Juvenile Green Turtles Research Articles

Sensitivity of turtles to anticoagulant rodenticides: Risk assessment for green sea turtles (Chelonia mydas) in the Ogasawara Islands and comparison of warfarin sensitivity among turtle species

Although anticoagulant rodenticides (ARs) are effectively used for the control of invasive rodents, nontarget species are also frequently exposed to ARs and secondary poisonings occur widely. However, little data is available on the effects of ARs, especially on marine organisms. To evaluate the effects of ARs on marine wildlife, we chose green sea turtles (Chelonia mydas), which are one of the most common marine organisms around the Ogasawara islands, as our primary study species. The sensitivity of these turtles to ARs was assessed using both in vivo and in vitro approaches. We administered 4 mg/kg of warfarin sodium either orally or intravenously to juvenile green sea turtles. The turtles exhibited slow pharmacokinetics, and prolongation of prothrombin time (PT) was observed only with intravenous warfarin administration. We also conducted an in vitro investigation using liver microsomes from green sea turtles, and two other turtle species (softshell turtle and red-eared slider) and rats. The cytochrome P450 metabolic activity in the liver of green sea turtles was lower than in rats. Additionally, vitamin K epoxide reductase (VKOR), which is the target enzyme of ARs, was inhibited by warfarin in the turtles at lower concentration levels than in rats. These data indicate that turtles may be more sensitive to ARs than rats. We expect that these findings will be helpful for sea turtle conservation following accidental AR-broadcast incidents.

Serotonin-manipulated juvenile green sea turtles Chelonia mydas exhibit reduced fear-like behaviour

Animals display fear-like behaviours before escaping from predators. This response triggers both behavioural and physiological changes in multiple body systems, allowing animals to escape danger and ensure survival. Fear-like behaviour is modulated by the serotonergic system in the brain of vertebrates, which shapes social behaviour and cooperative behaviours. Using fluoxetine (FLX), a common pharmaceutical that alters the levels of serotonin in the brain, we aimed to clarify whether the same is true in solitary animals like green turtles Chelonia mydas. Green turtles exhibit individual differences in their response to risk. If fear-related behaviours are regulated by the serotonin system in turtles, the fear-like responses of individuals injected with FLX could change. We therefore assessed the effect of FLX injection on the behavioural responses to a fear stimulus in 9 wild juvenile green turtles in an aquarium setting. We inserted a hand net as a stimulus into the aquarium (within a designated inspection zone) to elicit a fear-like behaviour and measured the time that turtles spent in this zone. All turtles exhibited fear-like behaviour and fled from the stimulus prior to any injection treatment. Turtles with control injection (no FLX) also fled and avoided the inspection zone with the fear stimulus. FLX injection appeared to reduce the turtles’ fear of the stimulus: The total time turtles injected with FLX spent in the inspection zone was significantly longer than for turtles that received a control medium injection. Control turtles fled from the stimulus and were initially vigilant and avoided the area with the stimulus, but then moved throughout the aquarium, including the inspection zone. These data suggest that fear-like behaviour is modulated by the serotonin-mediated nerve system in juvenile green turtles.

Trophic ecology of juvenile green turtles in the Southwestern Atlantic Ocean: insights from stable isotope analysis and niche modelling

Determining the diet and trophic status of endangered species can provide insights into their key habitats and predator-prey relationships, both essential for conservation. Integrating dietary information from live-captured and dead-stranded turtles from the same area can also shed light on their ecological diversity. Here, diet intake and prey diversity are determined for juvenile green turtles Chelonia mydas from a mixed stock foraging aggregation in the Southwestern Atlantic Ocean (SWAO) using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. Skin samples were collected from 117 live-captured (LC) turtles and 66 dead-stranded (DS) individuals along the Paraná coast, southern Brazil. Bayesian isotope ellipse space was determined using the program SIBER. A larger isotopic niche space was found among DS turtles, probably because it included long-term resident turtles and recently settled individuals, the latter of which presented low δ15N values compared to larger putative local turtles. The Bayesian stable isotope mixing model MixSIAR was used to determine dietary contributions, using isotopic values of putative prey. MixSIAR results indicated invertebrates and macroalgae as primary prey groups, showing the omnivorous strategy of green turtles in the SWAO. Moreover, many of the smallest DS turtles had δ15N values suggestive of seagrass consumption, which may reflect individual- and/or life-stage-based diet variability. These findings underscore the value of integrating stranding monitoring protocols with research on live green turtles to evaluate habitat use and diet intake assembled in a neritic foraging area. The data also further knowledge about green turtle foraging ecology and are relevant for species and habitat conservation throughout the SWAO.

