MEPS 182:161-173 (1999)  -  doi:10.3354/meps182161

ABSTRACT: The tropical pearl oysters Pinctada margaritifera (Linnaeus) and P. maxima Jameson are suspension feeders of major economic importance. P. margaritifera occurs in coral reef waters characterised by oligotrophy and low turbidity. P. maxima habitats are generally characterised by high terrigenous sediment and nutrient inputs, and productivity levels. These differences in habitat suggest that P. margaritifera will feed more successfully at low food concentrations, while P. maxima will cope with a wider range of food concentrations and more silty conditions. The effect of varying concentrations of natural suspended particulate matter (SPM) on clearance rate (CR), pseudofaeces production, absorption efficiency (abs.eff.), respired energy (RE) and excreted energy (EE) was determined for P. margaritifera and P. maxima. The resultant scope for growth (SFG) was determined and related to habitat differences between the oysters. There was no selective feeding on organic particles in either species. P. margaritifera had higher CR at low SPM concentration (<2 mg l^-1), while P. maxima had higher CR under turbid conditions (SPM: 13-45 mg l^-1). The latter species produced less pseudofaeces in relation to its filtration rates; consequently, this species ingested more SPM than P. margaritifera. P. maxima had positive SFG over a wider range of SPM concentrations (up to 30-40 mg l^-1) while P. margaritifera maximised SFG under low SPM conditions (<3 mg l^-1). Thus feeding responses and energy balance reflected the typical habitats of each species. P. margaritifera retained smaller particles than P. maxima, enabling it to consume a wider particle size range of SPM at low food levels. P. maxima was adapted to its environments of greater SPM load through greater ingestion rates and higher digestive ability. The optimum SPM concentrations and particle size range for P. margaritifera (SPM < 5 mg l^-1, size > 3 µm) and P. maxima (SPM = ca 3 to 15 mg l^-1, size > 4 µm) may be used for selection of optimum pearl culture sites.

KEY WORDS: Suspended particulate matter · Turbidity · Pinctada margaritifera · Pinctada maxima · Suspension-feeding · Scope for growth