The influence of riparian vegetation on the functional organization of four Hong Kong stream communities

Pontoporeia affinis Lindström predominated profundal macroinvertebrate communities in eutrophic Lake Mälaren. Amphipod densities, at both stations studied, averaged > 50% of overall total macroinvertebrate densities. The life history of P. affinis was two years, with two cohorts distinguished, both exhibiting similar patterns in annual growth. During the sixteen years of this study, amphipod growth seemed to exhibit long-term cyclic fluctuations, with periods of 9–10 yrs. at Görväln and 5–6 yrs. at Grönsöfjärden. Amphipod growth was significantly (negatively) correlated with conspecific density and biomass. The mechanism(s) governing Pontoporeia population oscillations is (are) not clear. It is postulated that changes in food availability, as the result of overgrazing, may adversely affect Pontoporeia recruitment and subsequently be observed in the form of long-term population oscillations as noted in Lake Mälaren.