Marine Mammals Help Mitigate Climate Impacts on Ocean Ecosystems


Sea Otter        Photo: Marshal Hedin, Wiki CC

By Ashira Morris, ODP Staff Writer

Kelp forests along the U.S. West Coast are threatened because of an exploding sea urchin population caused by the climate crisis, but in Monterey Bay, sea otters keep the urchin population in check and kelp forests healthy. While many natural underwater systems are out of whack because of climate change, sea others aren’t the only marine mammals helping maintain some equilibrium:

  • In Fiji, reef sharks aren’t just predators — they also patrol coral reefs to keep seaweeds safe from fish that like to eat plants
  • Endangered North Atlantic right whales act as ocean fertilizers, spreading nutrients underwater with their poop
  • In Ecuador’s Gulf of Guayaquil, bottlenose dolphins are the top predator, keeping fish populations in check

Why this Matters: Marine mammals play an important role in global ecosystems as “apex predators, ecosystem engineers and even organic ocean fertilisers,” The Conservation writesMarine mammals worldwide are threatened by changing temperatures, shifting food sources, and acidification. That’s on top of threats they face from human activity like fishing and ship strikes. Allowing marine mammals — and the ecosystems they inhabit — to thrive is part of the push for protecting 30% of the world’s ocean by 2030. These marine protected areas have the added benefit of sequestering carbon as well as protecting wildlife, according to recent research.

Sea Otters Historic Range Includes Estuaries. They Could Return. 

But back to the sea otters: although their place in the kelp forest ecosystem is well-known, California sea otters also used to live in estuaries before the fur trade wiped them out in the 1800s. When conservationists were helping sea otters recover, they only focused on the small remaining pockets where the current population lived, not the massive swaths of coastal estuary that they used to call home. This is one of the many ways that shifting baselines, which skew our sense of “normal” so even as otters are found in fewer places, for example, that depleted state is seen as the baseline.   

However, as Hakai Magazine reports, some scientists want to reintroduce sea otters to California’s estuaries. A study of otters who returned to Elkhorn Slough, an estuary inland from Monterey Bay, found that they helped the native endangered eelgrass return. Just like the sea otters keep sea urchin populations from exploding in other ecosystems, in the estuary, the otters were eating crabs and preventing them from overeating microorganisms that keep algae blooms in check. 

“That was the aha moment,” biologist Brent Hughes, who did the study, told Hakai. “That’s when we realized, okay, these animals really should be in these estuaries.”

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