The green turtle, Chelonia mydas, is a circumglobal species that exhibits several important developmental or ontogenetic shifts throughout its life history. The first major shift occurs when juvenile turtles migrate from pelagic habitat, where they forage as omnivores, to coastal neritic habitat, where they become primarily herbivores, foraging on algae and seagrass. Anecdotal evidence and gut-content analyses suggest that juvenile green turtles in south Texas bays, such as the lower Laguna Madre and Aransas Bay, undergo an additional ontogenetic shift during this important life history stage. Evidence from stable isotope analysis (SIA) of scute tissues of green turtles from Texas' lower Laguna Madre and Aransas Bay supports an intermediate stage between this species' shift from pelagic waters to seagrass beds in neritic waters; this additional shift comprises an initial recruitment of post-pelagic juveniles to jetty habitat located on the channel passes Gulf-ward of adjacent bays before subsequently recruiting to seagrass beds in these bays. Examination of stable carbon ([delta]¹³C) and nitrogen ([delta]¹⁵N) isotopes in microlayers of scute tissue from several size classes of green turtles from the lower Laguna Madre and Aransas Bay was used to confirm the occurrence of two ontogenetic shifts. Smaller green turtles (< 35 cm SCL) exhibited more depleted [delta]¹³C signatures and more enriched [delta]¹⁵N signatures, consistent with jetty habitat, compared to those of larger counterparts (> 45 cm SCL) that displayed enriched [delta]¹³C signatures and depleted ¹⁵N signatures, consistent with seagrass habitat. Changes in the isotopic composition between these size classes indicate distinct shifts in diet. Post-pelagic juveniles first recruit to jetty habitat and forage primarily on algae, before subsequently shifting to seagrass beds and foraging primarily on seagrass. These findings indicate the use of a characteristic sequence of distinct habitats by multiple life history stages of green turtles in Texas bays, a conclusion with broad management implications for this endangered species.

Loggerheads (Caretta caretta) are listed as Threatened and green turtles (Chelonia mydas) are listed as Endangered under the United States Endangered Species Act. While green turtle nest production in Florida has increased markedly in recent years, loggerhead nest production has followed a more tenuous path. Reasons for these differences are unknown. Limited demographic information is available for these species of conservation concern. I used Barker models, which incorporated mark-recapture, live-resight and dead recovery data, implemented in Program MARK. These models were used to estimate apparent survival for immature loggerhead (

Seagrass is a valuable and important habitat, providing services such as coastal protection, supporting fisheries, and carbon sequestration. However, it is challenging to map accurately, as remote sensing has limits to how deep in the water column it can penetrate, and uncertainties such as distinguishing between algae and seagrass. Seagrass can exist at depths of theoretically 90 m deep in ultraoligotrophic waters, meaning that there is much of this habitat that cannot be mapped by remote sensing. Green turtles are an ideal candidate to help find seagrass blue carbon resources in the Red Sea. They go through an ontogenetic dietary shift to become almost completely herbivorous, and have a high fidelity to foraging sites. In this study we aim to assess the use of green turtles Chelonia mydas in discovering seagrass blue carbon. We use telemetry from 53 turtles tagged over 2018, 2019, and 2021 to map their foraging areas. 50 out of the 53 (94.34%) foraging sites had not been visited by previous seagrass studies in the Red Sea. We visited 18 locations in 14 of these foraging sites to ground truth them, and all 14 foraging sites (100%) had seagrass present. Comparatively, 18 out of 30 sites where seagrass was indicated by the remote sensing-based Allen Coral Atlas showed no seagrass. The turtles were seen to favour travelling shorter distances, thus it will be necessary to expand the area of tagging in order to achieve complete coverage of the Red Sea. Approximately 1/3 of the visited sites were deeper than 8 m, and so out of range of remote sensing, showing that considerable blue carbon resources may be discovered with the use of turtles. Samples were taken for carbon stock estimation from the ground truthed sites. A mean carbon stock of 4.89 ± 0.83 kg Corg m-2 was estimated for 1 m depth sediment. In the future it is important to develop methods for mapping the surface areas of the deep and inaccessible seagrass habitats that the turtles discover.

