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The Effects of Acute Bleaching on Attachment of the Soft Coral Sarcophyton Elegans

Permanent Link: http://ncf.sobek.ufl.edu/NCFE004292/00001

Material Information

Title: The Effects of Acute Bleaching on Attachment of the Soft Coral Sarcophyton Elegans
Physical Description: Book
Language: English
Creator: McDavid, Amy
Publisher: New College of Florida
Place of Publication: Sarasota, Fla.
Creation Date: 2010
Publication Date: 2010

Subjects

Subjects / Keywords: Coral Bleaching
Attachment
Settlement
Soft Coral
Genre: bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Coral reefs are important ecosystems that support life for a plethora of organisms. With the raising of the ocean temperatures due to global warming over the past thirty years, corals have begun to bleach, or expel their zooxanthellae, a symbiotic dinoflagellate, crucial to coral health and survival. Little is known of how well corals can recover after bleaching. In this pilot study, I investigate the attachment of a soft coral, Sarcophyton elegans, after bleaching. Six fragments were acutely bleached in sea water with an elevated temperature for 1.5 hours. These six fragments were then placed next to six fragments that did not undergo acute bleaching. All twelve fragments were maintained under normal growing conditions. Attachment to substrate between the two groups was compared. Noteworthy differences between attachments of the two groups of fragments were not observed.
Statement of Responsibility: by Amy McDavid
Thesis: Thesis (B.A.) -- New College of Florida, 2010
Electronic Access: RESTRICTED TO NCF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE
Bibliography: Includes bibliographical references.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The New College of Florida, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Local: Faculty Sponsor: Gilchrist, Sandra

Record Information

Source Institution: New College of Florida
Holding Location: New College of Florida
Rights Management: Applicable rights reserved.
Classification: local - S.T. 2010 M1
System ID: NCFE004292:00001

Permanent Link: http://ncf.sobek.ufl.edu/NCFE004292/00001

Material Information

Title: The Effects of Acute Bleaching on Attachment of the Soft Coral Sarcophyton Elegans
Physical Description: Book
Language: English
Creator: McDavid, Amy
Publisher: New College of Florida
Place of Publication: Sarasota, Fla.
Creation Date: 2010
Publication Date: 2010

Subjects

Subjects / Keywords: Coral Bleaching
Attachment
Settlement
Soft Coral
Genre: bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Coral reefs are important ecosystems that support life for a plethora of organisms. With the raising of the ocean temperatures due to global warming over the past thirty years, corals have begun to bleach, or expel their zooxanthellae, a symbiotic dinoflagellate, crucial to coral health and survival. Little is known of how well corals can recover after bleaching. In this pilot study, I investigate the attachment of a soft coral, Sarcophyton elegans, after bleaching. Six fragments were acutely bleached in sea water with an elevated temperature for 1.5 hours. These six fragments were then placed next to six fragments that did not undergo acute bleaching. All twelve fragments were maintained under normal growing conditions. Attachment to substrate between the two groups was compared. Noteworthy differences between attachments of the two groups of fragments were not observed.
Statement of Responsibility: by Amy McDavid
Thesis: Thesis (B.A.) -- New College of Florida, 2010
Electronic Access: RESTRICTED TO NCF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE
Bibliography: Includes bibliographical references.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The New College of Florida, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Local: Faculty Sponsor: Gilchrist, Sandra

Record Information

Source Institution: New College of Florida
Holding Location: New College of Florida
Rights Management: Applicable rights reserved.
Classification: local - S.T. 2010 M1
System ID: NCFE004292:00001


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THE EFFECTS OF ACUTE BLEACHI NG ON ATTACHMENT OF THE SOFT CORAL SARCOPHYTON ELEGANS BY AMY MCDAVID A Thesis Submitted to the Division of Natural Sciences New College of Florida in partial fulfillment of the requirements for the degree Bachelor of Arts Under the sponsorship of Dr. Sandra Gilchrist Sarasota, Florida May, 2010

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TABLE OF CONTENTS Abstract..iii List of Figures....iv List of Tables..v Introduction........6 Overview of Corals....6 Physiology and Settlement of Soft Corals. The Zooxanthellae Endosymbiont .......15 Coral Bleaching and the Re lease of Zooxanthellae......17 Methods.....21 Results... Observations..........24 Fragments Coming Displaced....................... Timing and Percentage of Attachment Between the Two Study Groups............................................................................ Discussion.....................................30 Bibliography..... ii

