JUANA SUMMERS, HOST:
Sea otters are some of the cutest animals in the world. We are journalists, and we deal in facts, so I have to allow that this is not exactly a quantifiable statement. But what is a fact is that they're helping defeat one of the most invasive species in the marine world - green crabs. Now, if you live on the West Coast, you may know about these crabs. They destroy marine habitats and aggressively hunt and eat small prey that other creatures in the ecosystem need to survive. And while coastal states have spent millions trying to manage green crab populations, ecologist Rikke Jeppesen and her team discovered otters can be a big part of the solution. She researches green crabs at Elkhorn Slough Reserve on the California coast and joins us now. Welcome.
RIKKE JEPPESEN: Thank you so much for having me.
SUMMERS: Now, I understand that you have been studying green crabs for almost two decades. You have studied them in their native habitat in Northern Europe, where you are from, and you've studied them on the U.S. Atlantic and Pacific coasts. Can you just tell us a little bit about the problems that they can cause?
JEPPESEN: Yes. The green crabs can cause various problems in the near coast ecosystems. They can damage oyster beds, which are valuable commercially. They can also damage seagrass beds. And seagrass beds, at least in Elkhorn Slough, California, provide a valuable habitat for commercially valuable fish species and also other crabs. And then last, green crabs can also consume small mudflat invertebrates that otherwise would have been available for shorebirds to eat. And the shorebirds use the estuaries as migratory stopovers. So the green crabs really have the potential to exert a disproportionately large effect on the ecosystems they invade.
SUMMERS: I mean, what you're describing sounds like a pretty massive problem. And I want to understand, how can these cute and cuddly sea otters help solve it? How did you stumble across this?
JEPPESEN: I started studying the green crabs back in 2003 for my dissertation at UC Santa Cruz, and we thought that green crabs were taking over Elkhorn Slough and the west coast of the U.S. What we found, though, as this study progressed - so in 2003, we were looking at a rapidly growing green crab population. About a decade later, the population remained high. But another decade later, the green crab population had diminished and remained at a low level.
At the same time, Elkhorn Slough is the only California estuary where the sea otter successfully has reestablished a substantial population. And the sea otter has been increasing in population size while the green crab was decreasing and remained low. So given that we do long-term monitoring and we studied the green crabs and our colleagues studied the sea otters, we overlaid the two graphs. And we found a striking pattern of when green crabs are high, sea otters were low. And when sea otters were the highest, green crabs were the lowest.
SUMMERS: What is it that makes these sea otters such efficient green crab predators?
JEPPESEN: Sea otters rely on fur for insulation as opposed to seals, which rely on blubber. Blubber insulates much better, so sea otters have to eat a lot to keep warm. So if you - it's basically a weasel in the water. And weasels are super active. They have a high metabolism. So to sustain sea otter health and keeping warm, they just need to eat a lot. And we did a high and a low estimate of how many green crabs can the sea otter population actually consume over the course of the year. And it's somewhere between 50,000, but maybe up to 120,000 green crabs.
SUMMERS: Am I correct that sea otters are an endangered species?
JEPPESEN: The sea otter is listed as threatened under the Endangered Species Act.
SUMMERS: OK, got it. I guess I'm curious then - does that create a bit of a catch there, given that they're endangered and yet they are these sort of efficient predators that are able to help provide some sort of control to the green crab population?
JEPPESEN: Yes. It's really a win-win scenario if we can support a native threatened species, the sea otter, which in turn then helps control an invasive invertebrate. So in other words, you can say that sea otters are our assistant managers of the estuary for invasive species control.
SUMMERS: That was ecologist Rikke Jeppesen of the Elkhorn Slough Reserve on the California coast. Thank you so much.
JEPPESEN: Thank you so much for having me. Transcript provided by NPR, Copyright NPR.
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