DIET CHARACTERIZATION IN IMMATURE, NERITIC GREEN...

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DIET CHARACTERIZATION IN IMMATURE, NERITIC GREEN TURTLES, CHELONIA MYDAS, USING GUT CONTENTS AND STABLE ISOTOPE ANALYSES

By

NATALIE CHRISTINE WILLIAMS

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE

UNIVERSITY OF FLORIDA

2012

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© 2012 Natalie Christine Williams

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To my Dad, who is with me every day

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ACKNOWLEDGMENTS

Firstly, I would like to thank my committee members Dr. Raymond R. Carthy, Dr.

Karen A. Bjorndal, Dr. H. Jane Brockmann and Dr. Margaret M. Lamont for their

support, guidance, time and patience.

I received much-appreciated support from the following: Brittany Burtner, Jean

Olbert, Sheri Johnson, Megan Shabram, Sarah Reintjes-Tolen, Jame McCray, Anthony

Lau, Jason Fidorra, Kyle Pias, Matt Smith, Andrew Hein and Daniel Sasson.

I thank Larisa Avens, Brian Stacy, Alan Bolten, Peter Eliazar, Michael Frick,

Melania Lopez-Castro, Mariela Pajuelo, Joseph Pfaller, Luciano Soares, Hannah

Vander Zanden, and Patricia Zarate for project and creative assistance. I also thank

Seth Farris, Caitlin Hackett, Jessica McKenzie, Jean Olbert, Kyle Pias, Kate Simon, and

Brail Stephens for field and laboratory assistance. I especially thank Seth Farris, Mariela

Pajuelo, and Brail Stephens for the collection of gastric contents. Numerous volunteers

helped during the cold stunning event and helped make this work possible.

I am grateful for support and assistance from the University of Florida, namely

Caprice McRae and Claire Williams of the Department of Wildlife Ecology and

Conservation. I would also like to thank J. Curtis at the Stable Isotope Lab (University of

Florida) for assistance with stable isotope analyses. I am forever thankful for the

emotional support and words of wisdom provided by Franklin Percival of the Florida

Cooperative Fish and Wildlife Research Unit, who “checked in with me” weekly.

This project would not have been possible without Meg Lamont, to whom I am

forever grateful. Her continuous encouragement, support, and advice kept me going

during times of doubt and taught me many valuable lessons. I am especially grateful for

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the friendship of Brail Stephens, who has supported me through many trials, both

professional and personal, and given me hope, motivation, and confidence.

I am thankful to Alison Hodges-Steverson, Heather Blanton, Mackenzie Kay, and

Lindsay Branciforte, who have always listened and supported me endlessly.

Finally, I thank my parents, who have provided love, support, and encouragement

to me throughout my life, in all my endeavors. I thank my Dad, whose wisdom and

guidance helped me through much of graduate school, and whom I know is proud of

this accomplishment. I thank my Mom, who is always there when needed and is the

most caring, loving and selfless person I know. I would also like to thank my Uncle Tom

and Aunt Jeri for providing wisdom and support.

The Florida Sea Turtle Grants Program, Knight Vision Foundation, and Jennings

Scholarship funded this research. All project work was performed under MTP # 094 and

MTP # 016.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS .................................................................................................. 4

LIST OF TABLES ............................................................................................................ 7

LIST OF FIGURES .......................................................................................................... 8

LIST OF ABBREVIATIONS ............................................................................................. 9

ABSTRACT ................................................................................................................... 10

CHAPTER

1 DIET OF GREEN TURTLES WORLDWIDE ........................................................... 12

2 DIET CHARACTERIZATION IN IMMATURE, NERITIC GREEN TURTLES, CHELONIA MYDAS, USING GUT CONTENTS AND STABLE ISOTOPE ANALYSES ............................................................................................................. 17

Introduction ............................................................................................................. 17

Materials and Methods............................................................................................ 21 Study Area ........................................................................................................ 21

Sample Collection ............................................................................................ 22

Stable Isotope Analyses ................................................................................... 24

Statistical Analyses .......................................................................................... 25 Results .................................................................................................................... 25 Discussion .............................................................................................................. 27

APPENDIX

A JANUARY 2008 DIET COMPOSITION ................................................................... 35

B JANUARY 2011 DIET COMPOSITION ................................................................... 37

C 2011 DIET AND BODY SIZE .................................................................................. 39

D 201115N AND BODY SIZE ................................................................................... 41

E DIET OF THE GREEN TURTLE, CHELONIA MYDAS ........................................... 42

LIST OF REFERENCES ............................................................................................... 62

BIOGRAPHICAL SKETCH ............................................................................................ 68

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LIST OF TABLES

Table page 2-1 Diet composition of juvenile green turtles in St. Joseph Bay, Florida ................. 31

E-1 Diet of the green turtle, Chelonia mydas ............................................................ 42

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LIST OF FIGURES

Figure page 2-1 Conceptual model of patterns of isotope values representing resource use

through time........................................................................................................ 32

2-2 Plot of stable isotope ratios of nitrogen and carbon from epidermis samples and major prey items of juvenile green turtles .................................................... 33

2-3 Chelonia mydas. Epidermis 13C vs. curved carapace length in St. Joseph Bay, Florida in 2011 ............................................................................................ 34

A-1 Diet composition in 12 juvenile green turtles from the cold stunning event in St. Joseph Bay, Florida in January 2008 ............................................................ 35

A-2 Diet composition in 12 juvenile green turtles from the cold stunning event in St. Joseph Bay, Florida in January 2008 ............................................................ 36

B-1 Diet composition of 31 juvenile green turtles from the cold stunning event in St. Joseph Bay, Florida in January 2011 ............................................................ 37

B-2 Diet composition of 31 juvenile green turtles from the cold stunning event in St. Joseph Bay, Florida in January 2011 ............................................................ 38

C-1 The relationship between green turtle body size (CCLmin) and seagrasses (Pseagrasses= 0.3127) in St. Joseph Bay, Florida ................................................... 39

C-2 The relationship between green turtle body size (CCLmin) and tunicates (Ptunicates= 0.2215) in St. Joseph Bay, Florida ..................................................... 40

D-1 Chelonia mydas. Epidermis δ15N vs. curved carapace length in St. Joseph Bay, Florida in 2011 ............................................................................................ 41

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LIST OF ABBREVIATIONS

C Carbon

CCLMIN Minimum curved carapace length

δ delta

GI Gastrointestinal

IRI Index of Relative Importance

N Nitrogen

SIA Stable Isotope Analysis

SJB St. Joseph Bay

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Masters of Science

DIET CHARACTERIZATION IN IMMATURE, NERITIC GREEN TURTLES, CHELONIA

MYDAS, USING GUT CONTENTS AND STABLE ISOTOPE ANALYSES

By

Natalie Christine Williams

August 2012 Chair: Raymond R. Carthy Cochair: Karen A. Bjorndal Major: Wildlife Ecology and Conservation

Recent developments in open water research have refined our understanding of

green turtle, Chelonia mydas, foraging ecology, but diet characterization among

populations remains understudied. Previous hypotheses state that once young green

turtles recruit to shallow water habitat they shift rapidly from an omnivorous to

herbivorous diet. Supporting evidence has primarily been derived from traditional gut

content analysis that only provides a small window in time to perceive the diet of an

animal. In contrast, stable isotope analysis explores how a consumer uses its resources

over a broad temporal scale. We tested the dietary shift hypothesis using gut content

and stable isotope analyses to assess the nutritional ecology of a juvenile green turtle

aggregation in the northern Gulf of Mexico. We examined the gut contents of 65 green

turtles collected from 2008 and 2011 hypothermic stunning events in St. Joseph Bay,

Florida. Gut contents were evaluated using volume, dry mass, percent frequency of

occurrence, and index of relative importance (IRI). Juvenile green turtles showed

omnivorous feeding behavior, feeding on a variety of animal and vegetal items with a

bias towards seagrass and tunicates. In addition, we evaluated feeding consistency by

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stable isotope patterns from epidermis tissue. We measured the stable carbon (13C)

and nitrogen (15N) isotope values in epidermis of 43 green turtles, ranging from 22.5 to

72.7cm in curved carapace length (CCLmin), and eight known prey items (e.g., algae,

seagrasses, invertebrates) collected in 2011. Our study provides a foundation for

characterizing the foraging ecology of green turtles in St. Joseph Bay and highlights the

value of utilizing isotopic ecology for further foraging studies.

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CHAPTER 1 DIET OF GREEN TURTLES WORLDWIDE

The green turtle, Chelonia mydas, is an endangered marine species that inhabits

tropical and subtropical regions worldwide. Understanding the foraging ecology of this

species is key to its conservation, as diet influences reproduction, survivorship, growth

rates and ultimately, population demography (Bjorndal 1982). For these reasons,

studies have focused on diet characterization, ranging from descriptions of gut contents

to detailed, quantitative examinations of nutritional content (Carr 1952, Bjorndal 1980,

Gilbert 2005). The life history of green turtles can be described as a series of

ontogenetic habitat shifts where use of habitats and resources varies depending on life

history stage. Green turtles maintain omnivorous diets in some habitats and herbivorous

diets in other habitats. The literature on the foraging ecology of green sea turtles was

reviewed and characterized the green turtle as an herbivore that may also eat animal

matter (Mortimer 1976, 1982). Since Mortimer’s review (1982), our knowledge of the

diet of green turtles worldwide has expanded. The literature on the diet of green turtles

as post-hatchlings, juveniles and adults is summarized in the first section of this review.

