Editor's Note: Occasionally a circumstance arises in nature that, treated imaginatively by a talented scholar, allows unusual insights into cause and effect. Yossi Loya, an Israeli ecologist, recognized such an opportunity in his studies of coral communities in the Gulf of Eilat and has used the chance to gather further insights into the patterns of diversity and dominance in natural communities under various types of stress. His observations not only reveal further details of the structure and function of these communities, but reconfirm the importance of long-continued studies of specific sites to determine changes under way in response to intensified human influence, details that would otherwise be lost as the biota moves inexorably through various stages of impoverishment in response to uncontrolled chronic disturbance.

Loya offers a case history study of a coral reef exposed in different places to oil pollution and climatic anomalies. While the circumstances seem specialized, they are increasingly common, and the observations Loya makes are emergent generalities, broadly applicable to natural communities under stress.

Introduction: The Reef at Eilat

One of the central questions of ecology deals with the mechanisms that generate and maintain the diversity of organisms. There have been many varied opinions and large numbers of publications on this subject. I review here briefly our studies of community structure of corals at Eilat, Red Sea, describe changes that have occurred in coral diversity due to human versus natural disturbances, and discuss mechanisms that promote and maintain high diversity of corals on the reef-flats of Eilat.