INGESTION OF SMALL-BODIED ZOOPLANKTON BY ZEBRA MUSSELS (DREISSENA-POLYMORPHA) - CAN CANNIBALISM ON LARVAE INFLUENCE POPULATION-DYNAMICS

The zebra mussel Dreissena polymorpha established populations in western Lake Erie in 1986 and achieved densities exceeding 3.4 X 10(5) individuals.m-2 during 1990. We assessed apparently incidental predation on Lake Erie and Erindale Pond zooplankton by adult mussels. Dreissena larvae and small rotifers (Polyarthra spp., Keratella spp., Trichocerca) sustained moderate to high predatory mortality whereas larger taxa (Bosmina, Scapholeberis) were invulnerable to predation. Larval Dreissena almost always sustain > 99% mortality in European lakes. While mortality has been ascribed primarily to lack of suitable settling substrate and unfavourable environmental conditions, it may be confounded by larval predation by adults. We demonstrate using STELLA(TM)-modelling that with a larval mortality rate of 99%, settled mussel densities observed in western Lake Erie during 1990 would not be achieved until at least 1994. A model that combines a lower rate (70%) of abiotic mortality with larval predation by adult mussels correctly predicts 1990 mussel densities. This model of Dreissena population growth is also consistent with larval settlement patterns in Lakes Erie and St. Clair and some European systems.