Feeding ecology of juvenile green turtles in food-poor habitats of the Persian Gulf

The Persian Gulf hosts marine mega-herbivores that forage in its coastal habitats. Some areas, mainly along its southern coast, contain abundant benthic plants; however, marine plant resources are limited throughout most of this warm sea, which presents nutritional challenges for large herbivores. We measured curved carapace length (CCL) for 102 green turtles (Chelonia mydas) from foraging grounds with relatively limited plant resources surrounding Qeshm Island at the eastern Persian Gulf. The mean CCL was 41.8 cm (SE = ± 1.3 cm; range = 18.5–99), and 93 turtles (91%) had CCL < 65 cm, indicating the area is primarily a juvenile developmental habitat. To study feeding ecology of green turtles in the area, we analyzed esophageal lavage samples from 36 individuals captured in muddy-bottom (n = 23) and sandy/rocky-bottom (n = 13) habitats. Diet data showed a generalist foraging population with dietary niche variation among individuals that targeted mixtures of macroalgae, seagrasses and mangrove. Green turtles showed a slight preference for green algae (Ulva sp.) at both sites. The mean Fulton’s body condition index for juvenile turtles was 1.14 (SE = ± 0.03; n = 72), which is comparable to values reported elsewhere, and indicates that these turtles were not under-nourished. This is intriguing in light of the paucity of local food resources, and perhaps due to the absence of large sub-adults and adults with higher food demand, and/or individual dietary niche variation among resident turtles, both of which reduce competition among local green turtles for the region’s available resources.

Approaching a Tipping Point? Herbivore Carrying Capacity Estimates in a Rapidly Changing, Seagrass-Dominated Florida Bay

Herbivory is a key structuring force that can have negative, positive, or mixed impacts on seagrasses. The identity and abundance of herbivores, as well environmental conditions such as solar insulation, can influence the impacts of herbivory. To understand the impact of herbivores on turtlegrass in warm, temperate St. Joseph Bay (SJB) in the northeastern Gulf of Mexico, we estimated densities of the most common herbivores: variegated sea urchins and green turtles. We also estimated SJB’s herbivore carrying capacities by estimating annual average turtlegrass production and variegated urchin consumption rates and by using previously calculated juvenile green turtle consumption rates and seagrass area. During summer, turtlegrass exhibited compensatory growth due to urchin herbivory, but during winter, turtlegrass growth was negatively affected by urchin grazing. Given our calculated annual turtlegrass production, urchin ingestion rates, and the average urchin density of 5.89 ± 0.09 (SE) urchins ha−1, the turtlegrass production not consumed by urchins can sustain 278.0 juveniles ha−1, or about 556,010 turtles, putting current average green turtle abundance of 26 ± 3.7 individuals ha−1 at 4.0–14.6% of carrying capacity. Previous work in this system has shown that simulated turtle herbivory can reduce turtlegrass productivity—with this potential reduction in production, SJB could not sustain a green turtle population at current urchin densities. Given the rapid global green turtle increase, evaluating densities and future carrying capacities of herbivores in higher latitude seagrass pastures is critical for updating and achieving recovery goals for both green turtles and globally declining seagrass meadows.

