Isolated Coral Reefs Are Not Safe from Decline

Isolated Coral Reefs Are Not Safe from Decline
August 30, 2016

Coral reefs are among the world’s most beautiful and biologically diverse ecosystems. They cover a tenth of a percent of the world’s ocean floor but account for a quarter of all the world’s marine species.

Studies have shown that these ecosystems can generate about half a million dollars per acre every year in tourism, fisheries and medicinal applications and 275 million people around the world depend on these ecosystems for food and work.

Giant ClamAnd they are declining.

All around the world, these ecosystems are breaking down, and new research from UNC Chapel Hill is showing that even the most isolated reefs, far away from human contact, are not being spared from the decline.

UNC marine biologist John Bruno analyzed data from more than 1,700 coral reefs across the globe and found that the reefs furthest from civilization are declining just as quickly as the ones nearest to people. The study was published in the journal Scientific Reports.

Coral reefs are built on the backs of billions of tiny animals. Tiny coral polyps latch onto rocks on the sea floor. They clone themselves thousands of times over, fight over territory with other polyp colonies and build themselves over dead corals to build sprawling reefs that provide homes and shelter for millions of fish, algae and invertebrate species.

Dead coral forms a hard, calcified skeleton that serves as the backbone for the reef and makes the coral you can sometimes find washed up on shore feel rough. Living coral polyps, however, are extremely fragile. They have a close relationship with the algae that grow along the reef. The polyps give the algae a safe place to anchor where they won’t get tossed around in the surf while the algae share food and other nutrients with the polyps.

Disturbing the polyps can disrupt that polyp-algae partnership and even structurally harm the polyps themselves, and many scientists and conservationists have thought that human interaction with coral reefs was the primary source of these disturbances and the decline of corals. Prime culprits have been tourism, where people touching, collecting or standing on the corals could be harmful; fishing, where equipment can structurally harm the polyps; or pollution, which could cause large scale breaking of the polyp-algae relationship—a process marine biologists call bleaching.

Sea Turtle EatingIsolated reefs, which Bruno determines by the number of people living within 50 kilometers, are experiencing bleaching just like those in populated areas. Remote reefs in the Caribbean and Hawaiian Islands have lost anywhere from 20 percent to almost all of their coral cover exactly like those in the South China Sea.

They found that even the Great Barrier Reef has shown a large degree of bleaching, even though it is one of the most protected reefs in the world.

What this means, says Abel Valdivia, a researcher with the Center for Biological Diversity in California and former graduate student at UNC, is that the major cause of coral decline is more global in scale. 

Climate change and rising ocean temperatures, for example, have been shown to cause coral bleaching. So, while measures like tourism, boating and pollution regulations can have some effect on coral decline, a more global approach is needed to protect these diverse but fragile habitats.

—Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.