What class do cope pods belong to, and what is their importance to the ecosystem?

Copepod, (subclass Copepoda), any member of the widely distributed crustacean subclass Copepoda. Copepods are of great ecological importance, providing food for many species of fish. Most of the 13,000 known species are free-living marine forms, occurring throughout the world's oceans.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.