Influence of exercise and fasting on blood parameters in juvenile green turtles (Chelonia mydas): implications for health assessments

This study investigated the influence of exercise and fasting state on haematologic and biochemical parameters in juvenile green turtles (Chelonia mydas). Animals were divided into two groups; one group was fasted for 72 h and one group was fed 1 h prior to exercise. Exercise was induced by repeated righting reflexes and blood values were measured prior to and post-exercise. Prior to exercise, fasted animals showed significantly decreased levels of urea, pH, PVCO2 and HCO3 - and significant increases in Cl- and PVO2, compared to fed animals and fasted animals had significantly poorer exercise performance. Following exercise both fasted and fed animals had significant increases in Na+, K+, Cl-, PVCO2, PVO2, urea and lactate and significant decreases in pH and HCO3 -. The magnitude of increase in lactate levels was significantly less in fasted animals. Prior to exercise, a significant correlation was calculated in fasted animals between pH and HCO3 -. Following exercise, significant correlations were calculated in fed animals between pH and HCO3 -, PVCO2 and lactate, and between pH and HCO3 - in fasted animals. These results show that analytical method, fasting state and the physiologic changes induced during the intense exercise can affect haematologic and biochemical analytes and these factors should be considered when interpreting results from health assessment of wild animals.

Evaluating different spatial scales of forage item availability to determine diet selection of juvenile green turtles (Chelonia mydas)

Diet selection by a species is determined by comparing the consumption (i.e., use) and abundance (i.e., availability) of prey within their area of occupancy. Because individuals commonly use only a portion of habitat available to them (e.g., a 10-ha home range within a 1000-ha foraging habitat), it is important to quantify forage availability within individuals’ home ranges and core areas, and include these availabilities when calculating diet selection. However, studies of diet selection often consider prey availability across the entire foraging habitat of a species and not within individual home ranges/core areas. Here, we explore how spatial variability in prey availability may influence the results of diet selection for juvenile green turtles, Chelonia mydas, foraging in Bimini, Bahamas. Stable isotope analysis was used to determine prey use and satellite telemetry to infer movements and forage availability for each turtle. Forage availability was assessed at three spatial scales: (1) the full extent of the foraging area (2) across each respective individual’s 95% utilization distribution (UD), or home ranges, and (3) across each individual’s 50% UD, or core areas. Further, we compared potential differences in diet selection by using three selection indices (Ivlev’s, Johnson’s and Chesson’s). Diet selection results varied among individuals and were influenced by the spatial scale of forage items available and the index used. Diet selection variability was observed at various spatial scales and in all indices. Our results highlight the need for careful consideration of the diet selection index and the spatial scale at which prey/forage availability is considered when determining a species’ diet selection. Selecting a more sensitive index will help identify priority resources and/or habitats that are important to species, which in turn carries conservation and management implications.

PLASMA BIOCHEMISTRY PROFILES OF JUVENILE GREEN TURTLES (CHELONIA MYDAS) FROM THE BAHAMAS WITH A POTENTIAL INFLUENCE OF DIET.

Plasma biochemistry profiles aid health assessment of marine turtles, but knowledge of the influence of regional biological factors (e.g., habitat, diet) on marine turtle blood plasma values is limited. To investigate the influence of diet on plasma biochemistry values in juvenile green turtles (Chelonia mydas), we used carbon and nitrogen stable isotopes to provide a quantitative estimate of forage items in green turtles feeding at two distinct areas (Bonefish Hole and South Flats) in Bimini, Bahamas. Plasma samples were obtained from 13 turtles in Bonefish Hole (a mangrove tidal estuary) and 15 turtles in South Flats (an open water seagrass bed) in 2018. All turtles appeared outwardly healthy. Sessile filter feeders contributed the largest proportion of diet in Bonefish Hole, and seagrass contributed the highest proportion of diet in South Flats. Turtles at Bonefish Hole presented significantly lower cholesterol, total protein, phosphorus, triglycerides, and aspartate transaminase compared to South Flats. Across all turtles, those feeding primarily on red algae presented the highest uric acid and alkaline phosphatase, and turtles with a seagrass-dominated diet had the highest cholesterol. Understanding dietary influence on plasma biochemistry may help explain variances seen in local health and nutritional evaluations, and the trends reported can aid the interpretation of plasma analyte values in marine turtles.

