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Phytoplankton community structure during bloom of Noctiluca scintillans (Macartney) Kofoid & Swezy in South Adriatic open sea waters

Phytoplankton community structure was investigated during mass occurrence of the mixotrophic dinoflagellate Noctiluca scintillans in the open sea of the South Adriatic. This study was conducted in April 2009 at three stations (P-100, P-300, P-1200) along transversal transect from the coast to Southern Adriatic Pit. Abundances of N. scintillans was determined using a Nansen net (250 mm mesh, 1 m in diameter and 255 cm in length). Water samples for the analysis of chlorophyll a concentrations and phytoplankton community were taken by 5-L Niskin bottles at standard oceanographic depths from surface to 100 m. Abundance of N. scintillans was exceptionally high (93 ind. m-3) in the upper 50 m and this has already connected with hydroclimatic changes in the East Mediterranean in last two decades. At the same time, average of chlorophyll a concentration for 0-50 m layer was 0.11 mg m-3. Phytoplankton community was dominated by dinoflagellates and coccolithophorids. Among diatoms, only small naviculoid cells (15-25 µm) were prominent. Only taxa of genera Diploneis, Cyclotella, Cocconeis, Navicula, Thalassiosira, Proboscia, Thalassionema, Licmophora and Biddulphia were occurred. During Noctiluca bloom low diversity and abundance of diatoms were found.

Noctiluca scintillans; bloom; phytoplankton; diatoms; South Adriatic

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