Green Turtles (Chelonia Mydas) in an Urban Estuary System: Lake Worth Lagoon, Florida

Biological Sciences

Green turtles (Chelonia mydas) in an urban estuary system: Lake Worth Lagoon, Florida

Jonathan C. Gorham(1), Michael J. Bresette(1), Jeffrey R. Guertin(1), Brian M. Shamblin(2), and Campbell J. Nairn(2)

(1)Inwater Research Group, Inc., 4160 NE Hyline Drive, Jensen Beach, FL 34957 (2)Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602

Abstract Estuarine environments in Florida provide important developmental habitat for sea turtles. We present the first systematic survey of green turtles (Chelonia mydas) inhabiting Lake Worth Lagoon (LWL), a heavily urbanized lagoon in Palm Beach County, Florida. We characterized the distribution, abundance, size class structure, diet, sex ratio, and genetic origin of green turtles in LWL using vessel-based visual transect surveys and captures over the period from 2005 to 2013. Data from 100 captured individuals showed the LWL population was comprised almost entirely of juveniles, with a mean straight standard carapace length of 40.4 centimeters. The distribution of green turtles in LWL coincides with areas where significant submersed aquatic vegetation is present. Dietary analysis from 31 individuals showed that seagrass species comprised 90% of the diet. We also quantified the prevalence and severity of fibropapillomatosis (FP) in the population, a disease associated with impaired water quality. The overall FP prevalence for the population was 48.7%, and both prevalence and severity of FP appear to be stable or slightly increasing over the period from 2005-2013. Long-term monitoring of this population may serve to provide an important barometer of overall lagoon health, and assess the progress of ongoing efforts in lagoon restoration.

Keywords Green sea turtle, Lake Worth Lagoon, fibropapilloma, developmental habitat

Introduction Lagoon and estuarine habitats in Florida provide important developmental habitat for several species of sea turtles, including the green sea turtle Chelonia mydas (Ehrhart et al. 2007, Kubis et al. 2009). Where the watersheds of these estuaries are heavily urbanized, impaired water quality may present threats to this developmental habitat. A major factor in habitat impairment is seagrass loss. Seagrasses are key species in coastal ecosystems, providing habitat structure, shelter, and sediment stabilization, among other ecosystem services (Orth et al. 2006). In the case of the green turtle, seagrass also represents a direct food resource (Bjorndal 1980, Bjorndal 1997, Arthur et al. 2008). Lake Worth Lagoon (LWL) in Palm Beach County, FL (Figure 1) has historically suffered extensive seagrass loss. Aerial surveys of LWL in 1940 documented 1728 hectares of seagrass, while a 1975 inventory identified only 69 hectares

Corresponding author: Jonathan Gorham, [email protected]

