Ingestion of bivalve larvae by Mytilus edulis: Experimental and field demonstrations of larviphagy in farmed blue mussels

Ingestion of bivalve larvae by Mytilus edulis was investigated. Laboratory experiments revealed that ∼ 90% of bivalve larvae offered to mussels was ingested and apparently fully digested. The shell of the bivalve larvae offered no protection against digestive processes, resulting in high larval mortality once inside the stomach. Stomach content analysis (September 2001-January 2003) showed that bivalve larvae were ingested by farmed mussels year-round, with the exception of March 2002. Numbers of ingested larvae were highest in October 2001 and May 2002, which coincides with known spawning times of farmed mussels in Ireland. Mussels ingested a large size-range of bivalve larvae, suggesting that all stages of the bivalve life cycle are vulnerable to predation. It is suggested that adult bivalves routinely filter larvae from the surrounding water and that, given the high biomass of mussels present in mussel farms, filtration by adult bivalves significantly reduces numbers of bivalve larvae in nearby waters.