Population structure as a response of coral communities to global change

Abstract

SYNOPSIS. Coral population size structure is generally highly skewed, with a preponderance of the smallest colony size class in populations. To begin to assess possible effects of global change on coral populations, which will be largely controlled in the next decade(s) by "non-climate variables" such as sedimentation, turbidity and nutrient load, we compared degraded reef environments with less degraded reefs. To consider population dynamics within and between parts of coral species metapopulations we use data over two spatial scales (10 and 2,000 km). Colony size distributions appear to be affected in degraded/marginal reefs. This implies changes in mortality patterns (or recruitment) that result in relatively fewer small and more large colonies in populations. We predict that the short-term ' effects of global change, deterioration of local conditions, will not affect the occurrence of large coral colonies (in terms of absolute size, and possibly mean size) but will limit the abundance of small corals. Long-term global change will increasingly include a component of climate change and the effect on coral populations may become more diverse, although effects such as a decreasing calcium carbonate saturation state will also first affect the abundance of coral recruits. We hypothesize that over the next decade(s) coral populations will become increasingly skewed toward larger colonies.