The remainder of this review is a table of reported diet species (see Appendix E) of

green turtles representing four life history stages (O = oceanic, post-hatchling, J =

juvenile, sub-adult, A = adult and U = unknown or not stated) in the Atlantic and

Pacific/Indian Oceans. Non-nutritive items (debris, feathers, etc.) are not included in the

table.

After leaving the nesting beach as 5 cm hatchlings, green turtles ‘disappear’ until

they recruit to neritic habitats (water depths < 200 m) as greater than 20 cm juveniles

(Reich et al. 2007). Relatively little is known of the ecology of post-hatchling green

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turtles while in the oceanic phase. Hypotheses (Reich et al. 2007) suggest that neonate

green turtles spend time in the open water, feeding primarily as carnivores. Parker et al.

(2011) examined gut contents in 10 oceanic, neonate green turtles from the northern

Pacific Ocean and found the turtles to be primarily carnivorous. The main diet

constituents are zooplankton, pelagic crustaceans and mollusks with coelenterates such

as Pyrosoma sp. also present in large amounts (see Appendix E; for all cited diet

species hereafter, refer to Appendix E). Davenport and Balazs (1991) posit that

pyrosomas may be targeted as prey not due to their gelatinous structure but for their

stomach contents, which are of high nutritional value being composed of phytoplankton,

zooplankton, and detritus. In Australia, two hatchlings were tethered for 4.5 months to

observe their feeding behavior; main diet items included hydrozoans, ctenophores and

oceanic tunicates (Booth & Peters 1972). Many factors (i.e., tag retention, sightability)

contribute to the difficulty in studying the oceanic phase, but recent advances in satellite

telemetry (Mansfield 2012) and stable isotope technology (Reich et al. 2007) have

improved our ability to gain insight into this elusive phase in sea turtle life history.

Four size classes of green turtle (8, 30, 48, 66 kg) in the Bahamas (Bjorndal 1980)

reportedly have diets consisting of mostly seagrass. In the Atlantic, Mendonça (1983)

found that green turtles foraged selectively on Rhodophyta and Chlorophyta in Mosquito

Lagoon, Florida. In contrast, Gilbert (2005) found immature turtles to be grazing

exclusively on seagrasses and avoiding the abundant algae species on Ambersand

Reef, Florida. Juvenile green turtles off the coast of Long Island, New York, feed

primarily on the seagrass Zostera sp. and marine algae (Burke et al. 1992). Burke’s

study represents one of the few available studies that examines green turtle diet at the

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edge of their range. Few reports are available on green turtle diet in the Gulf of Mexico.

In the northern Gulf of Mexico, Foley et al. (2007) found the primary diet constituent of

stranded turtles to be seagrass (Thalassia testudinum).

There are a number of studies available on the diet of immature green turtles in

Pacific waters. Studies on juvenile C. mydas diet in Australia (Read & Limpus 2002,

Arthur et al. 2009) and Hawaii (Balazs 1980) reported a diet primarily composed of

seagrass, red algae and green algae. In Oman, smaller green turtles (30 to 50 cm) feed

on the bases of seagrasses such as Halophila and Halodule spp. as well as marine

algae (Ross 1985). However, in the relatively dense seagrass beds of Shark Bay,

Australia, recent research has revealed that animal matter accounts for 76 – 99 % of the

nutrients for turtles between 29 and 59 cm CCL and for 53 – 76 % of the nutrients for

turtles > 59 cm CCL. The authors suggest that despite the abundant seagrass,

intraspecific competition may drive individual specialization in this habitat, with some

turtles foraging heavily on seagrass (Burkholder et al. 2011). In the Pacific Ocean,

green turtles have been documented consuming molluscs, crustaceans and sponges

(Garnett et al. 1985, Balazs et al. 1987). Off the coast of Ecuador, the stomach of a

large, immature female contained fish eggs attached to a small amount of sargassum

(Fritts 1981). Gut content analyses have shown that animal prey continues to be

consumed by green turtles after entering the neritic habitat off southwestern Colombia,

the Galapagos Islands, western Mexico, and in San Diego Bay (Seminoff et al. 2002,

Amorocho & Reina 2007, Carrión-Cortez et al. 2010, Lemons et al. 2011).

As adults, green turtles in the western Atlantic feed primarily on seagrasses and

algae (Appendix E). Mortimer (1981) examined the stomach contents of 243 adult and

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subadult turtles in Caribbean Nicaragua. The main diet items, in decreasing order of

importance, comprised: Thalassia, other species of seagrass, 40 different algae

species, benthic substrate, and animal matter. Turtles were found to modify their diet

opportunistically, based on the composition of available prey sources. For example,

during migrations to breeding grounds, where turtles travel near shore, they consume

more red algae and lignified terrestrial debris (Mortimer 1981). In northern Brazil,

Ferreira (1968) documented that green turtle diet is composed of approximately 88%

marine algae and less than 10% animal matter in an area where seagrass is not

abundant. The following types of animal matter were found: ascidians, molluscs,

sponges, bryozoans, crustaceans, and echinoderms. Seminoff et al. (2002) found the

diet of sub-adult and adult green turtles in the Gulf of California, Mexico to be primarily

composed of marine algae and some animal matter in a region lacking in seagrass

habitat. Frazier (1971) collected stomach samples from adults and subadults in the

Aldabra Atoll and found the species to be primarily herbivorous. Recent studies (Hatase

et al. 2006) in Japan have used satellite telemetry and stable isotope analysis to reveal

that females remain in the carnivorous, oceanic phase into their adult years.

An area of research that calls for further examination involves combining gut

content and stable isotope analyses for a long-term picture of diet composition. Lemons

et al. (2011) used stable isotope mixing models to determine that animal matter

contributed to the diet of green turtles in San Diego Bay over the course of the six-year

isotope series study. Mixing models determine the contribution of different prey groups

based on their isotope value relative to the isotope value of the consumer (Phillips &

Gregg 2003). The authors recommend that future studies should account for seasonal

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and annual fluctuations in prey isotope values. Stable isotope technology is a valuable

tool in reconstructing the diet of individuals; however, future research should fully its

explore its limitations to avoid misinterpretation of results.

My review also pointed out the need for studies that examine changes in diet

composition by season. For example, López-Mendilaharsu et al. (2008) showed that

juvenile green turtles fed preferentially on species that showed high fluctuations in

availability and abundance throughout the year. Diet preference and diet diversity

changes coincided with seasonal changes in prey biomass. These results underscore

an area of mostly unexplored research: what does a tropical green turtle do in cooler

temperatures with dynamic resources?

Further research is needed to quantify the nutritional and energetic

consequences of augmenting a herbivorous diet with animal matter. Our best insights

into the foraging ecology of green turtles are from studies conducted in “core” range

habitats with dense seagrass beds and algal communities, while relatively little is known

of foraging grounds at the extremes of the species range. In habitats where foliage is

not present year round, animal matter may play an important role in nutrition. Studies in

these habitats may provide insight into how animals modify their diets with variable

resource availability and influence management and conservation planning.

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CHAPTER 2 DIET CHARACTERIZATION IN IMMATURE, NERITIC GREEN TURTLES, CHELONIA

MYDAS, USING GUT CONTENTS AND STABLE ISOTOPE ANALYSES

Introduction

The life history of green turtles (Chelonia mydas) involves a series of habitat and

resource shifts depending on the life-history stage (Bolten 2003). After completing an

initial oceanic life stage, small juvenile green turtles (20 to 35 cm curved carapace

length) become residents of neritic habitats, where they feed primarily on seagrasses

and/or macroalgae, but may also consume animal matter (Mortimer 1981, Bjorndal

1997). Variation in feeding patterns is thought to be dependent on prey abundance and

availability (Guebert-Bartholo et al. 2011) but may also be affected by feeding selectivity

(Bjorndal 1985, Fuentes et al. 2006, López-Mendilaharsu et al. 2008). Variation in

feeding patterns has been observed in subtropical systems (Guebert-Bartholo et al.

2011, Nagaoka et al. 2012) where resource availability is relatively stable. In temperate

systems, resource availability is more variable; changes in seasonal biomass of

vegetation and animal material may lead to greater variation and plasticity in feeding

patterns. For these reasons, it is critical to understand how tropical/subtropical species

at the latitudinal extremes of their range cope with environmental variation.

