In pelagic food webs, zooplankton is the link between lower and higher trophic levels. It is thus essential to describe how zooplankton community structure varies with its environment. We investigated the seasonal and spatial variation in zooplankton diversity and community structure during two consecutive years in the Kalmar Sound, along the Swedish east coast, an area with a strong bathymetric gradient and of high ecological importance for commercial fish species. Two zooplankton communities were identified: a coastal/estuarine community in the south and an open-water community in the north, separated mainly by differing salinity and temperature conditions. The number of taxa increased from spring to autumn and was higher in the open waters. Our results indicate that the Kalmar Sound, with its characterizing zooplankton communities, is a potentially suitable area for the growth and recruitment of the main commercial fish species of the central Baltic Sea
