Otters surprise as sea grass saviors


Otters can help rejuvenate sea grasses, a vulnerable natural resource that protects coastlines and provides habitats for fish, according to new research.

Scientists examined how the sea grasses in one area of California rebounded when otters returned to the area, and found that the otters helped by eating crab populations.

By keeping the crab numbers low and the sizes of the remaining crabs smaller, the otters removed a key threat to sea slugs, which feed on algae and thus keep the leaves of sea grasses clean and healthy.

This meant that the presence of a top predator helped save the smallest players in the ecosystem and rendered it healthier.

“Our findings depart from a view of nature built largely around bottom-up control, which has been the dominant predictor in explaining sea grass loss,” said the study in the Proceedings of the National Academy of Sciences.

The research spanned several decades of records on sea grass and otter populations in the Elkhorn Slough, one of California’s largest estuaries along the central coast. Key periods were compared, including from 1971 to 1976, when there were no otters, to 2005 to 2009, or about two decades after otters were reintroduced to the area.

Eelgrass rebounded in the presence of otters. The weeds are where juvenile fish like Pacific herring, halibut and salmon make their homes. They also protect coastlines from storms and soak up carbon dioxide from the atmosphere.