OCEANHITCH · Oceanic hitchhikers: epizoic diatoms as health indicators of sea turtles

Diatoms, unicellular algae, grow on a wide range of submerged surfaces. However, some diatom species and even entire genera (Chelonicola, Poulinea, Tursiocola) are highly specialised and thrive exclusively on the surface of glabrous aquatic animals (sea turtles, sea snakes, cetaceans, manatees). These taxa tolerate frequent environmental changes related to the biology and lifestyle of their hosts but, in nature, cannot survive without them. We will use sea turtle biofilm samples to investigate whether this unique association makes epizoic diatoms suitable indicators of their hosts health. This proposition is based on our preliminary observations that in sea turtles, the relative abundance of epizoic diatoms is high (>35 %) on generally healthy individuals, but rarely exceeds 10 % in visibly debilitated animals. First, skin and carapace biofilm samples will be collected from 350 presumably healthy and 175 visibly debilitated sea turtles from three distant geographic regions (WP1). Second, the collected material will be used to determine diatom species composition based on molecular (metabarcoding) and morphological approaches (WP2). We will develop an automated diatom identification and counting method using deep learning technology to further simplify the morphology-based assessment of diatom community composition. Third, the relative abundance of specialist sea turtle diatoms will be assessed and tested for correlation with standard sea turtle health indices collected for every sampled animal (WP3). Diatom indices of sea turtle health will be designed should such correlation be found. Finally, we will test the newly developed tools in a zoo setting, where they will be used to gain insights into the overall health and wellbeing of captive sea turtles and other aquatic vertebrates (WP4). The proposed studies will develop novel, non-invasive, cost-efficient and straightforward diatom-based tools for sea turtle monitoring and the assessment of marine ecosystem health.