Surface microbiota of Mediterranean loggerhead sea turtles unravelled by 16S and 18S amplicon sequencing

Loggerhead sea turtle is considered a keystone species with major ecological role in Mediterranean marine environment. As with other wild reptiles, their outer microbiome is rarely studied. Although there are several studies on sea turtle’s macro-epibionts and endo-microbiota, there has been little research on epibiotic microbiota associated with sea turtles’ skin and carapace. Therefore, we provide the first identification of combined epibiotic eukaryotic and prokaryotic microbiota on Mediterranean loggerhead sea turtles. In this study, we sampled skin and carapace of 26 loggerheads from the Mediterranean Sea during 2018 and 2019. To investigate the overall microbial diversity and composition, amplicon sequencing of 16S and 18S rRNA genes was performed. We found that the Mediterranean loggerhead sea turtle epibiotic microbiota is a reservoir of a vast variety of microbial species. Microbial communities between samples mostly varied by different locations and seas, while within prokaryotic communities’ significant difference was observed between sampled body sites (carapace vs. skin). In terms of relative abundance, Proteobacteria and Bacteroidota were the most represented phyla within prokaryotes, while Alveolata and Stramenopiles thrived among eukaryotes. This study, besides providing a first survey of microbial eukaryotes on loggerheads via metabarcoding, identifies fine differences within both prokaryotic and eukaryotic microbial communities that seem to reflect the host anatomy and habitat. Multi-domain epi-microbiome surveys provide additional layers of information that are complementary with previous morphological studies and enable better understanding of the biology and ecology of these vulnerable marine reptiles. ### Competing Interest Statement The authors have declared no competing interest.