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THE EFFECTS OF ACUTE BLEACHI NG ON ATTACHMENT OF THE SOFT CORAL SARCOPHYTON ELEGANS Amy McDavid New College of Florida, 2010 ABSTRACT Coral reefs are important ecosystems that suppo rt life for a plethora of organisms. With the raising of the ocean temperatures due to global warming over the past thirty years, corals have begun to bleach, or expel thei r zooxanthellae, a symbiotic dinoflagellate, crucial to coral health and survival. Little is known of how well corals can recover after bleaching. In this pilot study, I investigat e the attachment of a soft coral, Sarcophyton elegans, after bleaching. Six fragments were ac utely bleached in sea water with an elevated temperature for 1.5 hours. These six fragments were then placed next to six fragments that did not undergo acute bleaching. All twelve fragments were maintained under normal growing conditions. Attachment to substrate between the two groups was compared. Noteworthy differences between atta chments of the two groups of fragments were not observed. ____________________________ Dr. Sandra Gilchrist Division of Natural Sciences iii

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LIST OF FIGURES Figure 1. World-wide Coral Distribution.. Figure 2. Structure of Alcyonarian Autozooid......................................................9 Figure 3. Structure of a Cross S ection of Alcyonarian Autozooid........................9 Figure 4. Asexual Reproduction by Budding in Hermatypic Corals...................11 Figure 5. Synchronized Mass Spawning..............................................................12 Figure 6. Root Like Processes in Dendronephthya hemprichi Six Days After Cutting................................................................................13 Figure 7. Overview of Dendronephthya hemprichi Attachment to Substrate.....14 Figure 8. Subcellular Release Mechanism of Zooxanthellae During Bleaching.................................................................................19 Figure 9. Top-Down View of Placement of Twelve Coral Fragments in Sea Table.....................................................................................................21 Figure 10. Attachment of Control Fragment (#9) Figure 11. Attachment of Bleached Fragment (#1)..23 Figure 12. Attachment of Bleached Fragment (#2).. Figure 13. Control Fragment of Sarcophyton elegans Containing Endosymbiotic Zooxanthellae...........................................................24 Figure 14. Acutely Bleached Fragment of Sarcophyton elegans........................25 Figure 15. Attachment of Bleached Fragments on Days 8, 16, 22, and 30.........28 Figure 16. Attachment of Control Fragments on Days 8, 16, 22, and 30............29 iv

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v LIST OF TABLES Table 1: Percent Attachment of Each Fragment (#1-12) on Days 16, 19, 22, and 30......... Table 2: Average Percent Attachment and Standard Deviation of Bleached Group and Control Group on Days 16, 19, 22, and 30..................

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INTRODUCTION Overview of Corals Corals have existed for a long time; fo r scleractinian corals, known as stony corals, this period has been 240 million years (Wood, 1999). Corals containing photosynthetic endosymbionts inhabit the warm, clear waters of the tropics and subtropics (Figure 1) (Wood, 1999 ).Over the past 30 years, s ea water temperatures have been steadily rising causing widespread bleaching events (Bouchard et al, 2008). Bleaching is the expulsion of endosymbi otic unicellular dinoflagellates, called zooxanthellae, from coral cells. Figure 1: World-wide Coral Distribution The locations of coral reefs world-wide. http://www.nasa.gov/vision/earth/look ingatearth/coralreef_image.html Even though they cover less than one percent of the ocean floor, coral reefs are very diverse ecosystems, supporting nearly 25% of all marine species, including more than 4,000 species of fish, 700 species of coral, a nd thousands of others plants and animals (Coral Reef Alliance, 2008) Coral reefs provide food and protection for countless sea animals and humans. They provide a natural barrier for the shoreline from rough waves. Tourism of reefs provides a livelihood for many nations. 6

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Compounds with pharmaceutical functions ar e being discovered in corals. Many compounds have been discovered in soft corals, specifically Sarcophyton spp, that are pharmaceutically active. A novel chlorinated bi scembranoid was discovered and isolated from S. glaucum This compound is cytotoxic to KB cells (Kusumi et al, 1990), a carcinomal cell line. A compound, chatancin, has been isolated from Sarcophyton spp. This compound is a PAF (Platelet Aggregat ing Factor) antagonist, thus platelet aggregation and binding of PAF to its r eceptors are inhibited (Sugano et al, 1990). Sarcophytol-A has been found in a single sample each of S. glaucum and S. infundibulifurme. This compound inhibits teleocidin, a tumor promoter, in studies using mice. It was found that this compound is contained within individuals of S. glaucum and S. infundibulifurme; its distribution is not species wide (Koh et al, 2000). With all of this potential within soft corals, it is import ant to understand what occurs during coral bleaching and how corals recover. Many changes are occurring in the climate around the world. Some of these are affecting coral reefs. Air and seawater temp eratures are increasing. Global temperatures are expected to rise at least 2 C betw een 2050 to 2100 (Hoegh-Guldberg et al, 2007). This value is much higher th an it has been for the past 420,000 years, during which most marine organisms evolved ( Hoegh-Guldberg et al, 2007). Atmospheric carbon dioxide levels are increasing, which is leading to acidification of the oceans. Higher temperatures and acidification cause carbonate accreti on of hermatypic corals to slow down dramatically (Hoegh-Guldberg et al, 2007). Sea levels are increasing. Weather patterns are changing. More extreme weather events are occurring, such as floods, droughts, and severe storms. Ocean circulation patterns may also be changing. The Fourth Assessment 7

