The Missing Mammal That May Have Shaped California’s Kelp Forests

“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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