Functional descriptions of feeding and energetics of the Pacific oyster Crassostrea gigas in New Zealand

Pacific oysters Crassostrea gigas were fed a mixed diet of algae and silt o ver a range of concentrations from 0.8 to 637 mg l(-1), and an organic cont ent ranging from 0.7 to 72%. These data were used to parameterise a set of functions describing the physiological response of oysters to varying envir onmental conditions. All parameters were standardised to body length. There was greater variation of size-specific clearance rate (CR) standardised to dry tissue weight than to length. CR increased hyperbolically with tempera ture with a maximum rate (0.24 l h(-1) cm(-1)) at 20.7 degreesC. Most feedi ng experiments were carried out at 10 to 13 degreesC, except for the measur ements of temperature effect. CR increased rapidly with increasing seston c oncentration, peaked at about 10 mg l(-1), above which it consistently decr eased. It was modelled as a function of pumping rate of water and extractio n efficiency of particles from water. The filtration rate was found to be a Type 2 hyperbolic function of seston concentration within the range tested . Ingestion rate was described as a function of food quantity, quality and selective ingestion of organic particles. A positive effect of organic cont ent on absorption efficiency was found only at a very low organic content o f less than 5 %, while above this level, absorption efficiency was constant at 86 %. Oxygen consumption rate had an allometric relationship to body si ze and increased over the range of experimental temperatures.