Certain coral reefs that have protected the oceans' fish for millions of years could be the "Noah's Ark" that continues to preserve their biodiversity, researchers say.
A study published today in the journal Science said protecting those reefs could play a large part in ensuring future fish diversity in all ocean waters. Stable reefs like those in the Coral Triangle region in and around Indonesia, the Philippines, Papua New Guinea and Australia have cradled the world's most diverse group of fish through ice ages and periods of extreme warmth, the study found.
"We have to maintain our coral reef in many parts of the planet, to represent a kind of 'Noah's Ark' to maintain fish species even during crisis," said David Mouillot, a professor in the department of biology, ecology and statistics at France's University of Montpellier 2 and one of the senior authors of the paper.
Mouillot said in a phone interview that during colder periods of the planet such as the ice ages of the Quaternary period, certain areas acted as refuges for species that couldn't survive elsewhere.
"It's kind of a museum effect with many old species," Mouillot said, protecting them the way a museum protects ancient artifacts. He said extinction of fish species in those refuge areas wasn't as common as in other parts of the ocean, where diversity has fluctuated more throughout history.
The farther you get from the refuge areas, the less diverse the fish populations are. "We found that the distance to a reef from the refugia explained most of the biodiversity gradient in the Earth," Mouillot said. "When you are far from refugias, it's hard to get high diversity again."
For example, the Coral Triangle harbors 2,000 to 3,000 fish species, but other parts of the eastern Pacific Ocean with the same geothermal conditions as well as similar depths and other conditions have fewer than 200.
"The weight of the past is huge," Mouillot said.
Emily Darling, a conservation research fellow at the University of North Carolina, Chapel Hill, is looking at similar questions of diversity related to coral. In an email, she said combining historical records with large-scale contemporary data sets, as this study did, is critically important to tackling climate change threats.
"This work can help managers and decisionmakers scale up how we conserve and manage coral reefs in a changing climate, especially with limited funding and shrinking budgets for science and conservation," she said.
Helen Fox, director of marine science at the World Wildlife Fund, said in a phone interview that the study confirms the group's strategy of focusing on protecting key habitat and large areas of different kinds of habitat. "The Indo-Pacific has been a key area, and this is definitely evidence of that."
However, a big problem is that many of the warm refuges that once protected species "may in turn be the first to be threatened by future warming," the paper said -- especially if temperatures rise too quickly before corals can adapt.
"We are really entering uncharted waters in terms of how fast and how hot temperatures are heating up," Darling said. "We don't know whether the same refugia will continue to cradle diversity as the oceans heat up, acidify and rise."
That means conservationists need to find today's stable habitats and focus on them in the face of "limited political will to curb carbon emissions," she said.
Mouillot said that even if corals die due to rapid temperature increases in the short term, the warmer temperatures could foster more coral and fish biodiversity in the future; fossils show that corals were more widely distributed in certain periods than they are today, indicating warmer periods may support more reefs overall.
Jack Kittinger, a social science fellow at the Center for Ocean Solutions at Stanford University, agreed. "We're actually going to create new reefs as a result of warming," he said in a phone interview, pointing to research showing areas such as the waters off Rottnest Island in southwest Australia could support coral reefs if they warmed up a little.
That doesn't let people off the hook now, though; Kittinger said most reef problems today are locally generated. "None of this climate change is going to matter at all because we are going to kill all these reefs before acidification even gets to them," he said.
Fox said practices like blast fishing are particularly harmful, and Darling pointed to pollution and invasive species.
The Coral Triangle Initiative, a six-country partnership, aims to protect the ecologically rich area against the "urgent threats" it faces. Organizations including WWF are helping with the initiative, signed by Indonesia, Malaysia, the Philippines, East Timor, the Solomon Islands and Papua New Guinea.
"All conservation is local," Kittinger said. "Most of it that matters is going to happen locally."