Studies on immature green turtles in the western Atlantic have reported a primarily

herbivorous diet augmented with small amounts of animal matter. Juveniles in the

Caribbean (Bjorndal 1980) reportedly have diets consisting of mostly seagrass and

algae. Mortimer (1981) examined the stomach contents of 243 adult and subadult

turtles in Caribbean Nicaragua. The main diet items, in decreasing order of importance,

comprised: Thalassia, three other species of seagrass, 40 different algae species,

benthic substrate, and animal matter. Turtles were found to modify their diet

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opportunistically, based on the composition of available prey sources. For example,

during migrations to breeding grounds, where turtles travel near shore, they consume

more red algae and lignified terrestrial debris (Mortimer 1981). Studies in several

foraging grounds along the coast of Brazil have reported varied diets between locations,

with some diets dominated by algae and others by animal matter. For example, in

northern Brazil, Ferreira (1968) documented that juvenile and adult (31 – 120 cm curved

carapace length, CCL) green turtle diet is composed of approximately 88% marine

algae and less than 10% animal matter in an area where seagrass is not abundant. The

following types of animal matter were found: ascidians, molluscs, sponges, bryozoans,

crustaceans, and echinoderms. In a lagoon complex in southeastern Brazil, main diet

items were ranked by frequency of occurrence as follows: 87.5% terrestrial plants and

algae, 50% invertebrates and 12.5% seagrasses (Nagaoka et al. 2012). In the western

Atlantic, Gilbert (2005) found that green turtles foraged selectively on Rhodophyta and

Chlorophyta on Ambersand Reef, Indian River County, Florida. In contrast, Mendonça

(1983) found immature turtles to be grazing exclusively on seagrasses and avoiding the

abundant algae species in Mosquito Lagoon, Florida. Juvenile green turtles off the coast

of Long Island, New York, feed primarily on the seagrass Zostera sp. and marine algae

(Burke et al.). New York waters provide a seasonal foraging ground for several sea

turtle species from June through November (Burke et al. 1993). Burke’s research

represents one of the few available studies that examine green turtle diet at the edge of

their range. During a three year study in South Padre Island, Texas, Coyne (1994)

reported subadult (22.2 – 81.5 cm straight carapace length, SCL) green turtles feeding

selectively on algae (Ulva fasciata, Rhodymenia pseudopalmata, Family Ceramiaceae,

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Bryocladia sp., Hypnea musciformis) and shoal grass (Halodule wrightii). Few reports

are available on green turtle diet in the Gulf of Mexico. In the northern Gulf of Mexico,

Foley et al. (2007) found the primary diet constituent of stranded turtles to be seagrass

(Thalassia testudinum). Tunicate species (Styela; Molgula; unidentifiable pieces) were

also found in small quantities (Lessmann 2002).

Some of the reported variation in diet composition of juvenile green turtles may

arise from changes in habitats used by these turtles among years or between seasons.

As poikilotherms, sea turtles depend on ambient temperature to regulate the body’s

core temperature for digestion and other physiological processes. Sea turtles may

display seasonal movements related to changes in temperature, emigrating from areas

that become seasonably cold (Witherington & Ehrhart 1989). In habitats with abrupt

changes in temperature, behavioral strategies are necessary to survive a dynamic

environment. To deal with cold-water temperatures, juveniles in neritic habitats can

either migrate to warmer waters or overwinter in the neritic habitat. In temperate

climates, adult turtles migrate long distances to overwinter in warmer waters (Meylan

1995). However, juvenile turtles foraging in shallow, neritic habitats may face rapid

decreases in water temperature and be unable to escape due to limited exit access,

creating a trapping effect (Mendonca & Ehrhart 1982). At temperatures less than 10°C,

turtles often become stunned and enter a torpid state (Foley et al. 2007) in which they

are unable to swim and they float to the surface. On average, the risk of being

susceptible to cold fronts appears to be an acceptable trade-off for the benefits of

inhabiting northern, temperate habitats during the summer (Ultsch 2006).

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Because juvenile turtles reside year-round in St. Joseph Bay, Florida, this area

provides an interesting site to observe foraging behavior of green turtles at the edge of

their range. St. Joseph Bay is at the northern edge of the range of year-round foraging

grounds of the tropical/subtropical green turtle. St. Joseph Bay has historically been

susceptible to cold stunning events, with 401 turtles stranding in December

2000/January 2001 (Foley et al. 2007) and 1,733 turtles stranding in 2010 (Avens et al.

2012). Foley et al. (2007) reported a diet dominated by seagrass and macroalgae prior

to the 2000/2001 cold stunning event. However, seagrasses are known to experience

decreases in abundance during the winter in St Joseph Bay (Leonard & McClintock

1999). The behavioral modifications of how tropical green turtles behave in temperate

foraging grounds, especially during winter foliage reductions, remain unknown. What do

herbivorous green turtles do during this time? Analysis of stomach contents from cold

stunning events allows the opportunity to reconstruct turtle diet prior to stranding and

begin to create a picture of winter behavior.

I investigate the diet of green turtles during winter in St Joseph Bay using two

approaches. Stomach contents, that give a direct measure of diet, but only for a short

window of time, and stable isotopes. Stable isotope analyses of epidermis samples can

be used to evaluate consistency of diet over a broader temporal scale because isotopes

reflect the average dietary record (Dalerum & Angerbjörn 2005). Incorporation of new

protein into tissues is a combination of turnover and growth. Protein turnover is related

to the metabolic rate of the tissue, so tissues with fast metabolic rates have high protein

turnover rate. Therefore, tissues with different turnover rates reflect average dietary

records over different lengths of time (Hobson & Clark 1992). Figure 2-1 presents a

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conceptual model comparing the isotope values of individuals in a population with

inconsistent and consistent feeding patterns. If individuals in a population have not fed

consistently, their stable isotope values will not be associated with the stable isotope

value of the major diet item from the stomach contents (Figure 2-1a). If individuals in a

population have maintained a relatively consistent diet over the previous months, their

epidermis stable isotope values should fall above the major diet item from the stomach

contents, the distance representing the discrimination value (Figure 2-1b).

To answer the question, what is the diet of primarily herbivorous green turtles

during the winter in a temperate region, I analyzed stomach contents from 64 green

turtles that died during cold stunning events in St. Joseph Bay, Gulf County, Florida in

2008 (n = 12) and 2011 (n = 52). Epidermis stable isotope values from 39 green turtles

from 2011 were used to evaluate consistency of the diet over the preceding months.

Materials and Methods

Study Area

St. Joseph Bay, Florida (29.76º N, 85.35º W), in the northeastern Gulf of Mexico,

covers an area just less than 30,000 hectares. The study site is a coastal habitat

located along the Florida panhandle in Gulf County. St. Joseph Bay is approximately 21

km in length, with a maximum width of 8 km. The maximum depth is 13.3 m in the

northern end, with a minimum depth of 1.0 m in the southern end (McMichael 2005).

The site has a tidal range of approximately 0.47 m, a very low current flow and highly

organic sediments. The salinity in the bay is usually identical to the Gulf of Mexico

(Stewart & Gorsline 1962) and averages 35.0 ppt (DEP 2008). Annual water

temperatures range from 4 to 35°C (McMichael 2005). Wind direction is usually north in

the winter and south in the summer. The bay is productive due to its salt marsh and

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seagrass habitats; seagrass beds are a prominent feature in the southern end and

cover approximately one-sixth of the bay (DEP 2008). The local, dominant seagrass

species include Thalassia testudinum, Halodule wrightii and Syringodium filiforme. St.

Joseph Bay is susceptible to cold stunning events because water temperature can

decline to less than 10°C, under which torpor and cold stunning can occur (Schwartz

1978, Witherington & Ehrhart 1989, Morreale et al. 1992).

Sample Collection

In January 2008 and 2011, volunteers collected green turtles (n = 64) that

stranded dead during cold stunning events in St. Joseph Bay, Florida. Cold stunned

turtles become lethargic and float to the surface, and can be easily retrieved from the

water or after they wash ashore (Witherington & Ehrhart 1989). Minimum curved

carapace length (CCLmin; cm) was measured using a tape measure (Bolten 1999).

Body mass (kg) was measured using a hanging spring scale. Stomach contents were

removed from the gastrointestinal (GI) tract and frozen pending analyses.

Epidermis tissue from the dorsal surface of the neck was collected using a 6-mm

biopsy punch and preserved in dry NaCl until analysis. For analysis, epidermis samples

were rinsed with distilled water to remove the NaCl and the outermost epidermis was

separated from the dermis tissue using a scalpel blade.

Known prey items identified from stomach contents were opportunistically

collected from SJB in fall 2011 for stable isotope analysis. This collection period was

chosen to best represent the time period in which diet item isotope values would be

incorporated and represented in epidermis tissue. The following known prey items were

sampled: seagrasses (Thalassia testudinum, Halodule wrightii, and Syringodium

filiforme), macroalgae (Gracilaria sp. and Enteromorpha sp.), and tunicates (Botrylloides

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sp.). The sample size was two for each species. Samples were put in a cool box for

transport, rinsed with distilled water, and then frozen at -20C pending analysis.

Frozen stomach contents were thawed and separated to species or the lowest

identifiable taxon, using a dissecting scope when necessary. Each diet item was

quantified using percent frequency of occurrence, volume, mass, and index of relative

importance (IRI). Percent volume was evaluated by water displacement using

graduated cylinders; diet items less than 0.2 mL were considered “trace”. Diet items

were dried at 60°C for 24 hours and then weighed to calculate mass. The index of

relative importance was modified from Hyslop (1980) by Bjorndal et al. (1997) for

application to herbivores. Each diet category was calculated by the following equation:

IRI 100(FiVi)

(FiVi)i1

n

(2-1)

where F is percent frequency of occurrence, V is percent volume, and n is the number

of diet categories. Each of these measures (volume and frequency) in isolation can yield

misleading interpretations (Hyslop 1980, Bjorndal et al. 1997). For example, a diet item

with a 100 % frequency of occurrence may only be present in each stomach in trace

amounts. The IRI provides a better interpretation for ranking the relative importance of

diet categories because both frequency and volume are included (Bjorndal et al. 1997).

