Sea otters could be saviours of world’s threatened coastal habitat say scientists

The reappearance of the endearing creatures at Elkhorn Slough, an estuary site in California, led to a “remarkable” transformation, said scientists.

Seagrass beds that had been in steep decline burst back into life, providing a vital “nursery” for hatchling fish, including Pacific herring, halibut and salmon.

Brent Hughes, from the University of California at Santa Cruz, said: “When we see seagrass beds recovering, especially in a degraded environment like Elkhorn Slough, people want to know why.

“The seagrass is really green and thriving where there are lots of sea otters, even compared to seagrass in more pristine systems.”

Flourishing green seagrass also protects shorelines from storms and waves, soaks up carbon dioxide greenhouse gas from the atmosphere, and provides a sheltered home for small delicate creatures such as seahorses and pipefish.

Around the world, seagrass meadows have come under increasing pressure from pollution, human disturbance and disease .

A key problem is nutrient chemicals from farms and urban areas spilling into the sea and promoting the overgrowth of algae, which stop the grasses getting enough sun.

This was the case at Elkhorn Slough in Monterey Bay, a major marine conservation area and tourist attraction, which has been hit by recurring algal blooms.

The change began when sea otters started moving back into Elkhorn Slough in 1984.

Scientists documented a chain reaction effect on the ecosystem caused by the otters’ eating habits. Sea otters love crabs, which they consume in huge amounts. As the crabs reduced in number and size, the grazing sea slugs they preyed on became larger and more abundant. The sea slugs, in turn, ate the algae growing on seagrass leaves, keeping them clean and once more able to soak up life-giving sunlight.

Small crustaceans known as Idotea also increased in number as a result of controlling the crab population and helped to hold the algae at bay.