The Rocky Intertidal Zone on the Washington Coast Supports a Community

The rocky intertidal zone on the Washington coast supports a community including a bivalve mussel, Mytilus, which is preyed upon by the sea star Pisaster.If sea stars are removed, the mussel becomes dominant and other space-occupying species, including algae, decline.This suggests that the sea star Pisaster in this community serves as a

A) keystone predator, indirectly controlling the diversity of the entire community.
B) top predator, controlling only the Mytilus population, but not affecting other species.
C) low-level predator, which has little effect on the community.
D) part-time member of the community, which comes and goes erratically.
E) less important member of the community than the mussel Mytilus.