September 21, 2005
Coral Reef Survival
New research predicts the damage from increased carbon dioxide in the oceans
VIRGINIA KEY, FL (Sept. 14, 2005) – Increases in carbon dioxide are bad for corals – no matter how you look at it. That’s the conclusion of two researchers in the September issue of the Journal of Geophysical Research-Oceans, who investigated the effects of doubling carbon dioxide on two coral species that are important reef builders in Kaneohe Bay, Hawaii.
“The ocean is known to absorb carbon dioxide, causing measurable changes in seawater chemistry of the surface ocean,” said Chris Langdon, associate director of the National Center for Caribbean Coral Reef Research and one of the paper’s authors. “If this process continues to increase at the current rate, we expect carbon dioxide levels (and consequently the acidity of the ocean) to increase 200-300 percent in the next 50-100 years, so it is important to learn how these changes might affect marine ecosystems.”
Langdon and his colleague and co-author, Marlin Atkinson from the Hawaii Institute of Marine Biology, found that this manipulation of seawater chemistry, carefully designed to mimic conditions that might happen in the next 50 to 100 years, significantly damaged the coral. Langdon and Atkinson observed a 50 percent decrease in skeletal growth at the same time that the photosynthesis of the guest algae within the coral increased. The results indicate a breakdown in the normally mutually beneficial relationship between this guest algae and host coral. A similar breakdown has been widely reported when corals are exposed to elevated nutrient concentrations. Competition for carbon between the algae and the coral may be the explanation, Langdon said.
“As much as we could, we tried to account for other environmental changes known to affect coral growth, such as conducting our experiments in both summer and winter to explore possible interactions between elevated carbon dioxide and seasonal change in temperature and light and by first exposing the corals to an elevated nutrient loading,” Langdon said.
While this study did not examine the effects of elevated water temperature associated with global warming, this is also known to be a result of increased carbon dioxide levels in the atmosphere. Scientists predict global ocean temperatures to increase two to five degrees Celsius by the year 2100. “Because many species of coral are already growing very near their thermal threshold, any warming will reduce their growth,” Langdon said. “The combined effects of global warming and ocean acidification on coral growth could be even worse than what we observed in our study. A major unknown is whether corals possess the capacity to adapt or acclimate to these environmental changes, if the rate of change is not too fast.”
The National Oceanic and Atmospheric Administration (NOAA) National Sea Grant Program, the David and Lucille Packard Foundation ,and a generous gift by Edward P. Bass to the Biosphere 2 Center funded this research.
The Rosenstiel School is part of the University of Miami and since its founding in the 1940s, has grown into one of the world’s premier marine and atmospheric research institutions.
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