14 Lake Worth Lagoon green turtles Gorham et al. remaining (PBCERM and FDEP 1998). In recent years, an extensive program of water quality remediation and habitat improvements has been undertaken by the Palm Beach County Environmental Resource Management Department (PBCERM) in cooperation with state and federal agencies. Aerial mapping in 2007 documented a significant recovery of seagrass habitat, with 754 hectares of seagrass identified in LWL. Restoration efforts are continuing, with 76 million dollars spent since 2008 on restoration, stormwater and wastewater management, and public outreach (PBCERM 2013). Given the dependence of green turtles on seagrass as a dietary resource, restoration of these habitats should increase the carrying capacity for green turtles in LWL. Monitoring demographic data for green turtles in LWL may provide a good barometer for the health of the estuary and the success of restoration efforts (Aguirre and Lutz 2004). Another potential impact to green turtles residing in an urbanized estuary is an increased prevalence of fibropapillomatosis (FP), which appears to be correlated with impaired water quality (Van Houtan et al. 2010). Fibropa- pillomatosis was first described in the 1930s in a single green turtle near the Florida Keys (Smith and Coates 1939). In more recent years this disease has become epizootic, with some populations exhibiting infection rates of more than 70% (Aguirre and Lutz 2004). Fibropapillomatosis is not necessarily fatal, but tumors associated with the disease can interfere with prey capture, predator avoidance, diving, swimming, and vision (Milton and Lutz 2003). Additionally, internal tumors can affect buoyancy, cardiac function, digestion, organ function, and respiration (Herbst 1994, Work and Balazs 1999). The cause of fibropapillomatosis is unknown. Nutrient runoff in the form of nitrogen has been implicated as a potential FP tumor promoter (Van Houtan et al. 2014) although this topic is under debate (Work et al. 2014). To the extent that water quality plays a role in FP, monitoring the prevalence and severity of FP in green turtles found in LWL may provide another important criterion with which to assess restoration success. In order to characterize and collect baseline data on the green turtle population in LWL, we conducted vessel-based visual transect surveys to produce distribution maps and identify “hotspots” of high abundance where capture efforts could be focused. The specific objectives of this study were to: (1) collect occurrence and abundance data on the LWL green turtle population, which has never been systematically studied; (2) identify the size class structure of the population, as compared with other Florida developmental habitats; (3) determine the diet of green turtles in LWL and whether turtles are feeding on food items in proportion to their availability; (4) determine the population sex ratio and the natal beach origin of green turtles in the lagoon; and (5) collect data on the prevalence and severity of FP in LWL green turtles. This information will aid state and federal resource managers charged with the conservation of this endangered species and, with continued monitoring, can serve to help assess the progress and success of comprehensive restoration efforts underway in the lagoon.

Florida Scientist 79(1) 2016 ß Florida Academy of Sciences 15 Gorham et al. Lake Worth Lagoon green turtles

Figure 1. Location of study area at Lake Worth Lagoon and Little Munyon Island, Palm Beach County, Florida.

Materials and Methods Field work was conducted in the LWL between 2005 and 2013 over an area between Little Lake Worth at the northern end of LWL and the Boynton Inlet at the southern end of LWL (Figure 1). A total of 59 days of field work was conducted for the project. Field work was conducted in all seasons, with the majority of the work occurring in the summer and fall months.

Vessel-based visual transect surveys. Two different vessel-based visual transect survey methods were used in the study. To cover the considerable area of LWL and generate a broad- brush picture of distribution and abundance, the Haphazard Unmarked Nonlinear Transect (HUNT) method (Bresette et al. 2010) was employed. In the HUNT method, two experienced observers were positioned on a two meter high elevated tower on a seven meter long flat bottom skiff. As the vessel moved slowly (,10 kilometers per hour [kph]) through the area, observers searched for turtles both at and below the surface. HUNT transect locations were distributed as widely as possible throughout LWL, consistent with the ability of the vessel to access shallow water areas, to generate a general picture of green turtle distribution throughout LWL. During HUNTs, a helmsman recorded GPS start and end coordinates for each transect and a data recorder noted turtle observation data including species, life history stage, position in the water column, and the cross-track distance of the observation (the perpendicular distance of the observation from the transect line). GPS software (Garmin Mapsource) determined the linear distance between transect start and end points, allowing for a calculation of abundance expressed as observations per transect kilometer. In addition to the HUNT transects, a 10 kilometer long fixed transect grid was established in an area of high turtle abundance in the northern portion of LWL near Little Munyon

16 Florida Scientist 79(1) 2016 ß Florida Academy of Sciences Lake Worth Lagoon green turtles Gorham et al.

Figure 2. Little Munyon Island fixed transect grid layout.

Island (Figure 2). Beginning in 2013, this transect grid was censused in the same manner as the HUNT transects. Using the distribution of the cross track distances for the observations, the program Distance 6.0 (Buckland et al. 2001) was used to calculate an effective strip width for each transect. This approach allowed for an estimation of actual density, expressed as individuals per

Florida Scientist 79(1) 2016 ß Florida Academy of Sciences 17 Gorham et al. Lake Worth Lagoon green turtles square kilometer. Surveys along a fixed transect grid reduce variability by surveying the same area repeatedly and are intended to be utilized in index sites for assessing long-term changes in abundance.