Physiological effects of incidental capture and seasonality on juvenile green sea turtles (Chelonia mydas)

Fishery is one of the main threats faced by sea turtles. However, literature relating to the physiological effects of incidental capture by fishing gears is scarce. The aim of this study is to establish blood reference values for a juvenile population of Chelonia mydas, from Ubatuba- Brazil, and compare them with incidental captured animals by fisheries in the same area, considering seasonal variation. Animals were captured during summer and winter, from direct capture (diving) and incidental capture (pound net and gillnet). Blood samples were collected from 96 healthy green sea turtles and, were analyzed for determining levels of glucose, lactate, total protein, uric acid, albumin, total lipids, triglycerides, VLDL cholesterol, total cholesterol, corticosterone concentrations, total antioxidant capacity, and lipid peroxidation. Corticosterone concentrations were significantly lower in animals captured by diving than in those captured by pound net and gillnet and were thought tso more closely represent baseline levels. Thus, the values found in animals captured by diving were used to establish reference values for this population. Turtles captured in summer had a significant increase in blood levels of glucose, total protein, uric acid, albumin, TBARS, and TEAC; and a decrease in total lipids compared with turtles captured in winter. Although pound nets are considered a low impact fishery to the turtles due to the low mortality rates, seven out of twelve parameters differed significantly from baseline values established for the species. Entanglement in gillnets caused greater perturbations than pound net and all parameters analyzed were significantly different from the reference values. These data indicate that incidental capture causes substantial alterations in health parameters of sea turtles. The results obtained in this study would help in future rehabilitation programs of sea turtles that are captured by fisheries. Additionally, reference values can be used for future comparisons with populations of the same species and with unhealthy and stressed individuals.

Movements of Juvenile Green Turtles (Chelonia mydas) in the Nearshore Waters of the Northwestern Gulf of Mexico

Satellite telemetry is a valuable tool for examining long-term, large scale movements of highly migratory species. Tracking data can be used by resource managers to protect habitat and ensure recovery of threatened and endangered species. Few tracking studies have focused on habitat use patterns of juvenile, neritic stage turtles. Satellite tracking surveys were conducted to assess juvenile green turtle movements in the northwestern Gulf of Mexico during 2006-2010. Fifteen turtles were equipped with platform terminal transmitters (PTT; 3 rehabilitated, 12 wild). Mean track duration was 129 days (range: 16-344 days). A hierarchical switching state-space model (hSSM) was applied to extrapolate population level foraging/resident versus migratory movements. All turtles displayed residency in Texas bays during summer months (March-November) while 5 individuals exhibited seasonal migrations into Mexican waters following passage of strong cold fronts in December and January. Winter (e.g. Mexico) versus summer (e.g. Texas) core areas were not significantly different. Winter 95% contours were significantly larger than summer (summer: 125.4 ± 47.5 km2, n = 15; winter: 274.4 ± 252.9 km2, n = 5). Space-time hot spot analysis provided a new and unique approach for conducting spatiotemporal cluster analysis, and was applied to migratory turtles to determine monthly changes in distribution and habitat associations. Changes in hot spots over time were detected within the lower regions of the Laguna Madre with punctuated intervals of hot spot activity. Upper regions of the Laguna Madre were identified as new hot spots in the later part of the year (e.g. Fall/Winter). Within core areas in Texas, seagrasses comprised an average density of 32.4% while 87.5% of the total available seagrass habitat occurred within the 95% KDE contour. Based on PTT and historic tide station surface water temperatures, all turtles tracked over winter migrations and residencies (n = 5) remained within waters > 15°C, suggesting a threshold temperature at which migration behavior may be initiated. Continued recovery of threatened and endangered sea turtle populations depends on a comprehensive examination of patterns in habitat use. These data suggest cooperation between the US and Mexico is needed to protect critical habitat and enhance recovery of this species.

Fibropapillomatosis in free-ranging green sea turtles (Chelonia mydas) off the central coast of Veracruz, Mexico

Fibropapillomatosis (FP) is a neoplastic disease affecting marine turtles around the tropics. Juvenile green sea turtles (Chelonia mydas) seem to be the most affected by the cutaneous tumors, which are not malignant but depending on their number, size, and location, can hamper survival. FP prevalence in sea turtles has increased over the past few decades in areas such as Espírito Santo (Brazil) and Texas (USA), but in Mexico few instances have been documented to date. Here we report a 12.2% FP prevalence in free-ranging turtles captured during 2017–2018 in the Veracruz Reef System National Park, a previously unreported site in Mexico, which is subject to environmental and anthropogenic pressures. Histopathological analysis of one tissue sample revealed tumors were consistent with the characteristics of fibropapillomas. They were not severe (0.01–7.16 cm), but the majority had a verrucous appearance and were mainly found on the flippers and eyes, being potentially detrimental to the health of juvenile turtles. We recommend continued monitoring of this population, and the information provided here can serve as a baseline for future studies in this area of the Gulf of Mexico, where FP had not been