Climate change is threatening biodiversity, causing populations and species to adapt, or otherwise, become extinct. Sea turtles have survived dramatic climate changes in the past, however, due to a history of intense human exploitation, and the current anthropogenic threats, their current resilience may be jeopardized. The main pursuits of this thesis were to i) evaluate the resistance of green turtles to predicted climate change impacts, using a globally significant rookery, in Poilão, Guinea-Bissau, as a case study; and ii) assess key population parameters to inform the conservation management of this resource. As the work developed I additionally had the opportunity to study the dynamics of an emerging disease in a juvenile foraging aggregation from Puerto Rico, which contributed to a broader understanding of resilience in this species. Specifically, I investigate the nest site selection behaviour of green turtles, their nesting environment, and the outcomes for their offspring, at Poilão, and apply this information to infer on the resilience of this population under future scenarios of climate change. I explore the connectivity established by the dispersal of post-hatchlings from Poilão, followed by their recruitment to foraging grounds, to set the geographical context of this major population. Lastly, I model the dynamics of Fibropapillomatosis, which affects juvenile green turtles globally, and examine the potential for disease recovery. The green turtle rookery in Poilão shows some resilience to expected climate change impacts. This significant population likely contributes to all juvenile foraging aggregations along the west coast of Africa, and to some extent to those in South America. Currently, green turtles are capable of recovery from Fibropapillomatosis, however, the incidence of disease may be enhanced by climate change.

Marine turtle reproductive success is strongly correlated with the stability and quality of the nesting environment. Because females show fidelity to key nesting beaches, the management and physical characteristics of these beaches directly affect future generations of marine turtles and may be essential for the recovery of these threatened and endangered species. The impacts of beach restoration on loggerhead turtles (Caretta caretta) and on green turtles (Chelonia mydas) were investigated. Previous studies concerning beach nourishment projects have focused on loggerhead turtles. I compared data between nourished and non-nourished areas and between loggerhead and green turtles. I found, at one season post-nourishment, negative effects on nesting success and no significant effect on reproductive success for both loggerheads and established the same relationships with green turtles. Physical attributes of the fill sand, which did not facilitate acute scarp formation or severe compaction, did not physically impede turtles in their attempts to nest. Instead, the decrease in nesting success was attributed to an absence of abiotic and or biotic factors that cue nesting behavior. The increase in loggerhead nesting success rates during the second season post-nourishment was attributed to the equilibration process of the seaward crest of the berm. After the beach was restored, both species of turtles placed nests significantly farther from the water in the nourished area than in the non-nourished area. Green turtles nested on or near the dune and loggerheads nested on the seaward crest of the berm. The tendency of loggerheads to nest closer to the water resulted in more loggerhead than green turtle nests being "washed out" by erosion during the equilibration process. There was a significant increase in hatching success only for loggerheads when wash outs were excluded, thus illustrating the importance of nest placement and the detrimental effects of the equilibration process to the reproductive success of loggerheads. A decrease in reproductive output occurred during the first season post-nourishment. The reduction in the estimated total number of hatchlings produced (reproductive output) was a consequence of decreased nesting success lowering nest numbers. This reduction demonstrates that, regardless of similar reproductive success rates, marine turtles incurred net losses during the first season following nourishment. These results further reveal the impacts of decreased nesting success and the importance of minimizing excessive non-nesting emergences associated with beach nourishment.

<p>This study monitored daily and seasonal locations of juvenile green turtles in three coastal bays of northwest Costa Rica, determining their home ranges and assessing their habitat use. My objective was to produce insights which might help future Pacific Ocean green turtle conservation efforts.</p> <p>I tracked 14 juvenile green turtles for 51-629 days using acoustic transmitters (VECOM v16) and 12 acoustic receivers (VECOM VR2Tx and VR2W) in 5 study area habitats: sandy areas, reef patches, macroalgae, rocky reefs, and mangroves. I divided these 14 turtles into large (equal to or larger than 65 cm CCL) and small (smaller than 65 cm CCL) size classes so I could highlight any changes as they grew toward adulthood. </p> <p>Both the large and small size turtles used habitats differently during the dry and rainy seasons. During the dry season, the large juveniles had a High Detection Rate (HDR) of 40% in the macroalgae area. During the rainy season, their HDR was 33% in the reef patch area. The small juveniles had their HDR in the reef patch area during both seasons: 33% in the dry season and 43% in the rainy season. The mean home range for the 14 turtles was 1.96 km²; their core use area was 0.19 km2. I saw no connection between body size and home range. The HDR findings suggest that juvenile green turtles preferred reef patches, rocky reefs, and macroalgae habitat types. The large juveniles prefer vegetation areas more as they grew; similar to that of adult green turtles. Some turtles moved between Matapalito Bay and Santa Elena Bay and along the coast to small bays east of Matapalito Bay. Travel speed varied between 0.23 km/h and 12.90 km/h with a mean of 1.57 km/h.  </p> <p>My findings highlight certain habitat areas preferred by Pacific juvenile green turtles. This can guide conservationists in identifying and protecting similar habitats in other inshore Pacific bays in Central America. By protecting habitat areas that are important for juvenile green turtles, this can help rebuild the green turtle population in the Pacific Ocean. </p>

