engleski

Diversity of pennate diatoms in the plankton of the southern Adriatic Sea

Marine diatoms that acquired a planktonic lifestyle predominantly belong to the radial and multipolar centrics and there are only several araphid and raphid pennate genera commonly found in the pelagic environment. The common adaptation to the planktonic existence is the formation of cell colonies which is acquired by pennate genera such as Thalassionema, Fragilariopsis and Pseudo- nitzschia. Single-celled pennates are commonly present in marine plankton samples, often filling two different ecological niches as they are found both as single cells and adhering to various larger particles e.g. marine snow, copepods, other diatom colonies. In our study, we sampled the diatoms from the oligotrophic environment ; South Adriatic Sea. The sampling campaign BIOTA (Bio-tracing Adriatic Water Masses) was conducted in late winter (February/March) in 2015 and 2016 at 15 stations ranging from coastal area to open waters (42º 20’-38’ N, 17º04’-18º02’ E). During the cruises we collected the plankton net samples from the sunlit surface layer (0-20m depth) together with the seawater samples from surface to 500m of depth. The samples were examined by both light and electron microscope. We found approx. 115 diatom morphotypes, of which the dominant were colonial species of Chaetoceros, Skeletonema and pennate Pseudo- nitzschia but also single celled Cylindrotheca closterium. However, unlike the other parts in the Adriatic Sea, the south-eastern planktonic diatom winter flora includes numerous pennate species belonging to the well-known genera such as Pleurosigma, Navicula, Nitzschia, Diploneis, Surirella, Entomoneis, Bacillaria or Haslea but also some rarely recorded genera such as Neodelphineis, Alveus or Tropidoneis. Additionally, the detailed morphological overview and novel information on small non colonial pennate species belonging to Nitzschia bicapitata complex, Opephora, Psammodyction and Entomoneis will be presented.

Adriatic Sea, diatoms, taxonomy, morphology, new species

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