Capture efforts. Turtles were captured using a combination of tangle net, dip net, and rodeo capture techniques. Tangle net captures utilized a large-mesh tangle net 150 meters long by 5 meters deep, consisting of 40 centimeter (cm) stretch (knot to knot) multi-filament mesh suspended from a foam core braided polyethylene top (float) line with fixed buoys spaced 3.5 meters apart. The bottom (lead) line consisted of small diameter lead core line. Each end of the net was secured with a small Danforth-type anchor. When turtles encountered the net and became entangled, they were quickly removed and placed on the deck of the boat. Dip net captures were conducted using a large mesh nylon net with a one meter diameter hoop mounted on a four meter long handle. Observers in the tower on the vessel guided the boat into position for the net operator on the bow to quickly "scoop" a resting or slowly swimming turtle. This capture method was used in conjunction with the HUNT transects described above. When a turtle was spotted on a HUNT transect its position was recorded and the HUNT transect was ended. The boat then slowly followed the turtle until a dip net capture attempt could be made. Rodeo captures (Ehrhart and Ogren 1999) consisted of the boat closely following a turtle at slow speed until a diver was able to jump from the boat to capture the turtle by hand. Rodeo captures were employed for turtles which were too large, in water too deep, or swimming too actively for the dip net capture method. This capture method was also used in conjunction with the HUNT transects as described above.

Data and sample collection and analysis. Morphometric data were collected for each turtle captured using forestry calipers and flexible tape as described in Pritchard et al. (1983). Measurements recorded included straight standard carapace length (SSCL), straight minimum carapace length, straight carapace width, straight plastron length, curved carapace length, curved carapace width, and head width. Inconel #681 tags were applied to the trailing edge of one or both front flippers and a passive integrated transponder (PIT) tag manufactured by Destron-Fearing was subcutaneously applied to the right front flipper. Before insertion of any tags, all flippers were scanned for the presence of any pre-existing PIT tags. Turtles were also weighed and photographed before they were released. Blood samples were taken for mtDNA and sex ratio analysis. Blood was collected within five minutes following capture and was drawn from the dorsal cervical sinus using a sterile vacutainer with no additive and a 2.5 cm 21 gauge sterile needle (Owens and Ruiz 1980). We collected approximately 4 milliliters (ml) of blood from each turtle and added a few drops to a lysis buffer (100 mM Tris-HCL, pH 8; 100 mM EDTA, pH 8, 10 mM NaCl; 1.0% SDS) in a 1:10 ratio. This blood was used for mtDNA haplotype analysis to determine the turtle’s natal beach origin. The remaining blood was placed in a sterile vacutainer with lithium heparin and spun for ten minutes in an Adams Physician centrifuge within eight hours of collection. Plasma was then pipetted into two 1.8 ml vials and used for testosterone radioimmunoassay to determine testosterone titer levels and gender. Plasma testosterone concentrations were determined using a standard competitive binding radioimmunoassay (RIA) according to previously described techniques (Wibbels et al. 1987; Blanvillain et al. 2008). Briefly, this assay utilizes competition for a specific antiserum between native and tritium-labeled hormone to measure plasma testosterone concentrations. All samples (500 microliters [ml]) were extracted with diethyl ether, dried under nitrogen gas, and analyzed in duplicate. Standard curves were prepared with known concentrations (19.5 to 1250 picograms (pg) per tube) of radioinert hormone, and testosterone antiserum (Esoterix Laboratory Services, Calabasas Hills, CA) and tritiated testosterone (10,000 cpm 100 ml-1, PerkinElmer Life Sciences, Shelton, CT) were delivered to all samples, standards, and controls. Bound and free hormone fractions were separated using dextran-coated charcoal and centrifugation. Radioactivity was counted using a Wallac 1414 liquid scintillation counter and the concentration of native hormone in each sample was determined from the standard curve with RIAMENU Software (P. Licht, University of California Berkeley). Samples exhibiting serum testosterone levels below 173

