engleski

The influence of sea turtles on the biogeography of marine diatoms based on a case study from the Mediterranean coasts

Marine turtles are known to be hosts of diverse groups of organisms (epibionts), both plants and animals, particularly on their carapaces. Many of these epibionts attach to a variety of substrates in habitats where sea turtles spend time between nesting events or while foraging ; however, a small group of taxa are limited in their distribution solely to the marine animals. The association between diatoms and turtles potentially exemplifies how epibiont data can be used to identify and corroborate patterns of turtle habitat use and movement. It is expected that vertebrates in general and marine turtles in particular play an important role in the dispersal of benthic diatoms, and could be significant contributors to the spread of invasive species. By studying diatom assemblages living on turtles, we expect to gain information about the role that turtles play in the dispersal of diatoms. We expect that benthic diatoms hosted by marine vertebrates will be characterized by a high degree of specialization, similar to other epibiont communities. In this study we have combined the analysis of species composition of diatoms incorporated into the biofilm formed on the carapaces of sea turtles with isolation and culture experiments. The diatom assemblages targeted inhabit the carapaces of loggerheads (Caretta caretta) and green turtles (Chelonia mydas) from the Mediterranean coasts in Turkey and Croatia. Altogether, several sampling seasons in the Aegean Sea in Turkey and one season in Croatia allowed us to isolate and successfully grow in culture ca. 120 strains. These include small Navicula Bory, Nitzschia Hassall, Diploneis (Ehrenb.) Cleve and Halamphora (Cleve) Levkov species, apparently incorporated into the carapace biofilm. Interestingly, stalk-forming species of Achnanthes Bory s. str. and tube-dwelling Parlibellus E. J. Cox were included among these epibionts, and grew well in culture. These species in particular may provide an insight into the role of sea turtles in diatom distribution. This will be tested determining the species composition from cleaned and processed samples as well as with molecular analysis of the isolated strains. Extraction of DNA from cultured strains and use of molecular markers (rbcL, psbC and SSU) was applied in testing the hypothesis that the diatoms present on turtle carapaces will exhibit biogeography and possess geographic ranges that match those of their hosts. Additionally, recent results based on species composition analysis solely suggest that the same epibiontic diatom species can be found on the loggerhead turtles and, for example, green turtles from the distant geographic regions e.g. Mediterranean and the Caribbean Sea.

sea turtles ; marine diatoms ; Mediterranean Sea ; Turkey ; Croatia ; diatom cultures ; molecular markers (rbcL, psbC and SSU)

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