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Composition of planktonic diatoms during bloom of Noctiluca scintillans (Macartney) Kofoid & Swezy in the open South Adriatic waters (NE Mediterranean)

Phytoplankton community structure was investigated during mass occurrence of the mixotrophic dinoflagellate Noctiluca scintillans (Macartney) Kofoid & Swezy in the open sea of the South Adriatic. This study was conducted in February, April and June 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 communities 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 April 2009) in the upper 50 m and this has already connected with hydroclimatic changes in the East Mediterranean in last two decades. Average of chlorophyll a concentration (0-50 m layer) was also relatively high. However, dinoflagellates and coccolithophorids prevailed in the samples. In general, during bloom of Noctiluca low diversity and abundance of diatoms were found. With the respect to abundance, only small naviculoid cells (15-25 µm) were prominent. Taxa of genera Diploneis Ehrenberg ex Cleve, Cyclotella (Kützing) Brébisson, Cocconeis Ehrenberg, Navicula Bory de Saint-Vincent, Thalassiosira Cleve, Proboscia Sundström, Thalassionema Grunow ex Mereschkowsky, Licmophora C.Agardh and Biddulphia S.F.Gray were the most common. Relationship between the distribution of diatom abundances and environmental variables is also presented.

Noctiluca blooms; phytoplankton; diatoms; South Adriatic

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