18 Florida Scientist 79(1) 2016 ß Florida Academy of Sciences Lake Worth Lagoon green turtles Gorham et al. picograms per milliliter (pg/ml) were classified as female, levels over 285 pg/ml were classified as male, and levels in intermediate range between 175 - 285 pg/ml were classified as unknown sex. DNA was extracted from blood samples of 81 individuals using a Qiagen DNEasy kit following the manufacturer’s protocols. An 817 base pair (bp) portion of the mitochondrial control region was amplified using primers LCM15382 and H950 (Abreu-Grobois et al. 2006). Sequences were truncated to 490 bp to facilitate pairwise haplotype frequency differentiation comparisons with other juvenile foraging aggregations in the Greater Caribbean region characterized in the literature (haplotype counts presented in Naro-Maciel et al. 2012). These juvenile foraging aggregations were sampled in Texas, northwestern Florida, off Hutchinson Island, Florida, the

Bahamas, North Carolina, and Barbados. Pairwise FST values were tested for significant differences using Arlequin 3.5 (Excoffier and Lischer 2010). Rookery contributions were estimated using a Bayesian many-to-many mixed stock analysis approach (MSA) as implemented in program MIXSTOCK (Bolker et al. 2007). Given the Caribbean focus, South Atlantic rookeries and foraging aggregations were excluded (except for Brazil) based on likely oceanic dispersal pathways highlighted by biophysical modeling (Putman and Naro-Maciel 2013). Rookeries considered as possible sources included Costa Rica, Mexico, Cuba, southern Florida, central eastern Florida, Aves, Suriname, and northern Brazil using haplotype counts presented in Naro-Maciel et al. (2012) and Shamblin et al. (2015). Because many rookeries in the region share three common control region haplotypes, rookery contributions were weighted by treating relative annual rookery size as outlined in Naro-Maciel et al. (2012) as a prior in the mixed stock analysis. Recent research has demonstrated that the Florida nesting aggregation represents at least two distinct nesting populations (Shamblin et al. 2014). Accordingly, the estimated 779 nesting females representing Florida (Seminoff 2004) were allocated to southern (319) and central eastern (461) Florida nesting populations based on proportional nest counts from the respective regions during 1995 through 2004 (Florida Fish and Wildlife Research Institute Statewide Nesting Beach Survey data). Central eastern Florida nest counts encompassed Volusia through St. Lucie County. Southern Florida nest counts encompassed Martin through Monroe County. Dietary samples were collected from captured green turtles by esophageal lavage. This method used a flow of water from a small hand pump to rinse out the mouth and esophagus. Fragments of recently eaten food items were collected and preserved in 4% formalin. Samples were filtered using a 0.5 millimeter (mm) filter paper and wet weight was determined to 0.01 gram (g) using a Denver Instrument Company electronic scale. After weighing, the samples were transferred to a petri dish that had a 4 x 4 cm grid etched on the bottom. The samples were smoothed to a single layer across the grid and examined at 0.79 x power using a Bausch & Lomb stereoscope fitted with a 071184 graticule. Forage items were identified to the lowest taxonomic level possible and recorded as percent volume of total sample. Tumors associated with FP were measured and recorded on a standardized tumor score sheet. A tumor score was calculated for each turtle that exhibited external evidence of FP, using the technique of Balazs (1991) to assign turtles to FP severity categories.

Results Four hundred and twenty HUNT transects were conducted between 2005 and 2013 totaling 910 kilometers (km) of survey effort. A total of 719 green turtles and six loggerhead turtles (Caretta caretta) were observed on HUNT transects. HUNT transect surveys yielded an overall index of green turtle abundance for LWL of 0.80 observations per transect kilometer (obs/km). Green turtles were not distributed evenly throughout LWL. Sightings were clustered in the vicinity of the two inlets (Lake Worth Inlet and Boynton Inlet) and most markedly in an area of the northern lagoon south of JD MacArthur State Park in the vicinity of Little Munyon Island. Three hundred and fifty HUNT transects conducted in the vicinity of Little Munyon Island yielded an index of green

Florida Scientist 79(1) 2016 ß Florida Academy of Sciences 19 Gorham et al. Lake Worth Lagoon green turtles

Figure 3. Size class distribution for green turtles captured in Lake Worth Lagoon, 2005 - 2013 (n 5 100).

