A tropical Pacific coral reef at Palmyra Atoll National Wildlife Refuge in the Pacific abounds with fish. Ocean warming and acidification, tied to climate change, are taking a toll on coral reefs. Photo: Jim Maragos, USFWS. Download.Photos: Coral reef photos by USFWS on Flickr
Tropical coral reefs are among the world’s most diverse ecosystems, harboring thousands of species in a complex community built by living corals. But in the Hawaiian and Pacific Islands, as elsewhere, these ecosystems are declining because of human impacts, including climate change.
“Coral reefs are on the front line of climate change,” explains Jeff Burgett, a U.S. Fish and Wildlife Service biologist and science manager for the Pacific Islands Climate Change Cooperative (PICCC), a conservation research coalition based in Honolulu and part of a national network of 21 such cooperatives. “Scientists around the world are documenting severe impacts to reefs from warming seas, and the lowering pH of the oceans will hurt their ability to recover.”
In the Pacific, where the Service manages more than one million acres of coral reef habitat in 11 refuges, including the Hawaiian Islands National Wildlife Refuge, Service scientists are seeking ways to reduce coral vulnerability.
High water temperatures stress corals, causing them to expel the algae they normally shelter and nourish. These algae do more than give coral their vivid colors; they also release glucose needed for healthy coral function. Without the symbiotic algae, the white skeleton of the translucent coral animal is exposed. Intense coral bleaching often leads to coral death, as the coral starves without the algae; even corals that regain their algae are weakened, and often succumb to opportunistic diseases.
Acropora corals subjected to seasonally high water temperatures off Tutuila in American Samoa appear bleached of color (left). After 24 hours of treatment (right) with cooled seawater, some of their color has returned. Photo: B. Von Herzen, Climate Foundation.
Coral bleaching is a growing global phenomenon. Last year high water temperatures caused a mass bleaching in the Indian Ocean, Thailand, the Philippines and Indonesia. The severe El Niño of 1998 raised ocean surface temperatures to historic levels, killing nearly 16 percent of the world’s coral. Such events are becoming more frequent as the ocean warms.
Ocean acidification is compounding the problem. As the ocean absorbs rising levels of carbon dioxide from the air, it acidifies, impeding the ability of corals to build new limestone skeletons.
At present, scientists can predict some coral bleaching events but can’t stop them. Managers focus instead on trying to reduce other stressors such as overfishing and runoff from deforestation and poor farming practices. Sediment runoff smothers coral, blocking vital sunlight. But enforcing laws to control these practices is often difficult.
PICCC is funding a study that might expand the range of management options.
This small colony of cauliflower coral (Pocillopora meandrina), located in the French Frigate Shoals, part of the part of the Hawaiian Islands National Wildlife Refuge and the Papahanaumokuakea Marine National Monument, hosts more than a hundred endemic Hawaiian Domino Damselfish (Dascyllus albisella, ‘alo’ilo’i). Hawaiian domino damsels prefer corals situated in open sand and along the edges of coral reefs to ensure priority access to their planktonic meals. Photo: Lindsey Kramer/USFWS. Download.
The Climate Foundation, a private nonprofit, has developed a field-based cooling system for reef water. Initial tests on the island of Tutuila in American Samoa, where coral undergoes seasonal bleaching, have shown that cooling peak water temperatures by about 1 to 2 degrees Celsius helps two sensitive species of coral retain their healthy color.
With the support of PICCC and other partners, The Climate Foundation is refining the system, testing solid-state cooling modules, solar-powered pumps that cool reef water, and other technologies. Their conservation potential will depend on their effectiveness, scalability, cost and adaptability to remote sites.
One possibility: exploiting the increasing use of industrial seawater air conditioning systems. Using such systems on tropical islands may provide a low-cost means to buffer near-shore reefs from climate change.
“We are looking for management actions that can give coral reefs a fighting chance in our changing climate,” explains Susan White, who manages coral reefs within the PICCC area as project leader for the Pacific Reefs National Wildlife Refuge Complex. “We can’t afford the death of these vital ecosystems.”
Climate Change Focus: Adaptation
Author: Deanna Spooner
- Deanna Spooner, U.S. Fish and Wildlife Service Administrator Coordinator, Pacific Islands Climate Change Cooperative, 808-687-6148, firstname.lastname@example.org
- David Patte, USFWS, 503 231-6210 email@example.com