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Report of the Intergovernmental Panel on Clim ate Change reports th at coral thermal and chemical limits will be reached by 2100 (Eak in et al, 2007). Researchers agree that drastic anthropogenic changes need to be established, such as limits on carbon dioxide emissions, for the health of coral reef ecosystems, and thus the oceans. To remain healthy after bleaching, corals ne ed to attach, grow, and reproduce. If bleached coral fragments do not attach, this co uld have implications for the health of a reef where several colonies are bleached. Fragments on the reef from fragmentation would not attach and the reef would grow at a much slower rate. Because endosymbiotic zooxanthellae provide the cora l host with compounds necessary for a healthy life and maintaining functions, I will explore in this thesis the notion that after bleaching, coral fragments will have a much lower attachment rate than fragments that are unbleached. Physiology and Settlement of Soft Corals Sarcophyton elegans a soft coral, was used in this study owing to its hardiness as well as fast attachment, r ecovery, and growth rates. Sarcophyton corals are commonly called leather or mushroom corals because of their leathery texture and mushroom-like shape (Borneman, 2001). These anthozoans are in the subclass Octocora llia and the order Alcyonacea, which includes all soft corals. Soft corals are ahermatypic, or non-reef building, but some species, such as S. elegans, do contain zooxanthellae. Soft corals are arranged in colonies made up of many indivi duals. Each individual animal in the colony is called an autozooid, in the form of a polyp, with a single body opening, called the gastrovascular cavity. There are three layers of tissue: the ectoderm (epidermis), mesoglea, and endoderm (gastrodermis) (B orneman, 2001). The cavity is divided by eight longitudinal sheets of ti ssue called mesenteries, which extend out of the cavity to 8

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form eight radial tentacles. A longitudinal groove, called the siphonoglyph, is present in the middle of the cavity, where the mesenterie s meet. Digestion occu rs here. Wastes from the gastrodermal cells are expelled th rough the siphonoglyph, through which water flows bidirectionally (Figures 2, 3) (Fautin et al, 1991). Figure 2: Structure of Alcyonarian Autozooid Figure 3: Structure of a Cross Section of Alcyonarian Autozooid View of a cross section of a soft coral polyp. http://www.accessscien ce.com/content.aspx ? The major components of an individual polyp of soft corals (Alcyonaria). searchStr=alcyonacea&id=021500 http://www.accessscien ce.com/content.aspx ? searchStr=alcyonacea&id=021500 All the polyps of a colony are embedded into the stiffer coenenchyme, a tissue permeated with canals connecting the gastrovasc ular cavities of each polyp (Atoda, http://www.accessscience.com/content.aspx ?searchStr=atoda&id=021400) (Fautin, http://www.accessscience.com/content.as px?searchStr=alcyo nacea&id=021500). The coenenchyme contains an internal skeleton of clumps of crystall ized calcite, called sclerites, secreted by scleroblast cells in the mesoglea (Fautin et al, 1991). Once a new colony forms, most species of soft corals focus on the growth of the colony through 9

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budding for as many as eight years before se xual reproduction begins (Benayahu et al, 1986). With asexual or sexual reproduction, sett lement of the fragments or the larvae, respectively, must occur. Asexual repr oduction includes budding and fragmentation. Budding is the formation of a new, cloned polyp from a parent polyp by sympodial growth. This is the production of new skel eton and tissue along th e growing edge or branch tip (Lewis, 2006). Budding can be extr atentacular where the new polyp forms in the coenosteum between two polyps. Intratentacular budding al so occurs where the new polyp forms in the middle of an already ex isting polyp. The two polyps then split into two clones (Figure 4) (Richmond, 1997). Luckily for these polyps, they do not need to attach. Fragmentation is the breaking off of a piece of the coral and settlement of the fragment onto a substrate. This fragment then grows and creates a new colony. These fragments must settle and attach to survive. During sexual reproduction, the newly produced larvae must settle and grow. 10

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Figure 4: Asexual Reproduction by Budding in Hermatypic Corals Asexual reproduction by budding in hermatypic corals proceeds via extratentacular or intratentacular budding. http://www.sbg.ac.at/ipk/avstudio/pierofun/reefs/ch2.htm#fig2-14a Most studies of soft corals, including those on reproduction, are on Sarcophyton glaucum due to its widespread distribution, but most Sarcophyton species behave very similarly to this species. These animals are gonochoric, with the gonads developing along the entire length of the mesenteries (McFadde n et al, 2001). They ar e broadcast spawners releasing the gametes during one to three days every year in a synchronized mass spawning event (Figure 5). On the Great Ba rrier Reef, Alino and Coll (1989) observed soft coral broadcast spawning two to five da ys after the full moon at the end of spring. 11

