SEASONAL DYNAMICS OF CHRYSOCHROMULINA SPECIES (PRYMNESIOPHYCEAE) IN ACOASTAL AREA AND A NUTRIENT-ENRICHED INLET OF THE NORTHERN BALTIC PROPER

Phytoplankton belonging to the prymnesiophycean genus Chrysochromulina were studied during 4 years (1985-1988) in a coastal area and an inle t differing in hydrographic and nutrient regimes in the northern Balti c proper. In both areas Chrysochromulina species were regular componen ts of the phytoplankton community and often made up a large fraction ( up to 65%) of the nanophytoplankton abundance in summer and early autu mn, and constituted occasionally over half of the total phytoplankton biomass. We found distinctive differences in the occurence of Chrysoch romulina spp. between the two stations. In the coastal station, abunda nce maxima usually occurred in July whereas in the nutrient enriched i nlet, maxima occurred in early summer or early autumn. In the inlet, a maximum of 9 x 10(6) cells L(-1) were found as compared to 3.0 x 10(6 ) cells L(-1) in the coastal area. Abundance maxima often followed a p eriod of low concentrations of inorganic phosphorus in the trophogenic layer. Our data indicate nutrient enriched conditions favoured the ob served species, either directly by higher nutrient availability or ind irectly through increased microbial activity. In a study of the vertic al distribution of Chrysochromulina spp. at the coastal station, three distinctive size groups were distinguished, which differed in their d epth distributions within the trophogenic layer. Critical identificati on of Chrysochromulina to species level is rarely possible without exa mination of the scales by transmission electron microscopy. In samples from the summer of 1992, nine species were identified on bases of the structures of their scales. Three species were abundant, Chrysochromu lina polylepis, C. minor and Chrysochromulina sp. 2. not yet described in the literature. Six other species, C. brachycylindra, C. hirta, C. simplex, C. leadbeateri, C. ericina and C. sp. 1. were rare. Five spe cies (C. hirta, C. leadbeateri, C. simplex, C. sp. 1. and C. sp. 2.) a re new to the northern Baltic proper. Scale morphology of C. polylepis differed from specimens collected in the Kattegat. A detailed descrip tion of C. minor scales and a short characterisation of the new specie s are given.