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i SEAGRASS PR OP SCAR RECOVERY IN SARASOTA BAY BY LAUREN ALI A Thesis Submitted to the Division of Natural Sciences New College of Florida In partial fulfilment of the requirements for the degree Bachelor of Arts Under the Sponsorship of Dr. Sandra Gilchrist Sarasota, Florida April 2013
ii Acknowledgements I would like to thank Jennifer Schafer, who taught me GIS, as well as Nicole Van Der Berg, Jon Perry and John Ryan for giving me job introducing me to the research w hich is subject of this thesis and for being helpful at every turn I would also like to thank Kelsey Dolan, Adrian Rosario and Rick Schader command, despit e birds and broken boats. Thanks are also due to my bacc committee, Dr. Diana Weber, Dr. Elzie McCord and particularly to my adviser Dr. Sandra Gilchrist without whom college and missed meals would have been significantly harder. I am also grateful to my f amily and friends, forever and for everything they continue to do in my life. Finally, I would like to thank New College of Florida and all the people who make it what it is. Lots of love, and s ee you later.
iii Table of Contents Acknowledgements ii Table of Contents iii List of Figures and Tables v Abstract ix Chapter 1: Introduction 1 The State of Seagrass Worldwide and in Sarasota Bay 2 Seagrass Growth 7 Vertical Rhizome Growth 8 Horizontal Rhizom e Growth and Clonal Reproductio n 8 Sexual Reproduction and Fragmentation 9 Ecological Functions of Seagrass 10 Sarasota Bay 1 1 Evaluating and Restoring Seagrass Beds 20 Threats 20 Prop Scarring 20 Ident ifying and Evaluating Prop Scars 22 M a nagement and Restoration 22 Chapter 2: Methods 24 Data Collection 24 Digitizing 24 Ground Truthing 27 Analysis 31 Species Composition of Seagrass Beds 31 Average Width and Depth 31
iv Scarring By Species Composition and Bay Segment 32 Comparison of Scar Proportions Over Three Years 32 2012 Scar Length Compariso n Between Field Data and Aerial Measurements 33 Scarring Hotspots 3 4 Chapter 3: Results 35 Species Composition of Seagrass Beds 35 Average Width and Depth 37 Scarring By Species Composition and Bay Segment 37 Comparison of Scar Proportions Over Three Years 47 2012 Scar Length Comparison Between Field Data and Aerial Measurements 48 Scarring Hotspots 5 4 Chapter 4: Discussion 60 Aerials, Digitizing and Apparent Scar Number 6 0 Prop Scarring in Sarasota Bay 61 Species Composition 61 Scarring Depth and Rhizome Depth 61 Bay Segments and Scarring Hotspots 62 Conclusion 63 References 64 Appendix 1.1 71 Appendix 1.2 76 Appendix 1.3 79
v List of Figures and Tables Figure 1: Prop Scarring in a Seagrass Bed 1 Figure: 2 Worldwide Seagrass Distribution and Average Ocean Temperature 2 Figure : 4 Table 1 : The average percentage of total available light, approximate 5 optimal temperature and approximate optimal salinity required by three different species of seagrasses for healthy growth. Figure 4 : Lacunae 7 Figure 5 : Segments of Sarasota Bay in Relation to Sarasot a County 12 Table 2 : List showing some of the bodies which regulate seagrass in 14 Sarasota Bay Table 3 : Trophic State Index Rating for Major Areas of Sarasota Bay 15 Table 4 : Measurements of Water Clarity for Major Areas of Sarasota Bay 16 Figure 6 : Secchi Disk 17 Figure 7: Thal assia testudinum (Turtle Grass) 18 Figure 8 : Halodule wri ghtii (Shoal Grass) 19 Figure 9 : Syringodium filiforme (Manatee Grass) 19 Figure 10 : Prop Scarring in Sarasota Bay 20 Table 5 : Prop scar regrowth times of three seagrass species 22 Figure 11 : Aerial Photograph of Sarasota County 26 Figure 12 : Map showing the sites in Upper Sarasota Bay, Sarasota County 28 (New College of Florida, Ken Thompson Park Boat Ramp, North of Coon Key, Big Pass) where field samples of prop scars were taken in 2012
vi Figure 13 : Map showing the site Northwest of Skiers Island in Ro berts Bay 29 where field samples of prop scars were taken in 2012 Figure 14 : Map showing the site in Little Sarasota Bay where field samples of 30 prop scars were taken in 2012 Table 6 : Number of points where d ifferent species compositions of seagrass 35 were observed Figure 15 : Map showing the different species compositions of seagrass beds 36 in Sarasota Bay and the points at which they occur Table 7 Summary of prop scar widths and depths in Sarasota Bay based on field 37 data collected in January 2012 Table 8 Summary of prop scarring in Sarasota Bay based on species 38 composition of seagrass beds for the year 2010. Table 9 : Summary of prop scarring in Sarasota Bay based on species 38 composition of seagrass beds for the year 2011. Table 10 : Summary of prop scarring in Sarasota Bay based on species 39 composition of seagrass beds for the ye ar 2012 Figure 16 : Percentage of the total apparent number of prop scars found in 40 seagrass beds of different species compostions fo r the years 2010, 2011 and 2012 Figure 17 : Percentage of the total apparent len gth/volume/area of prop scars 41 found in seagrass beds of different species composition in Sarasota Bay for the years 2010, 2011 and 2012 Figure 18 : Percentage of the total apparent number of prop scars found in 42 seagrass beds in the different bay segments of Sarasota Bay for the years 2010, 2011 and 2012
vii Figure 19 : Percentage of the total appar ent length/volume/area of prop 43 scarring found in seagrass beds in the different bay segments of Sarasota Bay for the years 2010, 2011 and 2012 Table 11 : Summary of apparent prop scarring in S arasota Bay based on bay 44 segment for the year 2010, including totals for the entire bay where appropriate Table 12 : Summary of apparent prop scarring in Sarasota Bay based on bay 45 segment for the year 2011, including totals for t he entire bay where appropriate Table 13 : Summary of apparent prop scarring in Sarasota Bay based on bay 46 segment for the year 2012, including totals for the entire bay where appropriate. Table 14 : Results of the Wilcoxon Rank Sum test for three comparisons of the 47 length of individual prop scars between years Table 15 : Length of scars as measured in the field during ground truthing in 48 January of 2012 and in the aerial photographs from that year. Figure 20 : Prop scars observed in 2012 at Big Pass 49 Figure 21 : Prop scars observed in 2012 at Ken Thompson Boat Ramp and 50 North of Coon Key Figure 22 : Prop scars observed in 2012 at N ew College of Florida 51 Figure 23 : Prop scars observed in 2012 at North West of Skiers Island 52 Table 16 : Results of the paired t test performed to test if a significant difference 53 existed between the length of individual scars as observed during the 2012 ground truthing and through the 2012 aerials. Figure 24 : Area in Blackburn Bay along Casey Key Road which appears to 55 be at risk for prop scarring over multiple years Figure 25 : Area in Lemon Bay from Lemon Bay Park to Indian Mound Park 56 which appears to be at risk for prop scarring over multiple years
viii Figure 26 : Area in Little Sarasota Bay from Vamo to Blackburn Point Road 57 which appears to be at risk for prop scarring over multiple years. Figure 27 : Area in Roberts Bay from Bay Island Park to South Coconut Bayou 58 which appears to be at risk for pro p scarring over multiple years. Figure 28 : Area in Upper Sarasota Bay, Sarasota County, from Button Wood 59 Harbour to South Lido County Park which appears to be at risk for prop scarring over multiple years.
ix Abstract Propeller ( Prop ) scarring is a widely recognized source of damage to seagrass beds. This study used aerial photographs taken over a three year period from 2010 2012 and field work done in January of 2012 to determine the number and dimensions of scars in Sarasota Bay, where scarring is occurring and whether it is healing at a significant rate An average width and depth for scars in Sarasota Bay was calculated based on measurements taken in field This was combined wi th the length of prop scars as observed in the aerial photographs to calculate the average apparent area and volume of prop scars in the Bay in general in different segments of the Bay, and in seagrass beds of different specie s composition. O f the three species of seagrass examined ( Halodule wrightii Thalassia testudinum and Syringodium filiforme ) the most scarring occurred in T. testudinum. Of the five bay segments examined, Upper Sarasota Bay, Sarasota County contained the most scars. A Wilcoxon Rank Sum test showed a significant difference in the length of prop scars between years. A paired t test showed a significant difference between data gathered from aerial photos and from ground truthing Measurements like depth and width were captured more acc urately from ground trothing while the photographs produced a better estimation of scar length. Scarring hotspots were identified in each segment of the Bay where further work is recommended. Dr. Sandra Gilchrist Natural Sciences
1 Chapter 1: Introduction Overview Coastal ecosystems serve many functions, including recreational, economic and environmental. Monitoring and conservation are necessary to maintain these assets against a wide variety of threats, many of which are anthropogenic. Seagrass is the foundation of one such ecosystem. Seagrasses are ma rine plants which grow in beds, and l arge beds may be referred to as meadows. These beds support a variety of fauna and provide many ecological services. Reduction in seagrass coverage is considered undesirable due to ensuing declines in the ecological benefits it provides (Waycott et al. 2009). Figure 1 Prop Scarring in a Seagrass B ed ( http://www.learner.org/jnorth/images/graphics/manatee/manatee_USGS0022.jpg ) These tracks are typical prop scarring in a heavily sca rred bed. T he worst scarring is highlighted by the black rectangle. Seagrass can be threatened in a variety of ways, including being scarred by boat To determine the extent of scarring and potential effects, a study of
2 prop scarring was conducted in Sarasota Bay, Florida, using GIS mapping technology for the years 2010 2012. A combination of ground truthing and analyses of aerial images was used to determine regrowth rates from prop scarring in Sarasota Bay. Ground truthing is field work that can be used to determine the correspondence between what can be seen in remote images and what can be observed at a site. Both types of data are needed to deter mine whether the seagrass in Sarasota Bay, an area with a history of ecological issues and extensive efforts at recovery, faces a significant threat from boating In addition, it is critical to identify if scarring poses a greater danger to some parts of t he Bay than others. Healing can be said to be occurring when the prop scars are reduced in width and length by the growth of new seagrass in the damaged area. This should restore the roots and rhizomes which prevent sediment erosion as well as the leaves w hich provide shade and habitat to residents of the bed Habitat fragmentation is also reduced Healing has been measured in this study by finding the length, width and depth of scars, which were used to calculate the area and volume of scarring for differe nt segments of the Bay. These data were used to determine if overall prop scars in Sarasota Bay exhibit a significant rate of healing over the three years observed. Once threatened areas are recognized recommendations can be made as to what actions, if an y, should be taken. In areas where damage is persistent it can be important for local government and watch groups to intervene to maintain the integrity of threatened ecosystems and their critical ecological services Seagrass ecosystems in particular prov ide a variety of benefits to the environment, acting in carbon storage, erosion prevention and the provision of food and habitat for numerous species, include many of commercial importance. The creation of prop s cars can also be damaging to boats which cre ate them, creating a hazard to the people on board. The State of Seagrass Worldwide and in Sarasota Bay Seagrass es a re marine angiosperm s that grow worldwide in shallow temperate and tropical waters (Figure 2). It is not a proper taxonomic grouping in th at its members are not necessarily closely related, but all seagrass belong to the superorder Alismatiflorae. There are four families, Zosteraceae, Cymodoceaceae, Posidoniaceae and Hydrocharitaceae although of the genera contained within the latter, only four are
3 considered seagrasses (Den Hartog and Kuo 2006). These four families contain a total of twelve genera of seagrasses. The three most populous of these are Posidonia Zostera and Halophila ( Hemminga and Duarte, 2000). Figure 2 Worldwide Seagrass Distribution and Average Ocean Temperature (Green and Short 2003). The location of seagrass beds worldwide, indicating that seagrass is able to thrive in both tropical and temperate climates. Differences in classification criteria have led to debate about the exact number of species, but approximately fifty to sixty have been identified. Each species consists of the same basic parts: leaves, roots and rhizomes (Figure 3) an d flowers and fruit are present during sexual reproduction Seagrass forms extensive clonal networks, allowing these parts to be further grouped into larger units. Rhizomes are separated by nodes, and from these grow fruit, flowers, roots and ramets, which are groups of leaves clustered at a node. A group of genetically identical ramets and their intervening rhizomes are called a genet (Short et al. 2007). Seagrass meadows tend to be fairly monospecific in temperate climates and mixed in warmer ones, howev er, even in mixed meadows one species tends to be dominant (Green and Short, 2003). For meadows to thrive, seagrass must have access to certain conditions and resources.
