Environmental preferences of Crangon crangon (Linnaeus, 1758), Palaemon adspersus Rathke, 1837, and Palaemon elegans Rathke, 1837 in the littoral zone of the Gulf of Gdansk

This study concerns the environmental requirements of the shrimp, Crangon crangon, and the prawns, Palaemon adspersus and Palaemon elegans, which occur in the Gulf of Gdansk. Specimens were sampled from the 0.5-1.0 m and 5.0-10.0 m depth layers in the southwestern part of the Gulf, near the seaside resort of Sopot, in 2002-2003. The dominant species was C. crangon, the largest concentrations of which were recorded at 5.0-10.0 m. Seasonal changes were observed in the composition of the population of these three species during the year. P elegans, a relative newcomer to the Polish zone of the Baltic Sea, has occupied a vacant ecological niche (the 0.5-1.0 m depth zone) and in doing so, has avoided competition with the native C. crangon. In the littoral zone (0.5-1.0 m) off Sopot, and also off Hel and Gdynia, R elegans occurred together with P adspersus. The diverse requirements of these three species with respect to biotic (e.g., food) and abiotic factors (e.g., substrate, dissolved oxygen) enable them to coexist in the waters of the Gulf of Gdansk.