Chuck Bednar for redOrbit.com – @BednarChuck
Restoring fish populations to coral reef systems could be the key to helping those ecosystems recover, according to a new study based on an assessment of fish biomass and functional groups from over 800 coral reefs worldwide and published in the journal Nature.
As part of their research, scientists from the Australian Institute of Marine Science, the Wildlife Conservation Society and elsewhere used their data to estimate recovery periods for both lightly fished and overfished reefs. The authors speculate reefs could become more resilient to climate change and other threats if their fish populations are maintained and/or restored.
“By studying remote and marine protected areas, we were able to estimate how much fish there would be on coral reefs without fishing, as well as how long it should take newly protected areas to recover,” lead author M. Aaron MacNeil from the Australian Institute of Marine Science said. “This is important because we can now gauge the impact reef fisheries have had historically and make informed management decisions that include time frames for recovery.”
Fish biomass thresholds for healthy coral reefs discovered
Based on current estimates, global warming, pollution, coastal development and other hazards have combined to threaten approximately three-fourth of the world’s coral reefs. Also, climate and fishing-related disturbances have caused 20 percent of reefs to disappear over the last 30 years, and just 27 percent of coral reefs are currently within marine protected areas.
In their new study, MacNeil and his colleagues found that a coral reef with no fishing averages 1,000 kilograms per hectare of fish biomass, while the fish biomass threshold for an extremely overfished reef (one that is close to total ecological failure) is 100 kilograms per hectare. Those which maintained 500 kilograms of fish biomass per hectare were found to have their ecological functions preserved while also sustaining fisheries, suggesting that this is a potential target.
Those findings are based on what the authors are calling the first-ever empirical estimate of coral reef fisheries recovery potential. The research included marine reserves and fishing closures as a control for estimating healthy fish biomass, as well as reefs located in sites representing a broad spectrum of fishing intensity rates, including heavily-fished locations in the Caribbean and those that were said to be high in fish biomass such as the Easter Islands.
Using the information to map out a coral reef recovery plan
MacNeil’s team found that 83 percent of the 832 reefs surveyed contained less than the 500 kilogram fish biomass threshold needed to stave off decline and keep their ecological integrity. They developed models to determine how much time it would take different reefs to recover, and found that a moderately-fished reef required an average of 35 years to rebound, while the most extremely damaged ones could take nearly six decades with adequate protection.
In addition, the study found that the certain types of fish could play key roles in restoring reef health. For instance, those reefs that were most degraded were found to be lacking in the types of fish known as browsers (such as parrotfish, rudderfish and surgeonfish), grazers (rabbitfish or damselfish), scrapers/excavators (parrotfish) and planktivores (fusiliers). The findings indicate that those species provide services which corals rely upon in order to recover.
“The methods used to estimate reef health in this study are simple enough that most fishers and managers can take the weight and pulse of their reef and keep it in the healthy range,” said Tim McClanahan, senior conservationist at WCS and a co-author on the study. “Fishers and managers now have the ability to map out a plan for recovery of reef health that will give them the best chance to adapt to climate change.”
“Reef fish play a range of important roles in the functioning of coral reef ecosystems, for example by grazing algae and controlling coral-eating invertebrates, that help to maintain the ecosystem as a whole,” added co-author Nick Graham of James Cook University. “By linking fisheries to ecology, we can now make informed statements about ecosystem function at a given level of fish biomass.”
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