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Figure 5: Synchronized Mass Spawning Gametes being released from mountainous star coral ( Montastraea faveolata ) during a synchronized mass spawning event. These gametes will travel and fuse into zygotes, then metamorphose and settle. (Bunch, G. 1993, http://www.gbund ersea.com/photo.htm) After the mass spawning, extern al fertilization occurs. These zygotes become blastulae 12 hours after spawning. Thirty six hours afte r spawning, the larva is fully developed. For 14 days, these larvae swim around via cilia, th en a lucky few settle on a substrate, and metamorphose into polyps (Benayahu, 1986). Many studies have been done on settleme nt, including its cellular processes and effectors. Attachment of hard coral fragm ents and planulae proceeds by secretion of calcium carbonate skeleton which attaches to the substrate. Soft coral attachment is more involved. Desmocytes, specialized attachment cells, have mostly been observed in attachment of tissue to the endoskeleton of corals (Muscatine et al, 1997), but have recently been found to play a role in the attachment of fragments of Dendronephthya hemprichi a soft, branching coral to substrate. When first cut, D. hemprichi grows root like processes (RLP) (Figure 6). 12

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Figure 6: Root Like Processes in Dendronephthya hemprichi Six Days After Cutting A photomicrograph of root like processes (RLP) in Dendronephthya hemprichi a branching soft coral, 6 days after cutting. Scale bar is 5 mm. (Barneah et al, 2002) The epidermis of these RLPs produce oval vesicl es that release an extracellular organic matrix (EOM) composed of polysaccharides (Barneah et al, 2002). The EOM is involved in preliminary attachment. Once initially att ached to a substrate, the epidermal cells transform into desmocytes. These cells contain a cell body and tenons. The tenons are oriented perpendicular to the substrate. They connect the EOM to the mesogleal cells of the polyp (Barneah et al, 2002). This process is reviewed in Figure 7. 13

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Figure 7: Overview of Dendronephthya hemprichi Attachment to Substrate The steps involved in D. hemprichi attachment to substrate. A .RLP. The circled portion is zoomed in during B-E B Epithelial cells of the RLP produce oval vesicles. C The oval vesicles excrete an extracellular organic matrix. D This EOM functions as preliminary attachment to substrate. E Epithelial cells become desmocytes, the tenons of which connect the EOM with mesogleal cells. Abbreviations : root like processes ( RLP), water canal ( C ), mesoglea ( m ), gastrodermis (gs ), epithelium ( ep ), oval vesicles ( OV ), extracellular organic matrix ( eom ), substrate ( st ), desmocyte tenons ( dt ). (Barneah et al, 2002) These RLP and desmocytes are the cellular mech anisms of attaching the soft coral to the substrate. This is the only mode of soft co ral fragment attachment observed to date. However, because so little has been done on reattachment, it is instructive to examine how planulae attach as well. Different cells involved in attachment of many different types of planulae have been studied. Planulae of the soft corals Litophyton arboretum and Dendronephthya 14

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hemprichi secrete mucus threads to attach to substrate (Abelson et al 1994). Planulae of the sea pen Ptilosarcus gurneyi use gland cells to attach (Chia et al, 1977). Many Hydrozoan planulae discharge nematocytes for attachment (Chia et al, 1978). Many different factors affect how we ll fragments and planulae settle. The effects of UV radiation on settleme nt of planulae are important to study because the reduction in the ozone layer over the past three decades has been allowing more UV radiation to reach Earth (Bouc her, 2010). Baker and colleagues (1995) collected newly released planulae of Pocillopora damicornis and removed different UV radiations from the environment. Planulae sett lement increased 24% with the removal of UV-A radiation compared with control conditio ns of neutral density filters. Settlement only increased seven percent with the removal of UV-B ra diation. UV-A radiation was shown to be the most detrimental to planulae settlement. Planulae settlement is affected by change s in water temperature. These results differ in different studies. Coles and collea gues (1995) found planulae to settle up to 10 times more near a power plant, where the wate r temperature is higher. Other factors, such as compounds emitted from the plant, must also be considered. Randall and colleagues (2009) found higher water temperatures to re duce planulae settlement of the coral Favia fragum by 13%. The settled larvae had a 17% decr ease in survival, suggesting the settling phase of the larvae is more fragile than the swimming phase of the planulae before settlement. The Zooxanthellae Endosymbiont Zooxanthellae are unicellular dinofla gellates of the genus and species Symbiodinium microadriaticum Genetic variability in z ooxanthellae leads to several 15

