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UNUSUAL OCCURENCE OF TROPICAL PLANKTONIC DIATOM SPECIES OF THE GENUS Chaetoceros IN THE SOUTH ADRIATIC SEA

Two fairly uncommon species of planktonic diatoms of the genus Chaetoceros, C. bacteriastriodes and C. pseudosymmetrycus, were recorded during the study along the South Adriatic transect Dubrovnik-Bari in 2012 and 2015. Species were recorded by observing water samples under inverted microscope. From a total of 89 examined samples unusual Chaetoceros species were recorded in 5 cases in the South Adriatic open waters (to a depth 0-100 m) during winter period. Their abundance did not exceed 102 cellsL-1. Both species have been described from tropical waters, showing Indo- Pacific distribution, and very rarely recorded in the Mediterranean Sea. Areal expansion and introduction of new phytoplankton species might be related to changes in sea circulation in the South Adriatic or ballast water transport. Recent investigations have shown that entering currents, of either Atlantic/Western Mediterranean or Eastern Mediterranean origin, modify the composition of the plankton community in the South Adriatic and each type of current brings different newcomers.

diatoms; genus Chaetoceros; South Adriatic; tropical species

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