Coral community adaptability to environmental change at the scales of regions, reefs and reef zones

Abstract

SYNOPSIS. Projected global increases in temperature, sea level, storminess and atmospheric carbon dioxide (CO2) are likely to cause changes in reef coral communities which the present human generation will view as deleterious. It is likely coral community trajectories will be influenced as much by the reduction in intervals between extreme events as the projected increases in means of environmental parameters such as temperature, atmospheric CO2, and sea-level. Depressed calcification rates in corals caused by reduced aragonite saturation state of water may increase vulnerability of corals to storms. Moreover, reduction in intervals between storms and other extreme events causing mass mortality in corals (coral predators, diseases, bleaching) are likely to more frequently "set back" reef coral communities to early successional stages or alternate states characterized by non-calcifying benthos (plants, soft corals, sponges). The greater the area and the longer the duration of dominance of putative "coral/coralline algae" zones of coral reefs by non-calcifying stages, the less will be the reefs capacity to accrete limestone bulk locked up 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 carrying capacity for other biota such as fish are unpredictable. A "shifting steady-state mosaic" null model may provide a useful conceptual tool for defining a baseline and tracking changes from that baseline through time.