Listen to the UVA Today Radio Show report on this story by Fariss Samarrai:
July 15, 2010 — Coral reefs are sometimes called "the rainforests of the sea." These ecosystems are among the most diverse and complex in the world, and, like rainforests, their health is a good indicator for how the rest of the planet is doing.
Unfortunately, coral reefs in many areas are not doing well. In the last 50 or so years, the collective health of coral reefs has declined significantly, with about 30 percent destroyed, and 60 percent of those that remain considered threatened, according to several studies.
Matt Reidenbach, a University of Virginia environmental scientist, has been studying the physical and biological interactions within coastal ecosystems, including coral reefs, since he was an undergraduate civil and environmental engineering student at Cornell University in the mid-1990s. He later earned a Ph.D. in civil and environmental engineering at Stanford University, where he studied the physical characteristics of coral reefs and how they protect coastlines from storms and erosion. He did postdoctoral research at the University of California-Berkeley, studying the health of reefs in Hawaii. He also has conducted research in the Red Sea, on Australia's Great Barrier Reef and in the Caribbean Sea.
Reidenbach came to U.Va. three years ago and is setting up a new long-term investigation at three reef sites in the Bahamas; off Andros, New Providence and Rose islands.
"I'm working to understand how the health of reefs are affected by natural and human influences," he said. "What we've learned about coral reefs in the past and how they are changing today can tell us a lot about what we might expect in the future."
Corals thrive in clear, clean tropical-to-subtropical waters worldwide. Though they appear to be plant-like, seemingly growing from the sea bottom, they are, in fact, animals. They build their own rocklike substrate by absorbing the mineral aragonite from the water and using it to form the fabulous and varied calcium carbonate structures that make them so distinctive and beautiful. Elkhorn coral, staghorn coral, brain coral – these are some of their descriptive common names.
Coral reefs are highly complex ecosystems, somewhat like aquatic cities, supporting a wide array of sea life; fishes, sponges, mollusks, crustaceans and more. When the corals themselves are healthy, the other species generally do well.
But when an imbalance occurs, due to overfishing, damage from physical contact, pollution, changes in water quality or temperature, the corals – the very infrastructure of the system – can begin a gradual or even rapid die-off, affecting every other member of the ecosystem.
"We know that sea temperatures are warming, and that that is stressing corals," Reidenbach said. "We need to begin predicting with accuracy the long-term consequences of that, including on the coastlines that the corals protect."
Coral reefs serve as energy buffers, dissipating the power of waves before they reach mainland or island coastlines. As sea temperatures increase and sea levels rise, diminished corals lying in deeper water will provide less erosion protection for shorelines from storm activity and the gradual effects of daily wave action.
"A loss of coral reefs can have a big negative effect on nearby human populations," Reidenbach said. "Many of these coastal communities depend on the reefs for food, for tourism, for their livelihoods."
He points out that most coral reefs lie off the coasts of developing countries that have few resources for protecting their shores from the inevitable erosion that occurs when reef systems fail.
"Developing nations cannot easily build seawalls or pump in sand to replenish their beaches," Reidenbach said. "And if the corals die, if fish leave, if the water becomes murky or silted, the tourism industry fails, too."
Reidenbach points to the 2004 tsunami in Sri Lanka as an example of how whole communities in highly populated areas were devastated by the results of undissipated wave action. It's an extreme example, but without healthy corals to buffer tropical shorelines, the risk for damage accelerates with every crashing wave.
In the Bahamas, Reidenbach is setting up underwater stations on reefs where he can continuously measure wave height, speed and angle, wave energy, water temperatures and clarity and other factors that affect the health of corals. He's correlating that with measurements of beach erosion and sedimentation to determine relations. His data will be added to numerical models designed to forecast long-term effects, based on this baseline knowledge.
"We want to be able to say, 'Well, if the water rises this much, we can expect some given amount of erosion on the beaches in 10 years, 20 years, 50 years.' "
Reidenbach notes that sea levels have risen and fallen through the ages as the Earth has undergone natural long-term cycles of heating and cooling. But in recent decades sea temperatures have increased remarkably and sea levels are rising at rapid rates, about 3 to 4 millimeters per year. This will add up to inches and feet over time.
"The rapid rate of change is the danger," he said. "And this is occurring in areas of the world with rapidly growing populations. They will be the most affected, with potentially devastating consequences."
Reidenbach said he came to U.Va. because of the strength of its environmental sciences department.
"We have a strong history here of interdisciplinary coastal research," he said. "We have biologists and hydrologists and ecologists all working together on big problems."
This past spring, Reidenbach won a grant to continue his coral reef research from the Fund for Excellence in Science and Technology, sponsored by the Office of the Vice President for Research.