4 Light levels regulate the lower limits at which seagrass can grow since it, like any p lant, relies on photosynthesis. The lowest depth at which seagrass can grow varies by species because each requires specific light levels (Table 1) that vary according to environmental influences, including temperature and soil chemistry. Whether this ligh t level is met depends on the level of light Figure 3 ( http://estuaries.noaa.gov/About/LearnMore.aspx?ID=356 ) A seagrass showing the components of the average seagrass plant. Displays individual features (roots, leaves, rhizomes, nodes, fruit, flowers) and grouped features (ramet, genet). attenuation present in the individual environment, making it difficult to determine a maximum depth of growth for a particular species. Instead, the limits of seagrass growth are more commonly measured using light attenuation, which is caused by factors that inhibit light from penetrating the water column, such as turbidity, phytoplankton, dissolved organic matter and epiphytes. Individual plants can acclimatize to change in light availability by producing few shoots and longer leaves to attain greater quantities of l ight and maintain photosynthetic output in unfavourable conditions (Dennison 1987, Duarte 1991, Ralph et al. 2007 ). Of the three species that were the focus of this study,
5 Thalassia testudinum has been shown to photacclimate, while Halodule wrightii and Syringodium filforme have not (Major and Dutton 2002). Table 1 The average percentage of total available light, approximate optimal temperature and approximate optimal salinity required by three different species of seagrasses for healthy growth. Data taken from Lee et al. 2007 unless stated otherwise. Seagrass Species Mean Annual Light Percentage Required Approximate Optimal Temperature Approximate Optimal Salinity Halodule wrightii 20.7% 30 C Very wide range. Limits unknown (Lirman and Cropper 2003) Syringodium filforme 23.1% 23 32 C (Lirman and Cropper 2003) Thalassia Testudinum 18.4% 23 31 C 30 (Lirman and Cropper 2003) The action of the water controls the upper limits of the depth at which seagrass can grow. The plant must b e able to withstand the wave force tides and currents in which it exists. Lower water velocities encourage plant growth, but if it is too strong, it can cause suspension a nd movement of substrate, impairing water clarity and light levels as well as injuring plants by uprooting them, exposing them, burying them when the sediment settles, or thwarting new shoots (Madsen 2001). Seagrass also needs a good site of attachment. T he majority of species need soft mud or sand for their roots to take hold and rhizome networks to expand, and it is this type of sediment that benefits from the carbon and nutrient cycling that seagrass initiates. Seagrass is able to accumulate more resour ces than needed to meet its immediate growth and reproduction, a phenomenon known as luxury consumption ( Romero et al. 2006 ).
6 These are sequestered in the leaf and rhizome tissues of the plant and used during periods when environmental conditions do not me et its needs. This is particularly useful where nutrient availability is seasonal. Larger seagrasses have a greater capacity to store and muster these resources than smaller ones do, and are therefore better able to detach their growth processes from the l imitations of their environment (Marb et al. 2006). The remaining environmental factors which can affect seagrasses are temperature and salinity. Temperature limits the geographical range over which seagrass can grow. This is because it controls the rate at which metabolic pathways operate. For example, when it is too hot photosynthesis may be outstripped by respiration, which is undesirable for healthy plant functions. When it is too cold, the plants may become dormant, decreasing their energy use. Salin ity influences the osmotic pressure within the plant cells. Many seagrasses are able to acclimate to salinity changes, and they are able to survive a range to Greve and Binzer 2004). The temperat ure and salinity ranges for three species Thalassia testudinum Syringodium filiforme and Halodule wrightii which are the focus for this study in Sarasota Bay are shown in Table 1. Other abiotic essentials include inorganic carbon, nitrogen, phosphorous and oxygen. Carbon exists in ocean water as CO 2 HCO 3 2 and CO 3 2 Seagrass is able to use CO 2 and HCO 3 2 but it is more proficient using phosphorous and nitrogen ( Fourqurean and Zieman 2002). Oxygen is a product of photosynthesis It travels from structures in the water column to those in th e anoxic substrate via lacunae (Figure 4) tubes specialized to carry air to the roots and rhizomes where it is needed for aerobic respiration (Borum et al. 2006). There are large differences between species in size, growth and reproduction, but all seagr asses are monocotyledons comprised of a series of units called internodes, also known as ramets, and separated by nodes (Figure 3). The internode length varies depending on the location of the seagrass within the bed. Near the center of the bed it is shorter, but on the edge of the bed greater length allows more effective colonization (Cunha et al. 2004). It also varies depending on plant size.
7 Figure 4 Lacunae (http://depts.washington.edu/fhl/mb/Phyllospadi x_Alex/morphology.html) Lacunae are present throughout seagrass plants as shown in this leaf. Size of the main structures which comprise seagrass are scaled to rhizome thickness, and thicker rhizomes are shorter than thinner ones. This means that they can sacrifice colonization potential, but they may contain wider channels used to transport resources from one part of the plant to another. Seagrasses with thicker rhizomes therefore have greater resource integration potential (Duarte 1991). Species size is an important determinant of other physiological factors. Blades range in size from a few centimeters to roughly four meters in length (Green and Short, 2003), and the branching angle of the rhizome clones of small species is roughly to 90 while the bra nching angle of larger species is roughly 40 The smaller species have a more accelerated rate of two dimensional spreading and have been speculated to be a pioneer species that are better equipped to recuperate from damage (Marb et al. 2004). Seagrass G rowth Vegetative growth is the main method by which seagrass beds can recover from damage, and is reliant on two things. One is elongation, which is the frequency at which rhizomes are added and increase in size. The other is branching pattern, which is t he angle and rate of branching. Both depend on the density and size of the rhizomes. Growth rate is dependent on the age of the ramet clone (Sintes et al. 2006), level of competition in a pre
8 existing population, as well as environmental factors like nutri ent concentration, the characteristics of the sediment and climate (Koch 2001). The direction of growth also plays a role, with most seagrasses having slower vertical growth than horizontal (Marb et. al. 2004) Seagrass growth is mainly a product of rhizom e productivity, as can be measured by spread efficiency. This is the number of square meters of ground covered in relation to the number of meters of rhizome produced (Marb and Duarte 1998). The size of the species determines patterns of rhizome growth. G enerally, there are two different growth strategies used by large species and small species, respectively. Large species generally species generally use Horizontal and vertical rhizome growth is dependent on branching capability per number of internodes, which decreases with increased rhizome width. This is because as species size increases, shoot produ ction rates, growth angles, branching rates and horizontal lengthening rates decrease, causing centrifugal growth. The opposite effects occur as species decrease in size, leading to spiral phalanx growth (Marb and Duarte 1998). Vertical Rhizome Growth Vertical rhizomes extend up from the sea floor through growth occurring at an apical meristem. The amount of sediment in which the seagrass occurs is a very important factor. Burial has been shown to result in shoot mortality, and sediment erosion negative ly affects vertical rhizome growth since the amount of sediment coverage is insufficient to trigger this response from the plant (Carbaco and Santos 2007). Horizontal Rhizome Growth and Clonal Reproduction Seagrass reproduction is closely linked to growth since clonal reproduction takes place through extension of horizontal rhizomes, which grow much faster than vertical rhizomes in most species (Cunha et al 2004). There are intraspecific differences in this process, but it is also unique in each species and scaled according to the species size, varying widely (Sintes et al. 2006). New clonal branches are formed after producing a certain
9 number of horizontal internodes, ranging from 6 in Halophila ovalis to 1800 in Thalassia testudinum. (Marb and Duarte, 1998). The usual branching angle for horizontal rhizomes is approximately 60 and normally less than 90 There is a negative relationship between the size of a seagrass species and its growth and branching rates, since as the size of the plant increases so does the cost of building new modules (Sintes et. al. 2006). Smaller seagrasses have slimmer rhizomes and wider internode spaces, and spread faster and a t wider angles than the larger ones with opposite rhizome and internode space characteristics. These traits are the direct cause of the difference in growth patterns between large and small species (Brun et al. 2007). Although the larger seagrasses branch slower they also live longer, possibly allowing them to build more intricate rhizome systems (Vermaat 2009). Their long life facilitates meadow stability. The opposite holds true for small species, which need consistently high shoot mortality rates for th e population to thrive due to density constraints. Regardless of species size, horizontal rhizomes which grow near the middle of a bed have a lot of intraspecific or interspecific competition, and would not be expected grow as quickly as those located near (Duarte et al. 2006). Those on the periphery are able to cover free ground, and can therefore be expected to maintain a faster growth rate. Sexual R eproduction and Fragmentation Sexual reproduction and fragmenta tion are important for generating new seagrass patches which can expand into beds. If a piece of seagrass rhizome is broken off it can drift to a new location and expand through clonal reproduction, establishing a new population (Hall et al. 2006). The oth er way for this to happen is reliant on flower and seed output in existing populations. All seagrasses are capable of both types of reproduction, but not much is known about the level of importance each type has per species (Rasheed 2004). Sexual reproduct ion in seagrasses is considered highly variable. There can be large differences in scale of reproductive activity between populations and years, and the larger the species, the less important sexual reproduction is for expansion of the bed This is because larger species live longer and are thought to benefit more from clonal growth,
10 while shorter lived smaller species are more likely to spread through seeding (Kenworthy 2000). However, sexual reproduction is important for recombination of characteristics d uring the meiotic process which can result in variation through outcrossing. Unfortunately, not much data exist on seed germination, but seeds face a variety of problems. They might be infertile, become damaged, be transported to areas which are inappropri ate for germination, or eaten by fish and invertebrates. Seedlings which germinate may not survive due to predation or death caused by lack of nutrients or other resources. Those which do can accomplish the vital task of pioneering new beds, a task aided b y the ability of many species to remain dormant until an appropriate time for germination, creating a seed bank (Jawad et al. 2000). Although its prominence varies, sexual reproduction is an essential factor in maintaining and increasing seagrass coverage particularly when coupled with the fact that not all seagrasses exhibit high rates of clonal growth. Ecological Functions of Seagrass The presence or absence of seagrass in an area has major impacts for its ecosystem. It is a primary producer, it is impo rtant in carbon sequestering, it is an important habitat and valuable food source to many organisms, it moderates light levels and sedimentation and it prevents erosion (Orth et. al. 2006). As is typical of photosynthetic life, seagrass uses light energy t o fix carbon dioxide and convert it into organic carbon used to carry out life processes, producing oxygen. While seagrass only accounts for 1% of all the primary production found in the ocean, it accounts for 12% of the aggregate carbon stockpiled in mari ne sediment (Terrados and Borum 2004). Seagrass also has a major impact on the sediment itself. It is a key influence on soil structure, binding the sediment together with its rhizomes and slowing the water flow through their canopies, capturing particles and reducing the size of particle which is able to settle in the bed area (Gacia et al. 2003, Boas et al. 2007). The bed is also an important habitat for a variety of organisms. These can use the area as a nursery, a permanent residence, or a feeding gro und (Jackson et al. 2001). Seagrass beds can also provide protection for its inhabitants. The extent of this is species specific,
11 and depends on their responses to factors such as the structure and complexity of the bed (Hovel 2003) and its proximity to ot her relevant habitat types, such as mangroves and coral reefs (Cocheret de La Morinire, E., et al. 2002). These organisms may provide reciprocal benefits. Mussels inhabiting seagrass beds decrease the epiphyte load through filter feeding and increase the available nutrient level of the substrate (Peterson and Heck 2001). Lessening the ephiphyte load decreases competition for light resources, benefiting seagrass (Drake et al. 2003). When organisms inhabit ing the seagrass die, their hard structures may fragm ent, contributing to the sediment, and their organic matter enriches the bed (Terrados and Borum 2004). Sarasota Bay Sarasota Bay is located on the West Coast of Florida, between Tampa Bay and Charlotte Harbour. It is a subtropical estuary covering 83.686 km 2 with a watershed spanning 241.402km 2 across both Sarasota County and Manatee County (National Estuary Program Coastal Condition Report 2007). It is divided into six segments: Blackburn Bay, Lemon Bay, Little Sarasota Bay, Roberts Bay, Upper Sarasota Ba y Sarasota County and Upper Sarasota Bay Manatee County (Figure 5). The main part of Sarasota Bay contains three passes, Longboat Pass, New washed away, contributi ng to better water quality than its smaller facets, including Roberts and Little Sarasota Bays. The entire area is home to a plethora of marine wildlife, particularly associated with the seagrass beds. Included among these are commercially relevant organi sms like shellfish, crabs and fish, protected animals such as dolphins, loggerhead sea turtles and manatees, as well as a multitude of seabirds (Dawes et al. 2004).
12 Figure 5 Segments of Sarasota Bay in Relation to Sarasota County. Map showing the area of Sarasota County, the Gulf of Mexico, Sarasota Bay and the different segments into which Sarasota Bay is divided. Map by author.
