Adjustment of the components of energy balance in response to temperature change in Ostrea edulis

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Abstract
Routine oxygen consumption (VO2μl 285 mg-1 h-1) by specimens of Ostrea acclimated to temperatures between 5° and 25°C increases with exposure temperature throughout much of the range 5 to 30°C. There is little evidence of a relative suppression of the acutely-measured rate: temperature curves for routine oxygen consumption following warm acclimation. Energetic costs in Ostrea thus rise sharply with increase of environmental temperature. The clearance rate (V w ,ml 285 mg-1 h-1) of Phaeodactylum measured synchronously shows a marked thermal optimum within the range 15–28°C, followed by a decline towards high exposure temperatures. Maximal clearance rates of 600–750 ml water h-1 occur approximately 5°C above the temperature to which the animals have been acclimated and are adjusted according to environmental temperature. The changes in filtration efficiency (V w /VO2, ml/μl) in Ostrea following thermmal acclimation are controlled by compensatory responses of the irrigation rate rather than by a relative reduction of energy losses from metabolism. Because the clearance rate declines in animals acclimated to 25°C, whereas the metabolic losses increase throughout the temperature range 5 to 30°C, maximum filtration efficiency is achieved at 20°C. Calculation of the energetic cost of filtration suggests that the improvement of filtration following warm acclimation offsets metabolic energy losses even at low food concentrations in Ostrea. Even if energy losses not accounted for in this study were substantial, a positive index of energy balance could be maintained during the summer months at ration levels which commonly occur in inshore waters.