Spatial and temporal distribution patterns of zooplankton in the central Baltic Sea and methods to detect them

The Baltic Sea is the largest semi-enclosed brackish sea in the world and consists of several consecutive deep basins. Due to fresh water input, physical processes and topographic structures pronounced hydrographic stratifications persist. These are created from water masses of incompatible densities due to different temperatures and salinities.A total of 832 multinet samples from different sites and depths were analysed for composition of the dominant zooplankton species and the relation to ambient environmental parameters by means of multivariate methods, weighted depth centroids and individual analyses of the vertical distribution. Species and developmental stages were bound to distinct layers and partially migrate between them during the season. The layers put different demands on the physiology of the individual species and can be conceived as habitats, determining the vertical distribution.When assessing the vertical distribution of plankton using nets the depth integration is a limiting factor intrinsic to the method, making a precise assessment of zooplankton species in different horizons more difficult. To solve these problem new concepts for optical in-situ detection of plankton species is introduced.