13 The Bay and its organisms have experienced a variety of threats. Many of these could be conside red to stem from the human population pressures imposed on the area. The largest industry in Sarasota County is tourism, with a total seasonal residency of 25% and over 70% seasonal residency in the barrier islands which define the bay segments, earning Sa rasota the largest urban land use percentage of all Gulf Coast NEP estuaries leading to predictable pollution, dredging, injured wildlife and habitat loss (National Estuary Program Coastal Condition Report 2007). From 1950 to 1988 the Bay experienced dredging and loss of water clarity that cut seagrass populations by 30% (Peatrowsky2010). After a turbulent ecological history, in 1989 the US Congress designated the Bay as an estuary of national significance, which appears to have contributed greatly to the commencement of initiatives focusing on its recovery and preservation ( http://sarasotabay.org/ ). This includes the Sarasota Bay Estuary Program a quasi governmental entity which monitors the health of the Bay an d educates citizens about bay related issues Sarasota County initiated a nitrogen pollutant reduction goal for the Bay of 48% in 1995 that has seen significant success ; this goal was inspired in part by guidelines from the EPA In 2010 seagrass coverage h ad expanded to 130% of the level present in 1950, with a 46% increase in water quality since 1988 ( Seagrass Recovery in Sarasota Bay Garners 1st Place Gulf Guardian Award for Sarasota Bay Estuary Program Partners and Citizens 2010) Seagrass falls under the jurisdiction of many governing bodies, from a federal to local level. Some of these are listed in Table 2. On a local level the Sarasota Bay Estuary Program manages seagrass in the majority of the Bay but Lemon Bay stretches into Charlotte County (Figu re 5). Along with Roberts Bay, it falls under the jurisdiction of the Charlotte Harbour National Estuary Program (http://www.chnep.org/). The wellbeing and management strategy fo r the Bay.
14 Table 2 List showing some of the bodies which regulate seagrass in Sarasota Bay Bodies Governing Seagrass in Sarasota Bay Sarasota County National Marine Fisheries Service (division of NOAA) US Fish and Wildlife Service Florida Department of Environmental Protection Florida Fish and Wildlife Conservation Commission Sarasota Bay received positive ratings for 2012 on the Trophic State Index used to measure levels of nitrogen, chlorophyll and phosphorous, essential components of plant 100) ( http://www.tampabay .wateratlas.usf.edu/bay/waterquality.asp?wbodyid=14268&wbody atlas=bay#trophic ). These represent sites which are oligotrophic to mid eutrophic, mid eutrophic eutrophic and hyper eutrophic respectively. The ratings for the main areas examined by this projec t are listed in Table 3, according to the Sarasota County Water Atlas ( http://www.sarasota.wateratlas.usf.edu ). Water clarity is another major indicator of the health of an aquatic system. It is essential for seagrass and the ecosystem it supports. It also influences the price of waterfront property, being a highly desired trait among people who want to live near wa ter, and therefore influences on the ways aquatic areas are used residentially or recreationally (Poor et al. 2007). Clear water is extr emely important for Sarasota Bay, which values its seagrass population and is a prime tourist destination rich in water sports and beach attractions. Water clarity is evaluated based on the secchi depth, which is normally measured using a disc with a 20 cm diameter and patterned with alternating black and white quadrants (Figure 6). The secchi depth is found where the disk is no longer visible. To measure
15 turbidity an optical sensor sends light into the water and measures it as it is reflected. With higher particle content in the water, more light is reflected, and the greater the turbidity. It is measured with a nephelomet er in Nephelometric Turbidity Units (NTU). The measurement tracks light which is the same bandwidth and reflected at precisely 90 from the light origin ( http://www.sarasota.wateratlas.usf.edu/shared/learnmore.asp?toolsection=lm_lakeclarity ). Table 3 Trophic State Index Rating for Major Areas of Sarasota Bay Bay Segment Trophic State Index Rating (2012) Historic Range (2000 2001) Lemon Bay 1 49 Good 41 43 Blackburn Bay 2 42 Good No Data Little Sarasota Bay 3 46 Good 34 48 Roberts Bay (Sarasota) 4 50 Fair No Data Sarasota Bay 5 33 Good 32 48 1 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 166#trophic 2 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 271#trophic 3 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayand wbodyid=14 268#trophic 4 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 157#trophic 5 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 147#trophic The Sarasota County Water Atlas, a cumulative pr oject amassing water data for Sarasota Bay ( http://www.sarasota.wateratlas.usf.edu/new/ ), collated data on the water clarity and turbidity of the area. Table 4 shows the secchi depth and turbidity measurements for the main areas of Sarasota Bay in 2012, as well as their historic ranges and the years these
16 cover. The table also includes the most recent measurements of light attenuation, which are from 1994, and its historic range. Table 4 Measurements of Water Clarity for Major Areas of Sarasota Bay Bay Segment Lemon Bay 6 Blackburn Bay 7 Little Sarasota Bay 8 Roberts Bay 9 Sarasota Bay S 10 Secchi Depth(m) (2012) 0.6096 1.58496 0.70104 0.9144 1.46304 Historic Range 0.09144 0.451104 (1980 2012) 0.3048 3.99288 (1980 2012) 0.3048 3.99288 (1978 2012) 0.3962 3.993 (1980 2012) 0.0 5.30352 (1979 2012) Turbidity (NTU) (2012) 4.6 3.1 16.0 7.0 2.9 Historic Range (1979 2012) 0.0 410.0 0.2 39.0 0.1 16 0.2 24.0 0.0 87.0 Light Attenuation (1994) 0.29 0.29 0.29 0.29 0.29 Historic Range (1990 1994) No Data 0.24 1.67 0.20 2.28 0.20 4.17 0.20 4.85
17 6 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 166 7 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 271 8 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 268 9 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 157 10 www.sarasota.wateratlas.usf.edu/bay/waterquality.asp?wbodyatlas=bayandwbodyid=14 147 Figure 6 Secchi Disk ( http://www.noc.soton.ac.uk/o4s/exp/img/001_secchi_drg.gif ) A diagram showing the parts and function of a secchi disk. From 2006 to 2008 a large increase in se agrass quantity occurred in Sarasota Bay (28%) and Lemon Bay (5.5%). The bulk of this was seen i n Upper Sarasota Bay Manatee County, with a smaller increase in Upper Sarasota Bay Sarasota County. Despite the overall gain ther e were seagrass losses in Blackburn and Roberts Bay over this time period. Seagrass in Sarasota Bay is currently considered t o be doing well and species composition is considered stable (Perry et al. 2011). There are three main types of seagrass in Sarasota Bay. These are turtle grass or Thalassia testudinum (Figure 7) shoal grass or Halodule wrightii (Figure 8) and manatee
18 grass or Syringodium filiforme (Figure 9) (Perry et al. 2005) Turtle grass ( Thalassia testudinum ) is the largest species found in Florida and has the deepest root system. It has densely packed rhizomes which are located about 20 cm into a sandy or m uddy substrate, and its leaves are long and flat like ribbons. The leaves have been reported to be between 0.4 and 1.2 cm wide and 10 cm 75 cm long ( http://www.dep.state.fl.us/coastal/habitats/seagrass/) Shoal grass ( Halodule wrightii ) has long, thin leaf blades, measuring 5 40 cm long and 1 3 mm in width. Its rhizomes grow shallow at around 5cm, although the roots go much further, up to 25 cm deep. It also tends to grow in shallower waters in a sandy or muddy substrate (Florida Fish and Wildlife Comission http://myfwc.com/research/habitat/seagrasses/information/gallery/halodule wrightii shoalgrass 1/ ). Finally, manatee grass ( Syringodium filifor me) has rhizomes found anywhere from 1 cm 10 cm below the substrate or even in the water column. It has a rounded blade with a 1 3 mm diameter that may get to 40 cm in length, and frequently grows with turtle grass, although monospecific beds are common ( http://www.dep.state.fl.us/coastal/habitats/seagrass/ ). Figure 7 Thalassia testudinum (Turtle Grass). 7 a A node sprouting a ramet of turtle grass and roots (Phillips and Meez 1988). 7 b A rhizome of turtle grass and the nodes which border it, along with roots (http://www.dep.state.fl.us/coastal/habitats/seagrass/).
19 Figure 8 Halodule wrightii (Shoal Grass). 8a Left: Blades of shoal grass have a distinctively shaped tip. Right: Genet of shoal grass (Phillips and Meez 1988. 8b Two ramets if shoal grass (http://www.dep.state.fl.us/coastal/habitats/seagrass/). Figure 9 Syringodium filiforme (Manatee Grass) 9a Left: A genet of manatee grass. Right: A ramet of manatee grass (Phillips and Meez, 1988). 9b Two ramets of manatee grass (http://www.dep.state.fl.us/coastal/habitats/seagrass/).
20 Evaluating and Restoring Seagrass Beds Threats Changes to the coast, manmade or otherwise, can wash sedimentation and pollutants into the ocean through rain water runoff (Orth et al. 2006) For example, on all three keys in Sarasota Bay, there are paved roads within a few meters of the shoreline, contributing to water run off as well as run off of pollutants such as motor oil. Sediment loading creates a murky envi ronment where photosynthesis is difficult, while pollutants can lead to eutrophication or susceptibility to disease for plants Eutrophication involves the production of large amounts of drift algae and other organic material which clog deep scars and can create an anoxic environment conducive to high H 2 S concentrations where the water meets the substrate, hindering seagrass regrowth (Kenworthy et al. 2002). Prop Scarring Figure 10 Prop Scarring in Sarasota Bay A large prop scar seen in Sarasota Bay near New Col lege of Florida. Photo by Sean Patton
21 The focus of this study is propeller scarring through seagrass areas Prop scars are formed when boat propellers create gouges in the seagrass bed which often have a long, slice like appearance (Figure 10 ). There is some controversy surrounding the issue of prop scarring as a significant ecological threat. There is no doubt that in large enough quantities elimination of seagrass can lead to erosion and habitat segmentation resulting in chain reactions throughout the ecosystem (Burfeind and Stunz, 2006; Macreadieet al. 2010) On the other hand, it ha s been suggested that not all prop scarring is serious (Ellet al. 2002) and it is possible for a boat propeller to cut only the blades while leaving the rhizomes intact. However, seagrass grows in shallow w ater, and boat propellers often reach the substrate, creating a prop scar. Prop scars occur even in areas where seagrass is protected due to negligence, illegal navigation tools or poor signage Boat owners may be unaware that they are taking their boat into shallow seagrass habitat. They may also do this purposefully to access shallow areas or take short cuts across beds (Dutton et. al., 2002, South Florida Natural Resource Center 2008). An early study done in Sarasota Bay showed that 41% of boaters admi tted motor to leave the bed area, 66% of those who did were likely to cause prop scar damage (Folit and Morris 1992). This study led to educational efforts and improv ed use of channel markers and signs which contributed to decreased incidents of prop scar damage. Scars can vary considerably in dimension, affecting their healing rates. Deeper, wider scars take a longer time to recover (Hammerstrom et al. 2007). Scar wid ths have been recorded as being between 0.2 0.6 m in Charlotte Harbour, and 0.2 0.9 m Tampa Bay (Bell et al. 2002). An average width of 0.4 5m has been recorded in the Florida Keys (Kenworthy et. al., 2002). Regrowth times vary by species ( Table 6 Of the types prevalent in Sarasota Bay, S. filiforme and H. wrightii are have a relatively fast re growth time (Foseca et. al. 2004) Thalassia testudinum is the slowest g rowing and likely to suffer the most from prop scar damage, since it may take up to 10 months for nascent apical meristem to form on the cut rhizomes which line a prop scar (Dawes et al. 1997). W ater which enters the scar can strip anaerobic bacteria from the sediment that are important components of the nutrient load required for successful growth, and slow
22 healing is partly caused by the need for bacterial recolonization (Ehringer and Anderson 2000). Table 5 Prop scar regrowth time s of three seagrass species. Unless stated otherwise, data are taken from Kenworthy et al. 2002, with an average scar width of 0.45m. Seagrass Species Regrowth Time (Years) Thalassia testudinum 9.5 3.5 7.6 (Dawes et al. 1997) Syringodium filiforme 1.4 Halodule wrightii 1.7 Identifying and Evaluating Prop Scars Knowledge of prop scar locations, abundance and dimensions are of high importance in evaluating the health of seagrass ecosystems, especially since certain species of seagrass are highly prone to negative impacts from prop scarring (Dunton et al., 2002) This knowledge can be gained in multiple ways, including visiting field sites to take measurements and observations, and by aerial phot ography which can be converted into map data. The photography can come from satellite data or be collected by air plane (Robbins, 1997 ; Phinn et al., 2009) Management and Restoration Once a problem area has been identified mitigation methods can be initiated. Zoning divides the area into sections where certain types of activity are and are not allowed. To determine if zoning has positive effects, this system was initiated i n Tampa Bay using four zones: exclusion zones where internal combustion engine use was banned, caution zones engine use was allowed, but causing injury to seagrass was penalized, required idle speed zones where engines were allowed within a greater exclusi on zones in order to access specific areas, and control areas which had no restrictions. This experiment
23 produced positive results, with a reduced increase rate of scarring observed after zoning. Additionally, the rate increased as the signs indicating the zones were lost or damaged over time (Stowers et al. 2000). In other areas where this system has been applied the difference between scarring in restricted and unrestricted areas is not always significant, but restricted areas do tend to suffer less damag e than unrestricted ones, so the presence of signs is considered a positive step toward mitigation scarring (Ehringer and Anderson 2000). There have also been attempts to repair existing damage. One way to do this is by replanting into scars. To replant, rhizomes and seeds are collected and kept in a nursery until they become seedlings and then taken to the chosen site. Planting can be done by hand or mechanically. In the mechanical method the boat floats above the bed and does not damage it. H owever, han d planting involves walking through the bed, which may cause some injury. Mechanical planting involves a boat fitted with a planting wheel that inserts plants or root pieces into the sediment. A mechanical replanting effort in Fort DeSoto produced a 48% su rvival rating for H. wrightii after one year ( Ehringer 1993 2000), however, other attempts have been less successful (Bell 2008). Other efforts focus on increasing nutrient levels in prop scars, particularly those related to ammonia and nitrogen since there is 60% less ammoniac nitrogen in sediment within prop scars than the sediment around the scarred area (Ehringer and Anderson 2000). Addition of nitrates has no effect on the scars but positive effect have been observed from addition of urea, which wh en combined in a solution with gibberellic acid and 6 benzyladenine has been shown to prompt Thalassia testudinum to grow, encouraging recovery along the edges of the scars In another approach nutrient enrichment project, posts have been placed in seagras s beds in the Florida Keys which are designed to attract birds to roost. The birds leave excrement in the water beneath the poles, fertilizing the beds and stimulating growth. These methods are best applied to areas where scarring is a serious threat. The focus of this study is to evaluate the extent and healing rates of prop scars in Sarasota Bay with the goal of identifying sites for further study which might benefit from such treatments.
