Coral reef assessments based on cover alone mask active dynamics of coral communities
Coral reef communities are often studied by tracking the percentage (or fraction) of the reef covered by coral through time. However, coral community dynamics result, in part, from underlying colony-level growth and mortality, which in turn depend on characteristics of individ- ual colonies, such as size, taxon, life history strategy, and morphology. Colonies are also subject to external disturbances that propel fission into smaller coral fragments and fusion where related fragments later fuse into contiguous colonies. To quantify how changes in coral growth through time depend on individual colony characteristics and colony fission and fusion processes, 4385 individual Caribbean coral colonies representing 4 dominant coral types (Madracis mirabilis, mounding coral species, Agaricia agaricites, and Millepora spp.) were tracked at 6 mo intervals for 4 yr. Despite overall stable percent coral cover, colonies belonging to different coral types experi- enced differential growth, shrinkage, mortality, fission, and fusion processes. All coral types dis- played size-dependent allometric growth patterns whereby relative, or proportional, growth in colony area decreased with increasing colony size. The largest changes in relative colony growth resulted from colony fission or fusion with other colonies, which occurred in 16.4% of all moni- tored colonies. Colony longevity, or survival, increased significantly with increasing colony size for all hard-coral groups that did not experience fission, fusion, or a combination of these pro- cesses. Our findings illustrate the usefulness of a size- and life-history-dependent approach to coral demography that elucidates the factors driving community dynamics of colonial organisms, which are not captured by traditional approaches based on benthic cover alone.