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New research finds that Marine Protected Areas can boost the recovery of globally important kelp forests following marine heat waves. The findings are published in the Journal of Applied Ecology.

Using four decades of satellite images, University of California, Los Angeles (UCLA) researchers have looked at the impacts Marine Protected Areas (MPAs) are having on kelp forests along the coast of California.

They found that although the overall effect of MPAs on kelp forest cover was modest, the benefits became clear in the aftermath of marine heat waves in 2014–2016, when kelp forests within MPAs were able to recover more quickly, particularly in southern California.

"We found that kelp forests inside MPAs showed better recovery after a major climate disturbance compared to similar unprotected areas," explained Emelly Ortiz-Villa, lead author of the study and a Ph.D. researcher at UCLA Department of Geography.

"Places where fishing is restricted and important predators like lobsters and sheephead are protected saw stronger kelp regrowth. This suggests that MPAs can support ecosystem resilience to climate events like marine heat waves."

Professor Rick Stafford, chair of the British Ecological Society Policy Committee, who was not involved in the study, said, "It's great to see these results and they clearly show that local action to protect biodiversity and ecosystem function can help prevent changes caused by global pressures such as climate change.

"However, it also demonstrates the need for effective MPAs. In this study, all the MPAs examined regulated fishing activity, and this is not the case for many sites which are designated as MPAs worldwide – including many in the UK."

Kelp forests: A globally important and threatened ecosystem

Kelp forests are found around coastlines all over the world, particularly in cool, temperate waters such as the Pacific coast of North America, the UK, South Africa, and Australia.

These complex ecosystems are havens for marine wildlife, including commercially important fish, and are one of the most productive habitats on Earth. They're also efficient in capturing carbon and protect coastlines by buffering against wave energy.

However, kelp forests across the west coast of North America have declined in recent years due to pressures such as marine heat waves, made more frequent and intense with climate change, and predation from increasing numbers of sea urchins, which have benefited from population collapses of sea stars, which predate them.

Kyle Cavanaugh, a senior author of the study and professor in the UCLA Department of Geography and Institute of the Environment and Sustainability, said, "Kelp forests are facing many threats, including ocean warming, overgrazing, and pollution. These forests can be remarkably resilient to individual stressors, but multi-stressor situations can overwhelm their capacity to recover. By mitigating certain stressors, MPAs can help enhance the resilience of kelp."

Marine protected areas as a conservation tool

MPAs are designated areas of the ocean where human activity is limited to support ecosystems and the species living there. However, protections vary widely and while some areas are no-take zones, others have few restrictions or lack comprehensive management and enforcement. Many even allow destructive practices like bottom trawling.

Effective MPAs form a key part of the Kunming-Montreal Global Biodiversity Framework, agreed at COP15 in 2022, which commits nations to protecting at least 30% of oceans and land by 2030.

"Our findings can inform decisions about where to establish new MPAs or implement other spatial protection measures," said Kyle Cavanaugh.

"MPAs will be most effective when located in areas that are inherently more resilient to ocean warming, such as regions with localized upwelling or kelp populations with higher thermal tolerance."

Emelly Villa added, "Our findings suggest that kelp forests could be a useful indicator for tracking the ecological health and climate resilience of protected areas and should be included in long-term monitoring strategies."

Measuring the impact of marine protected areas

To understand the effects MPAs were having on kelp, the researchers used satellite data from 1984-2022 to compare kelp forests inside and outside of 54 MPAs along the California coast.

By matching each MPA with a reference site with similar environmental conditions, they were able to test whether MPAs helped kelp forests resist loss or recover from extreme marine heat waves which took place in the North Pacific between 2014 and 2016.

The researchers warn that while their findings show that MPAs can help kelp recovery after marine heat waves, the effect was highly variable depending on location.

"On average, kelp within MPAs showed greater recovery than in the reference sites. However, not all MPAs outperformed their corresponding reference sites, suggesting that additional factors also play a role in determining resilience," said Kyle Cavanaugh.

The researchers say that future work could look to identify these factors to better understand where and when MPAs are most effective at enhancing kelp resilience.