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We investigated the effect of the cyanobacterium Microcystis aeruginosa (strain PCC7820) on the survival of juvenile and adult Daphnia pulex (Cladocera) in different food concentrations (the green alga Scenedesmus obtusiusculus). M. aeruginosa reduced survival in D. pulex. The peptide toxin microcystin‐LR is present in this strain of M. aeruginosa. The toxic effect decreased with increasing concentrations of S. obtusiusculus. Juvenile D. pulex generally died faster than adults at high concentrations of cyanobacteria. However, juvenile D. pulex did better than adults at the lowest concentration of S. obtusiusculus.

Pike, Esox lucius L., catch-per-unit-effort (CPUE) in rod and line fishing fluctuated considerably in the western Gulf of Finland between 1939 and 2007. Since the beginning of the 1980s, CPUE has been only 3-4% of the highest CPUE during the period, suggesting a drastic decrease in population size. The collapse of the population coincided with a rise in the nutrient level in the Baltic Sea and consequent changes in productivity, turbidity and vegetation. The differences in the food web that followed the environmental change may partly explain the variation both in CPUE and in the mean weight of pike caught. Long-term fluctuations in salinity and temperature, however, did not seem to affect the population size. The mean weight of pike fluctuated inversely with CPUE, indicating changes in the recruitment of pike to the study area.