Trophic interactions between native and alien palaemonid prawns and an alien gammarid in a brackish water ecosystem

摘要

Macroalgae are an important habitat for small mobile invertebrates such as gammarid amphipods and palaemonid prawns. Gammarid amphipods are important grazers of micro- and macroalgae whereas palaemonid prawns are feeding on macroalgae and small aquatic invertebrates including gammarids. Recently the invasive palaemonid prawn Palaemon elegans established in the Baltic Sea. As P. elegans occurs within the same habitats as the native Palaemon adspersus, it is expected that this invasion modifies the existing trophic interactions. To address this question, we experimentally investigated the feeding of the native P. adspersus and the invasive P. elegans on the benthic macroalga Cladophora glomerata and on the invasive gammarid amphipod Gammarus tigrinus. In the course of the experiment neither G. tigrinus nor Palaemon spp. had effects on filamentous macroalgae. The presence of prawns drastically increased the mortality of amphipods with no difference in the feeding efficiency between the two prawn species. To conclude, the alien prawn does not add an extra function to the trophic system of the coastal ecosystem of the Baltic Sea. Nevertheless, due to its progressively increasing densities and wide habitat range, P. elegans is expected to exert stronger predation pressure on gammarid amphipods as compared to P. adspersus alone.