Meet the extinct sea cow that cultivated Pacific kelp forests

Understanding the ancient creature's impact could help aid conservation efforts.
Steller's Sea Cow
A sketch of the extinct Steller's Sea Cow from a book published in 1896. Biodiversity Heritage Library/California Academy of Sciences

While manatees in the United States today are more associated with the state of Florida, a relative of theirs once swam the seas along North America’s Pacific coast. Millions of years ago, the Steller’s sea cow (Hydrodamalis gigas) grazed in the kelp forests along the Northern Pacific Ocean and the Bering Sea. This marine mammal is part of the Sirenia order that includes present-day manatees. It could weigh up to four tons and grow to lengths of 26 to 30 feet—much longer than today’s manatees. It grazed along the Northwest’s mighty kelp forests, which today stretches from Baja California, Mexico up the Pacific coastline to Alaska. The sea cow ate huge quantities of kelp from the upper canopy of kelp forests, which allowed needed sunlight to travel down to the forest’s understory.

According to the writings of Georg Wilhelm Steller, the sea cow was driven into extinction somewhere around 1768, only 27 years after its first encounter with Europeans. Steller, who the sea cow is named after, was a a scientist who accompanied Russian merchants on commercial voyages to the Commander Islands in the Bering Sea in the 18th Century.

[Related: How kelp farming is helping revive the economy and ecology of a Long Island bay.]

Overhunting likely drove the Steller’s sea cow to extinction and scientists believe that this change in the ecosystem was detrimental to the health of the west’s kelp forests.

In a paper published yesterday in the journal Frontiers in Ecology and Evolution, researchers from the California Academy of Sciences detail a new method that they used to figure out what historical kelp forests may have looked like when this marine megaherbivore was still grazing.

“Kelp forests are highly productive ecosystems. They act as storm buffers, are economically important for fishing, and are home to countless marine organisms, yet they are in steep decline throughout the Pacific,” Peter Roopnarine, study co-author and Academy Curator of Geology and Invertebrate Zoology, said in a statement. “When kelp forests were evolving millions of years ago, there were large marine herbivores like the Steller’s sea cow, which are now extinct. So when it comes to what’s driving their widespread decline, there might be a major component we’re missing.”

The tendency for scientists to evaluate a modern ecosystem based on its more recent past is called shifting baseline syndrome and it can leave out or hide what an ecosystem may have looked like over longer period of time, according to the study’s authors.

“We already see the consequences of this thinking with things like wildfire management,” Roopnarine said. “In the short-term, wildfires have been seen as something to suppress because of the damage they bring to forest ecosystems. But recently we have learned that, in the long run, wildfires are a natural part of those systems that can lead to healthier, more resilient forests.”

In an effort to avoid shifting baseline syndrome, the team in the study proposes using a new way to evaluate the overall health of ecosystems. The Past-Present-Future (PPF) approach combines historical evidence collected from museum specimens and the fossil record, Indigenous ecological knowledge, and current scientific data. The team says it can lead to more accurate mathematical models that better depict natural systems. The study proposes that these models can create more effective conservation techniques.

“Today, we are surrounded by severely degraded ecosystems, places that were far healthier a mere century ago, let alone a millennium or more,” study author and Academy Executive Director, Scott Sampson noted in the statement. “Growing numbers of these ecosystems are now in danger of collapse, even if we protect them. So if we are to help guide a given place toward a flourishing future, we must understand not only its current state of health, but past states as well, and then apply these insights toward calculated, regenerative interventions. This Past-Present-Future approach to conservation has the potential to be revolutionary.”

[Related: These now-extinct whales were kind of like manatees.]

To create a model that creates this more accurate picture of historical kelp forests, the researchers first input the effects from various players in the ecosystem, such as, sea urchins that prey on kelp and sea otters that prey on the urchins. Then, this model is compared with pre-exiting data on kelp forests to better show how the ecosystem really functions.

After the model is refined, the team adds the extinct Steller’s sea cow to the model to see how the marine mammal impacted the kelp forest and the ecosystem’s response.

“One of the more important and surprising findings was that including the Steller’s sea cow resulted in a totally different type of kelp forest,” said Roxanne Banker, study author and postdoctoral researcher at the Academy and the University of Nevada Las Vegas. “Instead of kelp-dominated, which is what we think of with modern forests, the sea cow’s presence and predation of the upper canopy would have resulted in more of a balance between kelp and algae as more sunlight would have reached the sea floor.”

This finding is particularly significant when looking at the state of current kelp forests. Today, they are heavily degraded, partially due to over-predation from sea urchins, but also pollution, the over harvesting of kelp, El Niño, and more. The presence of more algae in a kelp forest would gives sea urchins an additional food source, which might reduce their impact on kelp, according to Banker.

The study also found that the kelp forests as a whole were often more resilient when the Steller’s sea cow was grazing on their canopies. The forests were even healthier under duress from ocean warming or disease outbreaks. It says that the kelp forests of the past may have been less likely to turn into an urchin-dominated forest and could recover more quickly.

The researchers dubbed this the “sea cow effect,” and say it provides a blueprint for kelp conservation today.

“If our model was further validated through experimentation on test plots, it could allow us to build more resilience into kelp forests by modeling the efficacy of different interventions,” Roopnarine said. “Selectively harvesting the upper fronds of the kelp canopy, for instance, to recreate the role that was lost with the Steller’s sea cow.”