Sea otters have protected kelp forests for a century 

A study from Monterey Bay Aquarium has shed light on the pivotal role played by southern sea otters in preserving and enhancing the kelp forests of California. 

The research offers profound insights into the dynamics between a keystone species and its environment, providing a hopeful narrative in the face of environmental adversities.

According to the study, southern sea otters have prevented the widespread decline of California’s kelp forests over the past century. The research was focused on the period from 1910 to 2016.

A century of support from sea otters

Once on the brink of extinction due to rampant hunting in the 1800s, the southern sea otter has made a remarkable comeback along California’s central coast.

This resurgence has had a big impact on the kelp forests in the region. 

“Our study showed that kelp forests are more extensive and resilient to climate change where sea otters have reoccupied the California coastline during the last century,” explained study lead author Teri Nicholson, senior research biologist with the Monterey Bay Aquarium Sea Otter Program.

“Where sea otters are absent, kelp forests have declined dramatically. In fact, we found sea otter population density as the strongest predictor of change in kelp canopy coverage across this hundred-year span.”

Understanding climate trends 

Utilizing historical surveys of kelp forests, the researchers performed detailed analyses of canopy extent, biomass, and carbon storage.

The team accounted for annual variations and differences in survey methods to provide a comprehensive view of the trends over the last century. 

“The use of historical maps provided an important opportunity to help us examine long-term kelp forest trends,” said Jess Fujii, scientific and operational leader of the Aquarium’s Sea Otter Program.

“This broader view is important for understanding trends related to climate change, and developing effective science-based conservation strategies.”

Insights on sea otters and kelp forests

The study highlighted a significant increase in kelp forest canopy along the central coast, with an estimated 56 percent rise in coverage. 

By contrast, the northern and southern regions of California saw decreases of 63 and 52 percent, respectively. Remarkably, the overall decline in the state’s kelp canopy was just six percent from 1910 to 2016.

Through machine learning frameworks, the researchers identified sea otter population density as the strongest predictor of change in kelp coverage.

This finding underscores the otter’s role as a keystone species, vital in maintaining the health and balance of kelp ecosystems. 

Broader implications 

“Today, extreme heat in the ocean is intense and persistent. Beginning a decade ago, this threat now affects more than half the ocean’s surface,” said study senior author Kyle Van Houtan, a research scientist at Duke University.

“This is a major problem for kelp forests as chronic temperature stress undermines kelp growth and health. Ecosystems are complex, and to give them their best chance at surviving these extreme changes, they need all their component parts. Sea otters, of course, are hugely influential for Pacific kelp forests. Historical studies like this are a crucial demonstration of this dynamic over the long term.”

The study not only reinforces the importance of conserving the southern sea otter but also highlights the potential of nature-based solutions in restoring kelp forests. 

Healthy kelp forests provide numerous benefits, such as serving as nursery grounds for fisheries, mitigating coastal erosion, and aiding in carbon storage.

The reintroduction of sea otters to their historical ranges could be pivotal in reviving these ecosystems along more stretches of the California coast.

The study is published in the journal PLOS Climate.

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