CORAL-REEF ECOSYSTEMS - HOW MUCH GREATER IS THE WHOLE THAN THE SUM OFTHE PARTS

The ecosystem concept has been applied to coral reefs since the time o f Charles Darwin, perhaps because of the apparent integrity of the bio tic-abiotic nexus. The modern model of the ecosystem as a hierarchy wi th emergent properties is exemplified in reefs as massive structures f ormed by small colonial organisms, the self-similarity of these struct ures across large spatial scales, and the uniformity of function by di verse biological communities. Emergent properties arise through the in tegration of processes up the levels of organization and larger spatia l and temporal scales encompassed by a whole reef. The organic respons e of reef morphology to hydrodynamic forcing, the constancy and conser vatism of organic production across a broad range of environments, and the global persistence of reefs in the face of massive evolutionary c hange in species diversity are interpreted as emergent properties. Cor al reefs, of course, function by the same basic laws as other ecosyste ms, but there is cause to view them as an end member of a continuum be cause of their structural complexity and high internal cycling. Well-d efined boundary conditions mean that highly integrative measures of ec osystem process based on physical and biogeochemical models (e.g. comm unity metabolism) have provided the main applications of systems ecolo gy to questions of coral reef function. Organism-population approaches are being reconciled with form-functional models to yield new insight s to ecosystem processes and interactions among reefs and adjacent sys tems. The form and metabolism of reef production are strongly affected by phase shifts in benthic community structure, and most reef systems are more open to trans-boundary fluxes and external forcing than the early models suggest. The attractive paradigm of the reef as a self-su fficient ecosystem is dying slowly as research focus shifts from atoll s to more open fringing and bank barrier reefs, and organic inputs to system production are measured. Coral reefs contribute little in a net sense to global ecosystem processes, but on an areal basis their expo rts of organic products are significant. Holistic models and measures of ecosystem processes incorporate the unusual whole-part relationship of reefs and are practically essential to answering the key questions facing coral reef science in the next millennium.