While the importance of nanophytoplankton in marine environments is increasingly recognized, there is still little information about the dynamics and diversity of the organisms in coastal pelagic habitats, and about the influence of environmental factors. Thus, the focus of the project was on the diversity and ecology of nanophytoplankton in the coastal, eutrophic waters of the Gulf of Gdansk. The specifically addressed the following questions:1) Which groups of nanophytoplankton coexist in the Gulf of Gdansk?2) How do light and nutrient (nitrogen) limitation influence the community structure of nanophytoplankton in environmentally important taxa? The diversity of haptophytes was investigated by pyrosequencing of V4 fragment of 18S rRNA genes.