Restoring tropical coastal wetland water quality: ecosystem service provisioning by a native freshwater bivalve

Abstract

Freshwater bivalves can influence water quality by reducing phytoplankton levels through filter-feeding and altering nutrient levels through excretion and biodeposition. In northeast Australia, native freshwater bivalves (Corbicula australis) may help restore the water quality of coastal wetlands that receive high nutrient loads in runoff from nearby agricultural activity. We investigated the biofiltration and biodeposition capacity of C. australis and discuss their potential to provide an ecosystem service benefit of improved water quality to the Great Barrier Reef (GBR). The filtration and biodeposition rates of C. australis were measured in natural and artificial wetlands across: (1) the population’s size range; and (2) the temperature range of the wetlands they inhabit. High frequency water temperature loggers were deployed in wetlands throughout the year to determine water column temperature seasonality, population densities were measured to scale from individuals to ecosystem service provisioning potential. Bivalve filtration and biodeposition were quantified by measuring the rates of chlorophyll a removal and nutrient biodeposition, respectively. Biofiltration rates did not increase with size or differ between natural and artificial wetlands. In contrast, size was positively related to phosphorus (P) and nitrogen (N) biodepsoition rates, and N biodeposition rates differed between natural and artificial wetlands. Our results also suggest that biofiltration and biodeposition capacity of C. australis may be limited in high water temperatures only experienced in summer months. Overall, we demonstrate the importance of size, population density, and environmental context (i.e. wetland type and season) for the filtering capacity and biodeposition rate of C. australis. Larger individuals and denser populations mean that filtration and biodeposition rates are likely to be higher in artificial wetlands and may lead to greater processing of nutrient rich water.