DOMINANT ROTIFERS OF VORTSJARV (ESTONIA)

Rotifers form 71% of the zooplankton of the strongly eutrophic (total N 2 g m(-3), total P 53 mg m(-3)) Vortsjarv (Estonia). Altogether 150 taxa of rotifers occur. Species characteristic of oligo- and mesotroph ic waters have totally disappeared during the last 30 years, or are di sappearing now. Species whose numbers and biomass reached 20% or more of total zooplankton were considered dominants. These were Anuraeopsis fissa, Keratella cochlearis, K. quadrata frenzeli, Polyarthra dolicho ptera, P. luminosa, Synchaeta verrucosa and Trichocerca rousseleti. Th e contribution of dominant rotifers to total zooplankton and its bioma ss is as follows: S. verrucosa 25% and 39%, P.dolichoptera 34% and 25% , K. cochlearis 25% and 7%, K. quadrata frenzeli 9% and 7%, A. fissa 2 8% and 0.4%, T. rousseleti 20% and 0.6%, respectively.