An extensive survey on helminth community of Caretta caretta from the neritic feeding grounds of Northwestern Adriatic sea

The opportunistic diet of loggerhead sea turtles, Caretta caretta, their long life-span and migratory behavior contribute to shaping the diversity of the gastrointestinal helminthic community. Heteroxenous helminths are also sentinels of marine environmental health, reflecting any perturbation of the trophic chain and, indirectly, of abiotic components of the ecosystem. With the aim of studying the helminth community of a top predator such as the loggerhead sea turtle C. caretta, parasites were collected from the digestive tract of 157 individuals, stranded dead along NW Adriatic Sea in the period 2009-2023, and morphologically identified. Prevalence, intensity, abundance, relative abundance and importance index were calculated for each taxon. Ontogenetic stages and sex of the hosts, seasons and observation periods were compared to unveil any difference in parasite community structure. Overall, richness and diversity were similar to other neritic grounds in the Mediterranean Sea; helminths from 9 species were recovered, with the trematode Rhytidodes gelatinosus and the nematode Sulcascaris sulcata having the highest importance. Prevalence, intensity and abundance of helminthiases increased significantly in the period 2015-2023. Helminthic community composition and richness generally overlap with what observed in other similar neritic areas, confirming the role of the ecosystem in shaping C. caretta gastrointestinal helminthic community. Increase in prevalence and intensity of helminthiases and composition of the parasitic community throughout the observation period suggests potential alterations within the Adriatic ecosystem in its biotic and/or abiotic components, potentially associated with underlying global climate change.