This article is from the In-Depth Report 400 PPM: What's Next for a Warming Planet

Field Trip: Can Corals Survive Warming Ocean Temperatures? [Slide Show]

Data from remote coral reefs in the central Pacific suggest that, although many corals are harmed by heat, certain kinds can adapt to warmer water

Simon Donner

The long-term survival of coral reefs will depend on how well they can deal with rising ocean temperatures. Corals, the animals that famously build reefs, get most of their energy and color from microscopic algae that live inside their tissue. This unique arrangement is very sensitive to the surroundings, however. When the water gets too warm, the corals expel or consume the algae, and turn white. If the warm water persists, this "bleaching" process can starve corals to death.

In May I traveled from my lab at the University of British Columbia to the Gilbert Islands, part of the island nation of Kiribati, in the central equatorial Pacific. They offer a unique natural laboratory for studying how coral reefs respond to frequent ocean heat waves. When an El Niño climate event sets up in the Pacific, the ocean around Kiribati—in the heart of the El Niño zone—warms up. By studying changes in the coral community after El Niño events, we can evaluate what types of corals and reef habitats are most likely to survive in a warmer future.

View a slide show of the Kiribati corals

During this trip, my colleagues at Kiribati's Ministry of Fisheries and Marine Resource Development and I measured coral cover and the fish population at sites around four different atolls. We began alongside Tarawa Atoll, the densely populated capital of Kiribati, and proceeded northward for 160 kilometers, ending up in the remote Butaritari Atoll. Because Kiribati is a remote country with limited access to Western goods, few outside visitors and no fancy research vessels, field work there requires patience, flexibility and a strong stomach.

We are now analyzing the data to test our suspicion that certain "tough" coral species are spreading at sites with a history of frequent, strong El Niño–based heat waves. These sites could be the rare exception to the scientific prediction that the world's coral reefs will succumb to climate change before the end of this century.

View a slide show of the Kiribati corals

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