Repopulating sea otters in central California has significantly slowed erosion and offers a promising, low-cost approach to coastal ecosystem protection. A groundbreaking study published today in the journal Nature reveals that sea otters returning to their former habitat in central California estuaries slowed erosion of stream banks and marsh edges in the region by up to 90 percent.
The reappearance of these charismatic marine mammals—some of the habitat's apex predators—in Monterey County's saltmarsh-dominated Elkhorn Slough has raised hopes for those working to improve the health of our coastal ecosystems and marked an important ecological success story.
"This is a solutions-oriented paper that tells us there are some manageable actions we can take to produce positive results," said Dr. Cristina Angelini, one of the study's authors and director of the University of Florida's Center for Coastal Solutions. "In this case, restoring otter populations can be achieved without a huge effort, so we are now reaping decades of benefits from this conservation action."
The role of sea otters in ecosystem stability
The findings suggest that erosion of stream banks and marsh edges has slowed in areas with large sea otter populations, largely because sea otters voraciously prey on plant-eating marsh crabs at a time when rising sea levels, increased nutrients and stronger tidal currents should have had the opposite effect.
"Humans spend tens of millions of dollars rebuilding these creek banks and restoring these marshes. Sea otters stabilize these marshes for free in exchange for an all-you-can-eat crab meal," said senior author Brian Silliman, Ph.D., the Rachel Carson Distinguished Professor of Marine Conservation Biology at Duke University's Nicholas School of the Environment.
Researchers have documented for the first time that reintroducing an apex predator to its former habitat can bring stability to a collapsed ecosystem, raising the question: Can ecosystems around the world achieve similar results?
"Reintroducing sea otters didn't reverse the losses, but it did slow them down, allowing these systems to re-stabilize despite all the other stresses they were experiencing," said Dr. Brent Hughes, lead author of the study and an associate professor of biology at Sonoma State University. "This suggests that this could be a very effective and cost-effective new tool in our conservation toolkit."
The significance and research methods of conservation
Angelini said the tool is an encouraging sign for her and colleagues as they face similar threats to Florida's coastline from rising sea levels, severe storms and excess nutrients spilling into coastal waters.
"All of these challenges can feel overwhelming," Angelini said. "This study shows us that if we truly understand ecosystems and know which levers to pull, we can see huge benefits in the health and stability of these systems."
To understand the impact of sea otters on the landscape, the researchers conducted a large-scale survey of 13 tidal creeks and a six-year small-scale field experiment at five sites around the estuaries. Using a cage system designed by Angelini, the researchers excluded sea otters from some experimental sites but allowed them to recolonize in others.
"As a biology graduate student at UF, I mastered this skill set by setting up these cages in salt marshes in the southeastern United States, manipulating the entry and exit of predators and prey," Angelini said. "I will never forget building the cages in a parking lot at a California bayou. All these years later, we are now seeing these amazing results. It's an exciting story about the benefits of conservation and persistence in long-term research."
Compiled source: ScitechDaily