By Michael Fox
One of the more widely discussed threats associated with global climate change is the possible extinction of coral reefs. Rising sea surface temperatures and increasing CO2 concentrations in the ocean threaten the corals that create these incredible habitats, home to 25 percent of all known shallow-water marine species. Reef-building, or hermatypic, corals have a special relationship with microscopic algae called zooxanthellae that live within their tissues. The tiny zooxanthellae provide their coral hosts with important nutrients to help them survive but when water temperatures get too hot, corals expel these algae, losing their color in a process known as coral bleaching. This is one of the first steps in the death of a coral reef.
Coral reefs form islands and atolls that are home to millions of people, and they provide food, support fisheries and protect coastlines from storms. Coral reefs are the foundation of a multi-billion dollar tourism industry and are one of the most diverse ecosystems on the planet. Despite their importance, coral reefs make up only one tenth of 1 percent of the world’s oceans, increasing their susceptibility to the impacts of global climate change. However, coral reefs have been around for 250 million years, and they will not go down without a fight. Researchers from Stanford University led by Dr. Steve Palumbi, Director of the Hopkins Marine Station, have recently discovered a group of corals in the South Pacific that thrive in water temperatures that would cause most other corals to bleach. These “super corals” may be one of the keys to understanding the future of coral reefs.
The perfect location
Palumbi first began studying corals in the 1970s during a summer field course in Jamaica. Since then, he has traveled around the world studying coral reefs in every ocean. After joining Stanford in 2002, Palumbi continued bouncing from one exotic locale to the next, although this time he was searching for something special. “I was looking for a location in the central Pacific where I could begin long-term research, train students and maybe build a lab,” Palumbi explained. After receiving a tip from a colleague about the pristine reefs in American Samoa, Palumbi decided to investigate. On the small island of Ofu, he found just what he was looking for.
Ofu is a special place. There are very few stressors to the local reefs because there are no coastal residences, no road construction projects and very little runoff and pollution. Palumbi points out that, “Under these conditions, corals tend to be as healthy as they can be.” Not only are the reefs of Ofu pristine, some of the corals are exceptionally resilient. A paper published in 2001 by a marine biologist at the National Park Service on Ofu, Peter Craig, told the story of corals in the shallow lagoons of Ofu that survived very warm water at low tides without bleaching. After he realized what an incredible natural laboratory the local reefs and resilient corals provided, Palumbi made his decision. Along with students, dive gear and sampling equipment, Palumbi has been returning to Ofu twice a year since 2005 and plans to continue his research well into the future.
Practice makes perfect
The “super corals” studied by Palumbi and his team are found in a particular section of the back reef lagoon on the southern coast of Ofu. In this section of the lagoon, there are two distinct areas, or pools, that experience very different daily temperature extremes during summer low tides. The deeper of the two pools experiences small temperature changes throughout the day while the shallower pool can experience daily temperature changes of up to 6o C (about 11o F). The “super corals” all live in the shallow pool and experience temperatures almost 2oC higher than corals in the deeper pool. This short-term exposure to higher temperatures each day has allowed the corals living in the shallow pool to develop an unusual tolerance for warmer water. These “super corals” represent the same coral species that compose all the reefs around Ofu, but they have become more resilient to bleaching than other colonies because of where they live.
One of the “super coral” species uses a special type of zooxanthellae to increase its warm water tolerance. Acropora hyacinthus is a species of branching coral that forms a table shape with a “tabletop” sometimes reach several meters across. This is a common species of reef-building coral across the Indo-Pacific but only in Ofu has it been found to behave like a “super coral.” Palumbi and his colleagues believe the reason A. hyacinthus is so resilient in the waters of Ofu is because it has a special type of zooxanthellae referred to as clade-D. This type of zooxanthellae is genetically distinct from other zooxanthellae and functions more effectively at higher temperatures. A. hyacinthus was the only species in the shallow pool found to host only clade-D zooxanthellae. Palumbi and his colleagues are working to further understand the complex coral-zooxanthellae association and what implications it may have for the adaptation of corals to future climate change.
The search for other “super corals”
Palumbi’s research on Ofu also revealed that corals on the same reef do not necessarily experience the same environmental conditions. “Corals ten meters apart can experience very different temperatures and trying to understand corals as individuals in a varying environment is something we are trying to do.” The “super corals” of Ofu are only a few hundred feet away from other coral colonies of the same species that are incapable of surviving in the warm pools. The observation of small-scale adaptation to reef microclimates is not something that has been examined in detail and emphasizes the importance of understanding corals as individuals and not as large conglomerates that behave similarly over a large area. Knowing this, the search for “super corals” can begin by systematically identifying areas with environmental conditions similar to the shallow back reef pool on the southern coast of Ofu. “Super corals probably only make up one to five percent of the corals around Ofu, and we don’t yet know about other places,” says Palumbi whose goal is to begin locating other “super coral” hotspots around the Pacific.
To accomplish this goal Palumbi is working to develop what he calls a “portable coral stress tank.” This tank will allow researchers to subject corals from around the world to simulated bleaching events by exposing corals to high water temperatures and monitoring how they respond. This work will hopefully help locate resilient zones within coral reef ecosystems around the world so that conservation and management efforts can target these important areas. The location and preservation of global “super coral” populations has the potential to establish epicenters of resilience within coral reef communities and greatly improve the ability of corals to adapt to the challenges of climate change.
Connecting local people to the reef
One of the most important aspects of science is being able to effectively communicate it to non-scientists. When researchers are working in a foreign country, it’s even more important to build relationships and trust with the local people who can protect valuable assets like “super corals.” Palumbi and his team take outreach and education very seriously. “Science is a way of opening up the world so people who are not scientists can see the other part of it,” explained Palumbi. With the help of Stanford University, Palumbi is working to buy a saltwater aquarium for the middle school on Ofu. “We want to bring the ocean to the kids to inspire them to venture out to the reef and establish a connection to the environment.” By establishing a connection between the people and the reef, Palumbi hopes that he can teach them how truly special the corals of Ofu are and convince the people to protect them. Another excellent example of connecting science to the local community is a micro-documentary Palumbi created. American football could be considered a way of life in American Samoa, and it is taken very seriously by people of all ages. The pride American Samoan’s have in the strength of their football players and their culture inspired Palumbi to teach them about Ofu’s special corals so local people could also take pride in the strength of their “super corals”. Watch the microdoc "Tough! Football and Coral in America Samoa" below.
Ofu is a small island but that does not mean it is immune to the changes experienced by the rest of the world. Currently, Ofu is considering strengthening their revenue from tourism by expanding their runway to accommodate larger planes. One plan threatens to build the runway directly on top of the reef where the “super corals” live. Thanks to his interactions with the local community and his continued presence on the island, Palumbi and Stanford University have begun to discuss different airport expansion options with local officials and are continuing efforts to raise local pride in the “super corals” of Ofu.
Much is still unknown about how the “super corals” of Ofu are able to resist such high temperatures. Palumbi and his team are systematically addressing the different variables that could be responsible for this exceptional resilience. With each discovery, we are one step closer to understanding how corals may adapt to increasing ocean temperatures. Climate change is underway, but it’s encouraging that perhaps “super corals” are hope for the future of coral reefs.
The New York Times article on coral reef bleaching - http://www.nytimes.com/2011/06/05/weekinreview/05reefs.html?src=recg
Stanford magazine article - http://www.stanfordalumni.org/news/magazine/2010/julaug/features/palumbi.html