Which organism is most likely not functioning as a keystone species in its ecosystem?

The organisms that is most likely not functioning as a keystone species in its ecosystem is; the Zebra mussels-Compete with native species, reducing the biodiversity of the Great Lakes ecosystem. Keystone species are plants or animals that play unique and vital role in the way an ecosystem functions. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. 

Schist. hope it

The correct answer is d