The focus of this book is on how a coral reef functions: the jobs of individual residents and how they collectively create a sustainable community. We will explore how corals construct the structure of this city under the sea. The wisdom involved in integrating form and function should inspire the best of architects. How corals and reef communities acquire and efficiently use energy should impress any engineer. How raw materials are acquired and utilized without causing environmental disruption or pollution ought to give hope to any environmentalist. Sociologists and psychologists might find interesting parallels between how members of reef and human communities deal with issues such as public housing, dealing with conflict, finding a mate, living together, public health, and social security. And for those concerned about the future, we see reef communities existing in a dynamic equilibrium where forces of competition, destruction, and decay are balanced by cooperation, repair, and rejuvenation. Through ecological webs all creatures are inextricably bound together, each to the other, in a common destiny. Evolution and extinction go hand in hand, for as long as life existed on planet Earth spinning through eons of time.
        But this is also a story about humanity and the places where we live. Coral reefs are, in many ways, like cities even though there are certainly many differences at many different levels of organization. Yet by viewing coral reefs in the context of a city we can more easily see how they operate in ways that neither undermine their own survival nor that of others elsewhere; in other words, how the variety of species collectively enhances the survival of the entire community. 
        There may be lessons we can take away from this perspective. We humans need help and guidance in living more sustainably. Living sustainably is important for our own survival and absolutely critical for the health of coral reefs. Humans are destroying the health and vitality of reefs worldwide, directly and indirectly. Direct threats are mostly local. Indirect threats are mostly related to global climate change, such as global warming, that is a result of how we use and waste energy. This is an issue involving us all, no matter where we live. Some consider coral reefs as the canaries of our planet just as the health of canaries in mines indicated the quality of air miners were breathing. Sick reefs may indicate a sick planet, and we cannot afford to undermine the habitability of the only place we have to live.
        In the following pages we shall explore life in the coral city in greater depth. Ours will be an adventure of discovery. The subject matter is serious, but we will not take it so seriously that it won't be fun. When you finish I hope you will have a much better idea about how a coral reef functions and, based on this knowledge, how we might live a bit more gently on our planet.