Causes of morbidity and mortality were investigated for 108 green turtles (Chelonia mydas) stranded in south-east Queensland between 1990 and 1996. This study was undertaken as part of a broader carcass salvage program for south Queensland, and within the context of a population study of C. mydas in the Moreton Bay feeding ground. Accurate pathological characterisation of disease in C. mydas was achieved by detailed necropsy and histological examination. Varied inflammatory responses and degenerative changes were observed in stranded C. mydas. Supportive disciplines of microbiology, parasitology, and clinical chemistry were used to elucidate aetiology and pathogenesis of selected conditions. Heavy metal and pesticide levels were assessed in a sub-sample of turtles. Direct anthropogenic causes (including trauma, foreign body ingestion and drowning) accounted for 34% of mortalities of C. mydas in this study. The majority of the trauma cases were turtles with skull fractures resulting from blunt impacts. The remainder had boat propeller injuries, or miscellaneous trauma. Almost half of the turtles with lethal boat propeller damage had evidence of pre-existing disease which may well have predisposed them to boat strike, emphasising the importance of full necropsy examination, even when the cause of death appears obvious. Fishing line was the only ingested foreign body consistently implicated in the production of fatal intestinal obstruction. Marine turtle fibropapillomatosis, a panzootic viral disease which is considered to involve some indirect anthropogenic factors, accounted for 7% of mortalities. The findings in this study were consistent with much of the previously described pathology of this condition. Naturally-occurring diseases (for which human influences are unknown) accounted for the remaining 59% of strandings. Coccidiosis, caused by Caryospora cheloniae, was recorded for the first time in wild C. mydas. It occurred both as an epizootic (in 1991) and as sporadic cases. A variety of manifestations, including disseminated and enteric forms, were recognised. Infection with a Cryptosporidium-like protozoan appeared to occur concurrently with coccidiosis in one turtle in this study. Attempts to establish experimental coccidial infections in hatchling C. mydas were unsuccessful. Infections with cardiovascular (spirorchid) flukes were almost universal in stranded C. mydas in this study. They ranged from mild, incidental findings (such as occasional fluke vii egg granulomas evident microscopically in otherwise normal tissues) to a variety of severe changes, including thrombosis, which were likely to have produced morbidity. The present study clarified the range of cardiovascular lesions associated with spirorchidiasis, including the sequence of thrombus resolution and exteriorisation from vessels. In some cases spirorchid vasculitis was associated with fatal disseminated bacterial infections. Other sporadic, naturally-occurring diseases included mycotic pneumonia, bacterial meningoencephalitis and a miscellany of gastrointestinal conditions, including chronic intestinal tympany and obstipation, for which the underlying cause could not always be determined. Evidence indicated that gastrointestinal motility in C. mydas was prone to both direct and indirect disturbance and that tympany and obstipation could be final common outcomes of a range of insults. Eighteen abnormally buoyant turtles were examined during this study. The cause could usually be ascribed to an underlying disease, including (in decreasing order of frequency) trapped internal gas, usually intestinal; neurological disease such as traumatic brain injuries; and pulmonary disease. In two cases, no underlying cause was detected. Trace metal (arsenic, cadmium, mercury, selenium and zinc) concentrations were determined in the livers and kidneys of 50 turtles of mixed species (mostly C. mydas). These results were considered to provide baseline data for sea turtles in SE Qld. This study offered the largest dataset available for some metals in C. mydas, and provided evidence of high background levels of cadmium as a normal feature for the species. Some unusual age–related trends in metal accumulation were detected. Concentrations of cadmium, zinc and selenium in the kidney decreased with increasing age, whereas zinc concentrations in the liver tended to increase. Determining the impact of disease on wildlife populations is an increasingly necessary task, which will require multidisciplinary teams. Necropsy surveys like the present study are an essential component of the growing field of conservation medicine. In addition to providing data relevant to management, such as the relative proportions of anthropogenic and naturally-occurring mortalities, necropsy surveys can identify a range of endemic pathogens, and help to collect prevalence data for determining disease impacts at the population level.

