PELAGIC-BENTHIC COUPLING - THE IMPORTANCE OF DIATOM INTERANNUAL VARIABILITY FOR POPULATION OSCILLATIONS OF MONOPOREIA-AFFINIS

The amphipod Monoporeia affinis (Lindstrom) exhibits long-term population oscillations in oligotrophic Lake Vanern. Correlation showed profundal oxygen and temperature, and intraspecific and predatory interactions to be poor explanatory variables. Conversely, the interannual variability in food availability-diatom biovolume-was highly correlated with amphipod total density at t + 1 yr and the density of 0+ amphipods and growth (amphipod body length in August) of 0+, 1+, and 2+ generations. Amphipod recruitment success of 0+ animals may be an important factor governing long-term population dynamics, and strong 0+ year classes result in greater 1+ and 2+ population densities. Fish predation, although tentatively not an important population-regulating factor, was negatively correlated with amphipod total body lengths of the 1+ and 2+ age classes in May. Size-selective fish predation pressure on juveniles and adults may facilitate coexistence of the 3-yr age classes.