (LaBarbera, 1984). Since crinoids tend to fee d for extended periods of time, they are faced with much water flow over these maintaine d structural positions. Up to 40,000 liters of water can be passed through a filter unde r certain current and posture combinations during a feeding period (Magnus, 1963 phide Macurda and Meyer, 1974).
*8 Because postures are specialized to particular flow they are often indicative of ambient current conditions. These conditions, or cu rrent niches, are more generally divided into two groupings: those within the infras tructure and those above. Currents flowing within the reef infrastructure are slowed b y the shape of the reef and broken into a multi-directional flow (Meyer, 1979). Those curre nts traveling above the infrastructure are not as impeded by the topography of the reef an d are typically faster, flowing in one direction. The importance of current flow for comat ulids is illustrated in part on the Enewetak Atoll of the Marshall Islands where, in ar eas with exposure to constant currents, crinoids were found in the greatest numbe rs and diversity (Zmarzly, 1984). Current flow that is too strong or too weak can neg atively affect feeding. When current flow stronger than ideal, it will distort a feeding posture, rendering its form less effective. When current conditions are not favorabl e, i.e. not of the desired flow strength, different behaviors are witnessed between stalked a nd un-stalked crinoids. Stalked crinoids, such as the members of the family Isocrin idae, will let their arms hang during unfavorably slow current conditions (Young and Emso n, 1995), while feather stars, depending on their species and lifestyle, will ofte n remained closed in between feeding periods only to open into diverse forms for special ized feeding. When the appropriate conditions prevail there are s een a variety of posture categories that can vary in nomenclature, depending on the author, but can be classified into a few main groupings that show aspects of the diversity of the comatulids by their preferred perch types and current conditions. Of th ese distinct categories, feeding postures commonly exist as blends; all of which are indicative of the desired niches and
*3 external environment of the crinoid. These blends p rimarily concern the varying degree to which the disc arms are angled, as well as some other key aspects, such as the density, or rather, number of arms. Postures vary for flow in horizontal directions, bu t arms are oriented with the ambulacra facing downstream. In this flow, arms are oriented perpendicular to currents. The most common postures will be divided into the f ollowing groups or fans: Arcuate, Radial, Parabolic, Irregular, Arm, Multi-layered ar rays, multi-directional and Conical fans (Rutman and Fishelson; 1969, Meyer, 1979; Mess ing, 1994; Baumiller, 1997; Brower, 2007). The majority of posture forms hold t he pinnules in one plane, although some postures, such as the conical and multi-direct ional arrays hold the pinnules in multiple planes for the best particle capture. Crinoids that prefer unidirectional flow will typic ally face arm ambulacra down current with postures varying with bending of the a rms. Postures can be seen with more bowl-shaped formations to planar and radial ones, t o those in which the arms curve aborally to form the parabolic feeding posture The arcuate fan is a posture common to the Mariamet rid family and was commonly employed by some of the Mariametrids in th e present study. This posture is typically exhibited by crinoids experiencing unidir ectional flow on exposed perches, such as corals and rock (Meyer, 1984). It consists of tw o sheets of arms (with ambulacra facing downstream) that form an angle less than 180 degrees. Feather star species that exhibit this posture are typically nocturnal in nat ure and have between twenty and fifty arms (Messing, 1994). Typical genera that form the arcuate fan include Liparometa
14 Stephanometra, and Lamprometra, (Messing, 2011), including Lamprometra klunzingeri (Hartlaub, 1890), which is known to cling to Millepora to lift itself above the reef topography for better current flow. r : The postures of comatulid crinoids (amb = ambulac ral side of arm) (a) Arcuate fab (b) Radial fan (c) Parablic fan (d) Pos ture of species lacking cirri (e) Postures of cryptic species, including arm and mult i-directional fans (Meyer, originally from Meyer and Macurda, 1980)
1 r a and b: Arcuate fan exhibited by L. palamata form brachypecha and the radial fan (S. Sherman, 2010) The radial and parabolic feeding fans are postures exhibited by both stalked crinoids and those feather stars whose perches func tionally make them stalked by lifting them above them surrounding infrastructure (Meyer, 1982). The arms for this former posture are positioned with slight spacing in the f orm of a (typically flat) disc, which may be slightly curved aborally. With the parabolic pos ture, the arms curve back into the current, forming a parabolic shape. Its curved shap e allows for a more solid fan than the radial posture: a distinguishing feature as it mini mizes gaps between the arms and allows for the filtration of more water (Warner, 1977 phide Meyer 1982)
1' r0 a and b: Parabolic fan in Endoxcrinus wyvillethomsoni (Jeffreys, 1870) raised above the substrate by its stem approximately 12 cm (Conan e t al., 1981); Multi-directional posture of Nemaster grandis (S. Sherman, 2010) The multi-layered feeding posture is aesthetically less crisp than those previously mentioned as the arms do not lie in much of a simil ar plane as one another as not to interrupt arriving flow (Baumiller, 1997). Such pos ture formation is seen in crinoids of many arms (exceeding eighty) (Messing, 1994), such as Nemaster grandis which hold their arms in various twists and positions to form such an array. This seemingly tangled, dense mass of arms allows for the twisting individu al arms so that they remain normal to flow (i.e. ambulacra facing downstream) and works w ell for varied flow in a local. Meyer and colleagues (1984) found that the most com mon posture observed was the filtration fan amongst the feather stars studie d. Of the species that may employ gravitational deposition capture, Pentametrocrinus atlanticus uses a reduced filtration fan and orients its arms parallel to the current (Eleau me, 2002).
1 Feather stars often use their cirri to grip objects that bring them above the substrate to access more preferred currents, such a s the Mariametrids mentioned. These objects vary greatly and include gorgonians and eve n the stalks of sea lilies (Meyer and Macurda, 1977). Those that cling to such elevating perches essentially function as stalked crinoids (Messing, 1985). Perches are very importan t for feeding in crinoids. When unable to find an attachment site, feather stars wi ll become distressed to the point of death (Clark, 1921 phide Breimer 1978). Species that lack cirri, however, have differing po stures compared to other feather stars. These species, such as Comatula rotalaria (Lamarck, 1816) of Australian waters, use their arms to lift their bodies above the soft substrate and feed by extending their arms into the water column (Messing et al., 2006) a nd often form multi-layered arrays. Postures that hold the pinnules in multiple plains are seen in crinoids that experience multi-directional or slack flow and ofte n form arm and conical fans. Arm fans are typical of such cryptic-feeding specie s as Davidaster rubiginosus ( Pourtals, 1869) and Davidaster discoideus (Carpenter, 1888). These species keep their main body hidden within the reef infrastructure whi le exposing only their arms to feed. Exposed to multi-directional postures within the re ef, these crinoids do not orient their pinnules in one plane, as is common with the majori ty of other feeding postures, but hold their pinnules in a 4-row arrangement that consis ts of two planes of pinnules that alternate and form four rows (Meyer, 1973). Holding the pinnules in multiple planes more effectively exposes their tube feet to the mul tiple directions of currents that they are exposed to within the reef infrastructure.
1 r a and b: 4 Row Pinnular Posture (Messing, 2011) Ima ge a from: http://www.nova.edu/ocean/messing/crinoids/9%20Feed ing%20postures.html); Davidaster rubiginosa off the islands of Honduras, exhibiting the multi-d irectional of cryptic species (Photo Courtesy of Krzykwa, 2010) The conical feeding postures of crinoids concern a tighter and more acute angle of the arms in the adoral direction, forming a cone sh ape. This posture is typical of crinoids that experience slack currents and is exhibited by such species as Florometra serratissima and Antedon bifida (LaTouche, 1978; Byrne and Fontaine, 1981). With s uch currents, A. bifida typically deviates from single-planed pinnules by orienting them in triplets, or three rows, versus those of the Davidaster species, but remains quite the exception when compared to the majority of feeding postures discussed.
