Scientists Discover A Key Way To Help Save Coral Reefs

Apr 9, 2015 by


Redfin butterflyfish and coral reef.

Redfin butterflyfish and coral reef.

CREDIT: Tim McClanahan/WCS

The secret to a healthy coral reef is a healthy population of fish, a new study has found.

The study, published this week in Nature, looked at the fish biomass — the total mass of all fish species in a reef — of 832 reefs around the world, and used data on the reefs’ health to estimate the levels of fish biomass needed to sustain that health.

The researches found that reefs with no fishing had about 1,000 kilograms (2,204 pounds) of fish biomass per hectare (2.47 acres), and that to avoid a total collapse of ecosystem health, reefs needed to stay above a minimum of 100 kgs (about 220 lbs) of fish biomass per hectare. To keep their ecosystems healthy and be able to sustain fishing needs, reefs needed to keep fish biomass at at least 500 kgs (1,102 lbs) of fish biomass per hectare.

Unfortunately, according to the study, most of the world’s coral reefs aren’t succeeding at maintaining this biomass level. The researchers found that 83 percent of the coral reefs studied didn’t have a fish biomass of 1,102 lbs per 2.47 acres. But this doesn’t mean those reefs can’t still recover, said Aaron MacNeil, lead author of the study and senior research scientist for the Australian Institute of Marine Science.

MacNeil told ThinkProgress in an email that, because of the wide range of regulatory measures that can be put in place to regulate fishing methods or limit the amount or type of fish taken from a region, even poorer countries can take steps to improve their reef health.

“Our study is important because it shows that there are a range of management options available, including gear restrictions, limits on the species that can be caught, and caps on who can access the fishery,” he said. “Ultimately the most effective regulations are those that will be complied with and it is up to local people (and governments) to figure out what those are.”

MacNeil said that he has seen effective reef management in places like coastal Kenya, a region that’s “heavily dependent” on its reefs. Kenya has established six national marine reserves in an attempt to protect some of the reefs that surround the nation, and has also banned a way of fishing that uses beach seines, a type of large net that tends to capture the majority of the fish in an area rather than targeting one or two species, on its southern coast.

Other places have also seen success in reef recovery. Cabo Pulmo, a marine protected area on the coast of Mexico’s Baja Peninsula, was established in 1995 after a long history of overfishing caused a noticeable change in the reef’s fish population. Since the park was created and the fishing ban was put in place, fish biomass in the reef has increased by more than 460 percent, and the reef’s population of large fish has also increased.

But even though the benefits of fishing restrictions can be seen in reefs within a decade or so, the study said heavily-fished reefs that have seen their fish stock severely depleted would need about 59 years to recover completely under fishing restrictions. Averagely-fished reefs would need about 35 years.

Different species of fish play different ecosystem roles in reefs: Parrotfish and urchins, for instance, are key reef players because they eat algae off coral. That algae, if left to its own devices, can smother coral, so studies have shown that protecting parrotfish and other grazers is key to reef health.

But other types of fish also have major roles to play, MacNeil explained. Fish that feed on the reef’s dead organic material help clear out space for more coral to grow, and predators help keep the system balanced by controlling the population of smaller fish.

MacNeil said that one of the most exciting findings of the study was that these varying ecosystem functions can be protected “by such a diverse range of fisheries regulations.”

“This really got us excited because it means that people have many more options that just marine protected areas when it comes to managing their reef fisheries,” he said.

Despite the study’s confirmation that more fish leads to a healthier reef, and that there are many steps regions can take to protect their reefs, the authors write that marine reserves and fishing regulations aren’t enough to combat the threats reefs face from climate change and ocean acidification.

“Addressing the coral reef crisis ultimately demands long-term, international action on a global-scale issues such as ocean warming and acidification,” the study reads.

Still, better management will likely help reefs be more resilient to these challenges in the future. A report last year found that coral reefs protected from stressors like pollution and overfishing can bounce back from warming-induced events like bleaching.

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