Recent studies have shown that environmental changes can have serious short-term impacts on the world's coral reefs, but the long-term implications of these changes is less certain. Ten years of research conducted by Earthwatch teams working with Thomas McGrath (Corning Community College) in the Bahamas suggest that reef-building, hard corals are more resilient than anticipated.
McGrath presented his results at the 10th Symposium on the Natural History of the Bahamas held at Gerace Research Center, June 18-22, and organized by McGrath and colleague Sandra Buckner (College of the Bahamas). His paper was titled "Variations in scleractinian coral populations on patch reefs around San Salvador Island, Bahamas, over the past decade." Scleractinian corals are those with a calcium carbonate skeleton such as familiar brain, finger, horn, and leaf corals.
"The long-term stability of hard coral populations on these patch reefs suggests a greater resilience to bleaching events and other environmental impacts than has been suspected," said McGrath, principal investigator of the Earthwatch-supported Bahamian Reef Survey project. "Short-term damage may not be as devastating to some reefs as has been suggested."
Using refined survey techniques, Earthwatch teams documented episodes of widespread bleaching events, disease, and storms on three patch reefs with distinct coral communities. Bleaching occurs when environmental stresses induce the corals to expel symbiotic algae living in their tissues. This can happen to many kinds of corals, but it is particularly serious in reef-builders, which maintain the structure of the reef.
McGrath's results indicate that large coral colonies, those with more than 100 square centimeters of live tissue, were the most likely to exhibit long-term survival and resilience to environmental impacts. Small coral colonies, representing recent "recruits," suffered the most from these impacts, with as much as 30 percent change in the presence of such colonies occurring each year.
While this level of death and recruitment suggests a highly dynamic system, when population distributions of each coral species on each reef were examined, McGrath found them remarkably consistent across the decade. These data support recent ecological theory, which proposes systems with this sort of short-term dynamism and long-term stability.
"If the tendency toward some stability in the face of environmental insults is typical and not unique to our patch reefs, this could mean that reefs in general may have a brighter future than has been suspected," said McGrath. "That is, if we can control the anthropogenic factors that influence or create negative impacts on these systems. The reefs could be just waiting for us to get things right."
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