turtle abundance for that area of 1.29 obs/km. The 10 km fixed transect grid located in the Little Munyon Island area (Figure 2) was surveyed six times in 2013. Green turtle density estimates on these surveys ranged between 0.40 and 3.23 green turtles per square kilometer, with a mean of 1.94 green turtles per square kilometer. A total of 100 green turtles were captured during the course of the study (47 by tangle net, 31 by dip net, and 22 by rodeo). The SSCL of captured individuals ranged from 24.6 cm to 62.3 cm with a mean SSCL of 40.4 cm (SD 5 8.75 cm). Figure 3 presents the size-class distribution of the population. The majority of captured individuals were classified as juveniles (SSCL 10 to ,60 cm). Only two captured individuals were classified as subadults (SSCL 60 to ,85 cm) using the classification system employed by the Florida Fish and Wildlife Conservation Commission (pers. comm. M. Koperski, September 15, 2014). No adult green turtles were captured or observed in LWL. Variable positions in the mitochondrial control region resolved 11 haplotypes based on 490 bp sequences and 15 haplotypes based on 817 bp sequences in the LWL juvenile foraging aggregation. The 817 bp haplotype counts were: CM-A1.1 (20), CM-A1.2 (1), CM-A1.3 (1), CM-A1.4 (1), CM- A2.1 (1), CM-A3.1 (41), CM-A5.1 (5), CM-A8.1 (4), CM-A13.1 (1), CM-A16.1 (1), CM-A17.1 (1), CM-A18.1 (1), CM-A18.2 (1), CM-A22.1 (1), and CM- A28.1 (1). Haplotype sequences and Genbank accession numbers are available from: http://accstr.ufl.edu/resources/mtdna-sequences/. Two CM-A1 expanded haplotypes (CM-A1.3 and CM-A1.4) represent novel variants from unknown rookery sources (Genbank accession numbers X and Y, respectively). CM-A18 was also subdivided into two variants, one of which (CM-A18.1, Genbank

20 Florida Scientist 79(1) 2016 ß Florida Academy of Sciences Lake Worth Lagoon green turtles Gorham et al.

Figure 4. Foraging aggregation-centric rookery contribution estimates for LWL juvenile green turtles from mitochondrial DNA mixed stock analysis. TRT is Tortuguero, Costa Rica; QRM is Quintana Roo, Mexico; SWC is southwestern Cuba; SFL is southern Florida; CFL is central Florida; AVES is Aves Island, Venezuela; SUR is Suriname; NBR is northern Brazil. accession number) was not detected in the Florida nesting aggregation (Shamblin et al. 2015) and likely represents a Mexican haplotype. Haplotype frequencies of the LWL foraging aggregation were not significantly different from juvenile aggregations in Florida, the Bahamas, and North Carolina but were distinct from Texas (FST 5 0.051, p , 0.001) and Barbados (FST 5 0.061, p , 0.001). MSA clearly indicated that Costa Rica, Quintana Roo, Mexico, and the Florida nesting populations were major contributors along with measurable but small contributions from eastern Caribbean and South Atlantic rookeries (Figure 4). Serum testosterone analysis from 47 green turtles captured in the Lake Worth Lagoon from 2006 - 2012 revealed 27 individuals classified as females, 17 classified as males, and three classified as unknown sex. These results show a moderately female biased sex ratio in the Lake Worth Lagoon green turtle population of 1.6 females: 1 male. Esophageal lavage samples collected from 31 captured individuals showed a diet comprised predominately (approximately 90%) of seagrass species (Table 1). Turtle grass (Thalassia testudinium) was the most frequently occurring dietary item, representing 51% of sample volume. The percentage of captured turtles exhibiting external evidence of FP tumors ranged from a low of 29.5% in 2007 to a high of 78.6% in 2013. The mean rate of FP incidence over the study period was 48.7%. The FP tumor severity (Balazs tumor score) for captured turtles ranged from 1.5 in 2007 to 2.7 in 2013. Both the incidence and the severity of FP in the LWL green turtle population appeared to show a modest increase over the study period (Figure 5).

