Question

final review
why are otters considered a keystone species?
because they are the prettiest and most lovable of all the sea mammals
because if they were wiped out, they would not be missed
because they are a predator that keeps sea urchins in check which helps kelp forests thrive
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Explanation:

Keystone species have a disproportionately large impact on their ecosystem. Otters eat sea urchins. Sea urchins over - graze kelp if not controlled. By controlling sea urchin populations, otters help kelp forests thrive.

Answer:

because they are a predator that keeps sea urchins in check which helps kelp forests thrive