1* r : Conical feeding of an aggregation F. serratissima (Messing, 2011) Image from: http://www.nova.edu/ocean/messing/crinoids/9%20Feed ing%20postures.html 4$##")/##"&$# While feeding behaviors differ amongst the comatuli d crinoids, all comatulids are subject to the same main factors that affect the co mposition of their diet: the anatomy of their feeding structures, current flow, and particl e composition of the surrounding waters. Features of the crinoid filter, such as posture and the dimensions of feeding structures, vary between species. These aspects, su ch as the arms, pinnules, and tube feet are often indicative of specified feeding methods a nd habitat of a crinoid. It is the spacing of these physical features, more specifically the t ube feet, which are specified for current flow and affect a crinoids niche on the reef and a dditionally the composition of its diet. Tube foot spacing varies with the position of the c rinoid relative to the reef topography and subsequently the currents to which t hey are exposed. In species living above the reef infrastructure where unidirectional, stronger currents prevail, tube feet are
11 shorter and more tightly spaced, functioning as baf fles to slow and break up arriving currents. Species with longer and more widely space d tube feet live within reef infrastructure, where they are exposed to currents with greater turbulence and slowed speed (Meyer, 1973). Certain filter shapes and their ideal flow speeds h ave a range of particle sizes that optimal for capture by the filter. Particle sizes l ikely overlap between these two types of species, but their differences possibly allow for r esource partitioning between species to limit competition (Meyer, 1973b). According to Meyer (1982) on feather stars from Pal au, species with similar feeding methods, but of different taxonomic grouping, have similar tube foot length and spacing (Meyer 1982). Liddell (1984) found that food composition v aried slightly amongst the species studied and proposed the possibility that t he number of their arms, as well as arm and pinnule orientation, could have attributed to t his with their variance between the species. The positioning and form of their feeding structure s can alter these concentrations. Such factors include the particle c omponents of the water, the nutritional value of potential food sources, and the size of th e particles relative to the transportation grooves.
1. nnnn5#rrOne of the greatest limiting factors in the composi tion of the comatulid diet is the size of the particles. Size can determine whether o r not a suspended particle can be captured, and eventually ingested, by a feather sta r. The typical size of particles ingested by feather stars ranges between a few micrometers a nd a few hundred micrometers (Meyer, 1982 phide Leonard et al. 1988) and evidence suggests that pa rticles may be limited by the width of the ambulacral grooves down which they travel down to be ingested, particularly the pinnular grooves, althou gh ambulacra may expand. The width of the pinnular grooves is the primary limiting fac tor on particle size as these grooves tend to be narrower than the arm ambulacra to which they lead. While the majority of particle capture occurs long the pinnules, tube fee t line both the pinnular and arm ambulacra, the latter of which resulting in the dir ect transfer of potentially larger particles into the groove and thus in the diet. It is important to note that particles exceeding th e size of the ambulacral groove can be caught; however, in most cases they are move d with difficulty or not at all. Captured particles can also be manipulated to fit w idth-wise into the food grooves when their length exceeds the desired size and would oth erwise prevent capture. Rutman and Fishelson (1969) showed that ninety percent of inge sted organisms measured less than 400m, although large particles were occasionally c ollected, transported, and consumed by the crinoids.
18 While feather stars are able to discriminate amongs t appropriately-sized particles for those be ingested versus discarded (Holland, et al. 1991), a study by Holland and colleagues (1986) showed that feather stars are cap able of rejecting objects qualitatively by recognizing of lack of nutritional value, a feat ure that may not exist across all crinoids. Some feather stars, such as Oligometra serripinna are capable of selectively ingesting captured particles to avoid digestion of inert ones Other feather stars appear to be less discriminatory and ingest a variety of inert partic les in addition to living matter (Holland et al., 1991). This former method is potentially le ss efficient due to the more regular ejection of fecal pellets by these less-selective f eather stars, although many crinoids consume much detritus, which has a yet to be determ ined level of nutritional value (La Touche and West, 1980). Feather stars as a whole employ a number of mechani sms for determining the appropriateness of particles as they are capable of discriminating between non-nutritional or unfavorably tasting particles. Particle rejectio n occurs on a few levels, according to Holland and colleagues (1986) with tube feet being the first level of interaction, and thus subsequently the rejection and selection, of food p articles. Tube feet are capable of selection by mechanoreception, although chemorecept ion at interception may play a part in affecting its function. Once particles are accep ted at this level, they are passed into the food groove by the previously described methods. On ce in the food groove, particles come in contact with the epidermis and are then sub ject to its chemoreception, a feature whose presence possibly varies amongst species. All of these features help aid in sorting appropriate food particles from non-nutritional ino rganic matter for the final diet.
13 5#)##Feather stars and suspension feeding brittle stars are capable of capturing many minute organisms, thus reducing the chain of consum ers in the food web that would otherwise eat the smaller, individual phytoplankton (Jorgensen, 1966). The diet of feather stars is dependent on the particle composition with in the water, which often fluctuates seasonally with varying concentrations of food sour ces, such as planktonic organisms (Holland et al., 1991). While the crinoid diet can vary between species, lo cality, and season, is primarily composed of a diverse array of organisms and additi onally detritus, the latter of which can make up a large percentage of the diet, dependi ng on these factors, though its nutritional value may be significant although this has yet to be determined (La Touche and West, 1980). Overall the comatulid diet is composed of heavier, slower swimmers (compared to more pelagic prey) that, once caught, cannot easily swim free from the mucus. Strong swimmers, such as brine shrimp nauplii, can adhere to the mucus, but are large and mobile enough to swim free of its hold, thus compos ing a lesser percentage of the crinoid diet. Food composition has been found to vary when examin ed both at the genus and even within a species level, a feature likely based on l ocation and current exposure. Meyer (1982) found that the diet of L. palmata mostly consisted of protozoa and phytoplankton (over 60 and 12%, respectively). Red Sea specimens L. klunzingeri now considered a variant of L. palmata (Rankin and Messing, 2008), similarly showed a die t consisting of
.4 50% protozoans, 40% crustaceans and mollusks, and o nly 10% of phytoplankton (Rutman and Fishelson, 1969). In both of these form s the majority of protozoa consisted of tintinnids, while phytoplankton contributed arou nd a tenth of the diet. It is important to note that the organismal concentrations do not nece ssarily correspond to nutritional values gained. When exposed to high concentrations of food, feather stars will continue to feed gluttonously, forfeiting nutritional gain. Holland and colleagues (1991) found that after such extensive feeding, feather stars began p assing undigested and even living organisms through their digestive system. ,&'5#r Unlike the crinoids, ophiuroids as an order are ca pable of utilizing multiple methods, contrasting the sole method of feeding for crinoids, which is suspension feeding. It is the structure of the mouth, includin g the presence or absence of such features as the infradental papillae (not shown), c an be indicative of the feeding method of a brittle star. Brittle stars feed by a variety of methods with the ir most common feeding methods of carnivorous, filtering, and deposit feeding modes. Overall these organisms fall under being either macrophageous (the epibenthic predator s, scavengers, and deposit feeders) or microphageous consumers, according to Boos (2008). Those that are microphageous include the infaunal (surface and sub-surface depos it feeders and suspension feeders) and the epibenthic-cryptic (suspension feeders). Thus i t can be observed that brittle stars as a whole exhibit a greater range and more specificity when it comes to feeding that do feather stars, which are capable only of suspension feeding, although still exhibiting specificity to current niches and particle capture selectivity.