Of the total individual samples (n = 52) collected for 2011, only individual total

sample volumes greater than 9.0 mL were included as representative samples of turtle

diet (n = 31). I compared results from all samples with those from samples > 9.0 mL to

test for an effect of volume on estimates of diet composition. Small sample volumes

occurred only in 2011.

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Stable Isotope Analyses

For stable isotope analysis, approximately 0.5 to 0.6 mg of each epidermis sample

(1.0-15.0 mg for prey samples) was weighed and sealed in a tin capsule. Samples were

analyzed for δ13C and δ15N by combustion in a Thermo Finnigan DeltaPlus XL isotope

ratio mass spectrometer with a ConFlo III interface linked to a Costech ECS 4010

Elemental Combustion System (elemental analyzer) in the Stable Isotope Geochemistry

Lab at the University of Florida, Gainesville. Sample stable isotope ratios relative to the

isotope standard are expressed in the conventional delta (δ) notation in parts per

thousand (‰):

δ = [(Rsample/Rstandard) – 1] × 1000 (2-2)

where Rsample and Rstandard are the corresponding ratios of heavy to light isotopes

(13C/12C and 15N/14N) in the sample and international standard, respectively.

The standard used for 13C was Vienna Pee Dee Belemnite and atmospheric N2 for

15N. All analytical runs included samples of standard materials that were inserted at

regular intervals to calibrate the system. The reference material USGS40 (L-glutamic

acid) was used to normalize all results. The standard deviation of the reference

material was 0.04 ‰ for δ13C and 0.08 ‰ for δ15N values (n = 10). Repeated

measurements of a laboratory reference material, loggerhead scute, was used to

examine consistency in a homogeneous sample with similar isotopic composition to the

epidermis samples. The standard deviation of the loggerhead scute was 0.06 ‰ for

δ13C values and 0.10 ‰ for δ15N values (n = 4).

To evaluate feeding consistency, I assigned each turtle for which I had large

stomach values and isotope values (n = 19) to one of three categories based on their

stomach contents: > 50 % seagrasses, > 50 % macroalgae and > 50 % tunicates. I then

25

plotted the stable isotope values of these turtles and the prey species. I compared the

resulting graph (Figure 2-2) with the conceptual models to determine whether turtles

were feeding consistently.

Statistical Analyses

To test for annual difference in percent volume of diet items between 2008 and

2011, a two-way analysis of variance was conducted between years and diet

constituents. A Tukey HSD multiple comparison test for unequal sample size was used

when significant differences were detected from the ANOVA. Volume percentages of

diet items were arcsine square root transformed to improve normality and homogeneity

of variance. Regression analyses were used to evaluate relationships between turtle

size (CCLmin) and primary diet constituents (seagrasses and tunicates) and between

turtle size (CCLmin) and δ13C and δ15N values. All data were analyzed using program

JMP version 9.0.2 (JMP® 1989- 2010).

Results

In total, 43 stomach samples were collected from 2008 (n = 12) and 2011 (n = 31).

In 2008, curved carapace length of turtles ranged from 23.6 to 35.9 cm CCL (n = 12;

mean ± SD = 30.4 ± 4.34). In 2011, curved carapace length of turtles ranged from 22.5

to 72.7 cm in CCL (n = 51; mean ± SD = 35.9 ± 9.87) and body mass ranged from 1.2 to

40.8 kg (n = 50; mean ± SD = 6.73 ± 6.93). Samples were analyzed and thirteen

categories were identified: seagrass (n = 3), algae (n = 2), tunicate (n = 2), and other

materials (n = 6) were identified (Table 2-1). The proportion of Botrylloides sp. in the diet

of green turtles differed significantly (P= 0.0037) between 2008 and 2011. Therefore,

data from the two years were analyzed separately. In the 2008 samples (n = 12), three

species were considered major diet items (> 5 % volume in at least one sample;

26

(Garnett et al. 1985): Pyrosoma sp., Botrylloides sp. and Thalassia testudinum blades

(Table 2-1). In the 2011 samples (n = 31), six items were considered major diet

constituents: Thalassia testudinum, Gracilaria sp., Enteromorpha sp., Syringodium

filiforme, Botrylloides sp., and Pyrosoma sp. There was no significant difference in diet

composition between all samples (large + small) and only large samples in 2011 (Table

2-1). In 2011, epidermis samples were collected from 39 turtles for stable isotope

analyses. Stable isotope values in epidermis tissue ranged from -16.44‰ to -8.05‰ for

δ13C (mean ± SD: -12.84 ± 2.11; Figure 2-2). Epidermis δ15N values ranged from 7.05‰

to 11.97‰ (mean ± SD: 8.95 ± 1.14; Figure 2-2). Stable carbon and nitrogen values

were determined for six prey species: Thalassia testudinum, Syringodium filiforme,

Halodule wrightii, Gracilaria sp., Enteromorpha sp. and Botrylloides sp. (Figure 2-2).

These prey species were considered primary diet constituents of green turtles based on

stomach contents. I was unable to apply mixing models to this study due to the inability

to locate Pyrosoma sp. during searches in fall 2011 and winter 2012 (see discussion).

Body size did not have a significant effect on the proportion of seagrasses or

tunicates in the diet (Pseagrasses = 0.3127, Ptunicates = 0.2215) although large turtles had a

tendency toward higher tunicate consumption (see Appendix C). Body size had a

significant positive relationship with δ13C (R2 = 0.66, df = 38, p = < 0.001; Figure 2-3),

but no relationship with δ15N (p = 0.054; Appendix D).

Individuals in the population exhibited inconsistency in diet during the months before

stomach samples were collected (Figure 2-2). The stable isotope value of the epidermis

tissue was not associated with the stable isotope value of the major diet item from the

stomach contents.

27

Discussion

The diet of juvenile green turtles in St. Joseph Bay in winters of 2008 and 2011

was considered to be predominantly omnivorous. These results are similar to other

studies conducted in northwest Africa, Australia and San Diego Bay (Cardona et al.

2009, Burkholder et al. 2011, Lemons et al. 2011). Seagrass (Thalassia testudinum)

and tunicates (Pyrosoma sp. and Botrylloides sp.) presented high IRI values in both

years of this study.

The high degree of invertebrate consumption in this study highlights the

importance of quantifying the availability of animal prey and their nutritional contribution

to green turtles. Previous research (Davenport & Balazs 1991) examined the nutritional

content of Pyrosoma atlanticum in Leatherback (Dermochelys coriacea) diet and found

Pyrosoma bodies to be composed of 27% protein, 3% lipid, and 70% carbohydrate. It is

suggested that these tunicates may be targeted for their ‘valuable’ stomachs, which

contain digestible organic material, while the tunica passes through the gut relatively

undigested (Davenport & Balazs 1991). The digestibility of tunicates such as Salpa and

Pyrosoma spp. is not well known, considering their high protein concentration relative to

other gelatinous animals (Dubischar et al. 2012). It is possible that although tunicates

provide a high concentration of protein, the protein may be bound in compounds not

available to the turtle. Studies are needed that measure the digestibility and nutrient

availability of the many animal species ingested by green turtles to better understand

their role as a dietary component.

Stomach content analysis suggests a degree of individual variation, but isotope

data indicate no consistency over a few months. The wide distribution of 13C values

28

may result from (1) rapid tissue turnover, (2) the contribution of pelagic diet items and/or

(3) long-term individual inconsistency in feeding patterns. The former explanation can

be considered unlikely, as turtles are ectotherms inhabiting cool waters. Isotopic studies

that measure tissue turnover and incorporation rates in juvenile green turtles are

needed in order to confidently reconstruct the diet. The second possible explanation for

the wide distribution of 13C values in some turtles is that the Pyrosoma sp. that the

turtles consume may have low 13C values. Low 13C values would be expected in

pelagic organisms blown in from deeper waters of the GoM. Our inability to sample

these tunicates precludes our testing this idea.

Figure 2-1 presents a conceptual model of the isotope values through time if

individual turtles are feeding inconsistently (2-1a) or consistently (2-1b). If turtles were

feeding inconsistently over time (i.e., a mixed diet of tunicate/seagrass) there would be

no clustering around prey items as individuals would vary in their resource use. If

individuals were feeding consistently over a long period, it would be expected that

clustering would appear around each prey item (e.g., algae, seagrass and tunicate).

