A 30-YEAR STUDY OF CORAL ABUNDANCE, RECRUITMENT, AND DISTURBANCE AT SEVERAL SCALES IN SPACE AND TIME

TLDR

A 30‑year study of Heron Island corals revealed substantial natural variation in abundance. Coral cover ranged from <0.1 % to >80 %, with large spatial and temporal differences driven mainly by disturbance type, intensity, and scale; acute disturbances were usually recovered from, especially when they only killed corals, whereas chronic or gradual declines led to persistent losses, with faster recovery on sheltered sides and recruitment limited by space preemption and storm‑altered substrata.

Abstract

Observation over a 30-yr period revealed a considerable degree of natural variation in the abundance of corals on Heron Island, Great Barrier Reef, Queensland, Australia. Cover ranged from <0.1% to >80%, with a similar large range in colony density, at several temporal and spatial scales. Much of this variation was due to the type, intensity, and spatial scale of disturbances that occurred. Coral assemblages usually recovered from acute disturbances, both on Heron Island and on other Indo-Pacific reefs. In contrast, corals did not recover from chronic disturbances of either natural or human origins, or from gradual declines. Recovery was slower after acute disturbances that altered the physical environment than after disturbances that simply killed or damaged corals. The space and time scales of declines and recoveries in abundance were much smaller on the wave-exposed side of the reef than on the side protected from storms. Recruitment rates were reduced by preemption of space by corals or macroalgae, and by storms that altered the substratum. Thus, the dynamics of abundance in this coral community can be largely understood through the variation in types and scales of disturbances that occurred, and the processes that took place where disturbances were rare.