24 Chapter 2: Methods Data Collection Digitizing High quality aerial photographs were obtained from Sarasota County showing the entirety of Sarasota Bay for the years 2010, 2011 and 2012. To provide the most consistency possible, the photographs used were all taken during the same time of year. Before be ginning to map the scars, the aerial file for the appropriate year was loaded into ArcGIS, along with a shapefile showing Sarasota County. Only areas perpendicular to the county shapefile were examined. Waterways which entered the area of the county shapef ile were excluded since they were not considered part of the Bay. Non coastal areas were excluded because seagrass was obviously absent on land or in deep water. Figure 11 is a portion of the 2011 aerial images showing Sarasota County and the coastal areas in question. Using GIS, the designated area was examined at a magnification ratio of 1:750. This resolution was chosen since it produced the clearest picture while covering the most space, to reduce error stemming fro m noteworthy variations in seagrass cover occurring at a level too small to notice at a high resolution (Robbins 1997). Before digitizing, the aerial photographs underwent an informal, visual evaluation to gain familiarity with the area and determine the l ocations of seagrass beds and prop scars. It was noted that scars could be very long and were thickly grouped in certain areas, but in other areas were very sparse and difficult to locate. The methods used to digitize the scars dealt with this variation in density by splitting the digitization process into two steps. Large, easily distinguishable seagrass beds were examined first, followed by the entirety of the Sarasota Bay coastline. The large seagrass beds were processed first because they were noticeabl e target areas that contained many scars which were too long to be seen on a single screen in their entirety. All the large beds were observed from north to south, from the top left to the bottom right, o ne screen at a time. The whole of Sarasota Bay was a lso examined in this way. After this, the entire Bay was examined a second time to find
25 and correct any errors or omissions. Overall, the large seagrass beds were examined three times and the entire Bay was examined twice. A line shapefile was generated fo r each year and given an appropriate name. The attribute table for this file contained fields for the length of the scars in meters and notes, as well as the automatic fields FID and Shape. This shapefile for the year in question was loaded into the GIS wi ndow. Seagrass scars were located by zooming into the top left of the relevant area at the 1:750 magnification and performing a thorough search for visible prop scars on the screen, with particular attention given to areas near land since they would eviden tly be shallower and therefore prone to scarring. Any scars found were digitized by tracing the scar using the line drawing tool and saved in the appropriate shapefile. Additions to the file were saved repeatedly during the process to guard against potenti al computer malfunctions. Scars were only digitized if it was clear that they were indeed scars and not small imperfections in the aerial images, waves, pipelines or other features. The image on the screen was then scrolled to the right in a straight line repeating the digitization process described above, until the previous view was replaced by a view of the Sarasota County shapefile, at which point the image was dragged down until a new image had almost entirely replaced the old one. This image was exam ined and any scars present were digitized as described above, then scrolled to the left. The process was repeated until the image showed the Gulf of Mexico beyond the Bay, at which point the image was dragged down again. The entire process was repeated unt il the whole of the relevant area was covered. The process described above was repeated for all three years in question, producing shapefiles showing all the scars present in the Bay. Using a pre existing shapefile of seagrass beds and the selection featu re GIS, shapefiles were generated showing only the prop scars contained within seagrass beds for each of the three years. These were the files used to launch the final analyses, in conjunction with shapefiles showing the different segments of Sarasota Bay and showing the locations of different seagrass species within the Bay.
26 Figure 11 Aerial Photograph of Sarasota County. Excerpt from the 2011 aerial photograph used in the analyses, showing Sarasota County and its coastal areas. Map by author.
27 Ground Truthing The 2010 aerials were used to identify areas where scarring was prevalent, resulting in six research sites in Sarasota Bay. Four of these, Big Pass, Ken Thompson Park boat ramp, the Bay in front of New College of Florida and The Bay just north of Coon Key were located in Upper Sarasota Bay S arasota County (Figure 12 ). One site was in Roberts Bay, North west of Skiers Island (Figure 13 ) and another was at Blackburn Point i n Little Sarasota Bay (Figure 14 ).
28 Figure 12 Map showing the sites in Upper Sarasota Bay, Sarasota County (New College of Florida, Ken Thompson Park Boat Ramp, North of Coon Key, Big Pass) where field samples of prop scars were taken in 2012. Prop scars in the area which can be seen on the 2012 aerial images are shown in purple, while those which were observed in the field are shown in yellow. Yellow also indicates scars which could be seen on both the aerial photographs and the field. Seagrass beds are shown as pale polygons.
29 Figure 13 Map showing the site Northwest of Skiers Island in Roberts Bay where field samples of prop scars were taken in 2012. Prop scars in the area which can be seen on the 2012 aerial images are shown in purple, while those which were observed in the field are shown in yellow. Yellow also indicates scars which could be seen on both the aerial photographs and the field. Seagras s beds are shown as pale polygons.
30 Figure 14 Map showing the site in Little Sarasota Bay where field samples of prop scars were taken in 2012. Prop scars in the area which can be seen on the 2012 aerial images are shown in purple, while those which were observed in the field are shown in yellow. Yellow also indicates scars which could be seen on both the aerial photographs and the field. Seagrass beds are shown as pale polygons.
31 During the winter of 2012 these sites were vi sited to take physical measurements of any scars present. Research was conducted by a four person team at low tide, and sites were accessed either via boat or by wading. Scars were located and mapped on site using a handheld GIS/GPS device. Scar depth, sca r width and blade length of the seagrass were all measured using measuring tape at a minimum of three different points along each scar. These points were used to calculate an average for that scar. Data were also taken on the presence of the three targeted species of seagrass, Thalassia testudinum Halodule wrightii and Syringodium filiforme. The composition of the substrate was noted as being Analysis Species Composition of Seagrass Beds To determine the species composition of seagrass beds in Sarasota Bay a shapefile was acquired from Sarasota County containing data points which showed the different species present at each point. These were grouped into categories showing either a single species or a combination of species. The number of points contained in a certain category was counted to determine the prevalence of that category within the bay. GIS was used to combine the species data with the scarring data for each year in order to de termine the likely species present closest to each scar. The available species data was collected in 2008, so for the purposes of analysis the assumption was made that the composition of a seagrass bed was unlikely to change significantly between 2008 and the three year period of the study. Average Width and Depth An average width and depth was calculated for each prop scar measured during the 2012 ground truthing by adding the values for each of the points measured along each individual scar and dividing that figure by the number of points. These were then used to create an overall average width and depth of prop scars for Sarasota Bay by adding them and dividing that figure by the total number of scars observed during ground truthing.
32 Scarring By Specie s Composition and Bay Segment In addition to the shapefile containing species data, another shapefile was acquired from the South Florida Water Management District Shapefile Library ( http://www.swfwmd.state.fl.us/data/gis/layer_library/category/swim ) containing data on the location of the different Bay segments which comprise Sarasota Bay. The spatial join feature of GIS was used to combine data from the prop scar shapefiles with the pre existing shapefiles, creating new shapefiles containing data for the length of each prop scar, the bay segment it was found in and the seagrass species found closest to each scar. These files were used to determine the total number and length of scars per year and per bay segment per year, as well as the total number and length of scars found in seagrass beds with various species compositions. Also noted was the standard deviation, maximum, minimum and average scar length per year and per bay s egment per year. The sum of the lengths was used to calculate the apparent area and apparent volume of the prop scars for each year, bay segment per year, and species composition per year, based on the average width and depth determined from the January 20 12 field data. Comparison of Scar Proportions Over Three Years A GIS analysis determine d which scars remai ned visible over multiple years This was done between the 2010 and 2011 scars, the 2011 and 2012 scars and the 2010 and 2012 scars. The analysis was performed twice for each pair in order to reduce error. For example, in an analysis comparing the 2010 scars to those from 2011, the 2010 shapefile would first serve as the input feature and the 2011 shapefile as th e near feature. Then the analyse s were re peated with the positions of the shapefiles being switched. Due to differences in projected coordinate systems between shapefiles and human error in the digitization process, lines in the different shapefiles representing the same scar never overlap perfe ctly. To account for this 0.5 m was chosen as the maximum distance between lines for them to be considered representative of the same scar.
33 All instances of distances of 0.5 m and less between scars from different years were selected and examined to dete rmine which lines showed the same scar in both years and which showed two different scars that crossed or overlapped. Once it was determined which scars were visible in both years, their lengths were recorded for each year they were visible and difference in length between years was calculated. The total difference was used to calculate the average difference in scar length between the years for the Bay as a whole and by bay segment. Some of the differences found were negative, meaning that a scar appeared shorter in an earlier year and longer in a later one. Differences where the negative value was very small can be attributed to human error in the digitization process, while larger negative differences were possibly due to variability in lighting, tide an d photograph quality between years which may have affected what was visible on the aerials. It is also possible that boats may have passed over these scars in the time since the aerials were produced, warping and lengthening their original shape. Conversel y, scars which appeared shorter may also have been partially filled by drift algae. To determine if there was a statistically significant difference in the length of individual scars between years, three Wilcoxon Rank Sum tests were performed using only values which produced positive differences since negative differences would not be i ndicative of whether regrowth had occur r ed A test was done for each of the following year pairings: 2010 and 2011, 2011 and 2012, 2010 and 2012. These tests were non directional, and a two tailed p value was produced using an of 0.5. 2012 Scar Length Co mparison Between Field Data and Aerial Measurements Files containing the ground truthed scars and the prop scars mapped from the 2012 aerial files were loaded into GIS and a N ear analysis was performed to determine which scars were the same between the two files. A Wilcoxon Rank Sum test was performed on the resulting scars to determine if there was a significant difference between what could be seen on the ground and from the air. This test was non directional, and a two tailed p value was produced using a n of 0.5.
34 Scarring Hotspots The scarring shapefiles from 2010, 2011 and 2012 were loaded to GIS along with an aerial photograph of Sarasota County and used to observe areas which suffered persistent scarring through all three years. This qualitative visual examination led to the are identified in Figures 24 28 at the end of the results section
35 Chapter 3: Results Species Composition of Seagrass Beds Scarred seagrass beds were found to be comprised of at l east seven possible species groupings. Three of these consisted of only one species, Halodule wrightii, Thalassia testudinum or Syringodium filiforme while the other four contained a mixture of two or all three of the species. An eighth group of scarred seagrass beds was found where the species could not be determined based on the data present in the pre existing shapefiles used in the analysis, and i 15 shows the location of data points of different species groupings, and Table 6 shows the number of data points at which each species composition was present in 2008, as well as the total number of points sampled. The most p revalent bed composition found in the Bay was monospecific Halodule wrightii a species with relatively shallow roots and rhizomal networks which has a relatively fast regrowth period, and the second fastest of the three species under consideration. Second most prevalent were monospecific beds of Thalassia testudi num, the largest and slowest growing of the three with the deepest root and rhizomal system. The third most common bed composition consisted of a combination of these two species. Very little Syrin godi u m filiforme was observed. Table 6 Number of points where different species compositions of seagrass were observed Bed Composition Points Where Present Halodule wrightii 562 Thalassia testudinum 188 Syringodim filiforme 57 H. wrightii and T. testudinum 179 T. testudinum and S. filiforme 52 S. filiforme and H. wrightii 44 T. testudinum, H. wrightii and S. filiforme 28 Unknown 400 Total 1510
36 Figure 15 Map showing the different species compositions of seagrass beds in Sarasota Bay and the points at which they occur Indicates the overall composition of individual seagrass beds.
