Phosphorus recycling by zebra mussels in relation to density and food resource availability

Using flow-through microcosms, we examined phosphorus (P) recycling by zebra mussels under conditions of nearly constant food resource supply and varying zebra mussel population densities (600–5200 ind./m²). At all density levels, zebra mussels filtered substantial algae, measured as chlorophyll biomass. Because chlorophyll biomass inputs were low throughout the study, zebra mussel biomass-specific rates of chlorophyll filtration declined with increasing density, suggesting food resource limitation at the higher densities. We observed net total P export and high zebra mussel biomass-specific rates of P recycling over time in microcosms at high zebra mussel densities. In systems with a low zebra mussel density, net total P export did not occur over time. Our results suggest the occurrence of P remineralization by zebra mussels and net loss associated with emaciation during periods of temporary starvation. These findings have implications for P dynamics since zebra mussels can be subjected to periods of starvation over seasonal and annual time scales.