Unraveling the role of top predators and macrophytes in mediterranean ponds: the ecological significance of rotifers.

The Mediterranean area includes a wide variety of shallow water bodies which are recognized as hotspots of biodiversity. Here, we present the results of our study conducted on twenty-two small ponds, divided in two groups, fish free and fish stocked, along the coast and islands of the Adriatic Sea, in the Mediterranean. The main aims covered (1) the assessment of zooplankton structural and functional traits; (2) the impact of top predators (invasive mosquitofish) and macrophyte coverage on zooplankton diversity, abundance, and biomass. Overall, rotifers dominated in zooplankton diversity and abundance; it is likely that due to their small size they were not under direct fish predation. Rotifers prevailed in fish-stocked ponds, where their assemblage was shaped by food availability and macrophyte coverage. Macrophytes had a dual influence on rotifers: dense macrophyte coverage supported a high density of littoral species, while low macrophyte coverage provided a profitable condition for planktonic rotifers. In fish-stocked ponds, cladoceran and copepod density, biomass, and diversity were strongly reduced in relation to fish-free ponds. This study revealed high zooplankton diversity (77 taxa) in a Mediterranean region, structured by habitat heterogeneity and predation. [ABSTRACT FROM AUTHOR]