C oral reefs are the most diverse of all marine ecosystems, and they are rivaled in biodiversity by few ter- restrial ecosystems. They support peo- ple directly and indirectly by building islands and atolls. They protect shore- lines from coastal erosion, support fish- eries of economic and cultural value, provide diving-related tourism and serve as habitats for organisms that produce natural products of biomed- ical interest. They are also museums of the planet’s natural wealth and places of incredible natural beauty. Despite their recognized biological, economic and aesthetic value, coral reefs are being destroyed at an alarm- ing rate throughout the world. Some countries have seen 50 percent of their coral reefs destroyed by human activi- ties in the past 15 years. Some human influences are acute—for example, mining reefs for limestone, dumping mine tailings on them, fishing with ex- plosives and cyanide, and land recla- mation. Reefs that experience such in- sults often die; those that deteriorate but survive cannot recover to their original health as long as the distur- bances continue. In other countries the disturbances are more chronic than acute. Reefs are assaulted by muddy runoff, nutrients and pesticides from adjacent river catchments, overfishing and global-warming effects. These dis- turbances affect the key parameters permitting reef resilience: water and substratum quality. As a result, corals fail to reproduce successfully, and the coral larvae arriving from more pris- tine reefs are unable to settle and thrive on substrata covered by mud, cyano- bacteria or fleshy algae. Coral popula- tions thus fail to recover or reestablish themselves. Can science help save coral reefs? Despite much talk about managing coral reefs, the potential role of science is limited. But it is important: Scientists can demonstrate the key processes con- trolling the health of coral reefs and how human activities damage them. Then, we can hope, land-use managers and marine-resources managers will be able to modify human behavior to re- duce or reverse damage to coral reefs. Toward this end we have developed a large-scale model for illuminating reef degradation and predicting the impact of future human activity. The Coral Reef Ecosystem The ecological functioning of a coral reef relies on the symbiotic association between corals and dinoflagellate algae (zooxanthellae). In this system, the di- noflagellates reside as symbionts with- in the cells of the coral host; the sym- bionts take in nutrients and produce metabolites from which the corals de- rive much of their energy. (Corals con- struct their hard habitat the way mol- lusks grow their shells, by accreting calcium carbonate.) The main function- al components of a coral reef ecosys- tem include the hard corals, coralline algae, filamentous and fleshy algae, blue-green algae (cyanobacteria), and a host of invertebrates and fishes. Coralline algae are essential to a healthy reef because they cement reef structures and contain chemicals that induce metamorphosis in coral planula larvae. Filamentous and fleshy algae can be very abundant; indeed, the most telltale sign of a degraded coral reef is the replacement of corals by al- gae (Figure 2). Three genera of corals dominate Pa- cific reefs: Acropora, Porites and Pocillo- pora. Acropora corals are the most spec- tacular; they are also framework builders, providing habitat for a vari- ety of fishes and other reef organisms. They include the table, elkhorn, staghorn and fast-growing branching species. Porites corals include boulder or massive corals. Pocillopora corals in- clude both coarsely and finely branch- ing species, widely distributed across the Pacific and into the Red Sea. Natural disturbances—including hurricanes (tropical cyclones or ty- phoons), river floods (Figure 4), earth- quakes and lava flows—have affected coral reefs for millions of years; they are typically acute and have short-lived ef- fects. Reef areas away from human in- fluences often recover within a few years if water and substratum quality remain high. Acute, natural distur- bances thus help maintain diversity on coral reefs by knocking back dominant species and allowing less competitive species to reestablish themselves. 44 American Scientist, Volume 91 Mud, Marine Snow and Coral Reefs The survival of coral reefs requires integrated watershed-based management activities and marine conservation Eric Wolanski, Robert Richmond, Laurence McCook and Hugh Sweatman © 2003 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact perms@amsci.org. Eric Wolanski received his Ph.D. in environmental engineering from the Johns Hopkins University in 1972. He is a leading scientist at the Australian Institute of Marine Science, where he studies trop- ical coastal oceanography and its biological impli- cations for mangroves and coral reefs. Robert Rich- mond received his Ph.D. in biology from the State University of New York at Stony Brook in 1983. He is a professor of marine biology at the Universi- ty of Guam Marine Laboratory. His research inter- ests include sublethal stresses on coral reefs. Lau- rence McCook received his Ph.D. in biology from Dalhousie University in 1992; he is a research sci- entist specializing in the ecology of algae and reef degradation at the Australian Institute of Marine Science, working with the Cooperative Research Centre for the Great Barrier Reef World Heritage Area. Hugh Sweatman received his Ph.D. from Macquarie University in 1985; he is a research sci- entist at the Australian Institute of Marine Sci- ence where he leads the long-term reef-monitoring program. Address for Wolanski: AIMS, PMB No. 3, Townsville MC, Qld. 4810, Australia. E-mail: e.wolanksi@aims.gov.au