Zebra mussels feed on phytoplankton, a type of algae that can form harmful blooms. By consuming phytoplankton, zebra mussels can help to reduce the formation of harmful algal blooms, which can lead to improved water quality and reduced environmental damage. However, zebra mussels can also negatively impact native ecosystems by competing with native species for food and habitat, and by altering water quality through their filtration and excretion processes.