Phytoplankton in three freshwater lakes in the Neretva River delta (Eastern Adriatic, NE Mediterranean)

Abstract

Phytoplankton composition and temporal distribution were studied in the lakes Modro Oko, Desne and Kuti in the Neretva River delta throughout the seasons in 1994 and 1995. Physico-chemical parameters did not differ among three lakes, except for NO3 concentrations. Seventy-six phytoplankton taxa were found in all three lakes combined, including 29 Bacillariophyceae, 4 Chrysophyceae, 15 Chlorophyceae, 9 Charophyceae (Zygnematales), 16 Cyanophyceae, and 3 Dinophyceae. Lakes Modro Oko, Desne and Kuti showed 18, 24 and 57 taxa, respectively. Asterionella formosa, Fragilaria ulna and Pediastrum clathratum were common to all three lakes. Similarity coefficients (Jaccard index) of Modro Oko and Desne, Modro Oko and Kuti, and Kuti and Desne were, respectively, 13.2%, 12.3% and 23.9%. The highest mean values of surface phytoplankton density in Modro Oko (695 cells L-1), Desne (4308 cells L-1), and Kuti (103810 cells L-1) showed no significant differences. Bacillariophyceae and Cyanophyceae mostly dominated phytoplankton cell density. The most abundant (>105 cells L-1) taxa, Microcystis aeruginosa, M. wesenbergii and Aphanizomenon flos-aquae, were found in Lake Kuti during summer. Six taxa were recorded for the first time in Croatia: Cyclotella striata, Botryococcus braunii, Pediastrum sturmii, Desmidium swartzii, Chamaesiphon cylindricus, and Woronichinia naegeliana.