Les relations interspécifiques sont un indicateur naturel de l'état de santé d'un écosystème et de son éventuelle évolution. Dans le contexte actuel de changement climatique et d'intensification des activités humaines, nous décrivons, par une approche intégrée, les interactions existant entre les tortues vertes et leurs ressources trophiques, afin de contribuer à la compréhension de la dynamique de la biodiversité marine. La tortue verte est la seule tortue marine herbivore aux stades sub-adulte et adulte. Elle se nourrit principalement sur des herbiers de phanérogames marines et des algueraies en milieu côtier relativement peu profonds et constitue ainsi un modèle privilégié pour étudier l'écologie trophique et fonctionnelle des tortues marines en conditions naturelles. Le travail présenté dans ce manuscrit étudie deux populations de tortues vertes : la première s'alimentant de phanérogames marines sur le site de N'Gouja à Mayotte et la seconde d'algues benthiques sur la côte ouest de l'Ile de La Réunion. A ce stade de l'étude, le système tortues vertes-herbier est le mieux connu. Nous proposons une synthèse des relations existant entre le comportement de plongée et d'alimentation d'individus juvéniles et adultes avec la disponibilité trophique au sein d'un herbier marin plurispécifique. Ceci a été obtenu à partir de systèmes d'acquisition embarqués, d'observation directes de tortues vertes et de relevés phyto-écologiques conventionnels. Par ailleurs, notre étude a permis d'engager le suivi du système tortues vertes – herbier marin de N'Gouja et d'en décrire les premières tendances. En quatre ans, une diminution de près de 80 % de la biomasse végétale du site de N'Gouja accentue la pression d'herbivorie des tortues vertes sur l'herbier. Ce phénomène entraîne l'appauvrissement de la diversité spécifique des phanérogames en faveur des espèces végétales pionnières. La diminution parallèle de l'effectif de la population de tortues vertes du site de N'Gouja suggère un modèle alimentaire basé sur le principe de densité-dépendance. Les conséquences d'une surexploitation de l'herbier par les tortues vertes sont alors en opposition avec celles obtenues suite à la simulation d'une pression d'herbivorie nulle. Nous montrons que sous une pression d'herbivorie modérée, un stade successionel intermédiaire de l'herbier est maintenu et la diversité spécifique est favorisée par la diminution des capacités compétitives des espèces consommées. Il découle ainsi de notre étude des indicateurs du stade phytodynamique d'un herbier plurispécifique et de la pression d'herbivorie exercée par les tortues vertes qui permettent d'envisager les réponses écosystémiques d'un système tel que celui de N'Gouja sous différents scénarios environnementaux. Enfin, dans un cadre plus large, nous posons la question de savoir si l'évolution statutaire de Mayotte peut contribuer à approfondir et pérenniser la protection des tortues marines qui se trouvent sur son territoire. Nous décrivons la départementalisation comme un moyen d'accentuer le processus de clarification du droit applicable à Mayotte et d'assurer des moyens humains, matériels, et financiers nécessaires à la protection de l'environnement. Des recensements aériens réalisés au dessus de la côte ouest de l'île de La Réunion révèlent la présence d'individus sexuellement matures et immatures, dont le nombre augmente depuis 1996. Cette approche nous aura permis d'identifier une fréquentation préférentielle des habitats coralliens et de décrire, à partir d'observations sous-marines parallèles, la côte ouest de l'île comme un site d'alimentation d'individus matures et d'individus en phase de croissance. Ce travail renforce les bases scientifiques nécessaires à la mise en place de stratégies de conservation des tortues marines et de leurs habitats. / Reproduction of sea turtles primarily relies on body reserves stored during the time spent on foraging grounds prior to the nesting season. Accordingly, the investigation of foraging behaviour of sea turtles is critical for better assessing their biology but also for conservation issues of these endangered species. Sea turtles contribute significantly to the consuming biomass of their ecosystem and hence to its functioning, thus providing natural indications of the health of the ecosystem. Yet the trophic ecology of sea turtles is poorly documented because their feeding grounds remain poorly known and for most of them hardly accessible. Among sea turtles the green turtle is the only species where sub-adults and adults are mostly herbivorous feeding on seagrass and algae patches in shallow coastal waters. Such fairly accessible marine ecosystems provide a unique opportunity to investigate sea turtle ecology under natural conditions. The study was conducted in two foraging sites of green turtles located in the south-western Indian Ocean: Mayotte (seagrass meadow) and Reunion Island (algae spots). Thanks to fine-scale sampling of feeding activities, we addressed the lack of research investigating the food requirements and the trophic role of green turtles. To day, feeding activities of green turtles are better known on seagrass. We described the habitat use, the food intake, and the herbivory pressure of green turtles exploiting a multi-sepcies seagrass meadow of Mayotte. In Reunion Island, first results provide some information about the habitat use of green turtles. Such results are paramount for the management and conservation sea turtles and their habitats.