37 Average Width and Depth Table 7 shows the average, maximum and minimum for both scar width and depth based on data collected during the 2012 ground truthing. Table 7 Summary of prop scar widths and depths in Sarasota Bay based on field data collected in January 2012 Prop Scar Width in Sarasota Bay Prop Scar Depth in Sarasota Bay Average 0.3m 0.04m Maximum 0.8m 0.005m Minimum 0.03m 0.105m Scarring By Species Composition and Bay Segment The averages shown in Table 7 allowed the calculation of the apparent scar area. Volume was found for beds of different seagrass composition and for the different Bay segments in each of the three years studied. Tables 8 10 show total number of scars observed and the apparent area an d volume of scarring for seagrass beds based on species composition for the years 2010, 2011 and 2012 respectively. The final row of each table represents the totals for entire Bay during that year. These data indicate that beds composed entirely of Thalas sia testudinum experienced the most apparent scarring even though this was not the most prevalent bed composition. In 2010 and 2011 beds composed entirely of Halodule wrightii experienced the second most apparent scarring, but in 2012 the second highest level of observed scarring is found in beds containing a combination of both Halodule wrightii and Thalassia testudinum
38 Table 8 Summary of prop scarr ing in Sarasota Bay based on species composition of seagrass beds for the year 2010. Includes apparent area and volume of prop scarring for different species based on the average width and depth of prop scars shown in Table 7 2010 Bed Composition Number of Scars Observed Scar Length (m) Apparent Scar Area (m 2 ) Apparent Scar Volume (m 3 ) Halodule wrightii 717 16107.12 4832.14 1932.85 Thalassia testudinum 835 17700.40 5310.12 2124.05 Syringodim filiforme 61 825.09 247.53 99.01 H. wrightii and T. testudinum 467 10344.69 3103.41 1241.36 T. testudinum and S. filiforme 341 5236.29 1570.89 628.35 S. filiforme and H. wrightii 75 1315.45 394.64 157.85 T. testudinumtestudinum, H. wrightii and S. filiforme 58 1142.44 342.73 137.09 Unknown 188 3560.07 1068.02 427.21 Total 2742 56231.55 16869.47 6747.79 Table 9 Summary of prop scarring in Sarasota Bay based on species composition of seagrass beds for the year 2011. Includes apparent area and volume of prop scarring for different species based on the average width and depth of prop scars shown in Table 7 2011 Bed Composition Number of Scars Observed Scar Length (m) Apparent Scar Area (m 2 ) Apparent Scar Volume (m 3 ) Halodule wrightii 326 7203.30 2160.99 864.40 Thalassia testudinum 361 8321.73 2496.52 998.61 Syringodim filiforme 21 246.05 73.82 29.53 H. wrightii and T. testudinum 205 4902.52 1470.76 588.30 T. testudinum and S. filiforme 57 848.93 254.68 101.87 S. filiforme and H. wrightii 14 438.95 131.69 52.67 T. testudinum, H. wrightii and S. filiforme 18 200.80 60.24 24.10 Unknown 85 1954.57 586.37 234.55 Total 1087 24116.85 7235.06 2894.02
39 Table 10 Summary of prop scarring in Sarasota Bay based on species composition of seagrass beds for the year 2012. Includes apparent area and volume of prop scarring for different species based on the average width and depth of prop scars shown in Table 7 2012 Bed Composition Number of Observed Scars Scar Length (m) Apparent Scar Area (m 2 ) Apparent Scar Volume (m 3 ) Halodule wrightii 74 1020.79 306.24 122.49 Thalassia testudinum 333 8392.15 2517.64 1007.06 Syringodim filiforme 21 279.47 83.84 33.54 H. wrightii and T. testudinum 178 3285.29 985.59 394.23 T. testudinum and S. filiforme 104 1425.57 427.67 171.07 S. filiforme and H. wrightii 14 224.48 67.34 26.94 T. testudinum, H. wrightii and S. filiforme 16 466.48 139.94 55.98 Unknown 28 266.49 79.95 31.98 Total 768 15360.71 4608.21 1843.28 Figure s 16 and 17 show the percentage of the total apparent scarring and the percentage of the total apparent length, area and volume present in each of the species groupings for the years studied, allowing a cross year comparison. These figures show that despite the fact that Halodule wrightii was found to be more abundant ( Table 7 ), beds consisting of only H. wrightii contained the second greatest number of scars in 2010 and 2011, with a much lower percentage in 2012. Beds which had only of Thalassia testudinum the secon d most common species in 2008, contained the most scarring in all three years with regards to both number of scars ( Figure 16 ) as well as length, volume and area ( Figure 17 ). Halodule wrightii contained the second greatest apparent length, area and volume of scars in 2011 and 2012, but these figures were much lower in 2010 ( Figure 17 ). A visual comparison of the two figures demonstrates that a larger number of scars does not always mean a higher percentage of total scarring length/area/volume.
40 Figure 16 P ercentage of the total apparent number of prop scars found in seagrass beds of different species compostions for the years 2010, 2011 and 2012. 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 Percentage of Scarring Per Year Species Composition of Scarred Seagrass Beds Apparent Number of Prop Scars: Percentage by Species Composition for 2010, 2011 and 2012 2010 2011 2012
41 Figure 17 P ercentage of the total apparent le ngth/volume/area of prop scars found in seagrass beds of different species composition in Sarasota Bay for the years 2010, 2011 and 2012 Tables 11 13 summarize prop scarring by bay segment for 2010, 2011 and 2012 respectively. These results are further illustrated by Figures 18 and 19 the first of which shows the percentage of the total number of scars found in each bay segment per year, and the second of which shows the percentage of the total length/area/volume of prop scarring found in each bay segment per year. These tables and figures show that in 2010 the highest apparent average scar length w as found in Little Sarasota Bay. I n 2011 it was 0.00 10.00 20.00 30.00 40.00 50.00 60.00 Percentage of Scarring Per Year Species Composition of Scarred Seagrass Beds Apparent Length/Volume/Area of Prop Scarring: Percentage by Species Composition for 2010, 2011 and 2012 2010 2011 2012
42 found in Roberts Bay and in 2012 it was found in Upper Sarasota Bay Sarasota County with the apparent average scar length in Roberts Bay holding a close second for that year. Despite these differences in apparent average length per bay segment per year, Upper Sarasota Bay, Sarasota County consistently contained the hig hest apparent number of scars and consequently the largest apparent area and apparent volume. As with Figures 1 6 and 1 7 it is clear that a greater number of scars does not necessarily equate to a higher percentage of total scarring length/area/volume. Figure 18 P ercentage of the total apparent number of prop scars found in seagrass beds in the different bay segments of Sarasota Bay for the years 2010, 2011 and 2012 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 BLACKBURN BAY LEMON BAY LITTLE SARASOTA BAY ROBERTS BAY UPPER SARASOTA BAY-S Percent Total Apparent Scarring Bay Segment Apparent Total Number of Prop Scars: Percentage by Bay Segment for 2010, 2011 and 2012 2010 2011 2012
43 Figure 19 P ercentage of the total apparent length/volume/area of prop scarring found in seagrass beds in the different bay segments of Sarasota Bay for the years 2010, 2011 and 2012 Some scars observed in 2010 were not seen in 2011, but were present in 2012 (Appendices 1.1 1.3). This may b e attributable to weather and tidal differences at the time the photographs were taken. Sarasota County only takes aerial photographs during specific weather conditions which will produce the best images, and this provides a degree of consistency. However, it is practically impossible to replicate weather and tidal conditions between years. This, combined with the difference in filters used for aquatic and land surveying, should be responsible for variation in what was visible 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 BLACKBURN BAY LEMON BAY LITTLE SARASOTA BAY ROBERTS BAY UPPER SARASOTA BAY-S Percentage of Scarring Per Year Bay Segment Apparent Length/Volume/Area of Prop Scarring: Percentage by Bay Segment for 2010, 2011 and 2012 2010 2011 2012
44 Table 11 Summary of apparent prop scarring in Sarasota Bay based on bay segment for the year 2010, including totals for the entire bay where appropriate. Includes apparent area and volume of prop scarring for different bay segments based on the average width and depth of prop scars shown in Table 8 The maximum and minimum scar lengths for the year underlined and italicized, and totals listed in the bottom row of the tables in bold. 2010 BAY SEGMENT Number of Scars Minimum Length (m) Maximum Length (m) Average Length (m) Sum Standard Deviation Average Area (m 2 ) Average Volume (m 3 ) BLACKBURN BAY 146 1.02 248.78 19.71 2877.93 27.43 863.38 345.35 LEMON BAY 160 0.18 127.46 15.68 2508.23 16.09 752.47 300.99 LITTLE SARASOTA BAY 478 0.04 300.12 24.59 11754.58 26.48 3526.37 1410.55 ROBERTS BAY 223 0.71 289.04 22.75 5072.42 31.69 1521.72 608.69 UPPER SARASOTA BAY S 1735 0.03 434.97 19.61 34018.41 27.78 10205.52 4082.21 Total 2742 20.47 56231.56 16869.47 6747.79
45 Table 12 Summary of apparent prop scarring in Sarasota Bay based on bay segment for the year 2011, including totals for the entire bay where appropriate. Includes apparent area and volume of prop scarring for different bay segments based on the average wid th and de pth of prop scars shown in Table 8 The maximum and minimum scar lengths for the year underlined and italicized, and totals listed in the bo ttom row of the tables in bold. 2011 BAY SEGMENT Number of Scars Minimum Length (m) Maximum Length (m) Average Length (m) Sum Standard Deviation Average Area (m 2 ) Average Volume (m 3 ) BLACKBURN BAY 28 2.30 17.66 8.29 232.13 3.95 69.64 572.25 LEMON BAY 176 1.63 248.26 27.10 4768.77 30.25 1430.63 607.50 LITTLE SARASOTA BAY 245 0.32 143.57 20.66 5062.49 18.25 1518.75 461.44 ROBERTS BAY 123 0.83 280.21 31.26 3845.30 49.17 1153.59 1224.98 UPPER SARASOTA BAY S 515 1.88 631.00 19.82 10208.15 38.11 3062.44 2894.02 TOTAL 1087 21.43 24116.84 7235.05 5760.19
46 Table 13 Summary of apparent prop scarring in Sarasota Bay based on bay segment for the year 2012, including totals for the entire bay where appropriate. Includes apparent area and volume of prop scarring for different bay segments based on the average wid th and de pth of prop scars shown in Table 8. The maximum and minimum scar lengths for the year underlined and italicized, and totals listed in the bo ttom row of the tables in bold. 2012 BAY SEGMENT Number of Scars Minimum Length (m) Maximum Length (m) Average Length (m) Sum Standard Deviation Average Area (m 2 ) Average Volume (m 3 ) BLACKBURN BAY 26 3.13 71.11 18.83 489.50 18.41 146.85 58.74 LEMON BAY 8 4.80 30.41 12.04 96.30 8.08 28.89 11.56 LITTLE SARASOTA BAY 28 0.13 71.58 15.34 429.47 15.73 128.84 51.54 ROBERTS BAY 65 1.64 105.13 20.30 1319.60 20.86 395.88 158.35 UPPER SARASOTA BAY S 641 0.94 561.50 20.32 13025.85 37.53 3907.76 1563.10 TOTAL 768 17.36 15360.71 4608.21 1843.29
47 Comparison of Scar Proportions Over Three Years T he data for scar length over the 3 year period did not follow the normal distribution, necessitating use of a non parametric assessment to test the hypothesis that there was no significant difference in scar length between different years. A Wilcoxo n Rank Sum test showed that there was a significant difference in the lengths of those scars which were identified in multiple years, and that the differences were significant for all three comparisons between years ( Table 1 4 ). They were particularly signi ficant for the 2010 2011 and 2011 2012 comparisons. Table 14 Results of the Wilcoxon Rank Sum test for three comparisons of the length of individual prop scars between years Comparison Number of scars present in both years Mean Standard Deviation Wilcoxon Signed Rank 2010 and 2011 93 23.07 30.34 <.0001 2011 and 2012 36 12.36 15.57 <.0001 2010 and 2012 10 34.04 39.75 0.002
48 2012 Scar Length Comparison Between Field Data and Aerial Measurements Table 1 5 shows the fourteen scars that were visible in both the field data and aerials for 2012. Although field samples were taken from three bay segments, all but one of the scars which were ground truthed and also vi sible on the aerials were found in Sarasota Bay, Sarasota County. The scars are shown in Figures 20 23. Table 15 Length of scars as measured in the field during ground truthing in January of 2012 and in the aerial photographs from that year. Scars show n in figures 20 23. Ground Truthed Scar Length Aerial Scar Length Site Bay Segment 15.15 16.67 Bay in front of NCF UPPER SARASOTA BAY S 19.02 10.61 Bay in front of NCF UPPER SARASOTA BAY S 27.04 26.94 Bay in front of NCF UPPER SARASOTA BAY S 29.99 32.60 Bay in front of NCF UPPER SARASOTA BAY S 16.69 10.12 Ken Thompson Park Boat Ramp UPPER SARASOTA BAY S 30.84 27.89 Just North of Coon Key UPPER SARASOTA BAY S 80.26 322.55 Just North of Coon Key UPPER SARASOTA BAY S 25.47 99.71 Just North of Coon Key UPPER SARASOTA BAY S 34.84 161.05 Just North of Coon Key UPPER SARASOTA BAY S 5.56 5.19 Just North of Coon Key UPPER SARASOTA BAY S 25.36 16.00 Just North of Coon Key UPPER SARASOTA BAY S 13.69 13.39 Big Pass UPPER SARASOTA BAY S 66.77 47.02 Big Pass UPPER SARASOTA BAY S 2.61 35.70 Northwest of Skiers Island ROBERTS BAY
49 Figure 20 P rop scars observed in 2012 at Big Pass. Scars observed both in the field and in the aerial photographs are shown in red, while those which were only observed via aerial photograph are shown in yellow.
