Mortality, growth and reproduction in scleractinian corals following bleaching on the Great Barrier Reef

Abstract

Despite extensive research into the coral bleaching phenomena there are very few data which examine the population biology of affected species. These data are required in order to predict the capacity of corals to respond to environmental change. We monitored individual colonies of 4 common coral species for 8 mo following historically high sea-surface temperatures on the Great Barrier Reef in 1998 to compare their response to, and recovery from, thermal stress and to examine the effect of bleaching on growth and reproduction in 2 Acropora species. Platygyra daedalea and P. lobata colonies took longer to bleach, longer to recover and longer to die. In contrast, Acropora hyacinthus and A. millepora colonies bleached quickly and most had either recovered, or died, within 14 wk of the initial reports of bleaching. Whole colony mortality was high in A. hyacinthus (88%) and A. millepora (32%) and partial mortality rare. In contrast, most colonies of P. daedalea and P. lobata lost some tissue and few whole colonies died. The mean proportion of tissue lost per colony was 43 6.6 % and 11 1.1 % respectively. Consequently, observed hierarchies of species susceptibility will depend critically on the time since the onset of stress and must consider both whole and partial colony mortality. Colony mortality was highly dependent on visual estimates of the severity of bleaching but independent of size. Growth rates of Acropora colonies were highly variable and largely independent of the severity of bleaching. A. hyacinthus was more susceptible to bleaching than A. millepora with 45% of surviving colonies gravid compared to 88%. High whole-colony mortality combined with a reduction in the reproductive output of surviving Acropora suggests that recovery to former levels of abundance is likely to be slow.