Coral suspension feeding on fine particulate matter

Abstract

High concentrations of fine suspended particulate matter (SPM) on nearshore coral reefs are generally assumed to be a stress factor for corals. However, the extent to which SPM serves as a food source for corals has not been quantified. Using 14C-labelled natural particulate matter, this study investigates the relationship between concentration and suspension feeding on fine SPM by four common species of Scleractinian coral on the Great Barrier Reef (GBR), Australia. In ingestion trials, only one species ( Porites cylindrica Dana) conformed to traditional saturation-kinetic models (Michaelis–Menten, Hollings type I) with ingestion rates reaching maximum at low to moderate SPM concentrations (4–8 mg l −1). For the remaining three species ( Pocillopora damicornis Linnaeus, Montipora digitata Dana and Acropora millepora Ehrenberg) ingestion rates increased linearly over the full range of SPM concentrations (1–30 mg l −1). All study species assimilated a major proportion of the ingested label, but assimilation efficiency was inversely related to SPM concentration. At low concentrations (1 mg l −1), estimates of assimilation efficiency ranged from 89 to 95% of the ingested SPM, decreasing to 40–50% at the highest concentrations (30 mg SPM l −1). The maximum rate of SPM carbon assimilation can cover less than 5% of basic metabolic costs, which is not significantly different from reported contributions of zooplankton feeding to coral energy budgets. More importantly, SPM feeding at high particle concentrations may cover up to half of the carbon and a third of the nitrogen required for tissue growth.