engleski

Seasonal changes of plankton in Butoniga reservoir

Investigation of phytoplankton was conducted seasonally during a four year period from 1999 to 2003 in Butoniga reservoir situated in central Istria, Croatia. Average depth of the reservoir was 5 m and plankton was sampled in the deepest part near the floodgate. Plankton densities were established by filtrating 10 L of the lake water through plankton net (25 &micro ; m). For chemical analysis water samples were taken simultaneously with plankton samples. Diatoms were the most prominent group, with Cyclotella being the most common genus. Accompanying groups were Dinophyta, Euglenophyta, Chlorophyta and Chrysophyta. Most abundant zooplankton group was Cladocera, especially species Bosmina longirostris. The second most representative group in terms of zooplankton density was copepod nauplii. Large numbers of Cladocera correlated with high abundance of centric diatoms. Most significant correlation was determined during spring time between Ceriodaphnia sp. and Cyclotella sp. Most copepods occurred during warmer part of the year when also higher abundances of Dinophyta and Chlorophyta were noted. Multidimensional scaling ordination conducted on abundance data sets for both phyto- and zooplankton revealed similar seasonal grouping.

plankton assemblages; phytoplankton; zooplankton

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