Diagnosis and Management of Marine Debris Ingestion and Entanglement by Using Advanced Imaging and Endoscopy in Sea Turtles

Marine debris ingestion and entanglement have caused morbidity and mortality in multiple marine species, including all seven species of sea turtles. This case series outlines six cases in which advanced imaging modalities were used to diagnose marine debris–induced foreign body obstructions and to aid in the treatment of wounds caused by marine debris entanglement. Prefemoral ultrasonography was used to correctly diagnose a monofilament fishing line linear foreign body obstruction in a juvenile female Kemp's Ridley sea turtle (Lepidochelys kempii) and a subadult female loggerhead sea turtle (Caretta caretta). Administration of iodinated contrast confirmed a complete upper gastrointestinal obstruction in a juvenile green sea turtle (Chelonia mydas). Traditional radiographs were nondiagnostic in all three animals. Barium-impregnated polyethylene spheres were used to identify a partial gastrointestinal foreign body obstruction in a juvenile green sea turtle. Endoscopy was used in multiple cases as both a diagnostic and a therapeutic tool. This case series demonstrates that contrast radiography, ultrasonography, and endoscopy are accurate diagnostic tools for the identification of marine debris–induced foreign body obstructions in sea turtles.

Diatoms on sea turtles and floating debris in the Persian Gulf (Western Asia)

ABSTRACT The current study investigated diatom communities on juvenile green turtles foraging in neritic habitats around five Iranian islands. The primary objectives were to (1) compare species composition, growth form structure, and abundance of diatom communities associated with sea turtles foraging within the restricted boundaries of local feeding pastures, and (2) assess the level of uniqueness of the epizoic diatom flora in comparison with biofilms growing on floating debris. All observations and diatom counts were performed using scanning electron microscopy. The effect of the sampling location was apparent among sea turtle samples and reflected in significantly different cell densities. Diatom abundances were significantly higher on sea turtles (758–1836 cells mm−2) than on floating debris samples (9–189 cells mm−2). Epizoic diatom communities were composed of 20 diatom taxa and dominated by erect forms belonging to the so-called ‘marine gomphonemoids’, Chelonicola and Poulinea, previously reported on sea turtles from other geographical regions. The diatom flora found on floating debris was composed of 21 taxa. Only four taxa, Amphora cf. bigibba, Cocconeis cf. neothumensis var. marina, Psammodictyon constrictum, and Tabularia affinis, were recorded from both sea turtles and floating debris samples, and none of these exceeded 4% of the average relative abundance on the sea turtle carapaces. The study reveals a clear substratum preference in sea turtle-associated diatoms, with no evidence for species turnover across the investigated region over different sampling seasons, thus confirming previous speculations that sea turtle diatom communities would show a high level of uniqueness and stability.

High incidence of sea turtle stranding in the southwestern Atlantic Ocean

AbstractSea turtles are globally threatened due to short- and long-term exposure to anthropogenic activities. Many life-history traits make it difficult to study these species in the wild. Stranding events provide invaluable data to infer key aspects of sea turtle ecology, such as regional occurrence, health status, mortality rates, and potential threats. In this study, we investigate spatial and temporal patterns of sea turtle occurrence and mortality in the southwestern Atlantic Ocean based on a systematic, large-scale survey programme covering 1040 km of coastline during 732 d of two consecutive years. From the 12 571 animals recovered, juvenile green turtles were the most common (90.4%), but four other species were also recorded. A significant non-linear effect of time and space in the number of stranding events was observed. The most parsimonious mixed linear model further indicated that stranding events were influenced by individual (sex, size), health (body condition, pathologies, decomposition), and oceanographic factors (chlorophyll-a, sea surface temperature, salinity, wave height). More than simply describing the spatiotemporal occurrence and aspects of sea turtles’ life history in an otherwise understudied area, this intensive field study provides evidence for relatively high mortality rates—an essential baseline information for guiding conservation efforts.