. It is the deposit and suspension feeding methods t hat are of special interest concerning O. suensonii and provides insight into their object habitations Brittle stars that are capable of deposit and suspe nsion feeding modes (Wofle, 1982) opportunistically switch between feeding methods de pending on the levels of current (Meyer, 1984)(Boos, 2008). Their suspension feeding methods are comparable to those of feather stars in that both organisms feed by the aerosol filtration method. The brittle stars in this study are known to depos it and passively suspensions feed, and share some basic similarities between these mod es of feeding with their cousin Ophiuroids, the Euryalida. While brittle stars do s uspension feed in manners comparable to crinoid, they only have around five arms, which they extend into the water column, often using at least two to cling to their elevated substrate. Basket stars feed by a similar net to crinoids, however in that they unfurl their branched arms during current flow and snag particles on their tube feet. Many euryalids parallel brittle stars like O. suensonii in that they found to employ the same feeding modes while inhabiting the surface of certain organisms. Capable of both deposit as ophiuroid brittle stars and suspension f eeding modes more comparable to crinoids, some euryalid brittle stars inhabit coral s and gorgonians, using their hosts as posts for suspension feeding as well as providing a food source for deposit feeding. Astrobrachion constrictum (Farquhar, 1900), a euryalid brittle star, is an e xample of an ophiuroid capable of both deposit and suspens ion feeding and frequently occupies a coral host. This snake star suspension feeds by ext ending two to three arms of its unbranched arms out to catch food particles on its tu be feet and arm spines. Deposit
.' feeding, on the other hand, is performed by wiping the surface of its host coral and ingesting the mucus-coated particles (Stewart, 1998 ). Suspension-feeding ophiuroid brittle stars are exhi bited by the species Ophiothrix fragilis (Abildgaard) and Ophiopholis aculeata (Linnaeus, 1767), with those of the Ophiothrix genus representing specialized suspension feeders (Warner, 1982). Ophiothrix fragilis parallels O. suensonii in that both congeners suspension feed and additio nally occur in dense aggregations. However this species d iffers from O. suensonii in that it is a benthic suspension feeder (Davoult and Gounin, 1994 ), whereas the former is lifted above the substrate with its attachment to sponges. Particle selection on a nutritional level is seen in some ophiuroids prior to ingestion. Feather stars also show particle discrim ination, which is known as gustatory discrimination for the level of the tube feet (LaT ouche and West, 1980). The tube feet of the Ophioromina nigra are capable of rejecting particles before they mak e it to the gut, while Ophiothrix lineata is a non-selective deposit feeder and differs from other Ophiothrix species in this respect ( Hendler, 1985 ). As a result of varied selectivity and feeding modes the diet of ophiuroids varies greatly. The study on Astrobrachion constrictum (Eurylida) showed that over 63% of stomach its contents were composed of detritus, fec al pellets, and mucus (Stewart, 1998). The remaining percentages consisted of, but were no t limited to, such organisms as copepods, mysids, and polyp bits. Mucus, such as th at collected from the surface of the coral or sponge, provides a nutritious food source in addition to the particles collected.
. While detritus alone has little to no nutrition, ba cterial coatings on detritus may provide some nutrition to both feather stars and brittle st ars (Latouche and West. 1980)
. 16,5,,%7The observations on ophiuroids and crinoids in this study aim to further elaborate on such details described in the literature review by expanding upon the knowledge on the ecological aspects and niches of these echinode rms, including those pertaining to feeding and the associations of ophiuroids and crin oids, on hosts and as hosts, respectively. nnnnnThe current study was conducted over a three week p eriod in the summer of 2009 (6/29-7/18) on the island preserve of Cayos Cochino s, Honduras. This island lies between the mainland of Honduras and Roatan at 16 degrees N 86 degrees W. The research area was located in the bay (pictured with cross-hatchin g in Figure 40). The site consists of shallow reefs, often boarded by grass flats or stre tches of sand. r* : Honduran mainland, Roatan, and the marked Hog Isla nds, or Cayos Cochinos (Flateland, 2010) Image from: http://picasaweb.google.com/lh/photo/DYHzFSYFQN82Fy BwWuIbOw
.* Twenty-seven sites with the brittle star Ophiothrix suensonii (Ltken. 1856) were examined. There was a prevalence of this species on the tube sponge Callyspongia vaginalis (Lamarck, 1814) While aggregations of O. suensonii occurred on other objects, they were less common and rarely exceeded five indi viduals. Sites were chosen to examine sponges containing such aggregations with f ive or more brittle stars, while sites with objects other than C. vaginalis with any number of O. suensonii were examined for comparison. The number of brittle star individuals at each site was counted and their color documented, as well as details of the site it self. These nonCallyspongia sites consisted of objects such as corals, gorgonians, an d vase sponges. Brittle stars found within the tubes of sponges, wh ile rare as this species seemed to almost exclusively inhabit the surface, were dif ficult to count and some individuals may not have been documented. One brittle star noti ced within the tube of a sponge was significantly smaller in size and appeared brown in color. Since it could not be clearly identified as a specimen of O. suensonii it was left out of the study. Any brittle stars found on the surrounding substrate of the sites wer e ignored for the purpose of the survey. All sites were marked with numbered flags f or identification and the majority of them were photographed for future reference. The he ight of each sites object and the depth of each site were recorded. All research took place during daylight hours in waters of 0.3-4.3 meters in depth and measurements were ta ken using a floating transect measure.
.1 r+ : Cayos Cochinos with cross-hatching indicated the bay of study (Modified from Google Maps, 2010)
.. r : Plantation Beach Bay, the research area. Approxim ate locations of some research sites are marked with red to show generally the area cove red in this survey. Small twin markings indicate grass beds, while light gray shows reefs (Modified from a map courtesy of Plantation Beach Resort). nnnnn While brittle stars were readily available in the field, it was more reliable to study feather stars in the lab since they tend to occur l ess frequently on the reef than brittle stars and often occupy deeper waters. All feather stars u sed originated in the Indo-Pacific region and were acquired from a local wholesaler. T hese organisms were kept in a forty gallon aquarium and studied in respect to their fee ding posture as well as general observations. Responses to various current flows we re executed in the tank. Current flow was tracked over the feeding fans using fluorescein dye. The dye was released upstream during feeding periods in a similar manner used by Meyer (1973b).
.8 Wilson (2003) found that the feeding postures of Ma riametrid crinoids did not seem to be influenced by changes in the diel cycle, but postures were altered with changes in ambient current, although Mariametrids were typical ly cryptic. Because crinoid species of this study appeared to feed at all times of day and did not vary their exposure when light, but when food was present, lighting was not taken into consideration for the study of their filtration fans. 2&$$#'$2#)All crinoids in this study were of the family Maria metridae. There were likely only three species used: Lamprometra palmata. Oxymetra sp, and one unidentified Mariametrid. Two of the individuals were L. palamata while a third, due to its coloration and behavior, was likely L. palmata form brachypecha Due to the physical characteristics of the three Oxymetra species, these specimens were most likely either Oxymetra finschii (Hartlaub, 1890) or Oxymetra erinacea (Hartlaub, 1890), although it is thought that these two may be the same species (Cha rles Messing, p ersonal communication, 2010). Feather stars came in three shipments: the first co ntaining the red and green L. palamata individuals, the second with three of the Oxymetra sp ., and the final containing one L. palamata form brachypecha and the unidentified Mariametrid. The second batch was introduced with the first after a few weeks of observation. The final batch of two crinoids was later kept in the same type of forty g allon aquarium, but was studied under different flow conditions and was not kept with the other batches of crinoids.
