The return of sea otters and their voracious appetites has helped rescue a section of California marshland, a new study shows.
Sea otters eat constantly and one of their favourite snacks is the striped shore crab.
These crabs dig burrows and nibble away roots of the marsh grass pickleweed that holds earth in place.
Left unchecked, the crabs turn the marsh banks “into Swiss cheese” which can collapse when big waves or storms hit, said Brent Hughes, a Sonoma State University marine ecologist and co-author of the new study published on Wednesday in the journal Nature.
Researchers found that the return of the crab-eating sea otters to a tidal estuary near Monterey, California, helped curb erosion.
“They don’t completely reverse erosion, but slow it down to natural levels,” said Mr Hughes.
For many years there were no sea otters in Elkhorn Slough.
The 19th century fur trade decimated their global population, which once stretched from Alaska to California and into Russia and Japan. At one point as few as 2,000 animals remained, mostly in Alaska.
Hunting bans and habitat restoration helped sea otters recover some of their former range.
The first ones were spotted in Elkhorn Slough in 1984. The Monterey Bay Aquarium’s programme for raising and releasing orphaned sea otters also boosted the estuary’s population.
For the new study, researchers analysed historic erosion rates dating back to the 1930s to assess the impact of the sea otters’ return.
They also set up fenced areas to keep otters away from some creek sections for three years – those creek banks eroded much faster.
Past studies about the return of top predators to various habitats, most famously, the reintroduction of grey wolves to Yellowstone National Park, show how such species maintain ecosystem stability.
Wolves curbed the number of elk and moose that ate saplings and slowed riverbank erosion.
Other research has shown that sea otters help kelp forests regrow by controlling the number of sea urchins that munch kelp.
Sea otters “are amazing finders and eaters”, said Brian Silliman, a Duke University coastal ecologist and co-author of the latest study.