Nearly three hundred years after the Steller’s sea cow went extinct due to overhunting, scientists have determined how the four-tonne marine mammal helped shape kelp forests along the Pacific coast of North America.
And in the process created what they say is a revolutionary new approach to understanding how best to conserve plants and animals.
Research published in the Frontiers in Ecology and Evolution journal shows that the sea cows, similar to Australian dugongs or manatees, would have eaten massive amounts of fronds in the upper canopies of kelp forests, allowing sunlight to filter to the understory and spur abundance.
The California Academy of Sciences (CAS) researchers reveal not only what kelp forests would have been like before the megaherbivore was driven to extinction. Their findings may help future conservation efforts of kelp forests take Steller’s sea cow absence from these ecosystems into account.
“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,” says author Dr Peter Roopnarine. “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.”
It is estimated that it took Europeans less than 30 years after they first encountered Steller’s sea cows to hunt them into extinction. The animals, closely related to manatees and dugongs, were described by Georg Wilhelm Steller in 1741 after they were found in the Behring Sea between Alaska and Russia.
Steller’s sea cows were already restricted in their range after having once been widespread throughout much of the northern Pacific during the last Ice Age.
Now scientists are beginning to think on the impact of their extinction on the environment on much greater timescales. Modern ecosystems are often evaluated based on their recent past – a tendency known as “shifting baseline syndrome.” But this approach can obscure how the habitat may have existed over much longer time periods.
“We already see the consequences of this thinking with things like wildfire management,” Roopnarine says. “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 the new paper, the researchers argue that a different approach called Past-Present-Future (PPF) is better when evaluating ecosystem health.
PPF combines historical evidence from museums and fossils with both indigenous knowledge and modern scientific data. The mathematical models produced more accurately depict natural systems and can be used to better inform conservation.
“Today, we are surrounded by severely degraded ecosystems, places that were far healthier a mere century ago, let alone a millennium or more,” says co-author and CAS Executive Director Dr Scott Sampson. “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.”
In their Steller’s sea cow and kelp forest case study, the researchers produced a mathematical model based on historical and modern data.
Different levels of organisms’ interactions were input, such as predation of kelp by sea urchins or predation of urchins by sea otters. The model was then compared against pre-existing data on kelp forests to ensure it accurately represented the ecosystem.
Then they entered the Steller’s sea cow into the picture.
“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,” explains co-author Dr Roxanne Banker, from CAS 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.”
The research shows that today’s kelp forests are under threat from sea urchins and were more resilient when the now extinct sea cows were around.
“Algae would provide an additional food source for urchins, potentially reducing their impact on kelp,” Banker says.
Even during climate or disease crises, kelp forests in the past were less likely to become barren and urchin-dominated as is often seen today. This historical effect has been dubbed the “sea cow effect”. The sea cow effect provides insights to help kelp conservation efforts.
“If our model was further validated through experimentation on test plots, it could allow us to build more resilience into kelp forests by modelling the efficacy of different interventions,” Roopnarine says. “Selectively harvesting the upper fronds of the kelp canopy, for instance, to recreate the role that was lost with the Steller’s sea cow.”
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