Sea otters help strengthen California’s kelp forests | Science

Not only are sea otters cute and adorable, they also help important habitats thrive.

It is well known that these creatures affect the ecosystem of kelp forests. In central California, mammals feed primarily on sea urchins, which feed on kelp. If the sea urchin population increases too much, they will eat enough kelp to destroy the underwater forest. But otters control sea urchin populations and allow kelp to thrive.

Gina Bentall, sea otter biologist and director of the advocacy group Sea Otter Savvy, said all of the sea otter’s ecological impacts may be related to their appetite. Otters have fast metabolisms and must eat about a quarter of their body weight each day. “They have to eat so much that their foraging somehow has a strong effect,” Bentall says.

Well, a new study was published this winter. PLOS climate We show that river otters help central California’s kelp forests survive environmental threats. Monterey Bay Aquarium scientists examined a century of kelp maps and found that the increase in sea otter populations over the past century has improved critical habitat. The findings highlight the role of sea otters in the ecosystem and support nature-based solutions to restore kelp forests into the future.

Kelp forests are living structures, fast-growing brown algae that provide habitat for fish, invertebrates, and marine mammals. Even if surrounded by strong currents, forests provide a calm environment and serve as a refuge for these species. Kelp buffers waves, absorbs power from storms, and protects coasts from erosion. And they are also a good source of carbon storage. One estimate suggests that kelp and other macroalgae can sequester about 190 million tons of carbon dioxide per year.

However, human activities on land have a direct impact on kelp forests off the coast, explains Kyle Van Houten, lead researcher on the study. “And that can have cascading effects throughout the ecosystem,” Van Houtan says. “When we cut down a kelp forest, we harvest more than just kelp.”

Runoff from agriculture, like pesticides and other pollutants, can end up in the ocean and damage kelp forests. Erosion has changed parts of the coastal ocean floor from rocky to sandy. This is bad news for kelp, which needs to cling to rocks to form a strong forest base. Rising ocean temperatures due to climate change are also threatening kelp, which prefers cold water.

To protect kelp forests and the ecosystems they support, scientists need to understand how they change over time. That’s why the researchers mapped kelp along the entire California coast for about 100 years.

Historical documents containing detailed measurements of kelp date back to the early 1900s. At the time, government scientists were tracking kelp that was burned to make gunpowder during World War I.

Compare historical maps from 1910 to 1912 with satellite imagery From 1989 to 2016, we created the most comprehensive map of changes in California’s kelp forests to date.

What the researchers discovered was surprising. From 1910 to recent years, kelp declined by about 7% along the California coast. However, we found something interesting when we broke down the states by region. While kelp decreased by 63 percent along the Northern California coast and 52 percent along the Southern California coast, central California actually saw a 58 percent increase in seaweed.

The researchers found that sea otter density was the biggest factor driving kelp survival in central California. As a result of the international fur trade, California’s sea otter population is now mostly confined to the Central Coast. At the beginning of the study period in 1911, otter populations were at their lowest levels and they were being hunted to near extinction for their fur. However, a small, unstable population remained off the coast of California’s Central Coast. In 1913, California declared the sea otter a fully protected mammal, and in 1977 it became protected under the Endangered Species Act, allowing the population to recover. It’s now possible.

“Over the last century, California’s kelp forests have undergone dramatic reorganization, or migration, to the Central Coast,” said Terry Nicholson, a sea otter biologist at the Monterey Bay Aquarium and another principal investigator on the study. I realized that,” he says. “This is the only place in the state where sea otter populations persist. … That means California’s kelp forests where sea otters thrive are more resilient.”

The researchers created a statistical model to determine what changes in the environment account for the growth of kelp forests. Other major factors driving changes in kelp in this study were changes in seafloor substrate and periods of extreme heat. “We’re experiencing some of the hottest temperatures we’ve ever seen in our oceans,” Van Houtan said. “So how do we set these ecosystems up for success given the challenges of extreme heat?”

New research shows that river otters naturally promote kelp conservation.

“Over the past 100 years, in areas where river otters range, despite dramatic warming, despite rapid population growth, despite much coastal pollution…despite all of this, kelp has largely disappeared. It’s grown, 60 percent in areas where there are otters,” Van Houtan said.

Bentall, who was not involved in the study, said humans need to protect sea otters that live in kelp forests. Direct human disturbance to sea otters, such as approaching them to take photographs, can be fatal to sea otters. In close quarters, otters become stressed and fatigued, making them more susceptible to health problems and predators.

Bentall explains that otters are the only marine mammals without a blubber layer and do not store energy, so they live “paycheck to paycheck.” If an otter suddenly has to jump off a kayaker that gets too close, it expends a lot of energy.

Where these failures occur repeatedly, there are cumulative costs. Otters do not “allocate” their energy for extra expenses, making them more susceptible to poor health and illness.

But Bentall explains that many people just don’t know what the otter crisis is. “Their one approach to her Instagram photos could be her one fatal accident with 1,000 kayaks,” she says. “They won’t be the first or last people to approach the otters that day.”

Otters may also become accustomed to being disturbed frequently by humans and become less wary not only of humans but also of other predators such as sharks.

“The only thing a normal person who is recreating in an otter’s home can do is give the otter space,” Bentall said. “This is a highly effective conservation action that anyone can do.”

On a larger scale, reintroducing river otters to areas where they once ranged, such as Northern California, Southern California, and Oregon, would help kelp and protect these coastal ecosystems from marine heatwaves and other Potentially more resilient to threats. The U.S. Fish and Wildlife Service has conducted a feasibility assessment to consider the potential impacts of reintroduction, but there are no plans to move forward at this time.

Otters not only have a dramatic positive impact on coastal habitats; It also generates economic benefits. California sea otters generate money and jobs through recreation and tourism. Some reintroduction skeptics question whether otters threaten California’s most economically valuable Dungeness crab fishery, but research suggests otter populations are It has been found that there is no negative impact on fisheries.

There are also important cultural reasons to support reintroducing sea otters into their historic range. The Cassia Band of Pomo Indians in Northern California supports reintroduction, and tribal leaders spoke at the Sea Otter Summit about thousands of years of coexistence between sea otters and humans before the fur trade. The Confederated Siletz Indian Tribes in Oregon have also expressed support for reintroduction in hopes of restoring historic relationships with sea otters.

Nicholson said this research will support the recovery of river otters across their historic range. “This is also strong evidence that we should adopt policies that leverage the immense value of wildlife protection and conservation along our coastlines,” she says. “Because healthy oceans with a diverse range of life forms are one of our best defenses against climate change.”