A particular concern about the predicted global mean temperature increase of 1 to 5 Degrees C by the year 2050 is that in the tropics, where many organisms live near their upper thermal tolerance, even a small increase in temperature could result in wide-spread mortality of ecologically and/or economically important species with a consequent change in the composition and character of tropical ecosystems (Peters and Darling 1985). Over the last decade there has been an increased incidence of so-called coral bleaching (Williams and Williams 1990, Langreth 1990, Glynn 1991), due to the loss by scleractinian corals of their algal symbionts or Hoegh-Guldberg and Smith 1989, Kleppel et al. 1989, Szmant and Gassman 1990). Many of the geographically extensive incidences of bleaching have followed periods of elevated seawater temperatures (Glynn 1991) and bleaching has been attributed to temperature stress to either the coral animals and/or their zooxanthellae (which of the two is not known for certain). The bleaching events have been taken by some to indicate that global climate warming has already begun (Roberts 1990), and temperature-sensitive coral reef cnidarians are being touted as potential important as indicators of small but real recent increases in seawater temperatures. Our ability to causally associate coral bleaching with global temperature increases is hampered by our lack of understanding of the fundamental causes and processes of the bleaching (Gladfelter 1988. Little is known about the particular conditions that trigger adaptive response to temperature increase. This information is needed to able to interpret coral bleaching from a global warming perspective, as well as to predict the long-term consequences of such warming. I hereby propose that the detection of heat-shock gene expression in tropical cnidarians and their algal symbionts may be a viable method for learning more about the temperature tolerance, physiology and adaptation of these organisms, and potentially as a monitoring tool for detecting climate change.