.3 Autotomized portions of the arms were also viewed of the 1st batch green L. palamata and an individual of Oxymetra sp Distal portions of the feather star arms were removed from aquaria and the actions of the primary podia and particle transport were filmed and photographed. Autotomized portions conti nued to feed after removal. Food was typically administered twice daily in bot h tank set-ups and consisted of rotifers, zooplankton, phytoplankton, and live brin e nauplii. #$ Two tank set-ups were used during the study, both o f which consisted of a forty gallon tank with rock and mesh substrates. The firs t current trial conditions consisted of the 1st and 2nd batch of crinoids. A mesh divider, filling the wid th of the tank, was placed approximately eight inches from the side of the tan k in order to separate the crinoids from the filter box while allowing room for the two powe r heads used to create current flow. These power heads were set to their wave-making s etting and alternatively switched in producing flow approximately every thirty seconds. Later in the trials, these power heads, while facing in the same direction (blowing out int o the tank from behind the mesh) were moved vertically and horizontally to observe any ch ange in posture in response to flow by these crinoids.
84 The second trial tank was set up differently for t he final and third batch of crinoids. No mesh divider was used. An under-gravel filter was used (versus a filter box) and filter heads were switched to a constant (versu s alternating) flow setting. These power heads were positioned in various corners of t he tank, where they could be swiveled horizontally to change the angle current flow. r a and b: Two tank formats: ( a ) Mesh separating the occupied portion of the tan k from the power heads and filter box (seen external to ta nk); ( b ) Power heads, capable of swiveling for changes in current direction, with alternate locati ons indicated with Xs. The side view shows the power heads and the approximate substrate set up, w hich both tanks had. (S. Sherman, 2010)
8 22 nnA total of 225 brittle stars were documented at Cay os Cochinos. Twenty-seven sites consisting of 17 C. vaginalis and 10 nonCallyspongia vaginalis sites were examined. NonC. vaginalis sites and their brittle star totals are given in T able 4. One Callyspongia site, in addition to a sea fan site, occurred with the branching fire coral, Milleporta alicornis (Linnaeus, 1758). The variation in the height rang e between Callyspongia sites was 30 cm-66 cm. Site # Common Name Species # Individuals 1 Purple Sea Fan Gorgonia sp. 1 2 Black Sea Rod Plexaurella homomalla 2 3 Bent Sea Rod Plexaurella flexuosa 4 4 Purple Sea Fan (w/ branching fire coral) Gorgonia sp. (w/ Millepora aclicornis) 3 8 Grooved-blade Sea Whip Pterogorgia guadalupensis 4 12 Black Sea Rod Plexaurella homomalla 2 20 Purple Sea Fan Gorgonia sp. 6 22 Knobby Sea Rod Eunicea spp. 5 27 Pink Vase Sponge Niphates digitalis 1 30 Knobby Sea Rod Eunicea spp. 5 ./ : Brittle Star Count by NonCallyspongia Site
8' r a and b: The Black Sea Rod, Plexaurella homomalla; the Bent Sea Rod, Plexaurella flexuosa with brittle stars clinging to its inner branches ( S. Sherman, 2010) r a and b: Site 8, a grooved blade sea whip Pterogorgia guadalupensis (S. Sherman, 2010)
8 r a d: ( a) Gorgonia sp with three brittle stars, indicated by the arrows Note that the top two cling to Millepora alcicornis, a fire coral commonly associated with such gorgoni ans ( c and d ) The Pink Vase Sponge, Niphates digitalis (S. Sherman, 2010)
8 r0 a and b: Knobby Sea Rod, Eunicea spp. with the 5 total brittle stars of the site in view, indicated by arrows approx. pointing to their disks ( b) (Site 22) (S. Sherman, 2010)
8* \ r : Brittle stars among M illeporta alicornis on a a Callyspongia vaginalis site (S. Sherman, 2010) : r a. and b: Comparative densities of brittle stars ( a C. vaginalis with 44 individuals, not all in view ( b) Knobby Sea Rod with 5 brittle stars (S. Sherman, 20 10)
81 r* : Brittle Star Count by Site Type (OS = Vase Sponge SF = Sea Fan, SR = Sea Rod, SW = Sea Whip, TS = Tube Sponge). This Chart combines the sea fans and the sea rods in their own categories respectively in order combine objects with relative ly similar resource categories. $/#$("8".$C. vaginalis showed the greatest range of brittle star numbers than any other site type. Although tube sponges with brittle stars in e xcess of five individuals were predominantly examined, it was much less common to find C. vaginalis sponges with any amount of brittle stars present to have less than f ive brittle stars. Two such C. vaginalis sites were found in the bay, but they totaled two a nd three brittle stars respectively and left out of the study since only C. vaginalis sites with excess of five individuals were examined for this portion of the study. Additionall y the relatively few nonCallyspongia sites that existed show the preference of O. suensonii for C. vaginalis in the Cayos
8. Cochinos bay since the former site type had signifi cantly lower numbers of brittle stars on average. Since the nonCallyspongia sites were much more limited and never exceeded six individuals, it shows that C. vaginalis provides not only preferred resources for this brittle star species, but resources that s upport a greater number of individuals per local. Tube sponge sites exceeding five individuals on tube sponges were readily available in the Cayos Cochinos bay, whereas nonCallyspongia sites, including other sponge sites, were not found to exceed six individu als, despite scouring the Bay for all nonCallyspongia sites. These sponges seem capable of supporting much highe r numbers of brittle stars on average, as well as being the preferred perch. B rittle stars were found in much higher aggregations on sponges with a mean percentage of 1 1.29 individuals per sponge (and 10.37 with the 2 omitted sites numbering two and th ree individuals). NonCallyspongia sites showed a mean of 3.3 individuals per site. While C. vaginalis readily supports O. suensonii not every C. vaginalis sponge in the bay was occupied by O. suenonii which suggests differences between resources provided by certain sponges of the species, whether due to their own qualities or that of their placement in relation external conditions, su ch as current flow. Of the nonCallyspongia sites, the sea fan gorgonians more readily exhibit ed brittle stars and additionally showed the greatest range of individuals when compared to the other nonCallyspongia sites. The sea whip gorgonian exhibited a slightly higher brittle stars count than the sea fan gorgonians, bu t consisted of only one site for its type.
