Surprise! Sea Otters Save Eelgrass

by Clark Tate

Aug. 27, 2013—Ah, the ecoweb. Ever changing, it updates itself even faster than Apple. A new sea otter study, to be published in the Proceedings of the National Academy of Sciences, shows that Elkhorn Slough has released a new and improved version of its (eco)system with the help of a few furry friends, reports the Santa Cruz Sentinel. The study’s authors were curious: Why did Elkhorn Slough support a healthy aquatic lawn of eelgrass, over 20 times larger than it was 10 years ago, when estuaries nearby are chocked with algae?

Algae, the result of nutrient overloading caused by fertilizers upstream, provides poor habitat and robs the water of oxygen. Meanwhile, eelgrass sequesters carbon (the climate-changing kind), buffers tidal swings and provides a perfect hiding place for baby fish. Since plants are the base of the food chain, or trophic system, and its main source of energy, they really matter. So the question was, why is Elkhorn's native flora doing so well?

Turns out the credit goes all the way to the top trophic tier, the increased sea otter population. Otters are the apex predators of the slough, eating mainly crabs and other shellfish. Crabs eat slugs and isopods. Slugs and isopods eat algae, allowing sea grass to grow. So as otters increase, crabs and algae decline while slugs, isopods, and eelgrass boom. “It’s kind of cool when it all fits together,” Ron Eby, a co-author of the study, told the Sentinel.

Generally ecosystem conservation and restoration work focuses on vegetation. “In this case, it’s clear you need to focus on the top and the bottom of the food web at the same time,” says Kerstin Wasson, an author of the study and research coordinator at the reserve, in the Sentinel. Grassroots meets executive powerhouse, proving that true change can start anywhere as long as it cascades along the web.