Comparative effects of temperature on suspension feeding and energy budgets of the pearl oysters Pinctada margaritifera and P-maxima

This study assessed the effects of seasonal temperatures on suspension feeding, related physiological parameters and energy budgets in 2 pearl oysters, Pinctada margaritifera and P. maxima. Pearl oysters that were acclimatised at approximately 19, 23, 28 and 32 degrees C in the field were tested in the laboratory at these temperatures. Clearance rate (CR), absorption efficiency (ae), absorbed energy (AE), respired energy (RE), excreted energy (EE) and the value of (AE - RE) were significantly affected by temperature. They usually increased with increasing temperature. ae, RE, EE and the value of (AE - RE) differed significantly between the pearl oyster species. P. margaritifera had a significantly higher CR than P. maxima at 19 degrees C. P. maxima had higher ae than P. margaritifera at 28 and 32 degrees C. As a result, P. margaritifera had greater AE than P. maxima at 19 degrees C, but the latter species had greater AE at 32 degrees C. Temperature significantly affected the RE of P. margaritifera over a wider temperature range (19 to 32 degrees C) than P. maxima (19 to 23 degrees C). However, interspecific differences in RE were only significant at 32 degrees C. P. maxima had significantly higher EE at 32 degrees C than P. margaritifera, although this energy accounted for a very small portion of AE (<5%). P. maxima exceeded P. margaritifera in Scope for Growth [SFG = (AE - RE) - EE] at 32 degrees C, but the latter species had greater SFG at 19 degrees C. These results agree with observations of the occurrence of P. margaritifera at higher latitudes and lower temperature habitats. The temperature effects on suspension feeding, related physiological parameters and SFG indicate that there will be marked seasonal variations in growth in both species in environments where water temperatures vary seasonally. In bioenergetic terms, the optimum temperature ranges for these pearl oysters are approximately 23 to 28 and 23 to 32 degrees C for P. margaritifera and P. maxima, respectively.