From 2004 to 2013, scientists donned snorkeling and diving gear to survey the marine life of nearly 1,800 tropical coral reefs.
The findings from these extensive field surveys, published in the Proceedings of the National Academy of Sciences, provide new insight into an ongoing debate over the effectiveness of marine reserves and how best to use resources to protect and restore ocean life.
“Part of the [conservation] community says remote wilderness areas are fundamentally different than managed systems near people and need to be protected,” said Joshua Cinner, lead author on the paper and a research fellow and chief investigator at the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University.
“Then, there is another side of the conservation community that says these places are protected already because they’re remote, and the money that we spend on them is a waste, and we should be conserving things where we’ll have a real impact.”
To help make sense of these questions, Cinner and his three dozen or so collaborators attempted to measure the conservation gains of marine reserves. They found that the level of activity outside of a coral reef protected area, measured by size and distance of the nearby human population and their access to the reef, had a strong influence over the effectiveness of protections.
While overall fish populations were higher in protected areas, they still tended to be much lower in reserves located near dense population centers than in those in remote, pristine areas.
On these remote reefs where there’s already not much fishing, marine reserves seemed to make little difference to overall fish abundance – findings that corroborate the argument that remote regions do not need protection. On the other hand, reserves placed in areas of moderate to high impacts “can provide substantial conservation gains in fish biomass,” according to the paper.
Such gains, however, hardly amount to fully restored ecosystems. On average, a marine reserve in a high-pressure area boasted about five times the amount of fish compared to an unprotected, heavily fished reef, according to the study. “The depressing side to this is that the absolute amount of fish in these high-pressure marine reserves is still only a quarter what you find in these low-impact areas,” Cinner said. In other words, the scientists found that enforced marine reserves can help to boost fish numbers in fished regions but not nearly close to anything resembling historical or unfished levels.
Of concern was the fact that reserves placed in areas of high or moderate human impact seemed to have few, if any, benefits for top predators, especially sharks, groupers, snappers and jacks. The authors reported seeing top predators on only 28 percent of the 1,798 reef sites studied. As the level of human activities increases in surrounding waters, the probability of encountering a top predator on tropical coral reefs “dropped to almost zero, regardless of management.” The authors concluded that no-fishing reserves in remote areas are, in fact, critical for sustaining populations of top predators.
Cinner said the takeaway from his and his colleagues’ research should not be that most marine reserves don’t work. For fishers, marine reserves clearly can offer substantial benefits. But when it comes to restoring a fully functional ecosystem, marine reserves may fall short of expectations.
“Our paper makes it clear that there are pros and cons of placing reserves in different areas, and that to decide how successful a reserve is, you need to know what your goal is,” he said.
The conclusions of Cinner’s work are consistent with other research showing that marine reserves may fail to produce anticipated benefits, especially when expectations are high. In a 2014 paper in the journal Nature, a research team, led by Graham Edgar of the University of Tasmania and also a coauthor on the new study, reported that 60 percent of 87 marine protected areas (MPAs) analyzed “were not ecologically distinguishable from fished sites.” The most effective reserves analyzed in that study were ones that were larger than 100 square km (39 square miles), older than 10 years, isolated by deep water or sand, and that had well-enforced no-take restrictions.
Another paper published in Nature Communications in 2016 found that even the distance from the nearest seafood market seemed to have more impact on the size and abundance of fish on coral reefs than its protected status.
However, Daniel Pauly, a professor of fisheries at the University of British Columbia, feels some conservationists set the bar too high for what they hope to gain from marine reserves. This can wind up skewing their own opinions of a marine reserve’s success, even when the reserve produces significant gains.
“The expectation we have of marine reserves is immense – that they can restore a fully functioning ecosystem, which they can’t,” he said. Returning to “what we had 200 years ago,” he said, is a “crazy expectation.” Rather, success should be gauged by “a more reasonable standard” that uses the ecological health of surrounding areas as a baseline.
“We should be asking if reserves have given us something better than what we’d have if we didn’t have a reserve at all,” he said. “By that measure most reserves can succeed.” Wide-ranging species such as tuna, as well as sea turtles, may experience virtually no benefits from marine reserves, however, he said.
A limitation of the study’s ability to draw broad conclusions is that it looked only at coral reefs. Mark Carr, a marine biologist at the University of California, Santa Cruz, said it isn’t clear if the results would have been similar in temperate regions. Marine reserves in tropical nations may often be relatively ineffective because of how intensively the surrounding areas may be fished, he noted.
“They went to a lot of developing countries where they’re fishing the hell out of the place, and that can really diminish the performance of a marine reserve,” he said. He noted that in many developing nations “there is no fishing management at all, and that’s just unheard of now in most temperate countries.
“Also, the reserves in these tropical countries aren’t set up in any kind of network, which we’ve found is really important,” Carr added.
For instance, California created a system of reserves, which he called “the posterchild for effectively designed marine protected areas.” The reserves were spaced strategically to create a network that now protects about 18 percent of coastal waters. That is on top of effective fisheries management. Populations of fish that were considered overfished 20 years ago – such as lingcod and many rockfish – are now recovered and abundant, thanks largely to temporary fishing closures and restrictions on harvest.
“You can’t just manage MPAs in a vacuum, and you can’t have fishery management in a vacuum,” Carr said.