engleski

INVASIVE FISH SPECIES HAVE A NEGATIVE EFFECT ON ZOOPLANKTON ASSEMBLAGES IN SHALLOW WATER BODIES

Freshwater zooplankton (Rotifera, Cladocera, and Copepoda) is an essential component of the biocoenosis in lentic ecosystems as it has a key role in transfer of energy, nutrients, and primary food particles (detritus and phytoplankton) to higher trophic levels (fish). Both “bottom-up” and “top-down” regulations can influence zooplankton species composition, density, and biomass. Here we present results of our investigation conducted in different shallow water bodies in the Mediterranean region of Croatia (Europe): Vrana Lake near Biograd na Moru, and twenty-one permanent and semi-permanent ponds along the coast and islands of the Adriatic Sea. We sampled zooplankton together with macrozoobenthos, fish, macrophytes, and physico-chemical parameters. The main aims were to determine the impact of top predators (fish) and other biotic and abiotic factors on zooplankton structure in the investigated shallow lakes and ponds. Overall, rotifers dominated in zooplankton, followed by cladocerans and copepods. In habitats with invasive fish species, zooplankton density, biomass, and diversity were strongly reduced. Fish presence negatively affected Cladocera and Copepoda. Rotifers were not under direct fish predation, and their assemblage was shaped by other biotic (e.g., macrophyte stands) and abiotic (e.g., increased salinity) factors. Our results indicate strong “top-down” regulation of zooplankton in shallow water bodies harbouring invasive fishes, primarily by excluding large- bodied algivorous cladocerans. Thus, invasive fishes promote phytoplankton growth, preventing zooplankton from maintaining a clear water state of investigated habitats, and deteriorating ecological functioning of shallow water bodies, particularly in warmer climate.

Rotifera, Cladocera, Copepoda, “top-down” factors

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