Benthic invertebrates, fish and zooplankton coupling in freshwater Mediterranean ponds

Mediterranean coastal and islands region abounds in small and shallow, mainly temporary freshwater ponds which have been rare subject of a scientific topic for a long time. They represent unique habitats in dry and arid climate inhabited numerous species, especially invertebrates with a short life cycle and can be rapidly colonized during the flooding season. Impact of benthic invertebrate predators and fish on zooplankton was assessed in the island freshwater ponds (island Korčula), and this is one of the first data for these habitats in the eastern Adriatic coast. The goals of this study were to investigate: i) interaction among benthic invertebrates, fish and zooplankton ; and ii) difference in shelter selection, bottom sediment vs. macrophytes. Analysis of ecosystem functioning shows decreased abundance of planktonic crustaceans in ponds with low macrophyte coverage, and vice versa, which highlighted role of macrophyte for zooplankton refuge against predators (acari, heteropterans, fish). Results suggest that macrophyte can serve as shelter for zooplankton, but in the case of high macrophyte abundance and numerous benthic invertebrate predators, role of macrophyte shelter is diminish, and zooplankton probably found refuge in sediment. This is confirmed by increased abundance, especially cladocerans, in the sediment. Through the dual impact of predators and low macrophyte coverage, as well as huge impact of benthic invertebrates among macrophytes, sediment was an efficient refuge for zooplankton. Interaction between predators (benthic invertebrates and fish) and zooplankton displayed higher complexity along habitat heterogeneity, while zooplankton share an important fraction in food resources among the trophic network.