The aim of the thesis was to analyze the feeding strategy of calanoid copepods in two areas of the Baltic Sea (Pomeranian Bight: PB, Gotland Sea: GS) which were characterized by different levels of eutrophication in the summer and early autumn.

The samples were analyzed using different methods: measurements of marker pigments (HPLC), cell counts using the Utermohl method, zooplankton counts and determination of d15N.

The main results of the thesis are summarized as follows. The copepods in the PB and in the GS exhibit different feeding strategies. Copepods in the PB, which has a mean phytoplankton biomass of 400 milligrams (mg) carbon (C) per liter feed selectively on crypto- and dinophyceae. In the GS, which has a mean biomass of 120 mg C per liter, feeding of copepods do not differ between the different phytoplankton groups. The assimilation efficiencies show that the ingested food was used increasingly less economically at high ingestion rates.

In the PB, feeding upon the primarily colonies-forming cyanobacteria was low. In contrast, in the GS, the ingestion of diazotrophic cyanobacteria probably depends on the physiological status of the bloom. It seems that at start of the bloom the cyanobacteria are hardly fed upon (2% of the cyanobacteria biomass, GS 1993). However, during the stationary and the regressing phase of the bloom, feeding on cyanobacteria increases considerably (20% of the cyanobacteria, GS 1994). 1.1% and 3.3% of the primary production were ingested by calanoid copepods in the PB and in the GS, respectively. In the nutrient limited system of the GS, 2.3 mg C per cubic meter per day were excreted by the copepods into the mixed layer.

The evaluation of the grazing experiments using cell counts and pigment measurements showed in the PB and the GS, that pigment analysis is a useful method to determine taxon-spezific ingestion rates by calanoid copepods. Pigment analysis enables good reproductible results to be obtained with a low time investment. Also, the variance is smaller when compared to that resulting from cell counts according to the Utermohl method.

The comparison between the chlorophyll-A-equivalents determined by chl-A/marker pigment ratios from algal cultures, and those determined by chl-A/marker pigment ratios from pigment measurement in the Pommeranian Bay and the GS, which were calculated by multiple regression analysis, showed that the estimation by multiple regression analysis is a good tool to consider the variation in the pigment composition caused by changing light conditions. The application of conversion factors gained from laboratory cultures is not recommended for the calculation of chl-A-equivalents from marker pigment concentrations in estuarine systems, which are characterized by variable light conditions due to horizontal and vertical mixing processes.