Stable isotope results indicate low consistency, which may be attributed to inconsistent

availability of seagrass and tunicates. Seasonal variation in seagrass biomass, algae

biomass and tunicate occurrence may lead to alternative feeding strategies. Although

seagrass species are present in SJB year round, there is a significant dieback of

Thalassia, Halodule, and Syringodium spp. in shallow areas of the bay. Additionally, it

appears that red algae coverage increases in the fall months, then decreases during

winter (pers. obs.). Pyrosoma are a pelagic species, known to form extensive, dense

colonies that occur in irregular swarms (Andersen & Sardou 1994) from temperate zone

29

to temperate zone. Mass deposition events of pyrosomids have been recorded off the

African coast (Lebrato & Jones 2009). In the Gulf of Mexico, tunicates are reportedly

patchily distributed in their environment (Graham 2001). For example, dense colonies of

Pyrosoma atlanticum were reported in the California current region in 1955 and 1956,

then became rare again (Berner 1967). The other tunicate species found in this study

(Botrylloides sp.) is a benthic tunicate that forms on blades of T. testudinum. These

tunicates appear when water temperatures decrease (Sheri Johnson, pers. comm.;

pers. obs.). Green turtle digestive efficiency increases with an increase in water

temperature (Bjorndal 1980), so during winter green turtles may select animal diet items

which are of higher digestibility. It appears that green turtles in St Joseph Bay exhibit

plasticity, feeding primarily as herbivores in some years (Foley et al. 2007) and as

omnivores in other years (present study). Foley et al. (2007) analyzed green turtle

stomach contents from the 2001 cold stunning event and found the primary diet item to

be Thalassia testudinum. ‘Other materials’ which included tunicate species (Styela;

Molgula; unknown) were present in small amounts (Lessmann 2002). Differences in diet

between years cannot be attributed to methodology, as stomach contents were

thoroughly sorted and analyzed using the same methods.

Finally, this study illustrates that care should be taken in setting a stomach sample

size for reasonable gut content conclusions, especially in gastric lavage where samples

tend to be small (Nagaoka et al. 2012). Of the stomach samples in 2011 with volume

< 9.0 mL (n = 18), two individuals had stomach contents composed of 100% seagrass,

two were 100% tunicates, and the remaining samples were mixed diets of seagrass,

tunicates and macroalgae. Although there were no significant differences between all

30

samples and only large samples in 2011, the number of turtles with 100% seagrass or

tunicates was greatly reduced after excluding small sample volumes. Small,

homogenous sample volumes may represent one feeding event and give a different

picture of diet based on volume.

In the present study, green turtles revealed flexible foraging strategies as a

species inhabiting the northern fringe of their range. Prior to the 2008 and 2011 SJB

cold stunning events, green turtles were feeding as omnivores; however, prior to the

cold stunning event in 2001, green turtles exhibited a herbivorous diet (Foley et al.

2007). Questions of feeding consistency should be further examined by measuring

seasonal and annual variation in prey availability and selection. Future studies should

address the relationship between diet selection, digestive efficiency, and the nutritional

value of animal matter in green turtle diet. Understanding the temporal and geographic

variation in sea turtle foraging ecology in peripheral habitats is necessary for

implementing effective, long-term conservation and management plans. This

information is essential to the conservation of endangered species such as the green

turtle, as well as other species, that reside in peripheral habitats and may be more

susceptible to environmental changes.

31

Table 2-1. Diet composition of juvenile green turtles in St. Joseph Bay, Florida

Percent volume, percent dry mass, index of relative importance (IRI), and frequency of occurrence (% F) for green turtles from cold stunning events in St. Joseph Bay, Florida, in January 2008 and 2011. “ALL” refers to both small and large volumes from 2011; 2011 includes only large volumes (> 9.0 mL). “tr”

refers to trace. Values are presented as mean (SD). UM: unidentified material; UPM: unidentified plant material.

Prey item % Volume (mL) % Dry Mass (g) IRI % F

2008

n = 12 2011

n = 31 2011 ALL

n = 49 2008

n = 12 2011

n = 31 2011 ALL

n = 49 2008

n = 12 2011

n = 31 2011 ALL

n =49 2008

n = 12 2011 n =31

2011 ALL n = 49

Seagrasses

T. t. blades 22.8

(11.9) 12.2 (10.7) 7.8

(9.8) 2.30 (1.28) 1.14 (1.02) 0.7

(0.94) 74.4 70.1 70.3 100 100 88.7

T. t. rhizome 0.4

(1.2) 0.1

(0.5) 0.1

(0.4) 0.03 (0.09) 0.02 (0.06) 0.01

(0.05) 0.21 0.13 0.11 16.67 16.13 11.3

H. wrightii 0.1

(0.4) 0.0 0.1

(0.3) 0.01 (0.03) 0.01 (0.01) 0.00

(0.02) 0.03 0.02 0.05 8.33 12.9 9.4

S. filiforme 0.0 1.8

(9.0) 1.2

(6.9) 0.00 0.08 (0.37) 0.05

(0.28) 0.00 0.65 0.66 0.00 6.45 5.7

Macroalgae

Gracilaria sp. 0.0 0.6

(3.1) 0.6

(2.5) 0.00 0.03 (0.12) 0.02

(0.10) 0.01 0.22 0.66 0.00 6.45 11.3

Enteromorpha sp. 0.0 0.9

(3.3) 0.5

(2.6) 0.00 0.01 (0.07) 0.01

(0.05) 0.00 0.49 0.30 0.00 9.68 5.7

Tunicates

Pyrosoma sp. 3.5 (2.7) 5.1

(4.9) 3.2

(4.3) 0.23 (0.39) 0.19 (0.21) 0.13

(0.19) 11.4 26.7 26.7 100 90.3 79.3

Botrylloides sp. 5.7 (7.0) 0.6

(1.1) 0.3 0.9) 0.27 (0.35) 0.04 (0.07)

0.02 (0.05) 14.0 1.66 1.20 75 45.2 30.2

Other materials

feather 0.0 tr tr tr tr tr 0.00 tr tr 0.00 tr tr

UM 0.0 tr tr 0.00 tr tr 0.00 tr tr 0.00 tr tr

plastic 0.0 tr tr 0.00 tr tr 0.00 tr tr 0.00 3.2 1.9

shell 0.0 tr tr tr tr tr 0.00 tr tr 0.00 tr tr

UPM 0.0 tr tr 0.00 tr tr 0.00 tr tr 0.00 tr tr

32

Figure 2-1. Conceptual model of patterns of isotope values representing resource use through time. Closed symbols represent prey items; open symbols represent individual turtles. (a) inconsistent feeding and (b) consistent feeding over time. See text for discussion of model

15N

13

C

(a)

Macroalgae

Tunicates

Seagrasses

15N

13

C

(b)

33

Figure 2-2. Plot of stable isotope ratios of nitrogen and carbon from epidermis samples

and major prey items of juvenile green turtles. Closed symbols represent prey items; open symbols represent individual turtles. Prey items are shown as mean ± standard deviation

0

2

4

6

8

10

12

14

-18 -16 -14 -12 -10 -8 -6 -4

15N

(‰

)

13C (‰)

Tunicates Macroalgae Seagrasses

> 50 % seagrasses > 50 % macroalgae > 50 % tunicates

34

Figure 2-3. Chelonia mydas. Epidermis 13C vs. curved carapace length in St. Joseph Bay, Florida in 2011. Relationship is significant (see ‘Results’)

R² = 0.662

-18

-16

-14

-12

-10

-8

-6

20 30 40 50 60

13C

(‰

)

Curved carapace length (cm)

35

APPENDIX A JANUARY 2008 DIET COMPOSITION

Figure A-1. Diet composition (proportion of volume; mL) in 12 juvenile green turtles from

the cold stunning event in St. Joseph Bay, Florida in January 2008

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n o

f vo

lum

e (

ml)

Individual turtles

Seagrasses Macroalgae Tunicates Other materials

36

Figure A-2. Diet composition (proportion of dry mass; mg) in 12 juvenile green turtles

from the cold stunning event in St. Joseph Bay, Florida in January 2008

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n o

f d

ry m

ass (

mg)

Individual turtles


37

APPENDIX B JANUARY 2011 DIET COMPOSITION

Figure B-1. Diet composition (proportion of volume; mL) of 31 juvenile green turtles from

the cold stunning event in St. Joseph Bay, Florida in January 2011. Each bar represents one turtle

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n o

f vo

lum

e (

ml)

Individual turtles


38

Figure B-2. Diet composition (proportion of dry mass; mg) of 31 juvenile green turtles

from the cold stunning event in St. Joseph Bay, Florida in January 2011. Each bar represents one turtle

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n o

f d

ry m

ass (

mg)

Individual turtles


39

APPENDIX C 2011 DIET AND BODY SIZE

Figure C-1. The relationship between green turtle body size (CCLmin) and seagrasses (Pseagrasses= 0.3127) in St. Joseph Bay, Florida. Figure is based on volume of stomach contents (n= 30)

40

Figure C-2. The relationship between green turtle body size (CCLmin) and tunicates (Ptunicates= 0.2215) in St. Joseph Bay, Florida. Figure is based on volume of stomach contents (n= 30)

41

APPENDIX D

201115N AND BODY SIZE

Figure D-1. Chelonia mydas. Epidermis δ15N vs. curved carapace length in St. Joseph Bay, Florida in 2011. Relationship is not significant (see ‘Results’)

0

2

4

6

8

10

12

14

20 30 40 50 60

15N

(‰

)

Curved carapace length (cm)

2011

42

APPENDIX E DIET OF THE GREEN TURTLE, CHELONIA MYDAS

Table E-1.Diet of the green turtle, Chelonia mydas

Item Location Life Stage Reference

Atlantic Pacific & Indian Atlantic

Pacific & Indian

Plantae

Angiosperms Seagrasses Cymodocea ovalis

Yemen

A Hirth et al. 1973

Cymodocea spp.