50 Figure 21 P rop scars observed in 2012 at Ken Thompson Boat Ramp and North of Coon Key. Scars observed both in the field and in the aerial photographs are shown in red, while those which were only observed via aerial photograph are shown in yellow.
51 Figure 22 P rop scars observed in 2012 at New College of Florida. Scars observed both in the field and in the aerial photographs are shown in red, while those which were only observed via aerial photograph are shown in yellow.
52 Figure 23 P rop scars observed in 2012 at North West of Skiers Island Scars observed both in the field and in the aerial photographs are shown in red while those which were only observed via aerial photograph are shown in yellow.
53 Th e s e data approximately followed a normal distribution. T herefore a paired t test was performed to test the hypothesis that there is no significant difference between the length of the scars as measured through ground truthing and aerial photography. The results of this test are shown in Table 1 6 The two tailed p value shows that there is a significant difference between the length of the scars observed in the field and the length as observed through the aerial photographs. Table 16 Results of the paired t test performed to test if a significant difference existed between the length of individual scars as observed during the 2012 ground truthing and through the 2012 aerials. Paired t Test Results Field Data Aerial Data Total N 14 14 28 Mean 28.0912 59.1029 43.5975 t 1.6 d f 13 One tailed 0.0668045 Two tailed p 0.133609 Both the three year healing comparison and the comparison between the field data and aerial data for 2012 shows the importance of location. In the latter, although three bay segments were sampled via ground truthing, on the aerials all scars but one were found in Sarasota Bay, Sarasota County. One reason for this was that the scars which were ground truthed in Litt le Sarasota Bay were not in the same immediate area as the scars observed on the aerials. The former w ere closer to land and easier to sample. This occurred because the field data were collected before the aerial data were processed. Use of different locations within a small area caused a loss of potential data. Despite limitations of this study imposed by the different qualit y of the aerial photographs between years, the fact that significant results were found for all three comparisons of scar length between different years indicates that the prop scars are healing at a substantial rate. This is likely influenced by the speci es composition and location of seagrass beds.
54 Scarring Hotspots Examination of each Bay segment led to the isolation of areas which showed persistent scarring over all three years in each Bay Segment. While Roberts Bay, Blackburn Bay and Lemon Bay each ha d one site of concern, two were found in Little Sarasota Bay and at least seven were found in Upper Sarasota Bay. These sites are shown in figures 24 28 along with nearby terrestrial reference points.
55 Figure 24 Area in Blackburn Bay along Casey Key Road which appears to be at risk for prop scarring over multiple years Reference point: Sea Grape Point Road.
56 Figure 25 Area in Lemon Bay from Lemon Bay Park to Indian Mound Park which appears to be at risk for prop scarring over multiple years Reference point: Manasota Key Road.
57 Figure 26 Area in Little Sarasota Bay from Vamo to Blackburn Point Road which appears to be at risk for prop scarring over multiple years. Reference point: Bird Keys.
58 Figure 27 Area in Roberts Bay from Bay Island Park to South Coconut Bayou which appears to be at risk for prop scarring over multiple years. Reference point: Coconut Bayou.
59 Figure 28 Area in Upper Sarasota Bay, S arasota County, from Button Wood Harbour to South Lido County Park which appears to be at risk for prop scarring over multiple years. Reference points: Buttonwood Harbour, Indian Beach/Sapphire Shore s, Gulf of Mexico Drive, City Island, St. Armands, Bird Key, Bay Isle.
60 Chapter 4: Discussion Aerials, Digitizing and Apparent Scar Number When choosing a resolution to examine seagrass beds on the aerial photographs the use of the 1:750 resolution allowed a clearer view of the prop scars compared to other resolutions, making seagrass easy to distinguish from other submerged aquatic vegetation. This was consistent with recommendation in previous studies which indicated that examining aerials at higher magnification than the commonly used 1:2400 (at which most aerials for seagrass are taken) would produce a more accurate analysis (Robbins 1997, Janicki et al. 2008) The difference in the total apparent number of scars found between years, particular ly the fact that there were much fewer scars observed in 2012, is likely attributable to differences in picture quality between years. The aerial photographs available for this project were provided by Sarasota County, and generated mainly for land surveying purposes. Roughly every two years aerials are taken which are a lso focused on aquatic surveying. The pictures are taken in wint er when conditions are clearest. H owever, what is visible can vary from year to year ba sed on picture quality and must be checked via field work (Janicki et al. 2008). The photographs used in this study showed this variation. The 2010 aerials were of the latter type, and are the best quality. The 2011 photographs were mainly focused on land surveys but still provide very good aquatic images. The 2012 photographs should have contained images generated equally for u se in aquatic and land surveys however, I was informed by Sarasota County that technical and production related problems rendered t he images lower quality than expected. They were still consider ed useful for this project because prop sc ars were still visible, but based on the number of scars observed in the previous two years it is likely that the apparent number of scars for 2012 i s much lower than the actual number present.
61 Prop Scarring in Sarasota Bay Species Composition Halodule wrightii the most prevalent species in the Bay, has a short prop scar recovery time of 1.7 years (Kenworthy et al. 2002). Th e abundance of this species in th e Bay may be related to the significant healing found between all of the years studied. Thalassia testudiunum, the second most common species in the Bay, has much longer recorded prop scar recovery time of 3.5 9.5 years (Da wes et al. 1997, Kenworthy et al. 2002). Thalassia testudiun um suffered the most prop scarring, despite this species being slightly less prevalent in the current study. This is consistent with knowledge of slow healing times for T. testudinu m (Dawes et al. 1997, Di Carlo 2008) and may therefore account for a higher number of observed scars. A study in Tampa Bay, where the top three dominant seagrass bed species compositions matched those in Sarasota Bay, found that H. wrightii was able to outcompete T. test udinum on un colonized sediment (Robbins and Bell 2000) It is possible that heavy prop scarring in an area colonized by T. testudinum might clear enough sediment for it cause it to give way to H. wrightii to move in and colonize and this is a possibility that requires further research. It is also recommended that potential links between highly scarred areas and facilities or locations based around boating be examined, such as marinas which rent boats to tourists. Due to the mixed nature of m any of the beds, this project contained insufficient data to further analyze the number and properties of scars in each individual species of seagrass in the Bay, but further investigation is recommended through multiyear field studies which focus on individual scars. These should be located in monospecific beds of each of the three main species found in Sara sota Bay, and multiple beds should be studied to account for environmental differences between areas where beds are found. Also recommended are studies in mixed beds to observe whether one species replaces another. Scarring Depth and Rhizome Depth The maxi mum and average scar widths recorded for Sarasota Bay are comparable to the range of widths reported in nearby Tampa Bay and Charlotte Bay (Bell et al. 2002), although the minimum scar width observed was much lower. This may be due to a
62 smaller average boa t size in Sarasota Bay. No previous studies could be found which looked at scar depth, but it would be interesting to examine this in relation to rhizome depth to determine the level of damage prop scarring causes to rhizomal networks. Bay Segments and Sc arring Hotspots Upper Sarasota Bay, Sarasota C ounty contains the most open water of the bay segments examined and therefore the most beds and scarring. The o ther bay segments are less open, with a single channel providing a straight, clear path for boats and having very few other features. This means that not only is there less area to be scarred, but there is potentially less cause for scarring, which is known to occur due to poor or purposefully negligent boat navigation, during which boats veer away fro m designated paths to quicker access areas of interest (Dunton et al. 2002) On the other hand, scarring in these areas was seen near to boat channels ( Figures 24 26 ), particularly near the bottom of Figure 26 It is possible that attempts to access the ch annels improperly caused the scars, implying that channels are directly linked to scar formation (Bell et al. 2002 ), but this would be in contrast to results from a study in Florida Bay which found that prop scars in that area were not related to any parti cular geographic feature other than shallow water depth (Hallac et al. 2012). It should be noted that even though many scars were not visible between years on the aerial photographs scarring frequently tended to occur in the same areas. This means that even though scars appear to be healing the bed may be suffering fairly consistent damage producing chronic stress. It is recommended that the areas identified as scarring hotspots within different Bay segments be specifically investigated over several year s to quantify the amount of scarring present, and how this may affect the ecosystems associated with them. In this study, scarring hotspots were identified qualitatively H owever, now that specific sites have been singled out, quantitative evaluation of sc ar density is possible Dunton and colleagues (2002) classified scarring as light, moderate and heavy based on percentages of scarring covering a designated area. It is recommended that these or other methods be applied to the identified scarred areas.
63 Co nclusion This study focuses on the entire Sarasota Bay, producing a broad picture of scarring in the area. It accumulates a variety of knowledge concerning prop scars in the Bay, including their dimensions and frequency in different areas and species of seagrass. However, it is limited by its inability to quantitatively examine specific locations within large bay segments It is recommended that further work be done concerning the scarring hotspots identified b y this study to determine if small scale restoration or improved preservation of seagrass is needed in these areas It is also recommended that signage schemes near areas shown to be scarring hotspots be re evaluated, and that pre existing education effort s targeted at boaters (Folit and Morris 1992) be continued and strengthened in those areas. Overall, p rop scars in Sarasota Bay appear to be healing at a significant rate indicating that large restoration efforts may be unneeded to remedy prop scarring. H owever, the capacity to heal is likely to vary by the species composition of individual seagrass beds and the areas in which they are located and it is suggested that prop scar studies in Sarasota C ounty can best be further pursued by the examination of i ndividual seagrass beds and individual prop scars found in target areas with a high scarring density
64 References Bell S, Tewfik A, Hall M, Fonseca M. 2008. Evaluation of seagrass planting and monitoring techniques: Implications for assessing restoration success and habitat equivalency. Restor ation Ecol ogy 16(3):407 16. Bell S, Hall M, Soffian S, Madley K. 2002. Assessing the impact of boat propeller scars on fish and shrimp utilizing seagrass beds. Ecol ogical Appl ications 12(1):206 17. Borum J San d Jensen K, Pedersen T, Greve T 2006. Chapter 10: Oxygen movement in seagrasses. In: Seagrasses: Biology, ecology and conservation. Anthony W. D. Larkum, Robert J. Orth,Carlos Duarte, editors. 1st ed. Neatherlands: Springer. 255 p. Bos A, Bouma T, de Kort G, van Katwijk M 2007. Ecosystem engineering by annual intertidal seagrass beds: Sediment accretion and modification. Estuarine, Coastal and Shelf Science 74(1):344 8. Brun F, Cummaudo F, Oliv I, Vergara J, Prez Llorns J 2007. Clonal extent, api cal dominance and networking features in the phalanx angiosperm Zostera noltii hornem. Mar ine Biol ogy 151(5):1917 27. Burfeind D and Stunz G 2006. The effects of boat propeller scarring intensity on nekton abundance in subtropical seagrass meadows. Marine Biology 148(5):953 62. Cabao S and Santos R. 2007. Effects of burial and erosion on the seagrass Zostera noltii J ournal of Exp erimental Mar ine Biol ogy and Ecol ogy 340(2):204 12. Cocheret de La Morinire, E, Pollux B, Nagelkerken I, Van der Velde G. 2002. Post settlement life cycle migration patterns and habitat preference of coral reef fish that use seagrass and mangrove habitats as nurseries. Estuarine, Coast and Shelf Science 55(2):309 21. Cunha AH, Duarte CM, Krause Jensen D. 2004. How long does it tak e to recolonize seagrass beds? In: European seagrasses: An introduction to monitoring and managment. Borum J, Duarte C, Krause Jensen D, et al, editors. The M&MS project. 72 p. Dawes C, Phillips R, Morrison G, Dawes C. 2004. Seagrass communities of the Gu lf Coast of Florida : Status and ecology. Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute. Dawes CJ, Andorfer J, Rose C, Uranowski C, Ehringer N. 1997. Regrowth of the seagrass Thalassia testudinum into propeller scars. Aquat ic Bot any 59(1):139 55. Den Hartog C and Kuo J. 2006. Taxonomy and biogeography of seagrasses. In: Seagrasses: Biology, ecology and conservation. Springer. 27 1 p p
65 Dennison W 1987. Effects of light on seagrass photosynthesis, growth and depth distribution. Aquat ic Bot any 27(1):15 26. Di Carlo G and Kenworthy W. 2008. Evaluation of aboveground and belowground biomass recovery in physically disturbed seagrass beds. Oecologia 158(2):285 98. Diez C Vlez Zuazo X, van Dam R. 2003. Hawksbill turtles in seagrass beds. Mar ine Turt le Newsl etter 102:8 10. Dixon L. 2000. Establishing light requirements for the seagrass Thalassia testudinum : An example from Tampa bay, F lorida. CRC Marine Science Series 16. Drake L, Dobbs F, Zimmerman R. 2003. Effects of epiphyte load on optical properties and photosynthetic potential of the seagrasses Thalassia testudinum Banks ex Knig and Zostera M arina L. Limnology and Oceanography 48(1):456 63. Duarte C 1991. Allometric scaling of seagrass form and productivity. Marine Ecology Progress Series. Oldendorf 77(2):289 300. Duarte C 1991. Seagrass depth limits. Aquat ic Bot any 40(4):363 77. Duarte C Fourqurean J, Krause Jensen D, Olesen B. 2006. Dynamics of seagrass stability and change. In: Seagrasses: Biology, ecology and conservation. Springer. 271 p p Duarte C, Merino M, Agawin N, Uri J, Fortes M, Gallegos M, Marb N, Hemminga MA. 1998. Root production and belowground seagrass biomass. Mar ine Ecol ogy Prog ress Ser ies 171:97 108. Dunton K and Schonberg S. 2002. Assessment of propeller scarring in seagrass beds of the south texas coast. J Coast Res (SPECIAL ISSUE NO. 37. IMPACTS OF MOTORIZED WATERCRAFT ON SHALLOW ESTUARINE AND COASTAL MARINE ENVIRONMENTS):100 10. Ehringer J and Anderson J. 2000. Seagrass transplanting and restoration in Tampa Bay Seagrass Management: It's Not just Nutrients :22 4. Folit R and Morris J. 1992. Beds, boats and buoys: A study in protecting seagrass beds from motorboat propeller damage. Sarasota Bay National Estuarine Program, Sarasota, FL Fonseca M, Whitfield P, Judson Kenworthy W, Colby D, Julius B. 2004. Use of two spatially explicit models t o determine the effect of injury geometry on natural resource recovery. Aquatic Conservation: Marine and Freshwater Ecosystems 14(3):281 98.
