After near-extinction, the California otter population off Big Sur has increased to 2,400. The catastrophic annihilation of sea otters followed by their dramatic rejuvenation has undoubtedly had a profound impact on the ecology of the Northwest coast, but just what kind of impact is not certain. We do know that otters are voracious eaters of shellfish, which may be a bad thing from both a human and clam perspective. We also know they eat the sea urchins that devour kelp, which can be a good thing. They also absorb wave energy, protecting the coast from erosion.
Sea urchins can clearcut and devour kelp forests with an average advance of a foot a day.
Eliminate kelp and you hurt the fish. Introduce otters to eat the urchins and the kelp comes back, and with it more fish. The algin that comes from kelp is used in a variety of food products, from ice cream to beer. Kelp also is used as biodegradable surgical thread. But humans also harvest urchins for the Japanese market.