Australia; Aldabra Atoll

A, J

Garnett et al. 1985; Fuentes et al. 2006; Frazier 1971

Diplanthera wrightii

Mosquito Lagoon, Florida; Nicaragua

J, U

Mendonca 1983; Mortimer 1976

Halodule pinifolia

Australia

U Limpus & Reed 1985

Halodule spp.

Australia

J Fuentes et al. 2006

Halodule uninervis

Oman; Australia; Yemen

U, J, A

Ross 1985; Limpus et al. 1994; Brand-Gardner et al. 1999; Hirth et al. 1973

Halodule wrightii

Nicaragua; Mosquito Lagoon, Florida;GoM;SE

Brazil;Texas

A, J

Mortimer 1981; Mendonca 1983; Foley et al. 2007; Guebert-Bartholo et al. 2011; Nagaoka et al. 2012; Coyne 1994; Santos et al. 2011

Halophila baillonis Nicaragua

A, J

Mortimer 1981

Halophila decipiens

Hawaii

J Arthur & Balazs 2008

Halophila engelmanni Mosquito Lagoon, Florida

J

Mendonca 1983

Halophila hawaiiana

Hawaii


Halophila ovalis

Oman;Australia; Yemen

U, A, J

Ross 1985; Limpus et al. 1994; Tucker & Read 2001; Brand-Gardner et al. 1999; Hirth et al. 1973

43

Table E-1. Continued

Item

Halophila ovata

Oman

U Ross 1985

Halophila spinulosa

Australia

A, O, J, U

Limpus et al. 1994; Garnett et al. 1985; Limpus & Reed 1985

Halophila spp.

Australia


Phyllospadix torreyi

Baja California

U Lopez-Mendilaharsu et al. 2005

Syringodium filiforme

Nicaragua;Mosquito Lagoon,

Florida;GoM;Texas

A, J, U

Mortimer 1976, 1981; Mendonca 1983; Foley et al. 2007; Coyne 1994

Syringodium isoetifolium

Yemen

A Hirth et al. 1973

Syringodium spp.

Australia


Thalassia spp.

Aldabra Atoll

A Frazier 1971

Thalassia hemprichii

Australia

A, J

Garnett et al. 1985; Tucker & Read 2001; Fuentes et al. 2006

Thalassia testudinum Nicaragua;Bahamas;GoM

A, O, J, U

Mortimer 1976, 1981; Bjorndal 1980; Foley et al. 2007

Thalassodendron ciliatum

Yemen

A Hirth et al. 1973

Zostera capricorni

Australia

A, O, J Limpus et al. 1994; Brand-Gardner et al. 1999

Zostera marina New York Baja California J U Lopez-Mendilaharsu et al. 2005; Burke et al. 1991

Angiosperms (terrestrial)

Avicennia germinans

Baja California


Avicennia marina Australia J Read & Limpus 2002

Avicennia shaueriana SE Brazil

J

Guebert-Bartholo et al. 2011; Nagaoka et al. 2012

Distichils spp.

Peru

A, J Hays Brown & Brown 1982

Ficus spp. leaves

Colombia

A, J Amorocho & Reina 2007

44


Item

Hibiscus spp. leaves

Colombia


Ochroma spp. leaves

Colombia


Rhizophora mangle

Galapagos Is.

A, J Carrion-Cortez et al. 2010

Spartina alterniflora SE Brazil

J

Nagaoka et al. 2012

Algae Phaeophyta Chnoospora

implexa

Australia

A, J Garnett et al. 1985

Colpomenia spp.

Australia


Cystoseira spp.

Australia


Dictoyota spp.

Australia; Hawaii; Galapagos Is.

A, J

Garnett et al. 1985; Fuentes et al. 2006; Arthur & Balazs 2008; Carrion-Cortez et al. 2010

Dictoyota dichotoma Brazil; Nicaragua

A, J, U

Ferreira 1968; Mortimer 1976

Dictyopteris delicatula Nicaragua; Brazil

A, J

Mortimer 1981; Ferreira 1968

Dictyota flabellata

Gulf of California

A Seminoff et al. 2002

Fucus spp. New York, Brazil

A, J

Burke et al. 1991; Ferreira 1968

Hydroclathrus clathratus

Australia


Ishige sinicola

Gulf of California


Lobophora variegata Nicaragua Hawaii U J Arthur & Balazs 2008; Mortimer 1976

Padina australis

Australia


Padina durvillaei

Gulf of California

A, J Seminoff et al. 2002

Padina pavonica

Oman

U Ross 1985

45


Item

Padina spp.

Australia;Hawaii

J Fuentes et al. 2006; Arthur & Balazs 2008

Padina vickersiae Nicaragua

U

Mortimer 1976

Phaeophyta spp.

Central, North Pacific

O Parker et al. 2011

Pocockiella variegata Brazil

A, J

Ferreira 1968

Sargassum cymosum Brazil

A, J

Ferreira 1968

Sargassum filipendula Nicaragua

A, J, U

Mortimer 1976, 1981

Sargassum fluitans Nicaragua

U

Mortimer 1976

Sargassum horridum

Baja California


Sargassum hystrix Nicaragua

A, J, U

Mortimer 1976, 1981

Sargassum illicifolium

Oman

U Ross 1985

Sargassum spp. SE Brazil; New York Australia;Gulf of California;Hawaii J A, J

Garnett et al. 1985; Tucker & Read 2001; Seminoff et al. 2002; Guebert-Bartholo et al. 2011; Fuentes et al. 2006; Arthur & Balazs 2008; Burke et al. 1991

Sargassum vulgare Nicaragua; Brazil

A, J


Spatoplossum schroederi Brazil

A, J

Ferreira 1968

Sphacelaria spp.

Australia


Sporochnus bolleanus

Gulf of California

J Seminoff et al. 2002

Sporochnus pedunculatus Nicaragua

A, J, U

Mortimer 1976, 1981

Turbinaria ornata

Australia;Hawaii

A, J Tucker & Read 2001;Arthur & Balazs 2008

46


Item

Turbinaria spp.

Australia

A, J Garnett et al. 1985;Fuentes et al. 2006

unidentified spp.

Australia

A Tucker & Read 2001

Zonaria spp.

Hawaii


Cyanophyta Lyngbya

majuscula

Hawaii


Lyngbya porphyrosiphonis

Hawaii


Lyngbya semiplena

Hawaii


Lyngbya spp.

Australia


Schizothrix spp.

Hawaii


Rhodophyta

Acanthophora spicifera Brazil Hawaii;Australia A, J A, J

Balazs et al. 1987;Garnett et al. 1985;Brand-Gardner et al. 1999; Arthur & Balazs 2008; Ferreira 1968

Acanthophora spp.

Australia


Agardhiella tenera Brazil

A, J

Ferreira 1968

Amansia glomerata

Hawaii;Australia

A, J

Balazs et al. 1987;Garnett et al. 1985;Arthur & Balazs 2008

Amansia multifida Nicaragua; Brazil

A, J, U

Mortimer 1976, 1981; Ferreira 1968

Amphiroa spp.

Hawaii


Anhfeltiopis spp.

Galapagos Is.


Bostrychia spp. SE Brazil Galapagos Is. J A, J Nagaoka et al. 2012; Carrion-Cortez et al. 2010

Botryocladia spp.

Australia


Bryocladia spp. Texas

J

Coyne 1994

Bryothamnion triquetrum Brazil

A, J

Ferreira 1968

Bryothamnion seaforthii Brazil; Nicaragua

A, J, U


47


Item

Caloglossa spp. SE Brazil Galapagos Is. J A, J Nagaoka et al. 2012; Carrion-Cortez et al. 2010

Callophylis spp.

Galapagos Is.


Catenella opuntia

Galapagos Is.


Caulacanthus spp.

Australia


Centroceras clavulatum

Hawaii


Centroceras spp.

Galapagos Is.


Ceramium spp.

Australia


Cerium spp.

Hawaii


Champia spp.

Australia


Chondracanthus canaliculatus

Baja California


Chondracanthus elegans SE Brazil

J

Santos et al. 2011

Chondria spp.

Australia;Hawaii

A, J Garnett et al. 1985; Arthur & Balazs 2008

Coelothrix spp.

Australia


Compsopogon spp. SE Brazil

J

Nagaoka et al. 2012

Corallina cubensis Nicaragua

A, J

Mortimer 1981

Coralina spp.

Galapagos Is.


Cryptonemia crennulata Nicaragua; Brazil

A, J


Cryptonemia luxurians Brazil; Nicaragua

A, J, U


Dasya spp.

Australia

A, J Garnett et al. 1985; Fuentes et al. 2006

Enantiocladia duperryi Nicaragua; Brazil

A, J


Euchema uncinatum

Gulf of California


48


Item

Eucheuma muricatum

Australia


Eucheuma spp. Brazil Australia A, J A, J Garnett et al. 1985; Ferreira 1968

Galaxaura obtusata Brazil

A, J

Ferreira 1968

Galaxaura spp.

