Tropical oceans host a high diversity of species, including large marine consumers. In these oligotrophic ecosystems, oceanic islands often favour the aggregation of species and biomass as they provide feeding opportunities related to the mechanisms of island mass effect. As such, the waters surrounding La Reunion (Southwest Indian Ocean) host seabirds, large pelagic teleosts, elasmobranchs, delphinids and sea turtles. Isotopic niche partitioning and comparison of trophic levels among these species (n = 21) were investigated using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. Overall, δ13C values were highly variable among taxa, indicating that the species exploit multiple foraging habitats along a coast-open ocean gradient. Overlap in δ15N values was limited, except for teleost species, the two species of sea turtles and two species of delphinids, the Indo-pacific bottlenose dolphin (Tursiops aduncus) and the Spinner dolphin (Stellena longirostris). Stable isotope analyses of samples collected over a 9-years period on different tissues with different integration times provide a consistent picture of the structure of the community of large marine vertebrates species around La Reunion and highlight the underlying mechanisms to limit the competition between species. The wide range of isotopic values confirms that large marine vertebrates have different trophic roles in coastal marine food webs around this oceanic island, which limits their potential of competitive interactions for resources.

In marine turtles, the sex of hatchlings is determined by their egg incubation temperature. Global warming may increase the extinction risk by skewing hatchling sex ratios. Assessment of this risk at the population level requires the identification of sex in hatchlings and juveniles. However, available methods are typically lethal, highly invasive, or difficult to conduct at a large scale. Changes in DNA methylation, an epigenetic modification, have been characterized as part of sex differentiation pathways in some species with environmentally determined sex, but so far not in marine turtles. Neither have epigenetic biomarkers for sex been developed into rapid assays suited to research on wildlife. In this study, we aimed to develop a rapid, minimally invasive, and inexpensive method to identify the sex of marine turtles. We used reduced representation bisulfite sequencing DNA methylation data from adult green sea turtle ( Chelonia mydas ) skin biopsies to identify 16 genomic regions exhibiting differential methylation between males and females (adjusted p-value < 0.01). We designed methylation sensitive qPCR assays for these regions and tested their capacity to identify the sex of turtles ranging in age between 3-34 years. The qPCR assay identified the correct sex in turtles > 17 years. However, the sex of younger turtles could not be accurately identified. This suggests the sex differences distinguishable by the assay were adult specific, reflecting the training data on which the sex-specific regions were identified, and likely linked to late-stage ontogenetic changes associated with sexual maturity. Epigenetic biomarkers are a promising tool for wildlife research because they can be minimally invasive and high throughput. Future research into sex-specific differentially methylated regions in hatchlings and juveniles should be based on genome-wide DNA methylation data from a wider age range, which includes hatchlings.

We analyzed plastic debris ingested by loggerheads from bycatch between 2007 and 2021 in the Southwest Indian Ocean (SWIO). We also analyzed plastic debris accumulated on beaches of the east coast of Madagascar as a proxy for ocean plastics to compare the characteristics of beached plastics and plastic ingested by turtles. We conducted a "brand audit" of the plastics to determine their country of origin. An oceanic circulation model was used to identify the most likely sources of plastics in the SWIO. In total, 202 of the 266 loggerheads analyzed had ingested plastics. Plastics categorized as "hard" and "white" were equally dominant in loggerheads and on beaches, suggesting no diet selectivity. Both the brand audit and circulation modeling demonstrated that Southeast Asia is the main source of plastic pollution in the region. This study demonstrates that loggerheads can be used as bioindicators of plastic pollution in the SWIO.

Age is a fundamental life history attribute that is used to understand the dynamics of wild animal populations. Unfortunately, most animals do not have a practical or nonlethal method to determine age. This makes it difficult for wildlife managers to carry out population assessments, particularly for elusive and long-lived fauna such as marine turtles. In this study, we present an epigenetic clock that predicts the age of marine turtles from skin biopsies. The model was developed and validated using DNA from known-age green turtles (Chelonia mydas) from two captive populations, and mark-recapture wild turtles with known time intervals between captures. Our method, based on DNA methylation levels at 18 CpG sites, was highly accurate with a median absolute error of 2.1 years (4.7% of maximum age in data set). This is the first epigenetic clock developed for a reptile and illustrates their broad applicability across a broad variety of vertebrate species. It has the potential to transform marine turtle management through a nonlethal and inexpensive method to provide key life history information.

