Coral Community Adaptability to Environmental Change at the Scales of Regions, Reefs and Reef Zones

SYNOPSIS. Projected global increases in temperature, sea level,storminess and atmospheric carbon dioxide (CO₂) are likely tocause changes in reef coral communities which the present humangeneration will view as deleterious. It is likely coral communitytrajectories will be influenced as much by the reduction inintervals between extreme events as the projected increasesin means of environmental parameters such as temperature, atmosphericCO₂ and sea-level. Depressed calcification rates in corals causedby reduced aragonite saturation state of water may increasevulnerability of corals to storms. Moreover, reduction in intervalsbetween storms and other extreme events causing mass mortalityin corals (coral predators, diseases, bleaching) are likelyto more frequently "set back" reef coral communities to earlysuccessional stages or alternate states characterized by non-calcifyingbenthos (plants, soft corals, sponges). The greater the areaand the longer the duration of dominance of putative "coral/corallinealgae" zones of coral reefs by non-calcifying stages, the lesswill be the reefs capacity to accrete limestone bulk lockedup in the big skeletal units of late successional stages (i.e.,very large old corals). Averaged over decades to centuries,the effects of such changes on the coral community's carryingcapacity for other biota such as fish are unpredictable. A "shiftingsteady-state mosaic" null model may provide a useful conceptualtool for defining a baseline and tracking changes from thatbaseline through time.