Comparative effects of microalgal species and food concentration on suspension feeding and energy budgets of the pearl oysters Pinctada margaritifera and P. maxima (Bivalvia:Pteriidae)

Abstract

This study aimed to determine the influence of microalgal species and food concentration on various physiological parameters and Scope for Growth (SFG) in adults of 2 pearl oysters, Pinctada margaritifera and P. maxima. Clearance rate, pseudofaecal production rate, absorption efficiency, respiration rate and excretion rate were determined over a range of food concentrations using 2 microalgal diets, Tahitian Isochrysis sp. (T-Iso) and Dunaliella primolecta at 28°C. Clearance, pseudofaecal production and respiration rates were significantly affected by microalgal diet. From these results, and because of the higher energy content of T-Iso, pearl oysters feeding on T-Iso had maximum values of SFG that were 1.5 to 2.1 times higher than when feeding on D. primolecta. Clearance rate and absorption efficiency were significantly related to food concentration as negative exponential relationships (p < 0.001). Generally, pseudofaecal production, respiration and excretion rates were significantly related to food concentration as positive linear relationships (p < 0.005). Optimal food concentrations for maximum SFG for P. margaritifera and P. maxima were 1 to 2 mg 1-1 and 2 to 3 mg l-¹, respectively. P. maxima was better adapted to a wider range of food concentrations. P. maxima maintained positive SFG up to 9 mg l-¹ food concentration when feeding on T-Iso and up to 7 mg l⁻¹ when feeding on D. primolecta, while equivalent values for P. margaritifera were 7 mg l⁻¹ and 5 mg l⁻¹, respectively. These results are in accordance with P. maxima occurring in a wider range of habitats than P. margaritifera, and experiencing greater concentration ranges of suspended particulate matter.