Using Environmental DNA Surveys to Assess Green Sea Turtle (Chelonia mydas) Presence in Mississippi and Louisiana

<p>The green sea turtle (<em>Chelonia mydas</em>) 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 <em>C. mydas</em> occur in these areas, yet the comprehensive spatial and temporal presence of this species is not well understood. Traditional methods of studying <em>C. mydas</em> 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 <em>C. mydas</em> 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 <em>in-vitro</em> with genomic DNA and <em>in-situ</em> via a tank experiment with a <em>C. mydas</em> individual. Locations of <em>C. mydas</em> 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 <em>in-situ</em> sample met all three positive criteria. The rare occurrence of <em>C. mydas</em> in Mississippi and Louisiana combined with the low shed rate of reptiles supports the negative eDNA results of this study. While <em>C. mydas</em> strandings were reported in Mississippi during eDNA sampling times, strandings were too far from sampling sites to be detected. Future use of the ddPCR^™ <em>C. mydas</em> assay should consider passive sampling alongside aerial surveys and statistical modeling.</p>

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Masters Thesis

Year dc:date.available

2025

Author dc:creator

• Humphreys, Emma M

Contributors dc:contributor

• Dr. Nicole Phillips
• Dr. Lisa Komoroske
• Dr. Melissa Cook

• green sea turtle
• eDNA
• stranding
• ddPCR
• Mississippi
• Louisiana
• Marine Biology
• Molecular Genetics
• Terrestrial and Aquatic Ecology

Repository record dc:identifier

https://aquila.usm.edu/masters_theses/1155

OAI identifier oai:identifier

oai:aquila.usm.edu:masters_theses-2245