ABSTRACT: The effect of predation by diving ducks (Aythya fuligula, Aythya ferina, and Aythya marila) on filter-feeding bivalves was evaluated in eutrophic estuarine lagoons, Lakes Nakaumi and Shinji, in Japan. Bivalves take up nutrients in the form of phytoplankton and detritus. Winter-migrating diving ducks feed on these bivalves during the cold season. In Lake Nakaumi, diving ducks chiefly consumed the biofouling mussel Musculista senhousia. The biomass of M. senhousia decreased markedly at most sampling points during duck wintering, averaging 1126 g m^-2 (wet weight) at 42 sampling points in November 1996 and 24 g m^-2 in March 1997. The amount of nitrogen in M. senhousia eaten by ducks during winter was estimated at 52 t and phosphorus at 3.8 t. In the absence of ducks, M. senhousia death in summer would add equivalent nitrogen and phosphorus loads to the lagoon. The decomposition of M. senhousia in summer when water mixing is weak would also accelerate oxygen depletion at the lagoon bottom. Mussel predation by wintering ducks would therefore decrease unfavorable effects of biofouling mussel decomposition in summer when nuisance phytoplankton blooms and anoxia occur easily.

KEY WORDS: Nitrogen · Phosphorus · Aythya fuligula · Aythya ferina · Aythya marila · Musculista senhousia · Corbicula japonica · Lake Nakaumi · Lake Shinji

Published in MEPS Vol. 174 (1998) on November 26
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1998