Seasonal Changes in the Occurrence of Bosmina longirostris and Bosmina fatalis in Relation to Microcystis Bloom in Lake Kasumigaura

Abstract

The seasonal, mutual succession between Bosmina longirostris and Bosmina fatalis occurred at Takahamairi Bay in Lake Kasumigaura. The same succession was observed in the enclosures set up in the bay. To reduce the amount of reactive phosphorus, the enclosures were treated with aluminum sulfate. The predominant period of B. fatalis in summer became shorter in the treated enclosures than in the untreated ones or open water. The appearance of B. fatalis seemed to accord with the time when netplankton larger than 20 μm increase; it varied in the treated and untreated enclosures. Since the netplankton was mostly Microcystis aeruginosa, the increase of this alga likely caused succession of the two species of Bosmina.