88 Number of brittle stars per site was looked at in t wo fashions: the total number of brittle stars relative to the depth of their and th eir site and total of individuals versus object height. This aspect was further broken down looking at this comparison by object category and no correlation was found. $'(,9$2#$Brittle stars were not only seen in association wit h the organisms, such as sponges and gorgonians, on which they were found, but a var iety of fishes. During brittle star observation, it was noticed both at the time of res earch and in photographs that certain fish species were common to the brittle star sites. These fish included know predators, such as Thalassoma bifasciatum (Bloch, 1791) and Canthigaster rostrata (Bloch, 1786) as well as those fish seemingly unassociated, but c o-occurring with the ophiuroids. Common Name Latin Name Cleaning Goby Elacatinus genie Various Gobies Elactinus sp. Yellow Tail Hamlet Hypoplectrus chlorurus Blue-Headed Wrasee Thalassoma bifasciatum Sharpnose Puffer Canthigaster rostrata Unidentified Fish --(*) Indicates known predator ./ Fishes Species of O. suensonii Sites The blue-headed wrasse, Thalassoma bifasciatum is a predator of brittle stars, including Ophiothrix species. These wrasses can have 30% of their diet m ade up of brittle stars (Hendler, 1985) and were frequently seen in t he vicinity of research sites. It is
83 possible that these fish may have been more-so draw n to the sites by the activities of the researcher near such brittle star-dense areas and i t should be noted that this species was relatively common throughout the bay of the researc h areas. At one of the sites rich in brittle stars, a young specimen of the Sharpnose Puffer, Canthigaster rostrata (Bloch, 1786), a predator of Ophiothrix species, was observed amongst the tubes of the sites sponge and can be s een in Fig. 50 a. At this site, a fish, likely the Yellowtail Hamlet Hypoplectrus chlorurus (Cuvier, 1828), was also noticed. A study examining the diet this species and its conge ners found that this slow-swimming genus subsists on benthic organisms (Randall, 2004) While no echinoderms were observed in their stomach contents of this study, i ts presence on the site amongst other predators raises question as to whether or not it, too preys upon brittle stars. Gobies of the genus Elactinus that occurred on multiple brittlestar sites and we re possibly represented by multiple species, including the species Elacatinus genie (Bhlke and Robins, 1968), known as the Cleaning Goby. Thes e sites included site numbers 5, 14, 16, 17, and 25 and included not just C. vaginalis but also that of the vase sponge, N. digitalis of site 2. It is not known whether this fish inte racts with the brittle stars, but it likely chooses the same structures associated with the brittle stars for reasons such as shelter.
34 r+ : a, b, and c: ( a ) Site 17 with the densest aggregation of brittle s tars with known predators circled in white, a goby in red. ( b ) The blue-headed T. bifasciatum male with the yellow female pictured below (NEAQ, 2008). ( c ) Elacatinus spp. next to a C. vaginalis site. (Photos 49 a and c by Author). Fig. 50 b: http://divers.neaq.org/2008_08_01_archive.html r : a, b, and c: ( a ) Sharpnose Puffer, Canthigaster rostrata ; ( b) Unidetified fish, likely a hamlet, with a female T. bifasciatum (c) Close up (S. Sherman, 2010)
3 r :a and b: Gobies of the genus Elacatinus on C. vaginalis site 16, possibly the shark goby, E. evelynae (Bhlke & Robins, 1968) (S. Sherman, 2010) r a and b: ( a ) Elacatinus sp. and an unidentified fish, shown in a close-up ( b ). This fish quite possibly utilizes the sponge as shelter, versus bei ng attracted by the brittle star (S. Sherman, 2010) /#Two-hundred and eight brittle stars were noted in t he present survey for their coloration. Each was assigned to one of the followi ng: orange, yellow, purple, yellow to orange, purple and orange, brown and white, and dar k to brown (See figures 57 to 60). The colors of orange, yellow, and purple were typic ally solidly and distinctly colored.
3' The dark to brown category contained individuals to o darkly colored to be identifiable as clearly purple to those mostly brown in color. Dist inction between color categories was not always clear to delineate, but colors were plac ed as close to the given categories as possible. Regardless these specific categories, the ir shading represent the overall color variation of brittle stars at this local. In terms of range of color categories, brown individuals occasionally had white bands along the arms, but were labeled as brown when the banding was not crisp. Purple and orange brittl e stars were found on sites 5 and 14, both tube sponge sites. This rare coloration exhibi ted varying amounts of purple and orange on an individual, composing different portio ns and percentages between the brittle stars. These individuals also varied in degree of o range to yellow coloration. The grouping of individuals ranging from yellow to oran ge was shaded within the spectrum of the two colors and not easily identifiable as disti nctly orange or yellow. This group was limited to six individuals on site 26. Results: Of the assigned categories, purple composed more th an half of the O. suensonii individuals examined for all sites. Figure 54 shows the overall percentages of colors. The results are as follows:
3 Brittle Star Color Count, Percent All Sites %*1 Orange, 2 Yellow, 3 Purple, 4 Brown, 5 Brown + White, 6 Orange to Yellow, 7 Grey, 8 Orange and Purple
3 Brittle Star Color Count, Percent Sponge Sites r : 1 Orange, 2Yellow. 3 Purple, 4, Brown, 5 Orange to Yellow, 7 Grey, 8 Orange and Purple To examine brittle star coloration by substrate sh ading, rather than substrate type, sites were labeled either as dark or as light. Thos e that are considered light include all C. vaginalis sites and the bent and knobby sea rods. The black sea rod, sea whip, gorgonian fans, and t he pink vase sponge were labeled dark. The follow color ratios by dark sit e types are given in the following chart. The pie charts of the light sites showed very littl e noticeable difference between the coloration for total brittle stars or for the spong e sites alone. This is potentially because of the majority of sponge sites both in the total as w ell as within this category, resulting in less of a disparity. Those sites that were dark how ever, were graphed in the following
3* chart and a significant variation was noticed in th at the majority of the brittle stars were not purple, but the second most common coloration o n the other sites: Orange. These sites additionally showed less variation in colorat ion, but this may very well be due to the fact that fewer sites in this category. Overall the se brittle stars at Cayos Cochinos were found to contrast their substrate in both light and dark substrate categories. Coloration of Brittle Stars on Dark Sites r0 : 1 Orange, 2 Yellow, 3 Purple, 4 Dark to B rown, 5 Brown and White. To see if individuals were colored in relation to the object on which they were found, percentages of coloration were examined for each type of object. Mean indi viduals per location type
31 r a and b: ( a ) Brown morph and ( b ) an odd coloration of a purple specimen with yello w spines (S. Sherman, 2010) r : Yellow morph with the distinct Ophiothrix banding apparent in the left photograph (S. Sherman, 2010)
3. %*3a, b, and c: ( a ) Grey Morph; ( b ) Brown and White Morph; (c) Purple and Orange Morph with orange legs and a distinctly purp le disc (S. Sherman, 2010)
38 %14: Orange variety on the left and an orange to yello w on the right (S. Sherman, 2010) nn%/'!$$ While brittle star behavior in this study was most ly limited to their object inhabitation and its subsequent implications of beh aviors pertaining to predator avoidance and feeding, a variety of crinoid behaviors, such a s posture formation, locomotion, interactions with non-crinoid organisms were observ ed amongst the various comatulids kept. Some of these behaviors were seemingly specie s specific. When disturbed by a physical force, crinoids often will close quickly by curling their arms over the body. This aspect was particularly ob served in L. palamata form brachypecha This crinoid, when it was touched or the shell su bstrate to which it clung was disturbed, responded rapidly in two fashions: o ne, in which it would quickly curl closed, and a second where it would open and extend its arms aborally in a fashion that
