Diatoms on sea turtles and floating debris in the Persian Gulf (Western Asia)

The current study investigated diatom communities on juvenile green turtles foraging in neritic habitats around five Iranian islands. The primary objectives were to (1) compare species composition, growth form structure, and abundance of diatom communities associated with sea turtles foraging within the restricted boundaries of local feeding pastures, and (2) assess the level of uniqueness of the epizoic diatom flora in comparison with biofilms growing on floating debris. All observations and diatom counts were performed using scanning electron microscopy. The effect of the sampling location was apparent among sea turtle samples and reflected in significantly different cell densities. Diatom abundances were significantly higher on sea turtles (758–1836 cells mm−2 ) than on floating debris samples (9–189 cells mm−2 ). Epizoic diatom communities were composed of 20 diatom taxa and dominated by erect forms belonging to the so-called ‘marine gomphonemoids’, Chelonicola and Poulinea, previously reported on sea turtles from other geographical regions. The diatom flora found on floating debris was composed of 21 taxa. Only four taxa, Amphora cf. bigibba, Cocconeis cf. neothumensis var. marina, Psammodictyon constrictum, and Tabularia affinis, were recorded from both sea turtles and floating debris samples, and none of these exceeded 4% of the average relative abundance on the sea turtle carapaces. The study reveals a clear substratum preference in sea turtle-associated diatoms, with no evidence for species turnover across the investigated region over different sampling seasons, thus confirming previous speculations that sea turtle diatom communities would show a high level of uniqueness and stability.