A physiological comparison between Pacific oysters Crassostrea gigas and Sydney Rock oysters Saccostrea glomerata: Food, feeding and growth in a shared estuarine habitat

Abstract

This field study had 2 objectives: (1) to test predictions from laboratory studies on growth and feeding behaviour in a comparison of 2 oyster species from the same estuary in NSW, Australia; and (2) to compare the feeding behaviour of these oysters with published accounts of other bivalve species from elsewhere. The predictions were that Pacific oysters Crassostrea gigas would feed and grow more quickly along with a greater metabolic efficiency than Sydney Rock oysters Saccostrea glomerata. Measurements were made at 3 sites in the Port Stephens estuary, NSW, and the predicted differences between species were confirmed. For both species, growth was quicker from March to May than from May to July (1999). Feeding was also faster in March and May than in July. Absorption efficiency was maintained at a relatively constant level over the experimental period by a compensatory response to changes in the organic content of the ingested material. Selection and absorption efficiencies for nitrogen altered over time, holding nitrogen absorption relatively independent of the nitrogen content of the food. Simple equations were fitted to the data to describe feeding behaviour as a function of properties of the diet, and these equations used to compare these oysters with relationships for other bivalves in the literature. A few such equations may be used to predict net absorption of food energy by oysters in the field, based on measurements of food only. At one rather coarse level, there are basic similarities between bivalve suspension feeders regarding feeding behaviour and its relation to growth. At a more detailed level, differences in physiological responses to diet may help in the interpretation of differences in growth, such as have been observed here for 2 oyster species growing in the same habitat. The competitive advantage enjoyed by C. gigas over S. glomerata is due to faster rates of feeding, particularly at higher food concentrations, and greater metabolic efficiencies of both feeding and growth.