33 clung to its substrate. This crinoid, when I tried to relocate it by moving the shell to which it was attached, deployed its arms as describ ed onto the surrounding substrate. Its cirri were attached to the shell and partly on the substrate around the shell. It was noted that the ends of the pinnules felt rough and somewh at as hooks, but not uncomfortably so, and stuck to the fingers of the observer, cementing the crinoid in its place. After the stimulus of the movement of the shell ceased, the c rinoid slowly resumed its position. The crinoid would close rapidly when the substrate of the shell was tapped, versus the gradual moving of its shell substrate. It may be po ssible that some physical contact with the observer elicited this latter response in part, but repeating with an additional light tap to the shell after the crinoid resumed to a neutral posture elicited the same response. Possible reasons for these particular behaviors cou ld deal with coloration and pattern, as Clark (1921) suggests, or protection of the animal or possibly even be both. It is possible that perhaps curling protects viscera when disturbe d by some types of stimulus, while other motions cause it to grip firmly to the substr ate to prevent its removal. Once the arms were deployed and curled around the surroundin g substrate, it was difficult to move this comatulid and it was thus left in place. Perha ps a potential fish predator would only be able to remove a portion of this crinoid while i t grips the substrate in such a manner. Clark (1921) observed a Mariametrid feather star (w hich he ascribed to the genus Lamprometra ), most likely this species variety with its yellow -tipped distal pinnules, to be one of the more interesting of comatulids he exa mined during his collections on his trip to the Torres Strait. He described the closing of the crinoid when it was turned over from its more hidden, rocky habitat:
44 When the rock was overturned, the arms would be mo re or less closed over the mouth, the whole animal appearing like a tuft of gr een sea-weed, but on being touched the arms instantly and all together were laid back flat against the rock and the broad white band flashed into view. The immediate effect was ob literative and ones first thought was that the animal had vanished H.L. Clark (1921) Modern observations witness this crinoid variety to inhabit macro algae and beds of sea grass (Messing, 2007), potentially supportin g the belief that its colorations and behaviors are for the purpose of camouflage in that its seaweed appearance would likely cause the crinoid to blend-in with its green surrou ndings when closed. rrAnother behavior that was predominately species-spe cific in this study was seen in O. erinacea. Before opening to feed, O. erinacea was observed to pump its arms repeatedly. During this motion, O. erinacea would move a partly curled arm up and down in rapid jerks, followed by a slightly slower retur n stroke. This behavior has been previously documented, but its exact function is un known. Typically after the stimulus of food, only one arm would begin with this motion, fr equently followed by the similar motions of others. When heavy quantities of brine s hrimp nauplii were added to the tank, pumping behavior occurred in multiple arms simultan eously. The L. palmata form brachypecha specimen was also observed to pump its arms. On th e upstroke, the pumping arm would repeatedly and swiftly run throug h the pinnules of a neighboring arm. While it is unknown why this behavior occurs, it may be in order to free the surface of the arms and pinnules from ectoparasites (Meyer, personal communication), debris, or excess food particles clinging to mucus. As Craig a nd Emson (1995) observed such rapid
4 movements in stalked isocrinids in reaction to the possible unwanted settling of small crustaceans, these reactions could likely be in res ponse to the nauplii. On the feather star Florometra serratissima, mucus occurs in thin strands of less than a millimeter and portions a few square millime ters in size. While these formations of mucus were not seen in the crinoids of the present study, those of F. serratissima were found to contain organic debris and diatoms (Byrne and Fontaine, 1981). Mucus in feather stars may additionally function to remove u ndesired material, such as excess food or undesirable particles. During some feeding periods, large densities of foo d were distributed. Excess mucus, heavy with particles, was flicked of by th e arm pumping during feeding of Unkown Mariametrid and L. palmata form bracheopecha In these particular cases, the feather stars possibly removed such heavy-laden muc us strands as a coincidental action of their pumping actions or purposefully to elimina te excess food within mucus. The brown unknown crinoid, when food was introduced and flowed over the organism, its pinnules would often move frantically against each other along the arm, possibly wiping the pinnules or the tube feet. r r !rrr"#!$% The various feather stars in this study had interac tions with other organisms while in aquaria: possible and known associations, and po tential threats.
4' All the crinoids of the first and second batch perf ormed well in aquaria until an accidental introduction, and subsequent bloom, of t he anemone Aipstasia Following introduction the majority of the organisms appeared stressed and began to autotomize pinnules, arms, and in some cases their cirri. As t he bloom increased, the condition of the crinoids declined and all (but one Oxymetra sp. ) of the crinoids eventually died. While there is no direct evidence of the Aiptasia causing stress and the eventual death of the specimens, its occurrence in the situation should n ot be ignored. The anemone Aiptasia is known to sting and it is possible that their stingi ng was stressful to the feather stars. Although anemone stings have not been known necessa rily to affect crinoids, it is also possible that some chemical nature of the Aiptasia may have been distressing to them (Meyer, Personal Communication). Being that they co uld not remove themselves from the situation, if they were bothered by the anemone s (whether by stinging or other qualities), these feather stars were stuck in an en vironment of the proliferating creatures. One specimen of the Oxymetra sp. seemed less affected (if at all) by the Aiptasia and continued to survive after the death of the two L. palmata and other Oxymetra sp. specimens kept during this period. A young, unident ified anemone, likely Aiptasia was found growing on the cirrus of this seemingly unaff ected individual. Note that the coloration of the anemone is likely artificial: upo n preserving the Oxymetra specimen, its red pigmentation bled into the surrounding 100% gly cerol solution (preservative) in which these portions were preserved and likely dyed the anemone in the process. Upon the death of one Lamprometra palmata specimen, an unidentified worm was found clinging to the calyx of the feather star Its association was not noticed until
4 after the death and its role in association is unkn own, although myzostomes and other worms have been known to inhabit, feeding off of th eir food-laded mucus (Lanterbecq et al., 2006). %1a and b: (a ) Unidetified anemone on the cirrus of the Oxymetra sp crinoid, seen as a small protrusion on the cirrus. ( b ) Dried worm on calyx and beginning of division series of L. palmata. (S. Sherman, 2010) Hickman (1967) states the common association of hyd roids along the bases of crinoids. This was found to be the case with L. palamata form brachyopecta in that shortly after its introduction to the aquarium, hyd roids were noticed to be growing along its base. These hydroids were noticed within a few days after the introduction of the feather star. The hydroids attached to the same she ll substrate as the crinoid and were not noticed at the base of the other crinoid introduced with it, nor were they observed elsewhere in the aquarium, despite searching.
4 r0: Unidentified hydroid colony around the base of L. palmata form brachypecha (S. Sherman, 2010) r0 : Close up of Hydroid under microscope, likely fill ed with brine nauplii (S. Sherman, 2010)
4* rnrAfter such periods of stress as transport, portions of the arms of the crinoids were autotomized by the crinoid and subsequently collect ed by the observer. These portions and their primary podia were observed microscopical ly for two individuals: both the L. palmata (green) and Oxymetra sp. Despite the fact that the arm portions were no long er attached to the organism, the primary podia remaine d extended and continued to feed for both species after removal. Capture continued as pa rticles were observed traveling down the ambulacra in a unidirectional fashion, despite their disconnection from the remaining tracts leading to the mouth. A rough comparison was made of the primary podia and their spacing between the species. The Oxymetra sp. specimen had shorter, more closely spaced primary podia compared to the L. palmata specimen (green), whose podia were clearly longer and more widely spaced. The pinnules in the latter were also more widely spaced in the portion of the arm examined. While au totomized arm portions of L. palamata form brachypecha were also examined microscopically, they were at a later time than the first two crinoids. Regardless, this specimen too had activity of the primary podia after autotomozation although no capture or t ravel of particles was specifically witnessed. While only a gross comparison of the length and spa cing of the tube feet of the two species of feather stars was done. Meyer (1982) found that the tube feet of L. palmata individuals from Palau were on average a half mill imeter long at a density of nine tube feet per millimeter. Pinnular ambulacra m easured 0.2 mm.
