Nitrogen and phosphorus recycling by the zebra mussel (Dreissena polymorpha) in the western basin of Lake Erie

The zebra mussel (Dreissena polymorpha) is an exotic mollusc that has invaded many North American habitats. Because of its abundance and ability to filter large quantities of water, zebra mussels may greatly affect the recycling of nutrients. Therefore, we quantified the nutrient cycling parameters of the zebra mussel in the western basin of Lake Erie. Small mussels excreted less N and more P per gram dry weight than did larger mussels and thus excreted at significantly lower N:P ratios (approximately 5:1 molar) than other size-classes. All size-classes excreted at N:P ratios below 20:1. These low ratios could cause a shift in phytoplankton community structure towards blue-green algae. The concentration of nutrients in the food of the mussels (seston) and mussel tissues also varied seasonally and among mussel size-classes. Furthermore, multiple regression analysis showed that seston and mussel nutrient concentrations can predict a significant amount of variation in mussel N and P excretion rates and ratios in some cases. Comparison of zebra mussel P recycling rates on a basin-wide scale with other P sources suggests that mussels are a major factor in the recycling and flux of P in the western basin of Lake Erie.