Spatial and temporal distribution of two new phytoplankton diatom species in the German Bight in the period 1988 and 1996

Several samplings in the German Eight between 1988 and 1996 showed that dur ing this time two phytoplankton diatom species which had not previously bee n present established themselves in the phytoplankton communities of this a rea. The species are Coscinodiscus wailesii Gran & Angst and Thalassiosira punctigera (Castracane) Hasle. Both species can be found during each season in special regions or in the whole area. Especially C. wailesii, the large st diatom in the German Eight with a diameter up to 500 mu m, is able to do minate phytoplankton standing stocks in respect to carbon biomass. During w inter this species is present in low abundance but during spring and summer it is able to produce blooms. The highest biomass during the sampling peri od was determined to be 360 mu g C l(-1) (corresponding to 2000 cells per l itre). The success of C. wailesii is due first of all to its wide tolerance to different temperatures and salinities and its big size, unsuitable for planktonic herbivores. T. punctigera showed a maximum biomass of 150 mu g C l(-1) during the cruises. This species also has a wide temperature and sal inity tolerance.