According to a recent study led by Texas A&M University researcher Dr. Katie Shamberger, some Pacific Ocean coral reefs can not only survive in waters with high levels of acidification, but can actually thrive in such an environment.
Dr. Shamberger is also an Oceanographer and Geology & Geophysics Postdoctoral Investigator for the Woods Hole Oceanographic Institution. She and colleagues from Woods Hole and the Palau International Coral Reef Center (PICRC) examined coral reefs around the islands of Palau in the western Pacific Ocean. Their findings have been published online in Geophysical Research Letters, a publication of the American Geophysical Union.
The research letter, entitled: “Diverse coral communities in naturally acidified waters of a Western Pacific reef” (first published online: 16 JAN 2014 DOI: 10.1002/2013GL058489) is co-authored by Kathryn E. F. Shamberger, Anne L. Cohen, Daniel C. McCorkle, Steven J. Lentz, and Hannah C. Barkley of Woods Hole Oceanographic Institution, and Yimnang Golbuu of the Palau International Coral Reef Center, Koror, Palau.
The co-authors note that anthropogenic carbon dioxide emissions are acidifying the oceans, reducing the concentration of carbonate ions that calcifying organisms need to build and cement coral reefs. They note that previous studies of a handful of naturally acidified reef systems have revealed reduced coral cover and calcification rates, consistent with results of laboratory-based studies. However, in this letter they report the existence of highly diverse, coral-dominated reef communities under chronically low pH and aragonite saturation state, noting that biological and hydrographic processes change the chemistry of seawater moving across barrier reefs and into Palau’s Rock Island bays, where levels of acidification approach those projected for the western tropical Pacific open ocean by 2100. Nevertheless, they found that coral diversity, cover, and calcification rates are maintained across this natural acidification gradient, and observe that Identifying the combination of biological and environmental factors that enable these communities to persist could provide important insights into the future of coral reefs under anthropogenic acidification.
Dr. Shamberger’s research focuses on the ocean carbon cycle, how it is being altered by anthropogenic ocean acidification, and the impacts of ocean acidification on calcifying organisms. She also interested in coastal ocean carbon cycling, specifically in coral reef ecosystems, and investigates the natural biogeochemical processes that control CO2 in coral reef ecosystems and how these processes (especially calcification) and coral reef organisms are affected by ocean acidification.
At Palau, Dr. Shamberger measured the pH levels of seawater on several coral reefs in Palau and found that coral reefs in the Rock Islands — a maze of small islands, where water there tends to ‘linger,’ staying around for a long time before being flushed out — have high levels of acidification that aren’t expected to occur in the open ocean in that region until the end of the century, and that contrary to what might have been expected, these reefs appeared healthier than nearby reefs in less acidic waters. “The processes that cause these high levels of acidification in the Rock Islands are completely natural,” Dr Shamberger says in a TAMU release. “The growth of the reef and the breathing of carbon dioxide into the water by organisms on the reef acidifies the water. That allows these natural processes to change the water chemistry on the reef dramatically over time.”
Dr. Shamberger says studies show worldwide that the oceans are becoming more acidic. While ocean chemistry varies naturally at different locations, it is changing around the world due to increased levels of carbon dioxide in the atmosphere. The ocean absorbs atmospheric carbon dioxide, which reacts with seawater, lowering its overall pH, and making it more acidic.
“This process also removes carbonate ions needed by corals and other organisms to build their skeletons and shells,” she observes. “Corals growing in low pH conditions, both in laboratory experiments that simulate future conditions and in other naturally low pH ocean environments, show a range of negative impacts. Impacts can include juveniles having difficulty constructing their skeletons, fewer varieties of corals, less coral cover, more algae growth, and more porous corals with greater signs of erosion from other organisms. We don’t yet know how the coral communities in Palau’s Rock Islands are able to survive in such high levels of acidification. Is it biological, the perfect combination of environmental factors, or both? We don’t know, and finding out is one of the next steps we take.”
Dr. Shamberger found that corals living in the acidified waters were surprisingly diverse and healthy. Previous work on naturally acidified coral reefs has shown these reefs to have lower coral diversity and sometimes lower coral cover than nearby less acidic reefs, but she she notes that “In fact, the opposite seems to be true in Palau. The corals seem to be thriving and growing. This area in Palau seems to be the exception of healthy coral communities in acidified waters.”
She emphasizes that this doesn’t necessarily mean other coral reefs will be okay under ocean acidification. “Somehow, conditions were just right for the coral communities in the Rock Islands to survive high levels of acidification, but that does not mean that conditions will be just right for other coral reefs dealing with ocean acidification,” she explains in the TAMU release. “Palau’s coral communities probably had thousands of years to develop while current ocean acidification is happening much more quickly. Even if there is the potential for coral reefs to adapt to ocean acidification, they might not have enough time to do so.”
TAMU notes that some coral reefs can be thousands of years old and live in waters 1,500 feet or more below the surface. Coral reefs play a key role in ocean processes and they are one of the most diverse ecosystems in the world, supporting numerous forms of marine life.
The Palau research project was funded by the National Science Foundation, the Woods Hole Oceanographic Institution and the Nature Conservancy.
Texas A&M University
Woods Hole Oceanographic Institution
American Geophysical Union Geophysical Research Letters
Texas A&M University
Woods Hole Oceanographic Institution