Larviphagy in native bivalves and an introduced oyster

Introduced Pacific oysters Crassostrea gigas have expanded rapidly in the Dutch Oosterschelde estuary, while stocks of native bivalves declined slightly. As a consequence, total filtration pressure increased significantly, which may affect the mortality of bivalve larvae. Better escape abilities in Pacific oyster larvae might be a contributing factor to their rapid geographic expansion. To study whether C gigas larvae are filtered less than larvae of native bivalves, we investigated filtration and ingestion of the larvae of the native Mytilus edulis and introduced C. gigas by the adults of C gigas and M. edulis as well as the native Cerastoderma edule. We measured filtration rates of C gigas and M. edulis larvae by the adult bivalves (C gigas, M. edulis and C. edule), and compared these to filtration rates of algae. Additionally, we studied the fate of filtered larvae. All three adult species filtered both C gigas and M. edulis larvae. M. edulis larvae were filtered by all three bivalve species with the same filtration rates as algae, whereas filtration rates of C gigas larvae were roughly 50% lower than filtration rates of algae. This suggests that C. gigas larvae can somehow reduce their filtration risk, whereas larvae of M. edulis cannot. The majority of filtered C. gigas and M. edulis larvae were ingested. (C) 2008 Elsevier B.V. All rights reserved.