A new study suggests that more than 10% of the fish swimming in coral reefs are there because their habitats have been protected.

Tropical reefs support vibrant communities of fish and other sea life, and they provide critical sustenance for many people living in coastal communities. As a result, they’re seen as key targets for conservation. In some places, that’s meant restrictions on when and where fishers can operate and the kind of gear they can use. Elsewhere, governments have established marine protected areas (MPAs) — essentially ocean-based parks that may not allow much fishing, if any at all.

On the whole, only about 8.4% of the ocean is covered by MPAs, according to the World Database on Protected Areas. And research drawing on a 2021 study in Science called The MPA Guide reveals that an even smaller proportion, less than 3%, is “fully or highly protected.”

Such statistics reveal that simply tracking the extent of protected spaces only gets us so far in understanding why some MPAs are successful in conserving sea life while others languish in holding back threats like overfishing.

“It’s a bit like judging the success of your stock portfolio by the number of shares you’ve bought, rather than how well they’ve performed,” Joshua Cinner, a professor of geography and the director of the Thriving Oceans Research Hub at Australia’s University of Sydney who co-authored the new study, told Mongabay in an email.

To get a read on how well MPAs and other conservation strategies for tropical reefs are performing, Cinner and his colleagues built a statistical model with data from fish surveys, on measures to safeguard biodiversity, and about local environments from around 2,600 reefs in the Atlantic, Indian and Pacific oceans.

They then ran simulations with the model to see how removing all protections would impact the total weight of fish, or fish biomass, living on those reefs. Leaving the reefs unguarded led to a drop in biomass of about 10% in their modeling, the team reported Oct. 7 in the journal Proceedings of the National Academy of Sciences (PNAS).

Some critics of MPAs say they can merely displace, rather than eliminate, the fishing that can winnow away biomass on coral reefs and other habitats. Though the authors note that the study wasn’t designed to address this question, the researchers did carry out a second analysis to 50 kilometers (31 miles) beyond the edges of MPAs, looking for changes between what their model predicted and the observed levels of biomass. They didn’t find widespread variation, suggesting that neither displacement nor “spillover” — in which the levels of fish inside MPAs would drive up biomass values just outside — were biasing the biomass gains they modeled.

“The 10% figure tells us that current protection efforts are having an impact,” Iain Caldwell, the study’s lead author and lead analyst for the coral reef health data platform MERMAID with the Wildlife Conservation Society, said in an email. “I think this should be heartening.”

Marine ecologist Kirsten Grorud-Colvert, an associate professor in integrative biology at the U.S.’s Oregon State University, who was not involved in the research, agreed that was an important finding.

“When you’re looking at things underwater, you can see the 10%,” Grorud-Colvert, the lead author of the 2021 Science paper, said in an interview. “It’s not negligible.”

The team’s simulations suggest further gains as the proportion of protected areas rises. Expanding coverage to 30% of the world’s reefs could bring the increase up to 28%, the authors report. In 2022, world leaders agreed to protect 30% of the ocean (and the land) by 2030, a goal often referred to as 30×30, and included it in the Global Biodiversity Framework developed at the meeting of the United Nations Convention on Biological Diversity in Montreal (COP15). Currently, discussions on how to reach those goals over the next five years are underway at the U.N. biodiversity conference in Cali, Colombia, known as COP16, which runs Oct. 21 through Nov. 1.

Crucially, it matters where and how marine protections happen, Caldwell and his colleagues write.

Part of what makes the PNAS study “an excellent analysis,” Grorud-Colvert said, was that the team accounted for what makes certain MPAs and other protective measures effective.

“It’s easy to just go underwater and count fish and estimate sizes and call it done,” she added, “but they really brought in the local context.”

The team drilled into the data to sort out why some reefs are doing better than others. In general, MPAs brought the most benefits for conservation. But a key determinant of their success, and that of less-stringent fishing restrictions, was whether fishers complied with the rules governing their use.

“Our paper highlights how substantial gains could be made by improving compliance in existing protected areas,” said Caldwell, also a senior research fellow at Australia’s James Cook University. And that finding should help guide future efforts, he added. “When new areas are established, the people that depend on coral reefs for their lives and livelihoods need to be part of the decision-making process of how and where to protect reefs — otherwise they are less likely to follow the rules.”

Indigenous and community leaders and human rights advocates have raised concerns about 30×30 and the danger that local rights could be cast aside in the name of conserving sweeping tracts of the globe.

Those rights must be respected, Grorud-Colvert said, and she pointed out that rights-based approaches for conservation are mentioned throughout the global framework, including the third target, which refers to the 30×30 aspiration.

In some cases, simpler fisheries restrictions could be a better choice than MPAs if they involve local communities and their needs, Cinner said.

“As we note in the paper, when governments and conservation groups single mindedly pursue no-take closures, they may be leaving potential conservation gains on the table,” he added.

Banner image: Fish at a coral reef in the Red Sea, Sharm el Sheikh, Egypt. Image by Renata Romeo / Ocean Image Bank.

John Cannon is a staff features writer with Mongabay. Find him on Bluesky.

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Citations:

Caldwell, I. R., McClanahan, T. R., Oddenyo, R. M., Graham, N. A., Beger, M., Vigliola, L., … Cinner, J. E. (2024). Protection efforts have resulted in ~10% of existing fish biomass on coral reefs. Proceedings of the National Academy of Sciences, 121(42), e2308605121. doi:10.1073/pnas.2308605121

Grorud-Colvert, K., Sullivan-Stack, J., Roberts, C., Constant, V., Horta e Costa, B., Pike, E. P., . . . Lubchenco, J. (2021). The MPA Guide: A framework to achieve global goals for the ocean. Science, 373(6560). doi:10.1126/science.abf0861

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