Florida Scientist 79(1) 2016 ß Florida Academy of Sciences 21 Gorham et al. Lake Worth Lagoon green turtles

Table 1. Dietary composition (percentage of total by volume) from lavage samples from LWL green turtles 2005 - 2013 (n 5 31).

Dietary Component Percentage of Total by Volume Thalassia testudinium 51% Syringodium filiforme 30% Halodule sp. 13% Unknown 4% Macroalgae 2%

Discussion Estuarine environments and the seagrass habitats they support are vulnerable to a wide variety of threats, from water quality degradation to climate change (Orth et al. 2006). The continued recovery of the Florida segment of the Atlantic green turtle population will in part depend on managing threats to developmental habitat such as estuarine seagrass systems (NMFS and USFWS 1991). In turn, monitoring of the abundance, distribution, and disease status of green turtle populations in developmental habitats can provide important criteria with which to evaluate both the functionality of seagrass systems and the progress and efficacy of restoration efforts. The overall green turtle abundance estimate for LWL from the HUNT transect surveys of 0.80 observations per kilometer indicates that LWL provides appropriate developmental habitat for juvenile green turtles. The abundance levels recorded were comparable to similar surveys conducted using the same method in other Florida developmental habitats, such as Indian River County nearshore reefs (0.86 green turtles / km; IRG 2010) and Palm Beach County nearshore reefs (0.56 green turtles / km; IRG 2011). It appears that the area of the northern LWL in the vicinity of Little Munyon Island represents particularly valuable green turtle developmental habitat, and would be a good candidate for an inwater "index site," where long term monitoring could

Figure 5. Fibropapillomatosis (FP) prevalence (solid line) and severity (dashed line) from turtles captured in the Lake Worth Lagoon, 2005 - 2013.

22 Florida Scientist 79(1) 2016 ß Florida Academy of Sciences Lake Worth Lagoon green turtles Gorham et al. provide vital information on population trends. The fixed transect grid established in that area and sampled in 2013 is intended to provide a baseline for future long-term monitoring. An examination of the turtle sighting locations with respect to available seagrass distribution maps (PBCERM 2013) revealed an apparent association between turtle sighting locations and locations within LWL with higher seagrass density. The turtles captured in LWL during this study were almost exclusively juveniles. The mean SSCL of 40.4 cm recorded was similar to that of green turtles in the St. Lucie County nearshore environment sampled by the St. Lucie Power plant (41.9 cm SSCL) and the Indian River County nearshore reefs near Sebastian Inlet (41.5 cm SSCL; Witherington et al. 2006, Kubis et al. 2009). LWL green turtles were somewhat smaller than green turtles in the Indian River Lagoon near Sebastian Inlet (43.7 cm SSCL; Kubis et al. 2009) and the Key West National Wildlife Refuge (44.0 cm SSCL; Bresette et al. 2010). This finding indicates that LWL, like other shallow water habitats in Florida, serves as developmental habitat for juvenile green turtles following their transition from open water pelagic habitats to shallow neritic habitats at approximately 20 cm SSCL (Redfoot and Ehrhart 2013). Green turtles may spend years in these shallow water developmental habitats before migrating to other areas when they approach subadult size at approximately 60 cm SSCL (Witherington et al. 2006, Bresette et al. 2010). MSA results indicate the importance of LWL as a developmental habitat for juveniles from the major western and northern Greater Caribbean rookeries. Findings of major contributions from Costa Rica and Mexico are concordant with ocean circulation modeling that suggested connectivity of eastern Florida foraging habitats and these rookeries via oceanic dispersal of post-hatchlings (Putman and Naro-Maciel 2013). However, contributions from Florida nesting populations, particularly central eastern Florida, cannot be explained by oceanic dispersal of hatchlings. The presence of juveniles of Florida origin is consistent with juvenile natal homing. Rookery contribution point estimates were coarse due to the widespread nature of CM-A1 and CM-A3 across Caribbean rookeries. Additional mitochondrial markers have been employed to improve resolution for other green turtle studies (Shamblin et al. 2012, Tikochinski et al. 2012), and application of these techniques on CM-A1 and CM-A3 turtles may better clarify the stock structure among rookeries and contributions to mixed foraging aggregations. Green turtles in LWL depend more heavily on seagrass species for forage than green turtles in several other estuarine environments on the east coast of Florida. Approximately 90% of the volume of dietary samples collected from LWL green turtles was comprised of various segrasses. Green turtles in developmental habitats in the Mosquito Lagoon had a diet comprised of 74.5% seagrass by volume, green turtles in the Indian River Lagoon near Fort Pierce Inlet had a diet comprised of 18.9% seagrass by volume, and green turtles in the Indian River Lagoon near Sebastian Inlet had a diet comprised of only 10.1% seagrass (Holloway-Adkins 2001). Algal species, which comprised the