41 Additional distinctions in physical features betwee n the two crinoids were most notably differences in cirri. Those of the Oxymetra sp had very long, curved cirri that were the same color as the main crinoid body. Those of L. palmata were very short, more greatly curved, and pale in color. r0 : Comparison of primary tube feet: Oxymetra sp. ( Left ) and L. palamata ( Right ) (S. Sherman, 2010) Oxymetra sp. was observed swimming multiple times, but never fu lly left the substrate. Its arms oscillated in a seemingly alter nate fashion while the cirri were dragged by the crinoid. Swimming was frequently observed af ter the introduction of a food cloud to the organism. The particle density or temperatur e change of the occasionally chilled food may have been indicative of poor surrounding c onditions for the crinoid and may be factors in stimulating swimming. None of the other crinoids in the study exhibited
4. swimming except L. palmata (green), which moved its arms in strokes comparabl e to swimming in is container during transport. 4$#$r'!The crinoids in this study formed various postures under the varying conditions, but all held the pinnules in one plane. Of the crin oids in the study, those of the Lamprometra genus would, either between feeding times or just a fter the introduction of food, extend only one or two arms before opening. S ee Figure 66 a to c. This behavior was described by Breimer (1978) as occurring before posture formation, but without further elaboration on why it may occur. Whether th is one arm was extended simply as the initial step in the process of opening or wheth er this was done to test the surrounding water cannot be definitively determined However, this aspect of behavior may likely be done as a means of testing the conten t of the water concerning appropriate food or particle concentration. If this is the case it would save the crinoid energy to determine first whether the external conditions wer e suitable for feeding before expending the energy to open fully while more-so ex posing themselves to predation. Since these crinoids were also known to perform thi s behavior prior to the introduction of food, it potentially suggests that they may utilize this behavior as a constant method of testing without fully exposing themselves to predat ors. Regardless of this behavior, many of the crinoids, if closed, would typically open after the introduction of food in roughly a twenty minute period, but could take as long as an excess of forty minutes. The brown Mariametrid s pecies remained exposed and opened during most hours of the day and was not obs erved to fully curl, while L. palmata form brachypecha would frequently curl between feedings, but would open after
48 exposure to food currents. It was common enough in both the L. palmata and the Oxymetra species to exhibit closure between feedings, but w hen this did occur, it was often not performed fully (i.e. arms were loose and partly opened). r0 ad: L. palmata (red) on 2 occasions ( a and b ) After 14 minutes and food introduction into a radial fan ( b and c ) Fully open after 15 minutes from clinging to the mesh to a multi-directional or irregular fan (S. Sherman, 2010) *The bottom left is additionally crawling form, alt hough here it is its stationary form before opening
43 %11a and b: Irregular to arcuate fans with (b) showing the importance of strong, unidirectional flow for these organisms as they ori ented themselves immediately in front of the power heads (S. Sherman, 2010) To illustrate the importance of flow for crinoids, certain behaviors of L. palamata form brachypecha must be described. Upon initial introduction into the tank, both crinoids of the final batch were dipped into the ta nk from their acclimatized containers and allowed to settle. This L. palmata specimen settled on the gravel floor and did not relocate by the fourth day, nor was it observed to open. While the brown crinoid remained at its initial location, it was responsive to food and exposed to current flow. The area where the Lamprometra crinoid rested appeared to be out of the way of th e current flow, as it was blocked by surrounding substrate ma terial. Since the crinoid did not appear to be feeding and was the more distressed of the two (upon arrival it showed more autotomization than the brown crinoid), it was relo cated to an exposed perch via the piece of shell to which it was attached in the gravel. He re it pumped two of its arms alternately, but was not observed to open. The foll owing day the crinoid was fully open and feeding, a behavior seemingly indicative of its new exposure to more suitable and
4 stronger current flow. When food was introduced on this day it adjusted its feeding posture more rigidly and in a more distinct form a flatter fan and more widely-spaced arms, ready to feed. Of the red and green colored L. palmata specimens, both of which confirmed the tendency of this species for strong, uni-directiona l flow by orienting themselves immediately in front of the power heads located beh ind the mesh, which can be seen in Figure 66. Species Posture Formed Reported Posture L. palmata Arcuate, Multi-layered Biplanar arcuate, funnel, or shallow bowl. Irregular radial L. palmata form brachypacha Arcuate, Irregular Oxymetra sp Parabolic --Oxymetra erinacea --Radial Bowl BROWN UNKNOWN Radial, Unidentified Posture, --./0 : Posture Formations by Species (*Species not used in this study, but for comparison) (Compiled from Meyer and Macurda, 1980; Messing, 19 94; Messing 2007 ) All of the species remained exposed at all times, b ut varied in degree and time opened. Regardless of the degree of curled posture, all species opened and appeared to feed when food was introduced, showing flexibility in the diel patterns of these Mariametrids in terms of particle availability.
The two specimens of L. palmata form the first trial both exhibit the arcuate feeding fan typical of Mariametrids, a multi-layere d array, and an irregular blend between these two postures. r0 a and b: Arcuate fan exhibited by L. palamata form brachypecha; The brown mariametrid, with fewer arms and a less dense fan, formed a Radial fan consistently and had the least variable postures of all the other crinoids i n the study. (S. Sherman, 2010) When it comes to the members of the Oxymetra genus, relatively little is known about their ecology, such as habitat and posture fo rmation, as when compared to Lamprometra species. Oxymetra sp formed the following postures: parabolic and pote ntially the radial. One specimen attached itself to the mesh below the pump heads and rested its arms against the glass and mesh. This positioning relati ve to the currents likely made this individual functionally stalked, making its posture formation comparable to other functionally stalked crinoids (Meyer and Macurda, 1 980). This posture is featured below in Figure 68.
' %18a and b: Front and side view of Oxymetra sp forming the Radial to Parabolic Fan as a functionally stalked crinoid (S. Sherman, 2010) r0* : Approx. sketch of such posture and its orientatio n to current flow. For the simplicity of the diagram: the pinnules are not alternating and i n the Top View, arms have been omitted for clarity, although the general shape of the fan pres erved (S. Sherman, 2010)
The unknown Mariametrid exhibited an odd posture fo rmation that may be previously undescribed in crinoids. All of the arms rested radially on the flat, angled substrate, but with the pinnules oriented perpendic ularly to the substrate (edges of the pinnules touching the rock) in what might be consid ered a horizontal version of the radial filtration fan. The substrate of the perch was angl ed and the current flowed directly across its surface and perpendicular to the pinnular plane Arms were seemingly oriented for unidirectional flow and slightly curved down curren t. Figure 65 represents an approximate sketch of this posture. Both Lamprometra palmata and Oxymetra sp. exhibited a 2-row planar pinnular arrangement described by Meyer (1973). Enough tank space was provided to create potential space between individuals, but despite th is, the L. palmata species exhibited overlapping filtration fans. This behavior occurred infrequently and never between different species. It is unknown whether this behav ior was done to create a better baffle beneficial (as described Wilson, 2005) for both org anisms or if this was the result of an incidental overlap due to the close proximity of in dividuals at a favorable position relative to current. Often, during the feeding periods, the crinoids wou ld uncurl one arm, usually after exposure to food. The extended arm would rema in so, often eventually followed by opening of the other arms. This extension may perfo rm as a method of the crinoid to test currents for food particles before expending the en ergy to open fully.
%.4a, b and c: Possible tester arms see in L. palmata form brachypecha in the left photo and one, tester arms for L. palamata in the center and two for the same individual in a different location in the far right image (S. Sherman, 2010) 5222,8:,82,8!"#"!"nn 2&r$$#4#$ Because the wrasse species, Thalassoma is not deterred by spicules or spiculated spongin (Hendler, 1985 phide Chanas & Pawlik 1995, 1996), these aspects of the sponges likely do not serve to protect brittle stars agains t fishes. While the sponges may still offer protection, it is likely the association of Ophiothrix suensonii with the sponges is primarily a mutualistic behavior related to feeding Although the occupation by these brittle stars within Callyspongia was a rare occurrence, a study by Chevarro and colleagues (2004) proposed that this behavior by th e brittle star might function for protection. On the densest Callyspongia sites in which predators frequented, the brittle stars in this survey showed no such behavior, raisi ng question as to why these brittle stars inhabit the sponges and if predation comes into pla y.
