Sea otters have helped save a California marshland from erosion after returning to the area where they were once hunted to near-extinction.

The big picture: That's according to a study published in the journal Nature Wednesday, which credits the semiaquatic mammals and their insatiable appetite for plant-eating marsh crabs for the turnaround.

• "It would cost millions of dollars for humans to rebuild these creekbanks and restore these marshes," said co-author Brian Silliman, a professor of marine conservation biology at Duke University, in a statement accompanying that study.
• "The sea otters are stabilizing them for free in exchange for an all-you-can-eat crab feast."

State of play: The landscape has changed notably since the sea otters returned to their former habitat in Elkhorn Slough, a salt marsh-dominated coastal estuary in Monterey Bay, central California, in the decades following the introduction of conservation efforts.

• "After a few decades, in areas the sea otters had recolonized, salt marshes and creekbanks were becoming more stable again, despite rising sea levels, increased water flow from inland sources, and greater pollution," said study lead author Brent Hughes, a Sonoma State University marine ecologist, in a statement.

What they did: The researchers undertook large-scale surveys across 13 tidal creeks and small-scale field experiments at five locations around the estuary for nearly a decade in order to examine sea otters' impact on the environment.

• The animals were excluded from some test sites, but were able to recolonize in other places.

What they found: The researchers discovered after conducting modeled simulations and collecting measurements and observations on the ground and using aerial photography that erosion had slowed by up to 80 to 90% at sites with large populations of otters — and some marshes were expanding.

• "The return of the sea otters didn't reverse the losses, but it did slow them to a point that these systems could restabilize despite all the other pressures they are subject to," Hughes said.
• "That suggests this could be a very effective and affordable new tool for our conservation toolkit."

Zoom out: Sea level rise is a climate change impact that's already being felt in coastal communities, along with extreme weather events, Axios' Andrew Freedman notes.

• "Climate changes, such as more frequent and intense rain events, can increase erosion and result in greater amounts of sediment washing into rivers, lakes and streams," per the EPA.

What we're watching: Study co-author Christine Angelini, director of the University of Florida's Center for Coastal Solutions, noted in a statement that "restoring the otter population was achievable without significant effort, and as a result, we are now unlocking several decades of benefits from that one act of conservation."

• Angelini said it's an encouraging sign as they confront similar threats to Florida's coastlines from sea level rise, intense storms and excess nutrients spilling into coastal waters.

Between the lines: Unlike previous research that depended on observations, this study conclusively showed the impact of otters on the environment, said Johan Eklöf, a Stockholm University marine biologist, to AP.

Yes, but: Eklöf, who was not involved in the new study, told ABC News the conservation of otter populations was only a short-term solution against coastal erosion and trying to prevent factors including pollution and sea level rise would be better in the long term.

The bottom line: "Most ecologists maintain that we need to reduce the stressors," he added.

Go deeper: Rising sea levels threaten hazardous waste facilities along U.S. coast