Antagonistic effects of invasive zebra mussels and nutrient enrichment on algal and rotifer biomass

Abstract

We conducted a mesocosm experiment to determine how multiple stressors including invasive zebra mussels (ZM), a nutrient pulse (NP), and the addition of herbivorous large-bodied zooplankton (Daphna pulex and Simocephalus vetulus; LBZ) affected resident plankton (phytoplankton and zooplankton) in both single-and multiple-factor treatments. We also assessed whether the establishment of LBZ was influenced by ZM and/or NP. Algal and rotifer biomass was significantly greater in treatments with nutrients than in treatments with both nutrients and zebra mussels indicating antagonistic effects of the two stressors. Zebra mussels also had several effects on zooplankton that were independent of the other stressors: zebra mussels reduced the biomass of the invertebrate predator Chaoborus sp., while the biomass of resident cladocerans and large-bodied zooplankton tended to be higher in at least some of the treatments with zebra mussels. Large-bodied zooplankton did not affect algal biomass or resident zooplankton in any of the treatments. Our results contribute to a growing body of research showing that invasive zebra mussels can be the primary drivers of plankton dynamics when multiple stressors are present in aquatic ecosystems.