Coral Reefs: Winners and Losers

Christopher Pala Science AAAS 10 Aug 11;

Scientists have just made the job of those trying to save the world's coral reefs a bit easier. A new map published today pinpoints the reefs that can still be saved—and those that are likely to die. The team hopes that the data will help reef managers better focus their conservation efforts.

Some corals (green spots) are located in places where climatic conditions are likely to allow them to survive global warming, whereas others (red dots) are likely to die early from more adverse regional conditions. Credit: Joseph Maina

Today, about 19% of the world's coral reefs have died as a result of overfishing of algae-eating fish, pollution, and temperature spikes, according to the Global Coral Reef Monitoring Network (based on the opinion of 370 coral reef scientists and managers from 96 countries). Another 15% are expected to die in the next 15 years. More than 100 million people depend on them for food, as a live reef supports many edible fish and crustaceans. In addition, many more people rely on reefs as a buffer against high waves.

Reef managers can help restore coral reefs by restricting fishing and reducing pollutants in the water that then runs off land near reefs. Until now, however, they've had a hard time figuring out which reefs to focus on. Their best measure was looking at how a reef resisted past bleaching events-periods of exceptionally warm water that kill the corals and turn them white-and how fast the corals recovered from these events. But this strategy is inefficient and costly because there are not enough coral reef field biologists to study all reef locations.

To help reef managers better focus their efforts, spatial ecologist Joseph Maina of Macquarie University in Sydney, Australia, and his colleagues performed a global assessment of areas most susceptible to bleaching. They mined satellite and tidal data to determine where the water has gotten warmer and where there is the least amount of wind (wind makes waves, which cool the sun-heated top layers by mixing them with the cooler ones underneath). Differences in ultraviolet radiation were also factored in.

Then they looked at the positive factors that make a heat wave bearable: high, swift tides; big variations in temperatures (corals that are used to big swings survive warming better than those that are not); and strong, cooling currents. They also factored in one of the main direct causes of coral mortality: runoff from rivers that dumps sediment and excessive nutrients into the sea, helping algae replace corals. This is the bit that humans can do something about by regulating the use of fertilizers and soil erosion.

The team then plugged all of its data into mathematical formulas and generated a map. The map, in a paper published online today in PLoS ONE, shows that some reefs have a much brighter future than others.

La Reunion, a French island in the Pacific that recently stepped up protection, won the "Most Likely to Succeed" award. On a scale where maximum stress is 1 and minimum is 0, it scored 0.13. On the other end of the spectrum, Lombok Island, which has Indonesia's best score, rates only 0.74, a high stress value.

Florida's Key Largo scored an impressive climatic score of 0.25, but because overfishing and runoff have damaged its reefs, its total stress level is a high 0.85. That makes it a perfect candidate for stepping up protection, Maina says.

Conversely, he says, other healthy reefs in places like Bonaire off Venezuela, the Hawaiian Islands, the Great Barrier Reef, and New Caledonia are already getting good protection. This study should encourage managers to maintain their efforts there, he says.

The study yielded some surprising results. Britain's largely untouched Chagos Islands, which sit in the middle of the biggest marine reserve in the world, nearly the size of Spain, in the central Indian Ocean, scored a high climatic stress level of 0.80. The Pacific nation of Kiribati's Phoenix Islands, whose reefs are protected, scored 0.87 and nearby Palmyra, probably the most studied pristine atoll in the world, 0.83. But Takapoto Atoll in French Polynesia scored a much better 0.66.

In Southeast Asia, however, climatic conditions are so bad that most of the corals are dying and disappearing much faster than reefs in lower-stress environments. The region contains the so-called Coral Triangle that's home to 500 of the world's 700 species of coral. The remarkable biodiversity has led to the Coral Triangle Initiative convened in 2009 in which the United States, the Asian Development Bank, and others pledged more than $400 million over 5 years to protect the reefs from overfishing and pollution. That's far more than in places that the new study predict have a rosier future, despite little success in curbing a declining coral cover in the Coral Triangle over the past 30 years.

"There are a lot of reefs around the world that are going to do much better, and together they're only getting a tiny fraction of that amount," says co-author Tim McClanahan of the Wildlife Conservation Society in Mombasa, Kenya. "A lot of money is being wasted on reefs that have a dismal future," he says.

"We need to focus on the winners, not losers," McClanahan adds. "They're off in the Pacific, southern East Africa, Sri Lanka, and the northern Red Sea. They're not very well protected and they'll do much, much better if they had more fish and less sediment."