* ,.;#6.##The height of brittle stars above the surrounding s ubstrate has proved to correlate for this species in terms of numbers in a previous study because, according to (Chevarro, et al. 2004), it elevates the brittle stars for bet ter suspension feeding as these organisms are: are dependent on sedentary coelenterates to place them in a position in the water column where they can effectively exploit the available resource. Emson, 1995 Although the depth and height of each site object a bove the surrounding substrate were measured in this study, neither showed any sig nificant correlation to the number of individuals present. Perhaps the lack of correlatio n to these values likely indicates that neither factor contributes to resources available b y the site to the brittle stars in the Cayos Cochinos Bay. Height likely showed no correlating f actor in this study because this value alone does not relay the dimension of the objects. If the size of an object were indicative of the resources provided by the object, objects su ch as sponges should then be looked at in terms of volume (i.e. pumping ability), or sea f ans their surface area. Depth showed no relation to the number of brittle s tars present. While O. suensonii is found in shallow waters, it is known from much greater depths than those covered in the survey. The depth range of this stud y was small: between zero and five meters. The lack of correlation between depth and b rittle star number indicates that within this range, depth is an insignificant factor If resources of the water do come into play when it comes to brittle star count, then othe r qualities of water may should be
1 considered, such as current flow, water content aro und the sites, and how these qualities pertained to the necessary requirements for s suspe nsion-feeding brittle star. Concerning the object habitation, the findings in t his study occurring with some of the findings reported by Devaney (1974) is his s urvey of Ophiothrichidae brittle stars from British Honduras as Ophiothrix orstedii has also been reported on Millepora hydrocorals. However, in his study, O. suensonii was reported on gorgonians and sponges, and he was unable to match a previous repo rt of this species additionally occurring on alcyonarian corals. This study also sh owed O. suensonii as inhabiting N. digitalis a finding supported by Chevarro and colleagues (2 004), but not by Devaney. /#This study found similar ratios of coloration for a ll lightly shaded objects on which brittle stars were found in the bay. Not only were these proportions mostly observed on Callyspongia versus nonCallyspongia sites, dark-colored sited showed a much greater portion of contrasting and bright colo rs (i.e. orange, yellow, or yelloworange). In effect, all lightly colored sites and t he overall distribution were darkly colored brittle stars on light substrates and lightly color ed brittle stars on darker substrates. Concerning coloration, different regions have not o nly different ratios of color morphs, but different color morphs (such as light p ink) than those found at the bay of Cayos Cochinos or noticed in the surrounding island s during casual diving observations. Few, if any, studies address the distribution of co loration of O. suenonii from a regiontypical standpoint so a general look at these regio nal differences as well as why they occur should be examined.
. Although Ophiothrix suenonii is typically brightly colored species where ever i ts recorded region, it is unknown why these brittle st art would contrast their perches, but perhaps the prevalence of these brittle stars in ex posed areas then raises question as to what factors protect O. suenonii on the reef from the mass amount of predators, suc h as T. bifasciatum Additionally, these stars can compose great perce ntages of reef fishes diet, though the spines of Ophiothrix species are distinctive features of this genus do not readily break down (Randall, 2004) during digestion s, potentially composed a greater percent of the identifiable species than that actua lly consumed by the reef fish relative to other prey. Since spicules do not deter Thalassoma which readily consume brittle stars and are not deterred by spicules, further examinati on into why these brittle stars are so colored in this environment, or what limiting facto rs control their predation. !"#"!"nn$$#,r$"$Although the various organisms with which O. suenonii inhabitss likely provide similar relationships between themselves and brittl e stars, those organisms associated with the crinoids in this study are more varied. Th e crinoideal associates of this study primarily concern worms, anemones, and hydroids. Before being purchased by the researcher, the final batch of crinoids, like all others used in the study, were acquired through a w holesaler as wild-caught specimens that were kept in small tanks with shared circulati on. Whether the hydroids attached in a non-natural setting, such as from one of these hold ing tanks, or if these organisms associated with this particular crinoid in its natu ral setting, cannot be definitively known, but these hydroids were almost certainly attached t o the crinoid prior to introduction to
8 the aquarium. The crinoid maintained to seem unaffe cted by the hydroid colony as it continued to regenerate rapidly during the study, d espite the gradual proliferation of the hydroids around its base. It remained on this shell perch until moved by the researcher. Concerning the Aiptaisia and eventual decline of the crinoids, further exam ination of the co-occurrence of these species and possible specific effects of the crinoids should be examined. Finally the worm found on L. palmata and observed on the calyx during life, while unidentified, is likely of a group of w orms known to associate with feather stars. %/'!$The pumping of the arms, while noted in one study o f stalked crinoids, may not be documented for feather stars, but the practice s eems to similarly function in response to large amounts of crustacean, although it may hav e additional functions pertaining to feeding. No materials as of yet have been uncovered by this researcher concerning the continued feeding of autotomized crinoid portions, although crinoids are known to survive severe attacks, including regenerating thei r removed viscera. This latter occurrence may shed light on the feeding of automiz ed portions in that a damaged crinoid, while missing portions, may continue to fu nction and feed with its remaining body while regeneration takes place an attack. #")Longer, more widely-spaced tube feet and shorter ci rri are traits of a feather star living in less exposed areas (Meyer, 1973). The Mar iametrid species exhibited traits of a
3 potentially less-rheophilic species compared to the Oxymetra sp. species in respect to podia and cirri. However, these organisms should st ill be considered those seeking faster, unidirectional flow for the following reasons: 1) T hat they never remained in infrastructure, but fed in areas of the tank expose d to current and exhibited postures for such currents; 2) Species did not vary exposure wit h diel patterns (Wilson, 2003); 3) These organisms not only sought flow, but the maxim um flow velocity available (in front of the power heads). Additionally it is known that Mariametrids have been found to be nocturnal and vary in crypticity based on diel patt erns (Fishelson, 1969?). Why these species, known for such behavior, remained exposed may be due to the fact of a predatorfree environment, as well as an environment that ci rculated the current supply (with food), although was filtered over time. 4$#$#/The feeding postures formed by the crinoids in thi s study agree with much of the previous observations of their formation at the spe cies level. The posture formed by the unknown brown crinoid is currently an undocumented posture and thus cannot be compared to other postures formed by this species o r by the extant crinoid population. Although the L. palmata and L. palmata form brachypecha represent the same species, L. palamta form brachypecha had notably varied posture formations and general behavior than the other two specimens of L. palmata and it has been debated as to whether or not these two organisms actually represe nt different species (Messing, Personal Communication). Based on their distinct be havioral differences and appearance, it seems quite likely that these organisms do repre sent organisms from slightly varied ecological niches, whether or not they are differen t species.
'4 Additionally, it was this crinoid that showed how c rucial current flow is for the well-being of the crinoid. Without the proper curre nt conditions, or even without general current flow, a crinoid is unable to feed. In its l ess-than-optimal placement in the aquarium, this crinoid would not open to feed and w as thus unable to feed. Feather stars in their natural habitat are known to seek more fav orable current conditions. Why this particular feather star did not seek a more favorab le perch cannot be definitively known; perhaps it was related to the recent stress of tran sport and new settings. This feather star remained closed at all times of observation for day s and soon opened upon exposure to current flow. It is almost certain that this organi sm would have remained closed in its non-feeding form for longer than it was, at cost to its health, if it were not relocated by the researcher. For how much longer it would have r emained closed without opening to feed or seeking a more favorable perch cannot be de termined.
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