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Many marine reserves aren’t built for a hotter planet. Now there’s a guide to fix that.

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Many marine reserves aren’t built for a hotter planet. Now there’s a guide to fix that.

A team of scientists mapped out a series of kelp forest “stepping stones” calibrated to where habitat will exist and how species might move.
November 1, 2023

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The Pacific waters that hug the coastlines of California and Mexico’s Baja California peninsula teem with wildlife. Great white sharks and killer whales patrol the waters of the Channel Islands. Vast 30-meter-tall kelp forests, home to everything from starfish to sea otters to gray whales, span the 800 kilometer-long waters known as the California Bight.

But the underwater inhabitants of this region face an increasingly uncertain future, thanks in part to climate change. Deadly marine heatwaves are predicted to become a yearly event there by the end of the century, if greenhouse gas pollution continues unabated. Even if people meet ambitious targets to staunch carbon dioxide emissions, underwater heatwaves are still expected there roughly half the years.

That imperils ecosystems and could weaken attempts to protect them using traditional methods of establishing protected areas where activities like fishing are restricted. As nations work to expand these reserves to meet recent commitments to protect 30% of the world’s oceans for biodiversity, scientists are working to figure out how to create protected areas better suited to a hotter future.

“Until now, marine protected areas have been designed for biodiversity conservation, but not necessarily for climate resilience,” said Nur Arafeh-Dalmau, a marine ecologist and postdoctoral researcher at Stanford University and the University of California, Los Angeles. “They suffer from climate impacts but aren’t designed to endure them.”

Arafeh-Dalmau and an international team of 50 fellow scientists saw opportunity in this region’s plight. It could serve as a case study for how to design marine protected areas (MPA’s) that can help border-straddling ecosystems withstand global warming. The researchers developed a set of guidelines—21 in all—meant to help devise a climate-conscious reserve system.

 

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Overall, the measures call for a more elaborate system of protected areas built to accommodate the varied movements of marine species and the ways in which climate change might eat away at existing habitat.

A number of the measures involve hedging—an approach used by gamblers and investors to guard against uncertainty—and one increasingly adopted by conservationists faced with a future where history isn’t a reliable guide. According to the proposed rules, people designing MPA’s should protect areas that represent at least 30% of each kind of habitat in different parts of a region, including three examples of each habitat type in widely separated reserves to increase the odds that at least some will endure.

Another major theme is accounting for the movement of species, which often don’t stop at international borders such as the line separating U.S. and Mexican waters. A third, is identifying and protecting areas that are likely to become refuges for key species as a warming planet turns some places from habitats into no-go zones.

The researchers used these rules to design MPAs for giant kelp forests and their inhabitants in the California Bight. The scientists found that kelp survival was higher in waters with variable temperatures, enabling them to build a detailed map of where kelp forests are most likely to endure as heatwaves become more common. They also noted that the movement of larvae from kelp dwellers varies wildly depending on the species. Larvae of the abalone shellfish, for example, will drift up to 100 kilometers over a week, while sea urchin and sea cucumber larvae are on the move for as much as two months, traveling up to 700 kilometers.

These insights into where habitat will exist and how species move shed light on how the region’s might function in the future, much like someone trying to sort out how many subway and train lines it will take to get from Manhattan to the LaGuardia Airport.

Overall they found that the number of functioning links between different pockets of kelp forest along the bight would be cut roughly by half in the future, making it harder for different populations to interbreed or populate new areas, the scientists reported Oct. 26 in One Earth.  

The increasing fragmentation of these kelp forests means a robust MPA system should prioritize “key stepping-stone nodes” to avoid the loss of ecological connections between different parts of the bight. Regulators might also need to step up restrictions on extractive industries such as fishing to help protect remnant populations in these nodes. That’s because models showed that even inside MPA’s, a regular battering from heatwaves could make it nearly impossible for populations of some key species to bounce back.

This future reserve system is a far cry from current conditions. California has created a network of MPA’s covering 16% of state waters, while in Mexico, less 1% of the marine ecosystems in the bight are shielded.

Arafeh-Dalmau has already glimpsed the dangers facing the bight. He studied the toll an underwater heatwave took on kelp forests off the Mexican coast between 2014 and 2016. Despite that gloomy news, though, he sees at least some reason for encouragement in the new findings.

The approach of mapping “stepping stones” connecting different patches of kelp forest “can be very cost-effective and cheaper for everyone,” he said. “Maybe you need fewer areas to be protected if you are protecting the important areas.”

Arafeh-Dalamu, et. al. “Integrating climate adaptation and transboundary management: Guidelines for designing climate-smart marine protected areas.” One Earth. Oct. 26, 2023.

Photo by Katie Davis-Koehn, University of California, Santa Barbara Marine Science Institute

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