Observations of three Idotea species (I. balthica, I. chelipes and I. granulosa) in Northern Europe, including the Baltic Sea

Marine isopods of the genus Idotea Fabricius 1798 are common meso-grazers of the benthos. Approximately 30 different species exist worldwide, including eight species in Europe. Only three species, namely Idotea balthica (Pallas, 1772), I. chelipes (Pallas, 1766) and I. granulosa Rathke, 1843, were able to colonize the brackish environment of the Baltic Sea. To understand the ecology and distribution patterns of these key species under on-going environmental changes, occurrence data were collected from museum collections and own sampling.