Phytoplankton distribution in the western and eastern Black Sea in spring and autumn 1995

Species composition, abundance, and biomass of micro- (>15 mu m) and nano(< 15 mu m) phytoplankton were studied in the western and eastern Black Sea du ring March-April and October 1995. A total of 142 species were identified, of which >50% were dinoflagellates. Abundance and biomass values were lower during the March-April period (average 129 +/- 28 thousand cells I-1 and 3 30 +/- 124 mu g I-1) than during the October period (average 364 +/- 161 th ousand cells I-1 and 1794 +/- 515 mu g I-1) and compared with previous inve stigations. Values for the north-westerly region were higher than for the s outherly areas, probably owing to effects of the Danube river, but were muc h lower than previously reported, possibly indicating improved ecological c onditions. In March-April, dinoflagellates (mainly Heterocapsa triquetra an d Scrippsiella trochoideum) were the most important groups, whereas, in Oct ober, diatoms (mainly Pseudosolenia calcar-avis) and coccolithophores (Emil iania huxleyi) were dominant. Nanophytoplankton constituted 57% and 84% of total abundance and 8% and 3% of total biomass in spring and autumn, respec tively. Microphytoplankton were dominant in the western Black Sea, whilst n anophytoplankton were dominant in the eastern region in spring. (C) 1999 In ternational Council for the Exploration of the Sea.