A free-ranging juvenile hawksbill sea turtle (Eretmochelys imbricata) presented to the rehabilitation centre with a chronic full thickness laceration of the right carpal joint, leaving the distal part of the flipper attached by only 2 cm of soft tissue. Open luxation of the carpal joint was noted on radiographs. Surgical reconstruction was elected despite extensive transection and osteo-articular damage. Soft tissues were debrided and sutured. A cerclage wire was used to improve bone apposition. A type II external skeletal fixator was placed to promote soft tissue healing and pseudojoint formation. The turtle adapted well to the external fixator. Osteolysis was documented on radiographs 4 weeks postoperatively, and lesions improved with florfenicol treatment. The fixator was removed 3.5 months after the procedure. A year postoperatively, the function of the operated limb was normal, and the turtle was released into the ocean.

All sea turtle species are listed on the Red List of the International Union for the Conservation of Nature due to multiple threats. Among these, disease is a frequent cause of stranded sea turtles encountered in rehabilitation centers. Since 2013, we found joint swelling in 13 sea turtles belonging to all four sea turtle species submitted to the Kélonia Sea Turtle Observatory of Reunion Island, France. Affected sea turtles presented with lameness, anorexia, and lethargy. Polyarthritis was radiographically confirmed and lesions were characterized by progressive osteolysis of bones surrounding joints. Anterior flippers were affected in all cases and posterior flippers were also involved in some cases. We isolated several bacterial agents from blood and synovial fluid. We attempted a collective treatment with injectable florfenicol, based on sensitivity results, which was continued for 4 wk and then as needed based on radiographic evolution of the lesions. Radiographic stabilization of the lesions occurred in nine of 13 cases. We reviewed environmental conditions and optimized them to minimize stress that could predispose these rehabilitated sea turtles to opportunistic infections. Handling techniques used to move sea turtles were also improved. While we can make no conclusion regarding the cause of polyarthritis in this population of sea turtles, we successfully managed this poorly described problem in a rehabilitation setting.

Photographic identification (photo-ID) has been increasingly used as a reliable tool to track individuals over time, which provides essential knowledge on a species' population dynamics. For photo-ID to work, natural markings must be individual-specific and stable over time. In sea turtle research, the use of facial scale patterns has been proposed and tested as a reliable means for individual recognition. Nevertheless, as sea turtles are migratory and long-lived individuals, the stability of those patterns over long periods of time is yet to be confirmed to validate this method. Stability of facial scale patterns was evaluated on green sea turtles, Chelonia mydas, sighted and photographed in coastal waters of Reunion Island (21°06 S, 55°36 E) or reared in captivity. From 53 free-ranging individuals previously identified, 90 head profiles were selected based on the photographic quality and the distinctiveness of facial scale patterns. The time interval between two sightings of a same individual ranged from 2 (738d) to 11years (3954d). Additionally, facial scale patterns of captive green turtles from two different age groups were compared: (1) from adult-sized individuals reared in captivity (n=13) and (2) from hatchlings and then at later developmental stages (until 1800d) to assess the stability of facial scale patterns throughout early juvenile development (n=16). In both the free-ranging and captive-reared groups, there were no significant changes in facial scale patterns over time. Conversely, changes in pigmentation were observed in free-ranging turtles at successive sightings and in captive-reared turtles at different developmental stages. These results on the stability of facial scale patterns over time, combined with previous findings on the uniqueness of patterns between individual green turtles, validate the method of using facial scale patterns as a long-term identification tool for green turtles. Nonetheless, the variability of pigmentation patterns should be kept in mind when using photo-identification on sea turtle species.