What Is the Future of Coral Reefs?

Coral researchers and conservation groups have spent over four decades sounding the alarm. The problem isn’t just that the world could lose a highly diverse class of organism. The much larger problem is that such a loss could devastate entire marine ecosystems. It is estimated that even though coral reefs cover less than 1% of the world’s oceans by area, a full 25% of marine organisms depend on them. Elizabeth Shaver, the coral conservation strategy lead for TNC in the Caribbean, says the loss of coral reefs would also be catastrophic for coastal communities, crippling fisheries and marine-based economies and exposing both residents and critical infrastructure to increased risk from tropical storms.

“The Caribbean is the most coral reef tourism-dependent region in the world,” Shaver says. For some island nations, “a large portion of their GDP is based on tourism related to coral reefs.”

Recently, however, scientists have made a hopeful discovery: Some coral reefs seem to fare better than others during marine heat waves. They recover more quickly. Mortality rates are lower. They seem to be more thermally tolerant. If protected, these resilient reefs have a greater chance of surviving in a warming ocean and serving as the “mother reefs” for future coral colonies. Think of them like an underwater seed bank, a store of genetic material from which damaged reefs might regenerate—either on their own or through active restoration.

In 2021, The Nature Conservancy teamed up with Woods Hole Oceanographic Institution and Stanford University to identify some of these “super reefs.” Working with local partners in Belize, Hawaii and the Republic of the Marshall Islands, the researchers built a three-dimensional model of water movement, waves and temperature to identify areas where they might find more thermally tolerant corals. They were especially interested in finding areas where temperatures vary daily, as they theorized that corals develop heat resistance when they are exposed to highly variable temperatures. (Similar work with different partners was undertaken in Indonesia and Palau.)

Around the same time, scientists working for TNC in the Caribbean were trying to determine which reefs might be safe from future climate changes. The team built computer models that combined historical and projected ocean temperatures, exposure to hurricane impacts and the connectivity of some reefs to other reefs that might serve as a source of restoration from future coral larvae. Researchers in other parts of the world, including Australia and Hawaii, have used similar strategies to identify and propagate corals that seem to have higher thermal tolerances.

The methods used by the super reefs collaborative and the Caribbean scientists are different, but heading toward the same goal: Identify the reefs most likely to survive in a warming world and protect them. This expands environmental groups’ historical approach to coral reef conservation and restoration efforts. In places like the Caribbean, coral restoration has centered on fast-growing species like staghorn coral. “It grows really fast,” Shaver says. Wirecutters can be used to take cuttings that continue growing, making it affordable. The problem is that while branching species like staghorn coral are important to reef structure, they are also more susceptible to bleaching. “Broadly speaking,” she says, “slower-growing corals tend to be better at dealing with heat stress.”

The discovery of resilient reefs is not a silver bullet. If anything, the attempt to identify resilient reefs has revealed just how complex coral ecosystems are. For example, when scientists at Stanford subjected potentially resilient corals to thermal stress tests, the results varied widely: A coral species from one reef would perform well, while that same species from another reef would not.

“Reefs are highly variable in terms of structure,” says Annick Cros, who is leading the super reefs work for TNC. “You have the patch reef, the barrier reef, the fringing reef, inside and outside the atolls, passes, and the windward and leeward sides.” It’s a dizzying array of variables that affect the coral’s capacity to adapt to thermal stress. The team ultimately pinpointed sections of reef in Belize and elsewhere that had the largest concentration of thermally tolerant corals and is sharing that data with marine managers on the ground.

Yimnang Golbuu, the conservation director for TNC in Micronesia and Polynesia, says the research—which in Palau was conducted in collaboration with the University of Queensland—has given the local government and its partners invaluable data about the potential resilience of Palau’s coral reefs. The mapping is helping inform a new national plan for nearshore areas and could influence the establishment of new marine protected areas, Golbuu says. Such conservation actions are underway in The Bahamas, Indonesia, Barbados and elsewhere. These actions build on community-supported marine management and efforts to address local non-heat-related stressors like water pollution.