Ecology and diversity of epizoic diatom communities on marine turtles

Although the first report of epizoic diatoms on cetaceans dates back to 1920, it is only since recent years that the micro-epibiotic communities on sea turtles receive scientific interest. This thesis investigated the epibiotic diatom communities associated with the carapace and skin of loggerhead sea turtles (Caretta caretta) from four geographically different populations: Amvrakikos Bay (Greece), Florida Bay (USA), Adriatic Sea (Croatia) and Kosi Bay (South Africa). Samples were collected using non-harmful methods and analysed using light microscopy and scanning electron microscopy. Five carapace samples from every locality and five skin samples from Greece were analysed. Four hundred-one taxa belonging to 102 genera were observed in 24 samples. Forty-one percent of the taxa was identified to species level. The samples from Florida were the least diverse of the carapace samples. The samples from South Africa had the highest number of taxa and the samples from Greece had the highest Shannon-Wiener diversity index and evenness. The samples from Greece and Croatia showed the highest similarity. The skin samples are less taxon rich than the carapace samples. Detrended correspondence analysis showed clustering, corresponding with the sampling localities. Principal component analysis showed skin and carapace samples clustering separately. Some typical epizoic genera were observed, such as Medlinella, Chelonicola and Poulinea. The epizoic abundance varied between loggerhead populations. Several undescribed taxa were observed, of which some are in the process of being published as species being new to science. It can be concluded that loggerheads contain a high diatom diversity, of which some presumably exclusively epizoic taxa, but the majority are likely opportunistic taxa able to thrive on both biotic and abiotic substrata. Loggerheads from different populations are dominated by different diatom taxa and there appears to be a difference between the epizoic communities living on the skin and carapace of these sea turtles.