It is no secret that in the midst of climate change, coral reefs around the world are suffering. However, a warming world is not the only factor putting these reefs in danger - overfishing also plagues these colorful ecosystems. And now new research offers a glimmer of hope, finding that fish are the answer to their problems.
According to scientists from the Australian Institute of Marine Science, Wildlife Conservation Society (WCS), James Cook University, and other organizations, fish are the key ingredients in a new recipe to diagnose and restore degraded coral reef ecosystems. At least, in those regions that are severely overfished.
For moderately or lightly fished reefs, success requires knowing which fish to catch, how many, and which to leave behind, the researchers say.
In the journal Nature, the authors assessed fish biomass and functional groups from more than 800 coral reefs worldwide and used them to estimate recovery periods for both lightly fished and overfished reefs. The scientists speculate that maintaining and restoring fish populations and the functions they provide can increase the resilience of reefs to large-scale threats such as climate change.
Climate change and ocean acidification - which is diminishing corals like those in the Great Barrier Reef - typically get all the attention. But other important factors are at play as well, such as overfishing, pollution and coastal development.
According to the World Resources Institute, some 75 percent of the world's coral reefs are now threatened and more than 20 percent have disappeared since climate and fishing disturbances have accelerated in the past 30 years. At the same time, only 27 percent of the world's coral reefs are contained within marine protected areas. At this rate, this combination of factors could cost the world its coral by the year 2100.
"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," study lead author M. Aaron MacNeil, Senior Research Scientist for the Australian Institute of Marine Science, said in a statement. "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."
"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," noted co-author Tim McClanahan, WCS Senior Conservationist. "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." (Scroll to read on...)
Coral reef experts agree that fishing is a primary driver in the degradation of reef function. By removing too many herbivorous and predatory fish species, it deprives coral reefs of critical ecosystem functions, and also hinders their ability to fight off other threats.
However, according to this study, knowing the right amount of fish to leave behind - keeping both fisheries and reefs happy - can result in a recipe for success.
The researchers analyzed data from approximately 832 coral reefs in 64 locations around the world, ranging from heavily fished reefs in the Caribbean to lightly fished reefs such as those in the Easter Islands. What they found was that the most that any one coral reef can be overfished - to the point of nearly total ecosystem failure - is 100 kilograms per hectare (reefs lacking any fishing averaged about 1,000 kg per hectare of fish).
It turns out the most important fish to conserve are browsers (rudderfish, parrotfish, and surgeonfish), scraper/excavators (parrotfish), grazers (rabbitfish, damselfish), and planktivores (fusiliers) - as the most degraded reefs lacked these types of fish.
The authors also found that 83 percent of the studied reefs contained less than the 500 kilogram fish biomass - the threshold needed to maintain ecological integrity and stave off decline.
"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," explained 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."
Such recovery efforts that can easily be implemented include gear restrictions (e.g. small-mesh nets), species selection or local customs. Approximately 64 percent of coral reefs with fishing regulations were found to maintain more than 50 percent of their potential fish biomass, offering a glimmer of hope for these amazing ecosystems.
"It demonstrates that managers can use a range of different management strategies in areas where it may not be culturally feasible to establish permanent marine reserves," added co-author Stacy Jupiter.
By simply harnessing the power of fish, the research models used in this study predict that a moderately fished coral reef system can recover within approximately 35 years on average. Meanwhile, the most depleted ecosystems may take as long as 59 years with adequate protection.
While this may seem like a long time, the important thing is that coral reefs worldwide, such as those in the iconic Great Barrier Reef, can be saved, and may in fact prosper once again in the future.
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