Zebra mussels were first discovered in North America in the Great Lakes in 1988. These invasive species eat phytoplankton and other microscopic organisms in freshwater. What would be the most likely effect if zebra mussels are introduced into a local freshwater lake? The ecosystem would be harmed, as other phytoplankton-eating organisms would have less to eat. The ecosystem would benefit from the increased competition for food and increased diversity. The zebra mussels would benefit the lake, especially species higher up on the food chain. The zebra mussels would only affect the lake if it already contained another species of mussels.