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different clades; clades A through C are most commonly found in corals (Trench, 1987). These algae are primary producer s living in a symbiotic relationship with the host coral, exhibiting rates of photosynthesi s comparable to free-livi ng macro and microalgae (Weis et al, 1989). They are coccoid al cells with a mean diameter of 8.4 micrometers. Alino and colleagues (1989) first obser ved the endosymbionts inside Sarcophyton tissue on the Great Barrier Reef 15 days after spawni ng, about the time of polyp formation from larvae. Zooxanthellae are phagocytosed by the ho st coral. They reside in symbiosomes, organelles surrounded by several membrane s composed of phagocytotic membrane material (Rands et al, 1993). Symbiosomes are located in endodermal cells and are highly concentrated in the tentacles, providi ng the coral with a means of regulating photosynthesis of the endosymbiont by retractio n of the tentacles (Glider et al, 1980). The major activity of zooxa nthellae is photosynthesis. Zooxanthellae and coral provide each ot her with certain nut rients and compounds. The major role of zooxanthellae is provi ding the host with ph otosynthetic products, mostly oxygen, carbohydrates, and glycerol for host respiration and amino acid synthesis. In a study done by Papina and co lleagues (2003), polyunsaturated fatty acids (PUFAs) were found in higher concentrati ons in zooxanthellae than in coral. Zooxanthellae marker PUFAs were found inside coral cells, indicati ng that zooxanthellae provide their host with PUFAs in addition to sa turated fatty acids. In return, corals give zooxanthellae a place to live. Zooxanthellae also obtain waste nutrients from corals, mostly nitrogen and ammonia. Carbon dioxide waste from respir ation is also provided for the endosymbiont (Delbeek et al, 1994). This is helpful for zooxanthellae because carbon stores in the ocean are mostly in the form of bicarbonate, versus carbon dioxide, due to 16

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the high salinity and pH of the water. Although this exchange is very import ant, it does not provide enough CO2 for the zooxanthellae, thus carbon stores in the seawater must be drawn upon. Goiran and colleagues (1996) investig ated three possible mechanisms of bicarbonate uptake in corals and symbiont: bica rbonate transporters, proton translocating ATPases, and membrane bound carbonic a nhydrase. Carbonic anhydrase was studied more thoroughly by Weis and colleagues (1989) and found to be the major mechanism of bicarbonate uptake. When carbonic anhydras e inhibitors were administered, photosynthetic rates greatly declined. Car bonic anhydrases function by pumping protons out of the cell, acidif ying the external environment, t hus bicarbonate is converted into carbon dioxide, which diffuses into the cell. This enzyme functions in both zooxanthellae and host. It is confirmed further by the fact that carbonic anhydrase is present in higher concentrations in zooxanthellate corals ve rsus non-zooxanthellate animals. Carbonic anhydrase was thought to play a role in calcification, but due to its presence in noncalcifying corals, this putative role is secondary to making accessible the carbon stores in the sea (Weis et al, 1989). Coral Bleaching and the Release of Zooxanthellae As evidenced by these roles played by host and symbiont, zooxanthellae are crucial to coral survival (Borneman, 2001). There are a few nonzooxanthellate coral, but they are small and found in small concentr ations (Schuhmacher et al, 1985). Coral bleaching, which is the expulsion of endosymbio tic zooxanthellae from the host cells, has been occurring in the oceans worldwide (B ouchard et al, 2008). It is caused by many environmental stressors. Recently, the most common one is the rising ocean 17

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temperatures. Other stressors include redu ced salinity, UV radiation, oil pollutants, disease, and predation (Gates, 1990). The dur ation and scale of the stressful event determines the severity of bleaching and the ab ility of the coral to recover. Many studies are currently being done to be tter understand bleaching, incl uding the subcellular events occurring during zooxanthellae expulsion. For zooxanthellae to be expelled, a signal must occur. It is not known if the animal or the algae initia tes the signal. Fang and colle agues (1997) discovered an increase of heat shock proteins (Hsps) in coral cells after exposure to increased water temperature. Because Hsp production requires an intracellular calcium signal, the calcium concentration was measured and found to be greater in coral cells than zooxanthellae cells when exposed to heat (Fang et al, 1997). Indeed, coral bleaching does not occur when calmodulin, the calcium binding protei n, is inhibited. Fang and colleagues (1998) went on to determine if the Hsp was produced in the coral or zooxanthellae first. Heat shock protein (Hsp) 35 was synthesized in co ral at 29 C, but not in zooxanthellae until 33 C. This indicates the higher sensitivity of coral to heat stress than algae, implying the calcium signal is initiated by the coral. It is thought that the calc ium signal is linked to zooxanthellae translocation. Bouchard and co lleagues (2008) discovered another possible signalnitric oxide (NO). Th e NO concentration increases wi th increasing temperature, but it is synthesized inside the algal symbiont not the host coral. Thus, both the host and symbiont may trigger zooxanthellae expulsion due to heat stress. Once signaling occurs, the zooxanthella e are released. Mi crotubules, actin filaments, and the motor proteins dynein and myosin were found to be active in zooxanthellae expulsion. With the administrati on of colchicine and cytochalasin D, 18

