Below are two food chains and two food webs to aid in comparing ecosystems with and without zebra mussels.
Food Chain without zebra mussels:
Food Chain with zebra mussels:
As you can see in the above pictures, zebra mussels will soon replace the mollusks and since not many species eat the zebra mussels, many aquatic animals will soon die out. Although, pochards eat zebra mussels and will continue to exist if zebra mussels were to appear in an ecosystem.
Food web without zebra mussels:
Food web with zebra mussels:
As shown in the two food webs above, when zebra mussels begin to appear in an ecosystem, they will replace the caddisfly larvae. Eventually this species will cease to exist. The green sunfish and other creatures which consume caddisfly larvae will then also have to switch to other sources of energy. Zebra mussels will also supply the pochards with more food, causing that species to multiply drastically, possibly causing a shortage of algae for pond snails and bullfrog tadpoles. Excess pochards may also cause the dabbling duck survival rate to increase as well. Of course, these changes to the ecosystem is not healthy for any of the creatures living in and around that area.