Using Environmental DNA Surveys to Assess Green Sea Turtle (Chelonia mydas) Presence in Mississippi and Louisiana
The green sea turtle (Chelonia mydas) is listed as Endangered on the International Union for the Conservation of Nature Red List of Threatened Species, largely due to anthropogenic impacts. In Mississippi and Louisiana, it is known that C. mydas occur in these areas, yet the comprehensive spatial and temporal presence of this species is not well understood. Traditional methods of studying C. mydas are challenging due to their evasive and migratory nature. Therefore, previously collected environmental DNA (eDNA) water samples (N=112) from Mississippi and Louisiana were screened to assess C. mydas seasonal presence. A species-specific quantitative PCR assay targeting a 130-base pair portion of the mitochondrial 16S ribosomal RNA gene was modified for use on the Droplet Digital™ PCR (ddPCR™) platform. The modified ddPCR™ assay was validated in-vitro with genomic DNA and in-situ via a tank experiment with a C. mydas individual. Locations of C. mydas strandings were also compared to locations of eDNA sampling sites. Zero eDNA field samples met any of the three criteria defined for positive samples, but the in-situ sample met all three positive criteria. The rare occurrence of C. mydas in Mississippi and Louisiana combined with the low shed rate of reptiles supports the negative eDNA results of this study. While C. mydas strandings were reported in Mississippi during eDNA sampling times, strandings were too far from sampling sites to be detected. Future use of the ddPCR™ C. mydas assay should consider passive sampling alongside aerial surveys and statistical modeling.
green sea turtle, eDNA, stranding, ddPCR, Mississippi, Louisiana, Marine Biology, Molecular Genetics, Terrestrial and Aquatic Ecology
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