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Epizoic diatoms associated with the neck skin of adriatic loggerhead seaturtle

Epibiotic communities of sea turtles have been subjected to growing scientific interest in the recent years. A variety of animals and photosynthetic organisms, such as crustaceans, annelids, molluscs or macroalgae, are well known to live as macro-epibionts on the sea turtle body surfaces. Some of these organisms require animal substrate to live and develop and their survival is intricately linked to the survival of the host species. However, as has recently been shown, sea turtles also host unique communities of diatoms – siliceous unicellular algae with several taxa, including newly described genera (e.g. Chelonicola, Medlinella, Poulinea) and species (e.g. Achnanthes elongata, A. squaliformis, Labellicula lecohuiana, Tursiocola denysii), known exclusively from the carapaces and skin of different marine turtle species, such as olive ridley, green turtle, and loggerhead. The scope of our study was to confirm or refute the presence of the epizoic diatom flora on the skin of loggerhead sea turtles found in the Adriatic Sea. We collected skin samples from the frozen necks and heads of 14 different loggerheads obtained between 1995 and 2002. The scrapings were processed with strong acids (sulfuric and nitric), which allowed to remove the organic matter and revealed the inorganic components of the samples, such as silica frustules of diatoms. The light (LM) and scanning electron microscopy (SEM) observations confirmed that 50% of the samples contained diatoms. In LM 25 morphologically different taxa were recognized. The majority of them occurred in low abundances. The SEM analysis revealed that the dominating diatom species were epizoic Achnathes elongata and Poulinea cf. lepidochelicola with the later species representing ca. 70% of diatoms in five samples. Poulinea species have been often recorded from skin and carapace samples of five other sea turtle species collected from various locations across the world. Detailed investigations on both morphological and molecular characteristics of different populations of Poulinea and other “so-called “marine gomphonemoids” (including Chelonicola and Tripterion) may indicate an evolutionary relationship among these epizoic microalgae and shed some light on dispersal modes and colonization strategies used by marine microbes.

epibionts, diatoms, marine vertebrates, sea turtles

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