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destroyers of microtubules and actin, resp ectively, and motor protein inhibitors, bleaching did not occur under increased temper ature. According to the model suggested by these results, vacuoles containing th e zooxanthellae are tr ansported along the cytoskeleton by motor proteins to the host cell membrane where the membrane ruptures and the vacuoles are released (Figure 8) (F ang et al, 1998). Gates and colleagues (1992) observed whole host endodermal cells with vi sible nuclei released from the reef coral Pocillopora damicornis In this case, detachment of endodermal cells occurs, possibly due to dysfunctioning adhesion proteins, versus exocytosis of solo algal cells. These new discoveries greatly progre ss the understanding of zooxanthellae release and coral bleaching. Figure 8: Subcellular Release Mechanis m of Zooxanthellae During Bleaching Putative events involved du ring release of zooxanthellae as a part of coral bleaching. First, a calcium signal is produced due to an environmental stresso r. Then, the vacuole cont aining zooxanthellae is translocated via motor proteins moving along th e cytoskeleton to the host cell membrane, where the membrane ruptures to allow release. Release of whole endodermal cells containing zooxanthellae has also been observed. Abbreviations : cytosolic calcium signal ( CCS ), zooxanthellae ( Z ), vacuole ( VO ), cytoskeleton ( CS ), motor protein (MP ). (Fang et al, 1999) 19

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New discoveries, such as the subcellu lar mechanisms involved in zooxanthellae release, are necessary for a deeper unders tanding of coral bleaching. Then, diagnostic tools for detecting coral sens itivity to thermal stress and preventative measures for bleaching can be crafted to help protect the worlds corals from bleaching. Few studies have been conducted on the attachment of so ft corals to substrate after bleaching, the focus of this pilot study. With the accumula tion of attachment knowledge of different species, potential measures could be taken to protect coral reefs in areas of heating, such as placing thermal tolerant species in these areas. 20

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METHODS An acclimated Sarcophyton elegans coral piece in Pritzker Marine Laboratory of New College of Florida was cut into 12 fragme nts. Six of these fragments were acutely bleached by placing in 31-32 C sea water for 1.5 hours. The other six fragments were used as controls. Then, all 12 fragments were tied onto flat, dead coral skeleton substrates with ridges, using 25 lb monofila ment line. In order to tie th e fragments to the substrate, one hole was poked through each fragment during the placing process. The substrates with placed Sarcophyton fragments were positioned 25.4 centimeters below the water surface of a 455 liter sea table system under normal growing conditions for four weeks. The sea water was pumped in from Sarasota Ba y, then filtered and sterilized. To keep track of the coral fragments, they we re numbered one through 12 (Figure 9). Figure 9: Top-Down View of Placement of Twelve Coral Fragments in Sea Table The fragments were numbered one through 12 and tied to a substrate. Here is a topdown view of the four rocky substrates ar ranged in a sea table. #1-6: bleached; #712: controls Water was maintained at a temperatur e of 23.6 C, pH of 8.3, calcium at 200 ppm, and carbonate hardness (KH) at 6. Saraso ta bay water pumped in during this study had lower values of calcium concentration and KH than normal marine aquarium conditions, but this did not a ffect the health of the cora l. A dual 400 watt metal-halide 21

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and 64 watt actinic lamp was used on a 12 hour light/dark cycle. The illuminance was 1050 lux at the surface of the water. Pictures were taken every week. When a fragment became displaced by disconnecting itself from the monofilament, it was retied to its same position, this time using 8 lb monofilament lin e. Attachment was measured and recorded throughout the process via number of attachment sites of coral to substrate and percentage of attachment of the outer edge of the fragment. It was difficult to observe percentage attached until 50% or greater wa s attached. Thus, percentage values were assigned for the first few number of attachme nt sites. One site was assigned to be 20%; two sites, 30%; and three sites, 50% (Figures 10, 11, 12). Figure 10: Attachment of Control Fragment (#9) This control fragment (fragment #9) is now 100% attached. It began with thr ee attachment sites (arrows). (Photograph by A. McDavid) 22

