No abstract

The aim of this paper was to describe rapid colonization of the nektobenthic crustacean Palaemon elegans in the Estonian coastal sea. The shrimp was caught for the first time from the Estonian coastal sea in July 2011. Within the same month the species was simultaneously found at high densities in four water basins: the Gulf of Finland, the Gulf of Riga, the West Estonian Archipelago Sea, and the Baltic Proper. Among individuals many mature females were found. Thus, having a wide distribution range, high densities, and great reproduction potential, P. elegans has most likely formed a permanent population all over the Estonian coastal sea.

Abstract. 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.

No abstract