Epizoic algae on loggerhead turtle (Caretta caretta Linnaeus) from Aeolian archipelago (Southern Tyrrhenian sea, Italy)

Algae are common epibionts on the carapace of the aquatic turtles (1, 2). Despite this, most of the papers on marine species concern to the animal component (3, 4, 5). The flora of the loggerhead turtle, Caretta caretta, is one of the best studied (5, 6). However, the data on Mediterranean individuals of this species are limited in number and are prevalently restricted to few areas (6, 7, 8, 9). Here we report the results obtained studying 41 individuals of Caretta caretta from the Aeolian Archipelago (Sicily, Italy). Yearly boat-based surveys were conducted in an area of about 280 Km2 around Filicudi Island and specimens were obtained from October 2015 to January 2017. A total number of 17 species of algae were sampled and identified. Some of these are reported for the first time as epibionts on C. caretta carapace. Moreover, a morphological and molecular analysis was conducted on individuals of a red alga with a four pericentral “Polysiphonia” habitus, occurring on 94% of the studied turtles. A comparison with other four “Polysiphonia-like” pericentral species is here reported. The main morphological characters used are habit, number of pericentral cells, cortication, origin of branches, origin and the morphology of the rhizoids, arrangement of tetrasporangia, origin of spermatangial axes, and the size and the shape of cystocarps (10, 11, 12, 13, 15). Our specimens presented several morphological similarities with P. carettia Hollenberg and Neosiphonia cheloniae (Hollenberg & J.N.Norris) J.N.Norris. Both species were collected on the carapaces of Californian individuals of Caretta caretta and Chelonia mydas, respectively, and described as new taxa (16, 17). Polysiphonia carettia has been reported also from the Atlantic Ocean and recently from some Mediterranean areas on the carapace of C. caretta individuals (6, 18, 19). Plastidial (rbcL) and mitochondrial (COI) markers were sequenced from our specimens. The sequences, contrasted on public online databases (BOLD and GenBank), revealed that the specimens from Filicudi Island should be ascribed to the genus Neosiphonia M.S.Kim & I.K.Lee. Unfortunately, no other DNA sequence is presently available for the epizoic Polysiphonia-like species, including those taxa described exclusively on the carapace of marine turtles (P. carettia, P. tsudana Hollenberg and N. cheloniae).