Over the last decades molecular methods have become increasingly available to organismal biologists. Molecular genetics has greatly contributed to the understanding of evolutionary processes and relationships among taxa both at inter- and intraspecific levels. The amount of genetic diversity and the degree of population genetic structuring (i.e. division into genetically distinct sub-populations) are essential characteristics of a species. Both diversity and structure reflect the evolutionary history and the possible futures, including ability to respond to environmental perturbations. The aim of this research group is to study the genetic diversity of some dominant invertebrate species - populations from the North Sea, North Atlantic and adjacent estuaries. Patterns of genetic diversity within and between species may be used to identify cryptic species, to reconstruct the evolutionary history of a group, and to accurately estimate biodiversity. Population genetic structure may be useful to provide quantitative estimates of dispersal (gene flow) across a species' geographic range and to understand the extent to which dispersal is determined by ocean currents. At the moment research is mainly focused on the genetic population structure of the hyperbenthic mysid, Neomysis integer in serveral European estuaries.