Phytoplankton Periodicity in a Eutrophic Coastal Water of the Baltic Sea

The phytoplankton periodicity in the Darss‐Zingst bodden chain, an estuary‐like coastal water of the southern Baltic Sea, was investigated from 1984 to 1990. The following functional groups were established: 1.) nitrogen‐fixing Cyanobacteria plusOscillatoria limnetica, 2.) coccoid Chlorophyceae,Gomphosphaeria pusilla, Lyngbya contortaandStephanodiscus hantzschii, 3.) coccoid Cyanobacteria exceptGomphosphaeria, 4.) diatoms exceptStephanodiscus, 5.) Cryptophyceae and some other flagellates. A general seasonal pattern was observable: in cold winters group 5 dominates; in spring a diatom bloom (= group 4) occurred, which was followed by the development of group 2; steep temperature increases caused a summer bloom of nitrogen‐fixing cyanobacteria (= group 1), which was followed by groups 2 and 3 in autumn; in bland winters group 2 lasts until spring. Grazing was shown to be of minor importance for the phytoplankton periodicity.