Feeding behaviour during brooding in the oyster Ostrea chilensis: gut retention time in adults and larvae and potential use of larval faeces by adults

The brooded larva of Ostrea chilensis is not an obligate lecithotroph, as h as often been supposed, because it removes particles from the mantle cavity of the parent oyster. The ingestion of exogenous particles by the larva be comes apparent when the shell length of the veliger is approximately 290 mu m, the same stage at which the velar ciliature is also visible for the firs t time. Experiments using red plastic marker particles showed that gut rete ntion time in brooding oysters was significantly greater (10 to 11 h) than in non-brooding oysters (8 h), providing a mechanism for more efficient use of the ingested food. Although there was no significant difference in gut retention time between oysters brooding early and late larval stages, the l ate brooders eliminated most of the faeces earlier than the early brooders, Experiments using C-14-labelled algae demonstrated a shorter gut retention time in the larva (6 h) than in the non-brooding adult (10 h). Faeces from larvae contained relatively more chlorophyll a and less phaeopigment than faeces from brooding adults. The data suggest that the digestive system of the larva is much less efficient than that of the adult. Following the intr oduction of larvae previously fed C-14-labelled algae into the pallial cavi ty of the brooding parent, the radiolabel was detected in the faeces of the adult, suggesting that the parent may ingest faeces produced by the larvae . The increase in gut retention time by the adult during the brooding perio d and the ingestion of larval faeces compensate for the high energy costs a ssociated with the brooding process.