Genetic Identity and Diversity of Loggerhead Sea Turtles in the Central Mediterranean Sea

Background: The conservation of loggerhead sea turtles (Caretta caretta) in the central Mediterranean benefits from an in-depth understanding of its population genetic structure and diversity. Methods: This study, therefore, investigates C. caretta in Maltese waters by genetically analysing 63 specimens collected through strandings and in-water sampling, using mitochondrial DNA control region and microsatellites. Additionally, the two nests detected in Malta in 2023 were analysed for the same markers. Results: Mitochondrial data identified 10 haplotypes, with mixed stock analyses tracing 87.5% of the specimens to Mediterranean origins, primarily from Libyan rookeries, with contributions from Lebanon, Israel and Turkey. Three Atlantic haplotypes were identified in six specimens, with CC-A17.1 linking central Mediterranean foraging individuals to rookeries in Cape Verde. Five of these six Atlantic haplotype records were from recently sampled individuals (2022-2023), possibly indicating a recent eastward expansion of Atlantic haplotypes into the Mediterranean. Bayesian clustering (K = 2) of microsatellite data using haplotypes as priori revealed similar proportions for clusters across most specimens, except for three specimens with Atlantic haplotypes CC-A1.1 and CC-A1.3, which exhibited distinct patterns. The two nests examined here displayed Mediterranean haplotypes, with nuclear DNA matching the predominant Mediterranean profiles found in foraging individuals, suggesting that local clutches originated from Mediterranean parents. Conclusions: Increasing nesting activity on Maltese beaches and this archipelago's geographical position highlight the need for ongoing genetic monitoring to track changes in genetic diversity and develop conservation strategies that support the effective protection of this species and its habitats.