Diet and recruitment of green turtles in Fiji, South Pacific, inferred from in-water capture and stable isotope analysis

Green turtles Chelonia mydas are listed as Endangered on the IUCN Red List, yet in the South Pacific few conservation-relevant data are available for the species, especially relating to foraging and habitat use. Here, in situ observations and stable isotope analysis (δ13C and δ15N) were used to evaluate green turtle diet and recruitment patterns at Yadua Island and Makogai Island, Fiji. Juvenile green turtles (N = 110) were hand-captured, measured, and sampled. Stable isotope analysis was performed on skin samples and on putative prey items. ‘Resident’ turtles versus ‘recent recruits’ were classified based on their bulk skin tissue isotope values, which were compared with stable isotope values of local prey items and analyzed via cluster analysis. Green turtle diet composition was estimated using MixSIAR, a Bayesian mixing model. Recent recruits were characterized by ‘low δ13C/high δ15N’ values and ranged in curved carapace length (CCL) from 25.5 to 60.0 cm (mean ± SD = 48.5 ± 5.7 cm). Recruitment mostly occurred in summer. Green turtles identified as ‘residents’ had CCLs ranging from 43.5 to 89.0 cm (mean ± SD = 57.4 ± 9.0 cm) and were characterized by ‘high δ13C/low δ15N’ values; mixing model results indicate they fed primarily on invertebrates (40%), fishes (31%), and marine plants (29%). This study confirms the value of seagrass pastures as both an essential habitat and a primary food source for green turtles, and can serve as a baseline for evaluations of natural and anthropogenic changes in local green turtle aggregations.

The impact of fibropapillomatosis on clinical characteristics, blood gas, plasma biochemistry, and hematological profiles in juvenile green turtles ( Chelonia mydas)

Fibropapillomatosis (FP) is a tumor- forming disease that afflicts all marine turtles and is the most common in green turtles (Chelonia mydas). In this study, the morphometric characteristics, blood gas, biochemistry, and hematological profiles of 28 (6 FP-positive and 22 FP-negative) green turtles from the coast of Taiwan were investigated. The results indicated that body weight ( P &lt; 0.001) and curved carapace length (CCL; P &lt; 0.001) in green turtles with FP were significantly higher than in turtles without FP. Furthermore, green turtles with FP had a significantly lower value of hemoglobin (HB; P = 0.010) and packed cell volume (PCV; P = 0.005) than turtles without FP. Blood cell counts of white blood cells (WBC; P = 0.008) and lymphocytes ( P = 0.022) were observed with significant difference; green turtles with FP had lower counts than turtles without FP. In addition, turtles with FP had significantly higher pH ( P = 0.036), base excess in extracellular fluid (BEecf; P = 0.012), bicarbonate (HCO3– ; P = 0.008), and total carbon dioxide (TCO2 ; P = 0.025) values than turtles without FP. The findings of this study provide valuable clinical parameters for the medical care of the species in sea turtle rehabilitation centers and help us to understand the physiological response of green turtles to different tumor-forming conditions.

Trade-offs between nutritional quality and abundance determine diet selection in juvenile benthic green turtles

Herbivores consume foods that are often low in many essential nutrients and high in structural constituents difficult to digest. In this situation, nutritional quality is of paramount relevance for food selection. Neritic juvenile green turtles (Chelonia mydas Linnaeus 1758) in the western South Atlantic are plant-based omnivores relying primarily on red macroalgae, although brown macroalgae are highly available. We investigated the digestibility coefficient and calculated the intake passage time of the red macroalgae Pterocladiella capillacea, the brown macroalgae Sargassum cf. vulgare and the fish Cynoscion leiarchus for juvenile green turtles ranging 42.7–62.0 cm in curved carapace length to test the hypothesis that macroalgae selection is based on nutritional quality. Results indicated that the apparent digestibility coefficient of Pterocladiella capilacea was similar to that of fish fillets (93.9% and 98.9% respectively) and significantly higher than that of the Sargassum cf. vulgare (75.8%), with a significant effect of body weight on the digestibility of certain macronutrients. Those differences arose partially because of the higher apparent digestibility of insoluble fiber of Pterocladiella capillacea compared to that of Sargassum cf. vulgare (95.2% and 84.0% respectively). The intake passage time, at 24.5 °C, was 20.6 ± 3.8 days for the three diets. The overall evidence indicates that foraging on Pterocladiella capillacea is more profitable than foraging on Sargassum cf. vulgare, which may explain the prevalence of red algae in the diet of green turtles off Brazil. Furthermore, evidence indicates that red algae diets are similar to animal diets as far as digestibility is considered, although a higher daily intake is necessary to acquire the same energy intake, due to a lower energy density.