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Figure 11: Attachment of Bleached Fragment (#1) This bleached fragment (fragment #1) is now 100% attached. It began with three attachment sites (arrows), two of which (outer arrows) became unattached once th e middle part of the fragment began to attach. Note that the fragment does not use the monofilament to remain in place anymore. (Photograph by A. McDavid) Figure 12: Attachment of Bleached Fragment (#2) This bleached fragment (fragment #2) is now 100% attached. This attachment is more bulbous and spread out than that of the other fragments. (Photograph by A. McDavid) 23

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RESULTS Observations The six experimental frag ments lost slight color af ter bleaching (Figure 14). Within four days, full color was restored. Figure 13: Control Fragment of Sarcophyton elegans Containing Endosymbio tic Zooxanthellae 24 The brown endosymbiotic zo oxanthellae (arrows) are visible in this control fragment of S. elegans. (Photograph by A. McDavid)

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Figure 14: Acutely Bleached Fragment of Sarcophyton elegans In this example, the brown endosymbiotic zooxanthellae of this S. elegans fragment have been completely bleached out due to extreme temperatures. The brown spots visibl e in the previous photo are not visible in this bleached fragment. The experimental fragments in the present study were not bleached as severely, thus some zooxanthellae remained after bleaching. (P hotograph by A. McDavid) Fragments Coming Displaced Fragment numbers one through six were acutely bleached; numbers seven through 12 were the controls. Three of the bleached fragments became displaced (coral flesh ripped off of monofilament so fragment was not tied onto rocky substrate anymore) (# 1, 2, 5), two of which occurred during the first week after bleaching and placement. Two of the control fragments became displaced (# 7, 10), one during the second week, and one during the third week. Timing and Percentage of Attachment Between the Two Study Groups The first fragment to begin attachment was fragment number two on the 13th day of the study. The control and experimental fr agments began attaching at the same time. 25

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On day 16, nine of the 12 fragments had begun to attach (Table 1). On day 16, the average percentages of attach ment of the control group and the experimental group were nearly identical. It was 23.3% for the c ontrol group and 20% for the bleached group (Table 2). By the end of the four weeks, all 12 fragments were at le ast partially attached. All of the bleached fragments were either 90% or 100% attached except for number five (30% attached), with a mean of 83.3%. The control fragments were all 70% attached or more, with a mean attachment percentage of 88.3% (Tables 1 and 2). Photographs of attachment of each fragment taken once per week throughout the study are below (Figures 15 and 16). Table 1: Percent Attachment of Each Fragment (#1-12) on Days 16, 19, 22, and 30 Fragment Number 1 2 3 4 5 6 7 8 9 10 11 12 16 0 50 20 0 20 30 50 20 30 0* 20 20 19 0* 60 40 40 30 50 60 30 70 0 50 30 22 30 60 90 90 30 85 60 85 95 0 80 70 Day of Study 30 90 100 90 100 30 90 70 90 100 100 80 90 The percentage of attachment of the outer edge of each fragment was meas ured on four different days. These percentages are recorded here fo r each fragment on each of the four days. *Fragment came out of place and was replaced the day prior to observing percent attachment. Bleached fragments (black): #1-6; Controls (red): #7-12 26

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Table 2: Average Percent Attachme nt and Standard Deviation of Bleached Group and Control Group on Days 16, 19, 22, and 30 Experimental Group Bleached Control 16 20 .8 (19.0) 23.3 .7 (16.3) 19 36.7 8.5 (20.7) 40 .3 (25.3) 22 64.2 .7 (28.7) 65 .9 (34.1) Day of Study 30 83.3 10.9 (26.6) 88.3 .8 (11.7) The average percentage of attachment is given on four different days for the bleached group and the control group. Standard deviati ons are given in parentheses. n=6 for both groups. All twelve fragments are clones. Bleached fragments: black; Controls: red 27

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Figure 15: Attachment of Bleached Fr agments on Days 8, 16, 22, and 30 Pictures of the bleached corals were taken on four different days during the study. The numbers on the left side of the rows are the fragment numbers. (Photographs by A. McDavid) 28

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Figure 16: Attachment of Control Fragments on Days 8, 16, 22, and 30 Pictures of the control corals were taken on four different days during the study. The numbers on the left side of the rows are the fragment numbers. (Photographs by A. McDavid) 29

