Sea otters may help combat harmful agricultural run-off in California

sea otter photo
CC BY-NC 3.0 Joe McKenna

As a keystone species, the importance of sea otters for the health of coastal ecosystems can't be understated. A new study shows that they may even play an indirect but key role in helping coastlines cope with agricultural run-off.

The study by University of California, Santa Cruz, published in mid-August, shows that by eating crabs, sea otters are helping sea grasses thrive even in the face of pollution.

According to The Republic, "Underwater sea grass, which has many environmental benefits including providing habitat for fish, is typically stifled by algae fueled by nutrients in agricultural runoff. But with otters present, the sea grass thrived through the cascading effect of the food chain...The sea otters eat crabs. Crabs prey on animals that clean the estuary's sea grass of algae caused by farm pollution. The otters keep the crab numbers low, allowing the grass to thrive, according to the researchers."

This is good news for species of fish like salmon and herring that use the grasses as nurseries, and good news for the planet as the grasses also help to sequester carbon.

In a parallel way, sea otters help kelp forest thrive by eating sea urchins. As demonstrated when sea otters returned to Monterey Bay, the species keeps sea urchin numbers in check, allowing the giant kelp to grow, which then acts as both a shelter and a restaurant for many other marine species. It also helps to combat global warming, according to a recent study. "According to the study, which looked at 40 years of data on sea otters and kelp blooms from Vancouver Island to the western edge of Alaska's Aleutian Islands, when sea otters are around, underwater kelp forests can absorb 12 times more carbon dioxide than when the plants aren't protected from urchins (those spikey little devils!)."

And to think that we nearly drove this important species into extinction. Sea otters are still endangered, with their numbers having come back up to around 2,800; they are far from out of the woods. Protecting them means protecting many vital aspects of marine ecosystems, as these studies have shown.

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