IntJEarthSciencesGeolRundsch)2001)90:426±437 DOI 10.1007/s005310000125 ORIGINAL PAPER Joan A. Kleypas ´ Robert W. Buddemeier Jean-Pierre Gattuso The future of coral reefs in an age of global change Received: 15 October 1999 / Accepted: 10 July 2000 / Published online: 18 October 2000  Springer-Verlag 2000 Abstract Coral reefs are the only ecosystem that is strongly defined by a geological component ± most definitions require that the biological community produces its own build-up of calcium carbonate. In terms of ªreef-building,º the geological record reveals that coral reefs have flourished over the past few mil- lion years, particularly during interglacial periods. Based on our observations of modern-day reefs, which are limited to the past few centuries, we tend to link ªcoral reef healthº to carbonate production; however, reef ecosystems face future global-scale environmental changes that may decrease their reef-building capacity. In contrast to past discussions of the factors which determine reef-building potential by a coral reef com- munity, the essential question that arises from this review is: How important is reef building to a coral reef community? Keywords Coral reef ´ Global change ´ Calcium carbonate ´ Saturation state ´ Temperature ´ CO 2 Introduction Coral reefs are threatened directly at local and regional scales by many human activities, including over-harvesting, deforestation, and general decline of coastal environments due to increasing population pressures. Over geological time, reefs have also been affected by global scale changes in seawater chemistry, temperature, and sea-level fluctuations. Of these three, global changes in both seawater chemistry and temperature will probably have the most profound impacts on coral reefs within the next century. In this paper we examine current definitions applied to reefs of the past as well as to those of the present. We then examine the implications of applying such definitions to coral reefs of the future. Past and present views of coral reefs ªC'est une merveille de voir chacun de ces atollons, environnØ d'un grand banc de pierre tout autour, n'y ayant point d'artifice humain.º ªIt is wonderful to see each of the atolls completely surrounded by a great bank of stone, of no human construction.º François Pyrard de Laval 1605) as quoted by Darwin 1842) Early references to reefs reveal fascination with the reef structure. The foregoing quotation by Pyrard de Laval reflects the natural curiosity of early explorers about the origins of the ªgreat banks of stoneº. Such fascination was due partly to the fact that so few Europeans, who provided the first records of coral reefs, had seen coral reefs before. Humans continue to focus on the rock component of reefs for several reasons. One is that coral reefs pose a major threat to navigation. Indeed, the term ªreefº was originally defined as a navigational hazard, and ªcoral reefº was merely a navigational hazard with corals on it. Another reason is that many of the early reef researchers concentrated on the reef struc- ture. Darwin 1842) was certainly preoccupied with just how reefs formed, as was Dana 1872), and many others of the present century Yonge 1930; Steers 1937; Stoddart et al. 1978). Davis 1928) exemplified the geologist's attitude in the following: J.A.Kleypas ) ) Oceanography Section, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, USA E-mail: kleypas@ncar.ucar.edu Phone: +11-303-4971316 Fax: +11-303-4971700 R. W. Buddemeier Kansas Geological Survey, University of Kansas, Lawrence, KS 66047, USA J.-P. Gattuso Observatoire OcØanologique, ESA 7076 CNRS-UPMC, B.P. 28, 06234 Villefranche-sur-mer Cedex, France