Zebra mussels are the worst. They get rid of food that native species eat or need. They also kill off native mussels. They also stick to boats and travel to other waters if your boat isn't cleaned appropriately. Several species of fish eat zebra mussels and water ducks. Humans can eat zebra mussels but it's not recommended. Zebra mussels are found most in the Caspian and Black Seas south of Russia and Ukraine.