engleski

Rotifers in the zooplankton community of Visovac Lake

During the 1995/96 years seasonal fluctuation and the vertical distribution of the rotifers fauna were investigated in the Visovac Lake. The number of species and density of their populations varied on the investigated vertical profile, seasonally and spatially. From a total of 43 determinated species, the largest number of species was found in the winter period (21), while the smallest number in the summer months (12). The whole year round the following species were present: Asplanchna priodonta, Gastropus stylifer, Keratella cochlearis, Polyarthra vulgaris, Synchaeta tremula and Trichocerca birostris. Taking into consideration the rotifer abundance per area on the whole vertical profile from the surface to the bottom, the greatest population density rotifers (12.3 x 106 individuals/m2) achieved in the summer period. The minimum populations density was observed in the winter months (0.017 x 106 individuals/m2). Seasonal fluctuations on the vertical profile were characterized by three rotifers: G. stylifer, S. tremula and T. birostris, which were exchanged in their domination in the lake Visovac successively. S. tremula and G. stylifer were dominant in the spring period in epilimnion, while T. birostris dominanted in hypolimnion. At the beginning of summer T. birostris was dominated on the whole vertical profile from the surface to the bottom. At the end of summer in the epilimnion the population development of rotifer T. birostris was suppressed by the dominance of the species S. tremula and G. stylifer. At the beginning of autumn the population abundance of T. birostris stagnated, while S. tremula was reached its peak of abundance in the epilimnion layer. At the end of autumn and beginning of winter the rotifer fauna has been stagnated more and more, and during the whole winter period it was presented by poor populations of G. stylifer, S. tremula and T. birostris.

rotifers; zooplankton; karstic lake

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