Australia

A, J Garnett et al. 1985; Fuentes et al. 2006

Gelidiella acerosa Brazil Australia A, J A, J Garnett et al. 1985; Ferreira 1968

Gelidiella spp.

Australia; Hawaii; Galapagos Is.

A, J

Fuentes et al. 2006; Arthur & Balazs 2008; Carrion-Cortez et al. 2010

Gelidiella trinitatensis Brazil

A, J

Ferreira 1968

Gelidiopsis acrocarpa

Australia


Gelidiopsis gracilis Brazil

A, J

Ferreira 1968

Gelidiopsis variabilis

Australia


Gelidium corneum Brazil

A, J

Ferreira 1968

Gelidium floridanum SE Brazil

J

Santos et al. 2011

Gelidium johnstonii

Gulf of California


Gelidium robustum

Baja California


Gelidium spp.

Oman; Colombia; Hawaii; Aldabra Atoll; Galapagos

Is.

A , J, U

Ross 1985; Amorocho & Reina 2007; Arthur & Balazs 2008; Frazier 1971; Galapagos Is.

Gigartina spp. SE Brazil Gulf of California;

Peru J A, J Seminoff et al. 2002;Guebert-Bartholo et al. 2011; Hays Brown & Brown 1982

49


Item

Gracilaria cervicornus Brazil

A, J

Ferreira 1968

Gracilaria crassa

Australia


Gracilaria cuneata Brazil

A, J

Ferreira 1968

Gracilaria cylindrica Nicaragua

A, J

Mortimer 1981

Gracilaria debilis Nicaragua

U

Mortimer 1976

Gracilaria domingensis Brazil

A, J

Ferreira 1968

Gracilaria foliifera Brazil

A, J

Ferreira 1968

Gracilaria ferox Brazil

A, J

Ferreira 1968

Gracilaria mammillaris Nicaragua; SE Brazil

A, J

Mortimer 1981; Santos et al. 2011

Gracilaria ornata Brazil

A, J

Ferreira 1968

Gracilaria pacifica

Baja California


Gracilaria spinigera

Gulf of California


Gracilaria spp. Nicaragua;SE Brazil Australia; Hawaii;

Galapagos Is. A, J A, J

Mortimer 1981;Garnett et al. 1985;Brand-Gardner et al. 1999;Guebert-Bartholo et al. 2011;Fuentes et al. 2006;Arthur & Balazs 2008; Carrion-Cortez et al. 2010

Gracilaria textorii

Baja California


Gracilaria verrucosa Nicaragua

A, J

Mortimer 1981

Gracilariopsis lemaneiformis

Baja California


Gracilariopsis sjoestedtii Brazil

A, J

Ferreira 1968

Gracilariopsis tenuifrons SE Brazil

J

Santos et al. 2011

Griffithsia spp.

Australia


50


Item

Gymnogrongus griffithsiae SE Brazil

J

Santos et al. 2011

Gymnogrongus spp.

Galapagos Is.


Haloplegma duperreyi Brazil

A, J

Ferreira 1968

Halymenia floresii Nicaragua; Brazil

A, J

Mortimer 1981; Santos et al. 2011; Ferreira 1968

Halymenia refugiensis

Gulf of California


Halymenia spp.

Australia; Galapagos Is.

A, J

Garnett et al. 1985; Carrion-Cortez et al. 2010

Heterosiphonia spp.

Australia


Hypnea cervicornis Brazil Australia A, J A, O, J Limpus et al. 1994; Ferreira

Hypnea johnstonii

Baja California


Hypnea musciformis Nicaragua;Texas; Brazil

A, J

Mortimer 1981;Coyne 1994 ; Santos et al. 2011; Ferreira 1968

Hypnea spp. SE Brazil

Oman; Australia; Hawaii;

Galapagos Is. J J, U, A

Ross 1985; Garnett et al. 1985; Tucker & Read 2001; Brand-Gardner et al. 1999; Guebert-Bartholo et al. 2011; Fuentes et al. 2006; Arthur & Balazs 2008; Carrion-Cortez et al. 2010

Hypoglossum spp.

Australia


Jania spp.

Australia


Laurencia brongniartii

Australia


Laurencia johnstonii

Gulf of California


Laurencia mariannensis

Hawaii

J Balazs et al. 1987

51


Item

Laurencia spp. GoM; Brazil Australia;Hawaii;

Aldabra Atoll A, J A

Garnett et al. 1985;Foley et al. 2007;Fuentes et al. 2006;Arthur & Balazs 2008;Santos et al. 2011; Ferreira 1968; Frazier 1971

Lenormandiopsis lorentzii

Australia


Lenormandiopsis spp.

Australia


Leveillea jungermannioides

Australia


Leveillea spp.

Australia


Lithophyllum spp.

Gulf of California


Mazzaela flaccida

Baja California


Peyssonnelia simulans Nicaragua

U

Mortimer 1976

Platysiphonia spp.

Australia


Polysiphonia spp. SE Brazil Australia; Hawaii;

Galapagos Is. J A, J

Garnett et al. 1985;Nagaoka et al. 2012;Arthur & Balazs 2008; Carrion-Cortez et al. 2010

Prionites obtusa

Australia


Prionites spp.

Galapagos Is.


Protokuetzingia schottii Brazil

A, J

Ferreira 1968

Pterocladia capillacea SE Brazil

Hawaii;Baja California J J, U

Balazs et al. 1987; Lopez-Mendilaharsu et al. 2005; Santos et al. 2011

Pterocladia spp.

Galapagos Is.


Pterocladiella spp.

Hawaii


Rhodymenia pseudopalmata Texas; SE Brazil

J

Coyne 1994 ;Santos et al. 2011

Rhodymenia spp.

Peru


52


Item

Schizymenia epiphytica

Baja California


Scinaia spp.

Australia


Spyridia filamentosa Nicaragua Australia A, J, U A, J Mortimer 1976, 1981;Garnett et al. 1985

Tolypiocladia glomerulata

Australia


unidentified Rhodomelaceae SE Brazil

J

Nagaoka et al. 2012

unidentified Rhodophyta Mosquito Lagoon, Florida

Central, North Pacific J O Parker et al. 2011; Mendonca 1983

Vidalia obtusiloba Nicaragua; Brazil

A, J, U


Vidalia spp.

Australia


Chlorophyta Acetabularia

crenulata Nicaragua

U

Mortimer 1976

Anadyomene spp.

Australia


Avrainvillea spp. Brazil

A, J Ferreira 1968

Bryopsis spp.

Hawaii


Caulerpa ashmeadii Nicaragua

U

Mortimer 1976

Caulerpa brachypus

Australia


Caulerpa cupressoides Brazil; Nicaragua Australia U A, J

Garnett et al. 1985; Ferreira 1968; Mortimer 1976

Caulerpa farlowii Nicaragua

U

Mortimer 1976

Caulerpa lentillifera

Australia


Caulerpa longiseta Nicaragua

U

Mortimer 1976

Caulerpa mexicana Brazil

A, J

Santos et al. 2011; Ferreira 1968

53


Item

Caulerpa opuntia Nicaragua

U

Mortimer 1976

Caulerpa paspaloides Nicaragua

U

Mortimer 1976

Caulerpa prolifera Nicaragua; Brazil

A, J, U


Caulerpa racemosa

Australia; Galapagos Is.

A, J

Garnett et al. 1985; Carrion-Cortez et al. 2010

Caulerpa sertularioides Nicaragua; Brazil Australia A, J, U A, J

Mortimer 1976, 1981; Garnett et al. 1985; Ferreira 1968

Caulerpa spp. Nicaragua Australia;

Aldabra Atoll U A Tucker & Read 2001; Frazier 1971; Mortimer 1976

Caulerpa spp. rhizoids

Australia


Caulerpa urvilliana

Australia


Chaetomorpha aerea SE Brazil Oman J U Ross 1985;Santos et al. 2011

Chaetomorpha antennina

Gulf of California


Chaetomorpha spp.

Australia


Cladophora spp.

Colombia;Hawaii

A, J Amorocho & Reina 2007;Arthur & Balazs 2008

Cladophora vagabunda SE Brazil

J

Santos et al. 2011

Codium amplivesiculatum

Baja California


Codium edule

Hawaii


Codium isthmocladum Nicaragua; Brazil

A, J


Codium simulans

Baja California


54


Item

Codium spp. New York; Nicaragua

Australia; Gulf of California;

Hawaii; Aldabra Atoll; Galapagos

Is. J, U A, J

Garnett et al. 1985;Tucker & Read 2001;Seminoff et al. 2002;Arthur & Balazs 2008; Frazier 1971; Burke et al. 1991; Mortimer 1976

Dictyosphaeria spp.

