The contents of the digestive tracts of 21 loggerhead turtles (20 juveniles and 1 adult) collected along the French Mediterranean coast were extracted during necropsies. Hard and soft items were collected and identified by visual observation. A 15-mL sample of the liquid from the rinsed contents of each digestive tract was collected and dietary DNA (dDNA) was extracted and amplified with a 18S universal eukaryotic primers. The obtained reads were compared with taxonomic DNA reference database. Ten taxonomic groups (annelids, cnidarians, crustaceans, echinoderms, fish, insects, molluscs, plants, poriferans and tunicates) were identified with visual observation and eight (ctenophores, cnidarians, crustaceans, fish, molluscs, poriferans, tunicates and plants) with dDNA metabarcoding. Annelids, echinoderms and insects were detected only with visual observation, whereas ctenophores were detected only with dDNA. The two methods were complementary to cover the range of prey, with more soft-bodied organisms detected by dDNA and more hard-shelled organisms detected by visual observation. The increased use of the dDNA metabarcoding method will help compare sea turtle diets of the different stages such as juveniles and adults, or specimens living in different areas, despite the limitations and complexity associated with its use.
Environmental policies, including the European Marine Strategy Framework Directive (MSFD), generally rely on the measurement of indicators to assess the good environmental status (GES) and ensure the protection of marine ecosystems. However, depending on available scientific knowledge and monitoring programs in place, quantitative GES assessments are not always feasible. This is specifically the case for marine turtle species, which are listed under the Biodiversity Descriptor of the MSFD. Relying on an expert consultation, the goal of this study was to develop indicators and a common assessment approach to be employed by European Union Member States to evaluate the status of marine turtle populations in the frame of the MSFD. A dedicated international expert group was created to explore and test potential assessment approaches, in coherence with other environmental policies (i.e. Habitats Directive, OSPAR and Barcelona Conventions). Following a series of workshops, the group provided recommendations for the GES assessment of marine turtles. In particular, indicators and assessment methods were defined, setting a solid basis for future MSFD assessments. Although knowledge gaps remain, data requirements identified in this study will guide future data collection initiatives and inform monitoring programs implemented by EU Member States. Overall this study highlights the value of international collaboration for the conservation of vulnerable species, such as marine turtles.
Climate-induced environmental changes are profoundly impacting marine ecosystems and altering species distribution worldwide. Migratory organisms, including sea turtles, are expected to be particularly sensitive to these variations. Here, we studied changes in the size structure and reproductive activity of loggerhead turtles in the French Mediterranean over 30 years. Overall, there was a significant increase in the size of observed loggerheads between 1990 and 2020. However, this increase was only significant during the breeding/nesting season (May to September) and was driven by the increased presence of adults. Furthermore, nesting activity along the French coast was detected in 2002 for the first time in more than 50 years, and has become frequent after 2014, with nests discovered every year. The number of eggs laid as well as incubation duration and success varied among sites but fell within the range reported at established Mediterranean nesting sites. These observations, along with recent reports of breeding activity and evidence of significant sea surface warming, suggest that the north-western Mediterranean basin has become increasingly suitable to loggerhead turtles. We postulate that this range expansion is the result of climate change and propose that emerging nesting activity in France should be closely monitored and guarded against human activities.
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