Sex, Symbiosis and Coral Reef Communities

SYNOPSIS. Questions about how today's corals and coral reefswill fare in a future that holds not only increasing directanthropogenic impacts, but also global change, cannot be satisfactorilyanswered if we do not understand the relations of corals andreef systems to today's environmental conditions. This paperdiscusses four aspects of modern reef biology: coral reproduction,coral population biology, the coral-zooxanthella symbiosis,and reef community ecology. Conclusions of this survey of currentknowledge are that complexities of cnidarian reproductive biology,and our rudimentary knowledge of reproductive patterns in reefcnidarians, make forecasting based on current knowledge uncertainat best; new discoveries about the coral algal symbiotic systemsuggest a possible mode of adjustment to environmental changethat warrants a strong research effort; coral communities ofthe future may well be unlike what we are familiar with today;and these new assemblages will be shaped by the interactionof novel environmental conditions and the characteristics ofindividual reef species.     

Reefs happen

Corals and coral reefs confront us with a variety of paradoxes in terms of their responses to global change. The species appear evolutionarily long-lived and stable, and combinations of organisms recur and persist at levels ranging from endosymbiosis to palaeocommunity structure. The fact that these organisms and communities occupy a seemingly precarious environment near the common interface of land, sea, and air suggests that they possess powerful adaptive and acclimative mechanisms, and the special characteristics associated with their range of reproductive options, their modular (colonial) form, and their symbiotic associations provide multiple pathways for adaptation. At the same time, they are widely considered to be vulnerable to anthropogenic stresses, and to show signs of deterioration on a global scale. Interest in corals is further enhanced by their unique position with regard to the carbon cycle, with inorganic and organic carbon metabolisms that are of comparable magnitudes. The durable limestone structures they create modify the shallow-water environment, and their mineral skeletons preserve in their isotopic, chemical, and structural characteristics records of past environmental conditions. Whether as survivors, recorders, or victims, their relationship to global change is fascinating and instructive. This paper provides a general background and context for the specific papers that make up this topical issue of Global Change Biology.