Shared Epizoic Taxa and Differences in Diatom Community Structure Between Green Turtles (Chelonia mydas) from Distant Habitats

Abstract

The first reports of diatoms growing on marine mammals date back to the early 1900s. However, only recently has direct evidence been provided for similar associations between diatoms and sea turtles. We present a comparison of diatom communities inhabiting carapaces of green turtles Chelonia mydas sampled at two remote sites located within the Indian (Iran) and Atlantic (Costa Rica) Ocean basins. Diatom observations and counts were carried out using scanning electron microscopy. Techniques involving critical point drying enabled observations of diatoms and other microepibionts still attached to sea turtle carapace and revealed specific aspects of the epizoic community structure. Species-poor, well-developed diatom communities were found on all examined sea turtles. Significant differences between the two host sea turtle populations were observed in terms of diatom abundance and their community structure (including growth form structure). A total of 12 and 22 diatom taxa were found from sea turtles in Iran and Costa Rica, respectively, and eight of these species belonging to Amphora, Chelonicola, Cocconeis, Navicula, Nitzschia and Poulinea genera were observed in samples from both locations. Potential mechanisms of diatom dispersal and the influence of the external environment, sea turtle behaviour, its life stage, and foraging and breeding habitats, as well as epibiotic bacterial flora on epizoic communities, are discussed.

DNA metabarcoding and microscopic analyses of sea turtles biofilms: Complementary to understand turtle behavior

“…Moreover, the species composition of epibiotic diatoms from freshwater turtles of the same species can differ based on turtle activities and their region of origin [ 46 ]. Similar differences have been observed with marine turtles [ 27 ]. Nevertheless, such differences were not observed between freshwater turtles ( Emys orbicularis ) coming from various ponds in South France (e.g., [ 47 ]) nor for certain marine turtles ( Lepidochelys olivacea , [ 28 ]).…”

“…Identification using light microscopy reaches its limits when small species are too abundant; therefore, microscopic counts introduce significant uncertainty. A large set of epibiotic diatoms samples from turtles were analyzed using scanning electron microscopy, thus bypassing this problem and enabling robust identification [ 27 ]. Nevertheless, scanning electron microscopy is expensive and cannot be undertaken routinely.…”

“…We believe that diatom composition of the sea turtle shells is related to the diatom composition of its surrounding environment as it has been stated by Majewska et al . [ 27 ].…”

Geographical variation in the diatom communities associated with loggerhead sea turtles (Caretta caretta)

“…The observed taxon richness is clearly higher than currently observed from any other sea turtle species sampled so far. Majewska et al [4] recorded only 21 taxa in 38 carapace samples from olive ridley sea turtles in Costa Rica whereas, in another study, Majewska et al [16] reported 26 taxa belonging to 20 genera in 76 carapace samples from green turtles in Costa Rica and Iran. It is possible that the applied sampling technique in the latter two studies (i.e.…”

Six new epibioticProschkinia(Bacillariophyta) species and new insights into the genus phylogeny

“…Currently, it is still unclear to what degree the sea turtle diatom communities overlap with those encountered by the animals within their feeding, grooming or mating areas. While some diatom taxa seem to be well-adapted to the challenging conditions on the animal body surface and may constitute a key element of the pioneer epizoic communities, some other species may be able to attach to and thrive on the sea turtle skin or carapace only at the later stages of biofilm formation (Majewska et al, 2017b.…”