engleski

Submerged macrophytes as a habitat for zooplankton development in two reservoirs of a flow-through system (Papuk Nature Park, Croatia)

Zooplankton and seston were sampled from May to October 2008 in order to determine the influence of the lentic habitats and macrophyte stands on the plankton development and seston flux within two reservoirs through the karst headwater Jankovac flow-through system (Papuk Nature Park, Croatia). The system was characterized by low abundance (1 to 116 ind L-1) and high diversity of identified zooplankton. 86 taxa, comprising 57 rotifers, 15 cladocerans, 8 copepods and 6 members of other groups of organisms. Spatial oscillations of environmental parameters revealed statistically significant differences between lotic and lentic habitats as well as between vegetated and non-vegetated stations. Results of PCA suggested that the main drivers of development of the planktonic community were the food resources and the avoidance of flow velocity. Accordingly, shoreline areas with submerged macrophyte stands of Hippuris vulgaris L. were the most productive parts, represented by highest zooplankton abundance, biomass and biodiversity. Flow velocity significantly affected crustaceans assemblage, so that higher abundances of the larger cladocerans and copepods were achieved in vegetated stations with low flow velocity, while rotifers showed to be rheotolerance organisms. Heterogeneity in zooplankton assemblage of the vegetated and non-vegetated areas may be the result of the pressure of visual predators in non-vegetated areas and, thereby, the refuge role of macrophyte stands. On the other hand, the longitudinal discontinuum of the stream channel by two man-made reservoirs, could offer new habitats to enrich seston with organic particles and bioseston.

rotifers; cladocerans; copepods; karst stream; seston flux

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