engleski

Trophic role of rotifers in plankton community of the Visovac Lake

The study on the position of the rotifer fauna in the functional feeding organization of zooplankton in the Visovac Lake was based on the seasonal fluctuation of rotifer fauna and its trophic structure. In the zooplankton of this lake macrofiltrators were the most dominant rotifers (> 64%), considering its species diversity and population density. Microfiltrator rotifers was less present. It can be, therefore, concluded that the rotifer fauna in the lake zooplankton has a more significant role in the utilization of larger phytoplankton fractions (net phytoplankton >50 ľm) than in the consummation of organic detritus, bacteria and nanophytoplanktons. Analysing the sesonal fluctuations of rotifer microfiltrators and macrofiltrators it can be concluded that the trophic role of rotifer fauna varied in the zooplankton of the Visovac Lake seasonally and spatially. Species Gastropus stylifer, Synchaeta tremula and Tricocerea birostris were the most dominant macrofiltrator rotifers. After a late-spring phytoplankton maximum in epilimnion, in the summer months phytophagous species G. stylifer and S. tremula dominated in epilimnion and species T. birostris in hypolimnion. Unlike the summer period, after the autumn phytoplankton maximum the net algae consumer S. tremula developed a reach population in epilimnion layer enormously. At the end of autumn and the beginning of winter phytoplankton stagnation caused the stagnation of macrofiltrator rotifer. In the same period we observed a development of microfiltrator populations. The dominat rotifer microfiltrator was Karatella cochlearis. We found that in epilimnion layer the considerable development of microfiltrators was caused by increase on concentration of bacteria-detritus suspension.

rotifers; zooplankton; trophic relationships; functional organization; karstic lake

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