The Steller’s sea cow, an extinct relative of the manatee, could grow to five tons and 25 feet long and roamed the coastal waters of the northern Pacific Ocean. Although they were named for him, Georg Wilhelm Steller, a German zoologist who observed the animals between Asia and North America in 1741, described them as something like seaweed-and-kelp gluttons.
“These animals are very voracious and eat incessantly, and because they are so greedy they keep their heads always under water, without regard to life and safety,” Steller wrote in his book “On the Beasts of the Sea.”
Only a couple of decades after Steller’s initial encounter, his namesake sea cow went extinct. The role of humans in this extinction is debated. The mainstream view is that hunting decimated the population, but more recent research argues that the species’ decline began long before the first human arrived in the Bering Sea region. Their epic appetite, though, is undisputed, and it may have been a good thing.
A paper published last month in the journal Frontiers in Ecology and Evolution argues that the appetite of the Steller’s sea cow played a major role in shaping coastal ecosystems in northern Pacific waters, particularly the kelp forests that have been devastated in recent years by factors linked to climate change. The paper claims that the sea cow would have made kelp forests more resilient to these changes, and that conservationists may be able to use this knowledge to better protect such ecosystems in the future.
“The world we’re living in right now is actually a very young one, because the changes that we’ve driven are not very old,” said Peter Roopnarine, a researcher at the California Academy of Sciences and a co-author of the paper. “As we think more and more about preserving and regenerating, we have to take history into account.”
Kelp forests, which in the northern Pacific primarily consist of giant kelp and bull kelp, are some of the most biodiverse places in the ocean. The seaweed algae can tower hundreds of feet above the ocean floor, providing protection and nutrients for scud, sea otters, snails, rockfish, anemones, eels, crabs, jellyfish and other marine life. The forests can also store atmospheric carbon.
Over the past decade, a majority of kelp forests off the coast of Northern California were destroyed. A surge of warm water to the region around 2014 — a warm water “blob” — elevated sea surface temperatures, throwing kelp forests into havoc. Around the same time, warmer water may have sped up sea star wasting disease, which causes sea stars to die and break apart. Sea stars are the primary predators of kelp-eating sea urchins. The mass die-out allowed the sea urchin population to explode, and in 2021, satellite imagery showed that 95 percent of California’s kelp forests had been destroyed and replaced by carpets of sickly sea urchin barrens.
Many details of this story are still unknown, but there is consensus that bringing the kelp forests back to their former health will be difficult.
Scott Sampson, a paleontologist, director of the California Academy of Sciences and a co-author of the paper, wondered whether anything could be learned about kelp forest decline, or ways to reverse it, by considering the Steller’s sea cow.
“You look at these animals living up and down the coast — they must have had a huge impact,” Dr. Sampson said.
Another co-author of the paper, Roxanne Banker, an ecologist at the California Academy of Sciences, added that ecosystems “are made of species that influence each other and interact in very nonlinear ways.”
She continued, “Sometimes adding one piece in will change how another piece works.”
Together, the co-authors created a simplified mathematical model of the kelp forest ecosystem, simulating an alternate reality where the Steller’s sea cow didn’t go extinct and lived in conditions similar to the status quo.
The model showed that the sea cow’s grazing would thin out the kelp forest canopy. Sunlight would reach deeper into the water, and a more robust algae understory would form and serve as an alternative feeding option for sea urchins. Under warming waters and sea star wasting disease, the model showed, this sea-cow-grazed ecosystem would bounce back faster than the existing ecosystem.
Maybe this resiliency could be replicated in conservation efforts, or at least inform conservationists about what might work. “What we’re advocating for here is a thoughtful way of partnering with nature to bring back the health of these places,” Dr. Sampson said.
Laura Rogers-Bennett, a marine biologist at the University of California, Davis, who was not involved in the research, said that, though there is value in crafting these kinds of simplified models, people should be careful about drawing any strong conclusions from them. Ecosystems are so complex and delicate, even a small change could throw things wildly around.
She added that modern kelp forests often have diverse algae understories, and that the interconnected web of alive and dead, dynamic and inert, big and small, is difficult to model. “Thinking about what the habitat looked like back then, I would argue that we don’t even know what the habitat looks like now,” she said.
The authors of the paper acknowledged these drawbacks, but, Dr. Roopnarine said, “We’ll always be limited in terms of knowing enough about all these species in the system.” He added, “Frankly, we’re running out of time to really understand these systems.”
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