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DISCUSSION There are no large differences between th e attachment rates of the bleached coral fragments and the control coral fragments that were cloned from the same colony of Sarcophyton Both groups began attaching close to the same number of days into the study. One of the bleached fragments (#2) began attaching slightly sooner than any of the control fragments. After starting near the sa me time, both groups also continued attaching at nearly the same rate. On each of the four days of recording the percent of attachment, the average percentages of attachment were ne arly identical. These results differ from the hypothesis that bleaching will slow down attachment rates. It is possible that the cells that function in attachment are not dependan t on zooxanthellae expelled during bleaching but the results from the presen t study are not absolutely conclu sive. Because not all of the zooxanthellae were expelled, they may have been used for attachment during the study. Recent studies (Rodrigues, 2005) have shown th at coral energy reserves can be used and corals can switch to heterotrophy for fixed carbon when the quantity of symbionts is decreased. This has great implications for cora l fragments on a reef that has recently been exposed to higher temperatures and where co rals are bleached. These fragments could attach despite bleaching. Soft coral fragments of D. hemprichi have been shown to attach via root like processes and desmocytes (Barneah et al, 2002 ). Some soft coral planulae attach via secretion of mucus threads. Sea pen and Hydr ozoan planulae have been shown to attach via gland cells and nematocytes, respectively. These attachment mechanisms or similar ones may be more widespread across soft corals for both planulae and fragment attachment. If these mechanisms are in use and soft coral fragments attach despite 30

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bleaching, then zooxanthellae are not necessary for these attachment mechanisms to function. Zooxanthellae seem necessary for hard coral fragment attachment because their mechanism is via secretion of calcium carbonate (Vandermuelen, 1975). Production of calcium carbonate requires energy that is usually acquired from the endosymbiont. During the acute bleaching period in the present study, the fragments only slightly lightened in color. Only a small percentage of zooxanthellae pres ent in the tissue was expelled. A longer, hotter blea ching period could be performe d in a future study. This type of extension to the study would be reas onable given the imp lications of climate change and potential im pacts on coral growth. Even if it is the case that coral bl eaching does not affect attachment, it has affected the health of some coral reef ecosy stems. Reefs in the Indian Ocean underwent a major bleaching event in 1998, but coral cover has recovered. In contrast, coral cover on western Atlantic reefs has not recovered from smaller ble aching events and secondary stressors, such as poor water clarity and b acterial infection (Berke lmans et al, 2006). In these cases, factors for recovery and non-recovery should be compared, including diversity of species, water conditions, and recruitment. Basti and colleagues (2009) studied the recovery of Acropora Formosa and Acropora yongei after bleaching. A. Formosa did not recover, while A. yongei did recover. In this case, strong water moveme nt removed necrotic tissue, aiding in the avoidance of secondary bacterial infection. Zooxanthellae from healthy tissue reproduced and were translocated to bleached tissue or were taken up from the environment. Similar methods of recovery were observe d by Rodrigues (2005) while studying Montipora capitata. In addition to these methods of recove ry, this species also switched from 31

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photoautotrophy to heterotrophy while ble ached to obtain energy as fixed carbon, resulting in a fast recovery of one and a half months. Zooxanthellae type affects coral recover y. It has been shown that clade D of Symbiodinium is the most heat tolerant. Reshuffli ng of zooxanthellae in side coral tissue from type C to D has been shown during in creased temperatures. This reshuffling can allow the coral to tolerate an increase in wate r temperature up to 2 C (Berkelmans et al, 2006). Coral reefs that recover from bleaching may have more clade D Symbiodinium present or may have a high percentage of th ermal tolerant coral species. There are many variables involved in rec overy after coral bleaching. Recovery of bleached corals depends on a few key factors. These include the susceptibility of coral to disease while bl eached, the ability of the water currents to remove necrotic tissue, the ab ility to switch to heterotrophy while bleached, the ability to use energy reserves while photosynthesis is in hibited, the temperatur e restraints of the zooxanthellae present, and coral morphology. Comparative bleaching and attachment need to be studied for a deeper understanding of coral bleaching on reefs. On ce we obtain a deeper understanding of host and symbiont aspects of bleaching, at the cellu lar and organismal levels, preventative as well as relief efforts could be undertaken pr ior to and after a bleaching event. Prediction methods including remote sensing observati on techniques and ocean -atmospheric climate models are currently in progress (Baker et al, 2008). Coral fragments that have been treated with antibodies agai nst the mechanisms of zooxanthellae release and corals incubated with thermally tolerant clades of zooxanthellae could be planted on a reef expected to experience bleaching due to ra ised temperatures. These fragments would 32

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survive the heating and could then reproduce and repopulate the bleached reef. After a bleaching event, recovery could be promoted by fixing species known to attach and prosper, despite bleaching, to the reef substr ate. These measures could help protect the oceans important cora l reef ecosystems. Baker and colleagues (2008) outline the major factors in coral reefs ability to function as prior to climate change. Future reef functi on will depend on how much and which species of coral die and do not recove r on a reef, ability of surviving coral to acclimate to temperature and other climate ch anges, the changing balance between reef accretion and reef erosion, and humans ability to promote reef recovery by controlling levels of predation, coral recruitment, and al gal cover. Anthropogeni c, as well as coral adjustments, are necessary for proper f unctioning of coral re efs in the future. 33

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