engleski

Rotifers in biotic interactions within the transparent vs. turbid state: a mesocosm contribution to the reestablishment of macrophytes

Rotifers assemblages affected by different biotic interactions were compared in two alternative states, transparent vs. turbid. Research was carried out in Sutla River backwater (NW Croatia), which consists of two interconnected basins: the upper, transparent and vegetated by a submerged macrophyte Ceratophyllum demersum and the lower, turbid and non-vegetated. Simultaneously, we investigated the capacity of submerged macrophytes for lake restoration. We set up an in situ mesocosms experiment using small (10 mm,  fish) and large (40 mm, + fish) mesh sizes enclosures for a period of 110 days, within turbid basin. The addition of C. demersum stems was quantitatively equalized in both treatments. In the mesocosms exposed to the fish top-down control, macrophytes became very sparse, and in plankton dominated microfilter-feeder rotifers and small cladocerans. This community was similar to the pelagial assemblage of turbid and unvegetated basin. In the mesocosms without fish, macrophytes remained very dense, and large cladocerans and copepods as well as littoral species of rotifers increased their abundance. In this treatment, protected from fish predation, during the initial 20 days of the experiment, the community was similar to that of the surrounding pelagial in the turbid basin, but later it changed and exhibited prominent similarity to the littoral stands in the transparent and vegetated basin. Results of this study indicate the following conclusions: (i) rotifers and large cladocerans have been more affected by fish predation than copepods, where an increase in the fish length and mass enhanced predation ; (ii) significant differences in abundance and diversity of zooplankton in interconnected shallow lakes as was a result of the diversity of microhabitats in the littoral zone and biotic interactions ; (iii) the reestablishment of macrophytes has a capacity to cause rapid changes of biocenosis and environmental conditions and could be applied, even on a major-spatial scale, in the lake restoration.

Rotifera; Cladocera; Copepoda; fish; backwater

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