66 Fourqurean J and Zieman J. 2002. Nutrient content of the seagrass thalassia testudinum reveals regional patterns of relative availability of nitrogen and phosphorus in the F lorida keys USA. Biogeochemistry 61(3):229 45. Gacia E, Duarte CM, Marb N, Terrados J, Kennedy H, Fortes M, Tri N. 2003. Sediment deposition and production in SE Asia seagrass meadows. Estuarine, C oastal and Shelf Science 56(5 6):909 19. Green E and Short F 2003. World atlas of seagrasses. In: World atlas of seagrasses. University of California Press. 21 p. Greve T and Binzer T. 2004. Which factors regulate seagrass growth and distribution. In: Eur opean seagrasses: An introduction to monitoring and management. Borum J, Duarte C, Krause Jensen D, et al, editors. The M&MS project. 19 p. Gulf of Mexico Program. 2004. Seagrass habitat in the northern Gulf of Mexico : Degradation, conservation and restoration of a valuable Resource. USGS. Hall L, Hanisak M, Virnstein R 2006. Fragments of the seagrasses Halodule wrightii and Halophila johnsonii as potential recruits in Indian River Lagoon Florida Mar ine Ecol ogy Prog ress Ser ies 310:109 17. Hallac D, Sadle J, Pearlstine L, Herling F, Shinde D. 2012. Boating impacts to seagrass in Florida Bay Everglades National Park Florida USA: Links with physical and visitor use factors and implications for management. Marine and Freshwater Research 63(11):1117 28. Hammerstrom K, Kenworthy W, Whitfield P, Merello M. 2007. Response and recovery dynamics of seagrasses Thalassia testudinum and Syringodium filiforme and macroalgae in experimental motor vessel disturbances. Marine Ecolo gy Progress Series 345:83 92. Hemminga M and Duarte C. 2000. Seagrass ecology. Cambridge University Press. 121 p. Hootsmans M Vermaa t J Van Vierssen W. 1987. Seed bank development, germination and early seedling survival of two seagrass species from the Netherlands : Zostera marina L. and Zostera noltii Hornem Aquat ic Bot any 28(3 4):275 85. Hovel K 2003. Habitat fragmentation in marine landscapes: Relative effects of habitat cover and configuration on juvenile crab survival in California and North Caroli na seagrass beds. Biol ogical Conserv ation 110(3):401 12. Jackson E Rowden A Attrill M Bossey S, Jones M. 2001. The importance of seagrass beds as a habitat for fishery species. Oceanography and Marine Biology 39:269 304.
67 Janicki A, Dema M, Nijbroek R. 2 008. Seagrass targets for the Sarasota Bay Estuary Program Sarasota Water Atlas Available from: http://www.sarasota.wateratlas.usf.edu/upload/documents/SBEP%20Seagrass%20Targets %20Final%20Report.pdf. Jawad J Lombana A, Moore K, Rhode J. 2000. A review of issues in seagrass seed dormancy and germination: Implications for conservation and restoration. Marine Ecology Progress Series 200:277 88. Kenworthy W and Fonseca M. 1996. Light requirements of seagrasses Halodule wrightii and Syringodium filiforme derived from the relationship between diffuse light attenuation and maximum depth distribution. Estuaries and Coasts 19(3):740 50. Kenworthy W, Fonseca M, Whitfield P, Hammerstrom K. 2002. Analysis of seagrass recovery in experimental excavations and prop eller scar disturbances in the Florida Keys National Marine Sanctuary J ournal of Coast al Res earch :75 85. Kenworthy W. 2000. The role of sexual reproduction in maintaining populations of 'Halophila decipiens ': Implications for the biodiversity and conserv ation of tropical seagrass ecosystems. Pacific Conservation Biology 5(4):260. Koch E. 2001. Beyond light: Physical, geological, and geochemical parameters as possible submersed aquatic vegetation habitat requirements. Estuaries 24(1):1 17. Lee K, Park S, K im Y 2007. Effects of irradiance, temperature, and nutrients on growth dynamics of seagrasses: A review. J ournal of Exp erimental Mar ine Biol ogy and Ecol ogy 350(1 2):144 75. Lirman D and Cropper W. 2003. The influence of salinity on seagrass growth, surviv orship, and distribution within Biscayne Bay Florida : Field, experimental, and modeling studies. Estuaries 26(1):131 41. Madsen J, Chambers P, James W, Koch E, Westlake D. 2001. The interaction between water movement, sediment dynamics and submersed macro phytes. Hydrobiologia 444(1 3):71 84. Major K and Dunton K. 2002. Variations in light harvesting characteristics of the seagrass, Thalassia testudinum : Evidence for photoacclimation. Journal of Experimental Marine Biology and Ecology 275(2):173 89. Marb N, Duarte CM, Alexandra A, Cabao S. 2004. How do seagrasses grow and spread? In: European seagrass: An intoduction to monitoring and management. Borum J, Duarte C, Krause Jensen D, et al, editors. The M&MS project. 11 p.
68 Marsh Jr J Dennison W, Alberte R. 1986. Effects of temperature on photosynthesis and respiration in eelgrass ( Zostera marina L.). J Exp Mar Biol Ecol 101(3):257 67. Nagelkerken I, Kleijnen S, Klop T, Van den Brand R, de La Moriniere, E Cocheret, Van der Velde G. 2001. Dependence of Carib bean reef fishes on mangroves and seagrass beds as nursery habitats: A comparison of fish faunas between bays with and without mangroves/seagrass beds. Mar ine Ecol ogy Prog ress Ser ies 214:225 35. Orth R Carruthers T, Dennison W, Duarte C, Fourqurean J, Hec k Jr K, Hughes A, Kendrick G, Kenworthy W, Olyarnik S. 2006. A global crisis for seagrass ecosystems. Bioscience 56(12):987 96. Peatrowsky S. 2010. Seagrass recovery in Sarasota Bay garners 1st place Gulf Guardian award for Sarasota Bay Estuary Program partners and citizens. Sarasota Bay Estuary Program Available from: http://www.sarasotabay.org/documents/Gulf Guardian Award_2 8 10.pdf. Perry J, Ashton J, Brown M, Kaufman K, Leverone J, Ott J. 2011. Seagrass integrated mapping and monitoring for the stat e of Florida mapping and monitoring report no. 1. Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute. Report nr 1. 119 p. Available from: http://myfwc.com/media/1591147/fullsimm1.pdf. Peterson B and Heck Jr K. 2001. Posi tive interactions between suspension feeding bivalves and seagrass a facultative mutualism. Mar Ecol ogy Prog ress Ser ies 213:143 55. Phillips R and Menez E. 1988. Seagrasses. Smithsonian Contributions to the Marine Sciences Phinn S, Roelfsema C, Dekker A, Brando V, Anstee J. 2008. Mapping seagrass species, cover and biomass in shallow waters: An assessment of satellite multi spectral and airborne hyper spectral imaging systems in Moreton Bay ( Australia ). Remote Sens ing of the Environ ment 112(8 ):3413 25. Poor P, Pessagno K, Paul R. 2007. Exploring the hedonic value of ambient water quality: A local watershed based study. Ecol ogical Econ omics 60(4):797 806. Provancha J and Hall C. 1991. Observations of associations between seagrass beds and manat ees in east central Florida Biological Sciences 54(2):87 98. Ralph P, Durako M, Enriquez S, Collier C, Doblin M. 2007. Impact of light limitation on seagrasses. Journal of Experimental Marine Biology and Ecology 350(1):176 93. Rasheed M 2004. Recovery a nd succession in a multi species tropical seagrass meadow following experimental disturbance: The role of sexual and asexual reproduction. Journal of Experimental Marine Biology and Ecology 310(1):13 45.
69 Restoration, monitoring and managment of boat propel ler scars in st. andrews bay, florida document Project. [April 16th]. Located at: Florida Fish and Wildlife Commission. http://gulfsci.usgs.gov/gom_ims/pdf/pubs_gom.pdf Robbins B 1997. Quantifying temporal change in seagrass areal coverage: The use of GIS and low resolution aerial photography. Aquat ic Bot any 58(3):259 67. Robbins B and Bell S. 2000. Dynamics of a subtidal seagrass landscape: Seasonal and annual change in relation to water depth. Ecology 81(5):1193 205. Romero J, Lee K, Perez M, Mateo M, Alcoverro T. 2006. Chapter 9: Nutrients dynamics in seagrass ecosystems. Larkum A, Orth R, Duarte C, editors. 1st ed. Netherlands: Springer. 227 p. Romero J, Lee K, Prez M, Mateo M, Alcoverro T. 2006. Nutrient dynamics in seagrass ecosystems. In: Seagrass es: Biology, ecology and conservation. Springer. 227 p. Short F, Carruthers T, Dennison W, Waycott M. 2007. Global seagrass distribution and diversity: A bioregional model. Journal of Experimental Marine Biology and Ecology 350(1):3 20. Sintes T, Marb N, Duarte C. 2006. Modeling nonlinear seagrass clonal growth: Assessing the efficiency of space occupation across the seagrass flora. Estuaries and Coasts 29(1):72 80. South Florida Natural Resources Center. 2008. Patterns of propeller scarring of seagrass in florida bay: Associations with physical and visitor use factors and implications for natural resource management. National Park Service. Report nr 1. Terrados J and Borum J. 2004. Why are seagrasses important? goods and services provided by seagrass meado ws. In: European seagrasses: An introduction to monitoring and management. Borum J, Duarte C, Krause Jensen D, et al, editors. The M&MS project. 8 p. Tomasko D Corbett C, Greening H, Raulerson G. 2005. Spatial and temporal variation in seagrass coverage in southwest Florida : Assessing the relative effects of anthropogenic nutrient load reductions and rainfall in four contiguous estuaries. Marine Pollution Bulletin 50(8):797 805. Vermaat J 2009. Linking clonal growth patterns and ecophysiology allows the prediction of meadow scale dynamics of seagrass beds. Perspectives in Plant Ecology, Evolution and Systematics 11(2):137 55. Waycott M, Duarte CM, Carruthers T, Orth R, Dennison W, Olyarnik S, Calladine A, Fourqurean J, Heck K, Hughes A. 2009. Accelerating loss of seagrasses across the globe
70 threatens coastal ecosystems. Proceedings of the National Academy of Sciences 106(30):12377 81. Zieman J. 1975. Seasonal variation of turtle grass, Thalassia testudinum knig, with reference to temperature and salinity e ffects. Aquat ic Bot any 1:107 23.
