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.

Impact of the 2005 coral bleaching event on Porites porites and Colpophyllia natans at Tektite Reef, US Virgin Islands

“…These results support the Wndings of others (Marshall and Baird 2000;Loya et al 2001;Baird and Marshall 2002;Kayanne et al 2002) that direct bleaching mortality of the fast growing branching corals species (P. porites-56% whole colony mortality) was greater than the slow growing massive species (C. natans-8%). Coral mortality has been associated with bleaching severity (Marshall and Baird 2000;Baird and Marshall 2002). In this study, mortality was also associated with severity of bleaching (bleaching status) for P. porites ( 2 = 29.1 df = 3, p < 0.005) but not for C. natans colonies.…”

“…Bleaching substantially aVected P. porites for over 7 months, whereas the C. natans colonies were generally aVected for only 4 months (Table 1). Species speciWc bleaching has been previously reported by Baird and Marshall (2002).…”

“…Colonies were classiWed as alive, if any portion of the colony was alive in January 2006. Hence, this was a conservative estimate of total colony mortality from the 2005 coral bleaching event, since mortality from coral bleaching has been reported to occur up to 40 weeks after bleaching (Baird and Marshall 2002).…”

“…There was no evidence of coral Table 2 Counts of Porites porites colonies by size class and degree of maximum surface area bleached followed by counts of colonies which died during the study and the percent mortality by size class and degree of maximum bleaching Complete 50 12 5 67 37 9 2 48 74 75 40 72 Total 62 17 9 88 38 9 2 49 61 53 22 56 disease on the P. porites colonies monitored during this study. Baird and Marshall (2002) reported no association between colony size class and bleaching mortality for scleractinian coral of reproductive size at two locations on the Great Barrier Reef. In contrast, Shenkar et al (2005) reported that large Oculina patagonica coral colonies had higher mortality from bleaching than small colonies, which were less likely to bleach for a site in the Mediterranean Sea.…”

Revisiting the Cassandra syndrome; the changing climate of coral reef research

“…While most corals have larvae capable of spending many months in the plankton , the actual dispersal distances are often in the order of 10 to 100 km (Hughes et al 2000). Furthermore, while coral bleaching can aVect coral fecundity and egg quality, most surviving individuals of even highly susceptible species produce viable gametes following bleaching, ensuring thermal tolerance can pass between generations (Baird and Marshall 2002).…”