New research by an Abu Dhabi-based scientist is helping to explain why the world’s coral reefs aren’t recovering from damage.
The stereotypical environmental image of the Arab world is dry sand dunes, but underneath the region’s waters once lay some of the world’s most thriving coral reefs. Coral reefs are home to some of the world’s most dense biodiversity, home to as many as nine million species and a largely untapped source of chemical resources that might yield new drugs. Those are some of the reasons scientists are concerned about the reefs’ health.
It’s estimated that only one sixth of the globe’s original coral reef systems remain intact and a recent report from the International Union for Conservation of Nature doesn’t paint an optimistic future for what’s left. Caribbean reefs, the organization says, will be all but lost within 20 years.
Rising sea temperatures, fluctuations in how salty the water is and the rise of seaweeds that smother the coral are all culprits—as are local issues such as pollution, acidification and land reclamation. The new research now adds a fresh cause to the mix: Coral larvae are picky.
A study published today in the journal Science has shown that coral larvae and juvenile fish are attracted by chemical cues emitted by healthy coral colonies and are repulsed by cues produced by the seaweeds that overpower reefs.
In other words, coral larvae actively shun reef systems that are declining. “This explains why some reefs are not recovering,” says Charles Sheppard from the University of Warwick, who has studied reefs in the Arabian Gulf and Red Sea for over 40 years and was not involved with the study.
The corals in the Gulf and Red Sea inhabit some of the most environmentally challenging waters of any reef system in the world. The temperatures are on the extreme edge of what most coral species can tolerate, which is why the study’s author, David Abrego at Zayed University in Abu Dhabi, is attracted to the region. “If you took coral from any other region in the world and brought it to the Gulf it would not survive very long,” says Abrego.
Abrego and his colleagues placed young fish and coral larvae in a “choice chamber” with two sources of water, one from a degraded reef and the other from a healthy one. “You just wait and watch them,” says Abrego, “and they will invariably choose to spend time in the water from good reefs.”
Back in 1998, an El Nino weather event, which temporarily disrupts ocean currents, struck the Indian Ocean. It caused exceptionally warm waters to migrate into the coral reefs off the Seychelles (a 155-island country in the Indian Ocean), Maldives and Mauritius—and also overflowed into the Gulf and Red Sea. This proved to be devastating for corals. “The Gulf is still in a very bad way,” says Sheppard, “some reefs haven’t recovered and I think this study could explain why they’ve been completely messed up beyond repair.” In parts of Qatar where there were once thriving coral reefs, Sheppard failed to spot a single live reef during a recent dive. Sheppard also thinks the large-scale development and land reclamation in the Gulf has done the reefs no favors.
Other ecologists agree. “It’s a fascinating situation that Red Sea reefs are doing relatively well despite high water temperatures,” says marine biologist Michael L. Berumen at King Abdullah University of Science and Technology, on Saudi Arabia’s Red Sea coast. Despite this, Berumen says that we don’t know as much about them as we could. “Various circumstances have caused most of the Red Sea to be inaccessible to researchers,” he says.
“Yemen and Sudan have their problems and Egypt recognizes that they have a valuable tourist resource in their reefs,” says Berumen. “They’ve got strict protection measures with the unintended consequence of making it very hard for foreigners to get a research permit.” That leaves Israel and Jordan with a combined Red Sea coastline of just 28 miles. “It’s hard to know if the research done there is representative of everything else in the Red Sea,” he adds.
Saudi Arabia on the other hand has about 1,100 miles of Red Sea coast with Berumen’s lab close to the middle of it. That gives him and his colleagues a chance to look at reefs that scientists have not carefully examined before. He believes these waters hold some potentially useful conservation secrets. “Hidden in the genetics of the Red Sea species is some insight as to how corals can handle extreme conditions.”
Based on this promise, Berumen is part of a Great Barrier Reef Foundation-funded project called “Sea-Quence,” which will gather all the details of the genetic code of 20 coral species over the next decade. “We want to identify coral strains that are more resilient to climate change, which we’d then use for transplants.”
Sheppard is reluctantly pessimistic about the chances of successfully relocating Red Sea corals to less healthy areas. He says transplants can be done in aquariums but things are different when you’re talking about oceanic scales. “When you stand on a hilltop in the Seychelles and look at the vastness of the reefs you’ll realize you can’t transplant thousands of square miles.”
The only hope, says Sheppard, is that you transplant a smaller coral colony and hope it spreads naturally, which is a painfully slow process hampered further by the latest findings that young larvae aren’t attracted to failing reefs.
But Berumen remains more hopeful about Abrego’s results. “Evidence that larvae won’t disperse to troubled reefs means that transplants become more important.”