Evolution and Function of Coral Reef Ecosystems

For biologists, a coral reef is a marine community characterized by abundant corals. For geologists, a coral reef is a rigid skeletal structure in which stony corals are major framework constituents, with coralline and calcareous algae, mollusks, foraminifers, and other calcifying organisms contributing to the total reef volume. Zooxanthellate corals are highly specialized symbioses between coral hosts and dinoflagellate algae called zooxanthellae. As a result of this symbiosis, coral reefs thrive in clear, nutrientpoor, shallow waters of tropical oceanic islands and continental shelves. Rapidly increasing human populations are threatening coral reefs on multiple fronts. Nutrification, sedimentation, chemical pollution, and overfishing are significant and often interrelated local threats of global extent. Increasing concentrations of atmospheric CO ₂ threaten to destabilize climate, induce global warming, and alter ocean chemistry. Corals under temperature stress become more sensitive to sunlight, thus, the combination of ozone depletion and global warming is particularly damaging. The fossil record of biogenic reefs and carbonate-producing communities has much to contribute to our understanding of living species and to predictions of how communities may respond to anthropogenically induced environmental change. Reef communities are geologically both productive and fragile, producing thick limestone buildups under favorable conditions, but suffering the most from widespread extinctions under regional or global environmental perturbations.