71 Appendix 1.1 Difference between prop scar lengths from 2010 2011 Shows bay segment, length of scars in 2010 and 2011, species of seagrass present nearest to each scar and difference in scar length between years. The numbers associated with the species indicates the percent of the total seagrass sampled in the area found to be of that species. T = Thalassia testudinum H= Halodule wrightii S = Syringodium filiforme Length Bay Segment 2010 2011 T H S Difference ROBERTS BAY 221.52 23.80 100 0 0 197.72 UPPER SARASOTA BAY S 193.79 48.59 100 0 0 145.20 UPPER SARASOTA BAY S 434.97 345.39 100 0 0 89.58 UPPER SARASOTA BAY S 91.38 18.09 100 0 0 73.28 UPPER SARASOTA BAY S 84.61 12.77 90 0 10 71.84 UPPER SARASOTA BAY S 152.46 80.93 10 10 80 71.53 UPPER SARASOTA BAY S 126.03 58.86 25 67.17 UPPER SARASOTA BAY S 133.00 66.55 100 0 0 66.46 UPPER SARASOTA BAY S 61.21 3.23 90 0 10 57.98 UPPER SARASOTA BAY S 83.80 27.16 100 0 0 56.64 UPPER SARASOTA BAY S 85.30 29.93 70 30 0 55.37 UPPER SARASOTA BAY S 86.88 32.71 95 5 0 54.17 UPPER SARASOTA BAY S 87.84 36.23 100 0 0 51.61 UPPER SARASOTA 60.48 11.22 100 0 0 49.26
72 BAY S LITTLE SARASOTA BAY 64.09 27.47 0 0 0 36.62 UPPER SARASOTA BAY S 87.20 51.42 0 100 0 35.78 UPPER SARASOTA BAY S 38.90 3.28 50 50 0 35.61 UPPER SARASOTA BAY S 52.32 17.34 80 20 0 34.97 LEMON BAY 52.91 17.99 100 0 0 34.92 LITTLE SARASOTA BAY 50.49 17.04 0 100 0 33.45 UPPER SARASOTA BAY S 51.10 17.85 100 0 0 33.25 UPPER SARASOTA BAY S 49.03 16.94 100 0 0 32.09 LEMON BAY 42.60 11.61 95 5 0 30.99 UPPER SARASOTA BAY S 49.96 19.61 0 100 0 30.34 LITTLE SARASOTA BAY 45.34 15.72 0 100 0 29.61 UPPER SARASOTA BAY S 36.72 7.98 100 0 0 28.74 LITTLE SARASOTA BAY 79.33 50.88 50 50 0 28.46 LITTLE SARASOTA BAY 77.61 49.59 0 100 0 28.02 UPPER SARASOTA BAY S 47.20 19.73 0 30 0 27.47 UPPER SARASOTA BAY S 53.66 26.63 100 0 0 27.03 LEMON BAY 118.45 91.62 100 0 0 26.83 LITTLE SARASOTA BAY 53.70 27.12 0 100 0 26.58 UPPER SARASOTA BAY S 39.99 15.36 100 0 0 24.63 UPPER SARASOTA BAY S 61.46 37.68 33 33 33 23.79 UPPER SARASOTA BAY S 27.17 6.67 40 0 60 20.50 LITTLE SARASOTA BAY 52.40 32.67 0 100 0 19.73 UPPER SARASOTA BAY S 29.11 9.68 100 0 0 19.44 ROBERTS BAY 36.60 18.74 50 50 0 17.85 UPPER SARASOTA 28.39 11.06 95 0 5 17.33
73 BAY S UPPER SARASOTA BAY S 21.05 4.57 100 0 0 16.49 UPPER SARASOTA BAY S 20.00 3.77 90 0 10 16.23 UPPER SARASOTA BAY S 22.93 8.25 10 10 80 14.68 UPPER SARASOTA BAY S 44.08 30.36 0 100 0 13.71 LITTLE SARASOTA BAY 27.54 14.45 50 100 50 13.09 UPPER SARASOTA BAY S 18.12 5.24 10 10 80 12.88 UPPER SARASOTA BAY S 18.75 5.97 100 0 0 12.78 UPPER SARASOTA BAY S 46.60 34.19 100 0 0 12.41 UPPER SARASOTA BAY S 46.60 34.19 100 0 0 12.41 UPPER SARASOTA BAY S 28.37 18.59 100 0 0 9.78 UPPER SARASOTA BAY S 28.46 18.74 90 0 10 9.72 UPPER SARASOTA BAY S 16.98 7.53 100 0 0 9.45 ROBERTS BAY 50.18 40.91 100 0 0 9.27 UPPER SARASOTA BAY S 21.22 12.01 10 10 80 9.21 UPPER SARASOTA BAY S 62.55 53.53 0 100 0 9.02 UPPER SARASOTA BAY S 36.56 28.21 100 0 0 8.35 ROBERTS BAY 11.92 3.81 0 0 0 8.11 UPPER SARASOTA BAY S 20.96 12.91 100 0 0 8.05 UPPER SARASOTA BAY S 13.51 5.84 100 0 0 7.67 UPPER SARASOTA BAY S 13.92 7.15 100 0 0 6.77 UPPER SARASOTA BAY S 13.92 7.15 100 0 0 6.77 UPPER SARASOTA BAY S 13.92 7.15 100 0 0 6.77 UPPER SARASOTA BAY S 11.76 5.10 90 0 10 6.65 UPPER SARASOTA 9.64 3.34 100 0 0 6.30
74 BAY S UPPER SARASOTA BAY S 20.58 14.40 0 0 100 6.18 UPPER SARASOTA BAY S 10.11 4.03 100 0 0 6.07 UPPER SARASOTA BAY S 19.48 13.44 100 0 0 6.05 LEMON BAY 15.55 10.16 100 0 0 5.38 UPPER SARASOTA BAY S 12.39 7.34 0 0 100 5.04 LEMON BAY 10.63 5.76 100 0 0 4.87 UPPER SARASOTA BAY S 17.22 12.37 100 0 0 4.85 UPPER SARASOTA BAY S 18.35 13.70 100 0 0 4.66 UPPER SARASOTA BAY S 31.24 27.49 60 40 0 3.75 LEMON BAY 9.22 5.79 0 0 0 3.43 UPPER SARASOTA BAY S 15.95 12.59 100 0 0 3.36 LITTLE SARASOTA BAY 9.21 5.86 0 100 0 3.35 UPPER SARASOTA BAY S 11.55 8.32 25 3.23 LITTLE SARASOTA BAY 43.85 40.98 0 0 0 2.87 LEMON BAY 12.27 9.52 0 0 0 2.75 UPPER SARASOTA BAY S 12.43 9.99 98 2 0 2.43 LITTLE SARASOTA BAY 23.42 21.27 100 0 0 2.15 UPPER SARASOTA BAY S 6.78 4.80 100 0 0 1.98 UPPER SARASOTA BAY S 16.67 14.72 100 100 100 1.96 UPPER SARASOTA BAY S 16.67 14.72 100 0 0 1.96 ROBERTS BAY 5.33 3.61 0 0 0 1.73 UPPER SARASOTA BAY S 12.19 10.54 100 0 0 1.65 UPPER SARASOTA BAY S 8.35 6.71 0 100 0 1.64 UPPER SARASOTA BAY S 8.35 6.71 1.64 UPPER SARASOTA BAY S 10.23 8.92 80 20 0 1.31
75 LITTLE SARASOTA BAY 15.67 14.39 0 100 0 1.29 UPPER SARASOTA BAY S 16.35 15.56 100 0 0 0.79 UPPER SARASOTA BAY S 9.22 8.63 100 0 0 0.59 UPPER SARASOTA BAY S 16.58 16.26 0 100 0 0.32 LEMON BAY 27.62 27.46 100 0 0 0.16 UPPER SARASOTA BAY S 9.85 10.15 1 0 99 0.30 UPPER SARASOTA BAY S 9.58 10.14 100 0 0 0.56 UPPER SARASOTA BAY S 17.83 18.98 40 60 0 1.14 LITTLE SARASOTA BAY 41.86 43.03 0 100 0 1.18 LEMON BAY 34.13 35.59 100 0 0 1.46 LITTLE SARASOTA BAY 41.85 44.11 0 100 0 2.26 LITTLE SARASOTA BAY 5.84 10.86 99 0 1 5.02 UPPER SARASOTA BAY S 16.75 22.76 100 0 0 6.01 UPPER SARASOTA BAY S 16.75 22.76 100 0 0 6.01 LITTLE SARASOTA BAY 17.69 24.14 0 95 0 6.45 LITTLE SARASOTA BAY 11.08 21.29 0 95 0 10.21 LEMON BAY 46.64 57.15 100 0 0 10.51 UPPER SARASOTA BAY S 39.41 63.65 25 75 0 24.24
76 Appendix 1.2 Difference between prop scar lengths from 2011 2012 Shows bay segment, length of scars in 2011 and 2012, species of seagrass present nearest to each scar and difference in scar length between years. The numbers associated with the species indicates the percent of the total seagrass sampled in the area found to be of that species. T = Thalassia testudinum H= Halodule wrightii S = Syringodium filiforme Bay Segment 2011 2012 T H S Difference ROBERTS BAY 96.81 25.48 50 50 0 71.33 UPPER SARASOTA BAY S 80.93 22.38 10 10 80 58.55 UPPER SARASOTA BAY S 56.96 25.08 100 0 0 31.88 UPPER SARASOTA BAY S 73.78 46.76 100 0 0 27.02 UPPER SARASOTA BAY S 345.39 322.55 100 0 0 22.84 LITTLE SARASOTA BAY 44.11 21.88 0 100 0 22.23 UPPER SARASOTA BAY S 109.74 87.89 100 0 0 21.85 UPPER SARASOTA BAY S 38.09 18.73 100 0 0 19.36 UPPER SARASOTA BAY S 49.61 31.29 100 0 0 18.32 UPPER SARASOTA BAY S 54.86 38.72 100 0 0 16.14 UPPER SARASOTA BAY S 22.62 7.37 60 40 0 15.26 UPPER SARASOTA BAY S 21.67 6.55 100 0 0 15.12 UPPER SARASOTA BAY S 42.60 30.89 100 0 0 11.72 UPPER SARASOTA BAY S 14.64 4.29 100 0 0 10.35
77 UPPER SARASOTA BAY S 12.81 2.76 100 0 0 10.05 UPPER SARASOTA BAY S 38.16 28.22 100 0 0 9.94 UPPER SARASOTA BAY S 14.48 5.08 40 0 60 9.40 UPPER SARASOTA BAY S 36.21 28.21 25 75 0 8.01 UPPER SARASOTA BAY S 15.75 8.34 100 0 0 7.41 UPPER SARASOTA BAY S 12.49 5.47 90 0 10 7.01 UPPER SARASOTA BAY S 37.23 32.36 100 0 0 4.87 ROBERTS BAY 10.17 5.89 100 0 0 4.28 ROBERTS BAY 12.23 8.72 50 25 25 3.51 UPPER SARASOTA BAY S 16.41 12.93 100 0 0 3.48 UPPER SARASOTA BAY S 9.33 5.95 100 0 0 3.38 UPPER SARASOTA BAY S 18.23 16.21 100 0 0 2.02 UPPER SARASOTA BAY S 35.70 33.84 49 49 0 1.86 UPPER SARASOTA BAY S 14.72 12.95 100 100 100 1.76 UPPER SARASOTA BAY S 14.72 12.95 100 0 0 1.76 UPPER SARASOTA BAY S 8.14 6.74 100 0 0 1.41 UPPER SARASOTA BAY S 6.40 5.17 100 0 0 1.23 UPPER SARASOTA BAY S 4.63 3.98 100 0 0 0.64 UPPER SARASOTA BAY S 3.57 3.00 0 0 100 0.57 UPPER SARASOTA BAY S 19.06 18.80 100 0 0 0.26 UPPER SARASOTA BAY S 9.15 8.96 100 0 0 0.19 UPPER SARASOTA BAY S 5.84 5.84 40 0 60 0.00 UPPER SARASOTA BAY S 11.89 11.99 100 0 0 0.10 UPPER SARASOTA BAY S 8.29 10.06 100 0 0 1.77
78 UPPER SARASOTA BAY S 18.09 20.74 100 0 0 2.64 UPPER SARASOTA BAY S 19.52 22.38 75 25 0 2.85 UPPER SARASOTA BAY S 12.80 16.33 100 0 0 3.53 UPPER SARASOTA BAY S 29.93 34.62 70 30 0 4.69 UPPER SARASOTA BAY S 52.13 58.99 100 0 0 6.87 ROBERTS BAY 36.08 45.68 50 25 25 9.60 UPPER SARASOTA BAY S 2.81 13.68 0 0 100 10.88 LITTLE SARASOTA BAY 98.40 109.56 0 100 0 11.16 UPPER SARASOTA BAY S 145.10 174.32 100 0 0 29.22 UPPER SARASOTA BAY S 48.59 99.71 100 0 0 51.12 UPPER SARASOTA BAY S 394.10 471.62 100 0 0 77.51
79 Appendix 1.3 Difference between prop scar lengths from 2010 2012 Shows bay segment, length of scars in 2010 and 2012, species of seagrass present nearest to each scar and difference in scar length between years. The numbers associated with the species indicates the percent of the total seagrass sampled in the area found to be of that species. T = Thalassia testudinum H= Halodule wrightii S = Syringodium filiforme Bay Segment 2010 2012 T H S Difference UPPER SARASOTA BAY S 434.97 322.55 100 0 0 112.42 UPPER SARASOTA BAY S 193.79 99.71 100 0 0 94.08 UPPER SARASOTA BAY S 85.30 34.62 70 30 0 50.68 UPPER SARASOTA BAY S 58.47 25.09 98 2 0 33.39 LITTLE SARASOTA BAY 41.85 21.88 0 100 0 19.98 UPPER SARASOTA BAY S 16.10 3.53 0 100 0 12.56 UPPER SARASOTA BAY S 16.86 11.13 0 5 0 5.73 ROBERTS BAY 9.26 3.85 0 0 0 5.41 UPPER SARASOTA BAY S 16.67 12.95 100 100 100 3.72 UPPER SARASOTA BAY S 41.87 39.39 75 25 0 2.48 UPPER SARASOTA BAY S 8.46 11.26 0 100 0 2.80