The 1982-2009 temperature data the study is based on is a good indicator of future trends, McClanahan says, because many oceanographic physical processes are stable enough to insure consistent patterns in temperature changes.

"This is a valuable contribution that helps to identify locations that will suffer the least from climate change and therefore benefit the most from local conservation measures," says Alan Friedlander, a marine biologist at the University of Hawaii, Manoa, who studies reefs.

But not everyone agrees. John Bruno, a marine ecologist at the University of North Carolina, Chapel Hill, says it's hard to tell which corals will bleach in the future. "The Bahamas bleached in 1998 but not in 2003, while the Virgin Islands bleached in 2010 but not before, and that's just in the Caribbean."

Worldwide Map Identifies Important Coral Reefs Exposed to Stress
ScienceDaily 11 Aug 11;

Marine researchers from the Wildlife Conservation Society and other groups have created a map of the world's corals and their exposure to stress factors, including high temperatures, ultra-violet radiation, weather systems, sedimentation, as well as stress-reducing factors such as temperature variability and tidal dynamics.

The study, say the authors, will help to conserve some of the world's most important coral reefs by identifying reef systems where biodiversity is high and stress is low, ecosystems where management has the best chance of success.

The paper appears online in journal PLoS One. The authors include: Joseph M. Maina of WCS and a doctoral student at Macquarie University, Sydney, Australia; Timothy R. McClanahan of WCS; Valentijn Venus of Netherlands Institute for Geo-Information Science and Earth Observation; Mebrahtu Ateweberhan of the University of Warwick; and Joshua Madin of Macquarie University.

"Coral reefs around the globe are under pressure from a variety of factors such as higher temperatures, sedimentation, and human-related activities such as fishing and coastal development," said Joseph M. Maina, WCS conservationist and lead author on the study. "The key to effectively identifying where conservation efforts are most likely to succeed is finding reefs where high biodiversity and low stress intersect."

Using a wide array of publicly available data sets from satellites and a branch of mathematics known as fuzzy logic, which can handle incomplete data on coral physiology and coral-environment interactions, the researchers grouped the world's tropical coral reef systems into clusters based on the sum of their stress exposure grades and the factors that reinforce and reduce these stresses.

The first cluster of coral regions -- Southeast Asia, Micronesia, the Eastern Pacific, and the central Indian Ocean -- is characterized by high radiation stress (sea surface temperature, ultra-violet radiation, and doldrums weather patterns with little wind) and few stress-reducing factors (temperature variability and tidal amplitude). The group also includes corals in coastal waters of the Middle East and Western Australia (both regions have high scores for reinforcing stress factors such as sedimentation and phytoplankton).

The second cluster -- including the Caribbean, Great Barrier Reef, Central Pacific, Polynesia, and the Western Indian Ocean -- contained regions with moderate to high rates of exposure as well as high rates of reducing factors, such as large tides and temperature variability.

Overall, stress factors such as surface temperature, ultra-violet radiation, and doldrums were the most significant factors, ones that ecosystem management has no control over. What is controllable is the mitigation of human impacts that reinforce radiation stress and where managers decide to locate their protected areas.

"When radiation stress and high fishing are combined, the reefs have little chance of surviving climate change disturbances because they both work against the survival of corals that are the foundation of the coral reef ecosystem," said Dr. Tim McClanahan, WCS Senior Conservationist and head of the society's coral reef research and conservation program.

The authors recommend that the study results be used to formulate management strategies that would include activities such as fishing restrictions, the management of watersheds through improved agricultural practices, and reforestation of coastal watersheds that play a role in healthy coral systems.

"The study provides marine park and ecosystem managers with a plan for spatially managing the effectiveness of conservation and sustainability," said Dr. Caleb McClennen, Director of the Wildlife Conservation Society's Marine Program. "The information will help formulate more effective strategies to protect corals from climate change and lead to improved management of reef systems globally."

The Macquarie University's Higher Degree Research (HDR) and the Wildlife Conservation Society Marine Program contributed to the mapping project, with support from the John D. and Catherine T. MacArthur Foundation.

Journal Reference:

Joseph Maina, Tim R. McClanahan, Valentijn Venus, Mebrahtu Ateweberhan, Joshua Madin. Global Gradients of Coral Exposure to Environmental Stresses and Implications for Local Management. PLoS ONE, 2011; 6 (8): e23064 DOI: 10.1371/journal.pone.0023064