California can say a big “thank you” to sea otters. Their big appetites are saving marshland.

Sea otters eat constantly. One of their favorite snacks is the striped shore crab. (Another favorite is the sea urchin.) These crabs dig burrows. They nibble away the roots of a marsh grass called pickleweed. Pickleweed holds dirt in place. Pretty soon, marsh banks turn as holey as Swiss cheese! Holey banks may collapse when big waves or storms hit.

Otter populations once stretched from Alaska to California and into Russia and Japan. Then people killed many of them for their fur. For years, there were no sea otters in California’s Elkhorn Slough. They disappeared from lots of other places too. At one point, as few as 2,000 of the animals remained, mostly in Alaska.

People worked hard to bring the marine mammals back. And now that work is paying off. The first returning otters were spotted in Elkhorn Slough. That was back in 1984.

Brent Hughes is a scientist who studies ocean life. He watched otters return to Elkhorn Slough. As the otters dined, marshes stopped wearing away so quickly. “They don’t completely reverse erosion,” Mr. Hughes says. But they do “slow it down to natural levels.”

O Lord, how manifold are your works! In wisdom have you made them all; the Earth is full of your creatures. — Psalm 104:24