Hawaii


Enteromorpha acanthophora

Gulf of California


Enteromorpha spp. GoM; New York Hawaii J J

Foley et al. 2007;Arthur & Balazs 2008; Burke et al. 1991

Gayralia spp. SE Brazil

J

Nagaoka et al. 2012

Halimeda incrassata Nicaragua

U

Mortimer 1976

Halimeda opuntia Nicaragua Hawaii U J Arthur & Balazs 2008; Mortimer 1976

Halimeda simulans Nicaragua

U

Mortimer 1976

Halimeda spp. Nicaragua Australia A, J, U A, J Mortimer 1976, 1981;Tucker & Read 2001;Fuentes et al. 2006

Monostroma oxyspermum Brazil

A, J

Ferreira 1968

Neomeris spp. Nicaragua

U

Mortimer 1976

Penicillus capitatus Nicaragua

A, J, U

Mortimer 1976, 1981

Penicillus spp. Nicaragua

U

Mortimer 1976

Rhipocephalus phoenix Nicaragua

U

Mortimer 1976

Rhipocephalus spp. Nicaragua

U

Mortimer 1976

55


Item

Rhizoclonium grande Hawaii J Arthur & Balazs 2008

Rhizoclonium spp. SE Brazil Australia J A, J Garnett et al. 1985;Nagaoka et al. 2012

Udotea conglutinata Nicaragua

U

Mortimer 1976

Udotea flabellum Nicaragua

A, J, U

Mortimer 1976, 1981

Udotea spinulosa Nicaragua

U

Mortimer 1976

Udotea spp. Nicaragua Australia U A, J Garnett et al. 1985; Mortimer 1976

Ulva fasciata Texas; Brazil

A, J

Coyne 1994; Ferreira 1968

Ulva lactuca

Gulf of California; Galapagos Is.

A, J

Seminoff et al. 2002; Carrion-Cortez et al. 2010

Ulva reticulata

Hawaii


Ulva spp. S. Brazil;SE Brazil; New

York Hawaii J J

Guebert-Bartholo et al. 2011;Nagaoka et al. 2012;Arthur & Balazs 2008; Burke et al. 1991

unidentified spp. SE Brazil

J

Mendonca 1983;Guebert-Bartholo et al. 2011

Chrysophyta Vaucheria spp. SE Brazil

J

Nagaoka et al. 2012

Animalia Pisces Hirundichthys

speculiger



Ostraciidae: Lactoria diaphana



Scombridae: Scomber japonicus



56


Item

unidentified spp.

Central, North Pacific; Peru

O, A, J

Parker et al. 2011; Hays Brown & Brown 1982

Mollusca Bivalvia Mytilus spp.

Peru


Semele spp.

Peru


Gastropoda Aplysia vaccaria

Gulf of California


Aplysua spp. eggs SE Brazil

J

Nagaoka et al. 2012

Cavoliniidae

southwest Pacific

O Boyle & Limpus 2008

Columbela fuscata

Gulf of California


Dentalium neohexagonum

Gulf of California


Dosidicus gigas

Gulf of California


gastropod eggs Nicaragua Gulf of California U A, J Seminoff et al. 2002; Mortimer 1976

Mytella guyanensis

Gulf of California


Nassarius spp.

Peru


Olivella dama

Gulf of California


Ptenoglossa: Janthina spp.



Pterioda

southwest Pacific


57


Item

Pteropoda: Cavolinia spp. including C. globulosa and C. tridentate



Pterotrachids including Carinaria spp.



Rissoina spp.

Colombia


Stylochilus spp.

Hawaii


Tonnidae

southwest Pacific


Triphora spp.

Colombia


Trypsica trypsica

Gulf of California


Turridae

Gulf of California


unidentified spp. New York Australia;

Galapagos Is. J A, J Garnett et al. 1985; Burke et al. 1991; Carrion-Cortez et al. 2010

Decopoda

Cephalopoda



Ommastrephes bartrami



Arthropoda

Amphipoda

Central, North Pacific; Peru

O, A, J

Parker et al. 2011; Hays Brown & Brown 1982

Class Insecta

southwest Pacific


Class Pycnogonida Nicaragua

U

Mortimer 1976

58


Item

Crustacea

Cirripedia

southwest Pacific

P Boyle & Limpus 2008

Cl. Malacostraca

southwest Pacific


Cl. Maxillopod

southwest Pacific


Copepod



Lepas spp.



Natantia spp.

Gulf of California


Penneus spp.

Colombia


Pleuroncodes planipes

Baja California


unidentified spp. New York

Central, North Pacific;Australia;

Hawaii; Peru J A, O, J

Parker et al. 2011;Garnett et al. 1985;Arthur & Balazs 2008; Burke et al. 1991; Hays Brown & Brown 1982

Echinodermata Brittle star

Australia

J Brand-Gardner et al. 1999

Clypeaster testudinarus

Gulf of California


unidentified spp.

Australia


Porifera Acarnus erithacus

Gulf of California


Chondrilla nucula Bahamas

U

Bjorndal 1990

Chondrosia chuchalla

Hawaii


Haliclona rubens Nicaragua

A, J

Mortimer 1981

Haliclona spp.

Gulf of California


Haliclona viridis Nicaragua

U

Mortimer 1976

59


Item

Halisarca spp.

Gulf of California


Hippiospongia gossipina Nicaragua

U

Mortimer 1976

Hymeniacidon rugosus

Gulf of California


Hymeniacidon sinapium

Gulf of California


Labrisomidae vertebra

Gulf of California


unidentified spp. Nicaragua

Australia;Gulf of California;Baja

California U A, J, U

Garnett et al. 1985;Seminoff et al. 2002;Lopez-Mendilaharsu et al. 2005; Mortimer 1976

Cnidaria



Antipathes galapagensis

Gulf of California


Catostylus mosaicus

Australia

A, J, O Limpus et al. 1994

Lytocarpus nuttingi

Gulf of California


Muricea spp.

Gulf of California


Pseudopterogorgia spp. Nicaragua

U

Mortimer 1976

Physalia spp.

Australia

O Booth & Peters 1972

Pocillopora spp.

Colombia


Porpita spp.

southwest Pacific; Australia

O

Boyle & Limpus 2008; Booth & Peters 1972

Ptilosarcus undulatus

Gulf of California


unidentified anemone Nicaragua Australia U J Brand-Gardner et al. 1999; Mortimer 1976

60


Item

unidentified Anthozoa

Australia


unidentified Medusozoa spp.

Peru


unidentified Scyphozoa

southwest Pacific;Australia

O, A

Boyle & Limpus 2008;Tucker & Read 2001

unidentified spp.

southwest Pacific; Australia;

Galapagos Is.

A, O, J Boyle & Limpus 2008; Brand-Gardner et al.1999; Carrion-Cortez et al. 2010

Hydrozoa Sertularia inflata Nicaragua

A, J, U

Mortimer 1976, 1981

unidentified spp. SE Brazil; Nicaragua Australia;

Galapagos Is. J, U A, J Nagaoka et al. 2012;Tucker & Read 2001; Mortimer 1976; Carrion-Cortez et al. 2010

Siphonophora

Galapagos Is.


Velella spp.

Australia

O Booth & Peters 1972

Bryozoa Hyppothoa spp.

Gulf of California


unidentified spp. SE Brazil; Nicaragua Australia J, U A Garnett et al. 1985; Nagaoka et al. 2012; Mortimer 1976

Scyphozoa unidentified spp.

Galapagos Is.


Ctenophora

unidentified spp.

Central, North Pacific; Australia

O Parker et al. 2011; Booth & Peters 1972

Tunicata Ascidia interrupta

Gulf of California


Doliolidae

Colombia


Pyrosoma atlanticum



61


Item

Salpidae

Central, North Pacific;Colombia

A, J, O

Parker et al. 2011;Amorocho & Reina 2007

unidentified ascidian

Australia

A, J

Tucker & Read 2001;Brand-Gardner et al. 1999;Fuentes et al. 2006

unidentified spp. Nicaragua Australia U A, J Garnett et al. 1985; Mortimer 1976

Annelida Sabellidae

Gulf of California


Spunalidae

Galapagos Is.


unidentified polychaete spp.

Peru


Nematoda unidentified spp.

Galapagos Is.


Eukaryota unidentified spp.

Australia


62

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68

BIOGRAPHICAL SKETCH

Natalie Christine Williams was born in 1985 in Milan, Tennessee and lived with her

parents, James and Lynn Williams, in Jackson, Tennessee until entering college. She

attended St. Mary’s Elementary, I.B. Tigrett Middle School, and the University School of

Jackson for high school. At the age of seven, her mother and godmother introduced her

to their love of sea turtles by sending her on her first nesting turtle patrol in Charleston,

South Carolina. After that, she knew she would study sea turtles and go to school in

Charleston. Upon graduating high school she studied biology and Spanish at the

College of Charleston in Charleston, South Carolina. She received her Bachelor of

Science degree in 2007 with honors. During 2008 she moved to Gainesville, Florida to

work with Dr. Jane Brockmann, studying mating behavior in horseshoe crabs. In 2009

she entered the University of Florida Department of Wildlife Ecology and Conservation

and began to work on her master’s thesis, studying habitat selection and foraging

ecology in green sea turtles. Upon completion she will spend a year working in the field

and traveling to gain experience with new species and habitats. She will then continue

her studies in habitat selection and foraging ecology in a PhD program. She hopes to

continue her work in wildlife ecology and conservation and enjoy each day of life.

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