Quempillen estuary, an experimental oyster cultivation station in southern Chile. Energy balance in Ostrea chilensis 1

Rates of filtration, ingestion, assimilation, biodeposition, excretion and respiration of the Chilean flat oyster Ostrea chilensis Philippi were determined in laboratory experiments in order to establish energy budgets in relation to body size and 2 different food concentrations of the unicellular green alga Dunaliella marina. Ingestion and assimilation rates are kept constant within the range of food concentrations tested due to corresponding reductions in filtration activity with increasing food densities. The most favourable energy budget (P = aWb) was obtained at the lowest food concentration tested (0.54 mg algal dry wt 1-l; 12OC, 20 %O S) with an a-value of 25.48, when relating the energy disposable for growth and reproduction (Pi cal d l ) to body size (W; dry-tissue wt, g). At the highest food concentration tested (1.07 mg 1 1 ) , the corresponding a-value of 17.38 was significantly lower. The relatively low scope for growth in 0. chilensis is explained by a low species-specific filter-feeding activity and by the high energetic costs of routine metabolism which in a 1 g oyster (dry-tissue wt) vary between 58 and 62 % of the energy ingested. The net growth efficiencies (K,) decreased with increasing body size (from 50 mg to 3000 mg dry-tissue wt) from 53.7 to 22.6 % at the lowest food level and from 51.1 to 13.9 % at the highest food level tested. Comparison of estimated growth (calculated on the basis of the most favourable energy budget), with growth actually measured in oysters from natural banks and tray cultures, shows that the energy budgets established in the present study indeed reflect the conditions experienced by the oysters in their natural environment.