Green turtle herbivory and its effects on the warm, temperate seagrass meadows of St. Joseph Bay, Florida (USA)

Green turtles Chelonia mydas occur sporadically in tropical and subtropical latitudes, but effective conservation efforts are leading to increasing abundances at higher latitudes. One consequence of increased green turtle abundance in some locations has been the overgrazing of seagrasses, their preferred food item. Recent, large increases in juvenile green turtle abundance in the warm temperate northern Gulf of Mexico, especially in the clear waters of St Joseph Bay, FL, make this a prime location to study effects of their feeding activities on the extensive turtlegrass Thalassia testudinum-dominated meadows. Using caging and simulated grazing to quantify green turtle effects, we found that excluding green turtles led to increased Thalassia shoot density, and that simulating turtle grazing resulted in narrowed leaves and decreased turtlegrass productivity. Naturally grazed areas protected from further turtle grazing did not recover after 14 wk of protection. Two years following relaxation of simulated grazing, turtlegrass continued to show residual stress symptoms, with narrower and fewer leaves per shoot than control areas. The future success of sea turtle conservation efforts is critically linked, and dependent on, the protection and sustainability of globally decreasing sea turtle feeding grounds. Thus, continued study of how increasing green turtle populations affect warm temperate turtlegrass meadows will provide important information on how best to manage both turtle and seagrass resources.

Cumulative threats to juvenile green turtles in the coastal waters of southern and southeastern Brazil

Management of marine turtles at broad spatial scales is challenging due to the costs and the logistical feasibility of collecting ecological data and information on multiple threats at this scale. Spatially explicit assessments of the exposure of marine turtles to cumulative threats provides an alternative approach by identifying regions that are impacted by multiple threats at broad scales. To inform future management of juvenile green turtles, Chelonia mydas, off the southern and southeastern Brazilian coast we determined their cumulative exposure to five pertinent anthropogenic activities (marine traffic, port areas, and artisanal, trawl and gillnet fisheries). Information on the spatial distribution of juvenile green turtles was obtained by satellite tagging 14 wild-caught turtles in the Paranagua Estuarine Complex, off the Parana coast in southern Brazil and human activity information was obtained from various databases. This allowed us to identify the anthropogenic activities that provide the greatest risk to marine turtles (artisanal fisheries and marine traffic) and five “hotspot” threat areas that require prompt local management intervention to protect marine turtles in the region. These results can be used to inform on the ground efforts where further impact assessments and management interventions can be prioritized and undertaken.

Seascape Genetics and the Spatial Ecology of Juvenile Green Turtles.

Understanding how ocean currents impact the distribution and connectivity of marine species, provides vital information for the effective conservation management of migratory marine animals. Here, we used a combination of molecular genetics and ocean drift simulations to investigate the spatial ecology of juvenile green turtle (Chelonia mydas) developmental habitats, and assess the role of ocean currents in driving the dispersal of green turtle hatchlings. We analyzed mitochondrial (mt)DNA sequenced from 358 juvenile green turtles, and from eight developmental areas located throughout the Southwest Indian Ocean (SWIO). A mixed stock analysis (MSA) was applied to estimate the level of connectivity between developmental sites and published genetic data from 38 known genetic stocks. The MSA showed that the juvenile turtles at all sites originated almost exclusively from the three known SWIO stocks, with a clear shift in stock contributions between sites in the South and Central Areas. The results from the genetic analysis could largely be explained by regional current patterns, as shown by the results of passive numerical drift simulations linking breeding sites to developmental areas utilized by juvenile green turtles. Integrating genetic and oceanographic data helps researchers to better understand how marine species interact with ocean currents at different stages of their lifecycle, and provides the scientific basis for effective conservation management.