Florida Scientist 79(1) 2016 ß Florida Academy of Sciences 23 Gorham et al. Lake Worth Lagoon green turtles bulk of dietary items at the Indian River Lagoon sites, comprised less than 10% of the dietary items by volume in LWL. Thus, the abundance of green turtles is likely to be particularly strongly correlated with the abundance, health, and density of seagrass in LWL. It also appears that LWL green turtles do not feed on seagrass species in proportion to their availability. Halodule wrightii is the most abundant species of seagrass in LWL (PBCERM 2013) but is the least common seagrass species in the diet analysis at 13% by volume. Conversely, Thalassia testudinium comprised the largest proportion of green turtle dietary items at 51%, but is the least frequently encountered seagrass species in the lagoon. The incidence of FP in a green turtle population is an important indicator of the health and viability of the population, and possibly of the health of the water body itself. The incidence of FP in Lake Worth Lagoon green turtles has shown an increasing trend since 2005, with 2013 having the highest incidence rates ever recorded (78.6%). Overall, from 2005 - 2013, the mean FP incidence rate for Lake Worth Lagoon green turtles was 48.7%. This compares with recent FP rates from other Florida inshore lagoon developmental habitats of 50.8% in the Indian River Lagoon near Sebastian Inlet and 63.1% in the Indian River Lagoon near Fort Pierce Inlet (Holloway-Adkins 2001). These rates from inshore lagoon habitats are much higher than the FP rates found in nearshore oceanic developmental habitats, such as the St. Lucie County, FL nearshore habitat sampled by the St. Lucie Power Plant (3.1%; Bresette et al. 2001) and the shallow-water nearshore reef adjacent to Sebastian Inlet, FL (14.8%; Hirama and Ehrhart 2007). The severity of FP among captured green turtles in the Lake Worth Lagoon also shows an increasing trend over the period of 2005 - 2013. The mean severity score for LWL green turtles over the study period was 2.15, higher than mean severity scores in either the Indian River Lagoon (1.63) or the nearshore reef near Sebastian Inlet, FL (1.05; Hirama and Ehrhart 2007). Long-term monitoring of both incidence and severity of FP in Florida developmental habitats would provide valuable information for management and conservation. Green turtles may be thought of as analogous to canaries in a coal mine, providing early warning of degradation in the environment. A recovering Atlantic green turtle population may begin to place additional demands on the supply of appropriate developmental habitat in Florida waters, while at the same time human population growth and climate change are impacting those habitats. Basic information on the demography of green turtle populations in a wide range of Florida developmental habitats will better inform conservation and management decisions.

Acknowledgements This work was performed under protected species research permits from the State of Florida (Florida Fish and Wildlife Conservation Commission Marine Turtle Permit TP- 125) and the National Marine Fisheries Service (permit # 14508). Funding for this project was provided by the Florida Sea Turtle Grants Program with revenue from the Florida sea turtle license plate and from the Palm Beach County Board of County Commissioners. We thank the staff of the

24 Florida Scientist 79(1) 2016 ß Florida Academy of Sciences Lake Worth Lagoon green turtles Gorham et al.

Palm Beach County Department of Environmental Resource Management, particularly Paul Davis and Jacey Biery, for their support of the project and assistance in the field.

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Submitted: April 29, 2015 Accepted: October 30, 2015

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