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 Bight between 1988 and 1996 showed that during this time two phytoplankton diatom species which had not previously been present established themselves in the phytoplankton communities of this area. The species are Coscinodiscus wailesii Gran & Angst and Thalassiosira punctigera (Castracene) Hasle. Both species can be found during each season in special regions or in the whole area Especially C. wailesii, the largest diatom in the German Bight with a diameter up to 500 μm, is able to dominate phytoplankton standing stocks in respect to carbon biomass. During winter this species is present in low abundance but during spring and summer it is able to produce blooms. The highest biomass during the sampling period was determined to be 360 μg C 1−1 (corresponding to 2000 cells per litre). 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 μg C 1−1 during the cruises. This species also has a wide temperature and salinity tolerance.