engleski

Vertical distribution of rotifers in three deep Mediterranean lakes

We studied rotifer assemblage in three deep, monomictic, karstic Mediterranean lakes of Croatia, differing in their hydrogeology: Lake Vrana (Cres Island) is a deep (74, 5 m) cryptodepression ; Lake Crniševo is deepest (31 m) of six interconnected karstic cryptodepressions (Baćinska Lakes) ; Lake Visovac (30 m) is a karstic barrage lake, a lentic dilatation of the Krka River. We investigated the impact of main physico- chemical parameters on vertical and temporal rotifer distribution. Altogether 58 rotifer taxa were identified. Dominant and constant species were Kellicottia longispina in Vrana and Synchaeta tremula/oblonga group in Crniševo and Visovac. According to CCA analysis, temperature was the most important factor influencing rotifer assemblage in all lakes. Rotifer density was higher in epilimnion (Visovac, Crniševo) and metalimnion (Vrana) in comparison to hypolimnion, where rotifer density declined. In Lake Vrana, rotifer density was generally low, and in other two lakes it was conspicuously decreased. This was likely influenced by two environmental gradients: in hypolimnion of Lake Visovac hypoxia occurred, while high values of conductivity in hypolimnion of Lake Crniševo indicated mixing with nearby sea. These unfavourable extreme conditions were also reflected in temporal dynamics of rotifers. Hypoxia and increased conductivity were recorded in early summer, when also a sudden drop in rotifer density was observed. Present data confirm that rotifer assemblage is a very dynamic component of freshwater food webs. Rotifers react rapidly to environmental gradients, which makes them good model- organisms for monitoring ecological status of deep lakes.

Rotifera, epilimnion, metalimnion, hypolimnion, freshwater food webs

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