Some coral species may be able to adapt to global warming
By Summit Voice
SUMMIT COUNTY — Some coral species previously thought to be susceptible to warming sea temperatures may yet be able to adapt and survive at least some level of global warming, according to Australian researchers who studied coral populations that were affected by El Niño-fueled bleaching events in 1998 and 2010.
While the results are encouraging, one of the researchers said they do not necessarily mean that the global threat to reefs has lessened. There are likely to be limits to thermal adaptation and acclimatisation, and there may be other costs to the corals, such as reduced growth and reproductive health. Reefs continue to be threatened by overfishing, pollution, diseases and ocean acidification.
“The results of the present study do indicate, however, that the effects of coral bleaching will not be as uniform as previously thought,” said Dr. James Guest, a joint research fellow at the UNSW Centre for Marine Bio-innovation. “Fast-growing, branching (coral types) are likely to persist in some locations despite increases in the frequency of thermal stress events,” Guest said.
The findings call into question the conclusion by many researchers that some types of coral have already reached thermal stress limits. Previous studies have indicated that fast-growing branch-type corals are hit especially hard by warming temperatures, and are likely to be replaced by slower-growing species.
The new research suggests that branched corals like the endangered staghorn can adapt, at least in some locations, based on the thermal history of the specific locations.
The marine biologists analyzed what happened at three sites during the 2010 event and found that in Indonesia, corals responded to higher sea temperatures in a typical way, with fast-growing branching species – such as staghorn corals – suffering severe die-offs. But at sites monitored in Singapore and Malaysia, the usual trend was reversed: normally susceptible colonies of fast-growing Acropora corals appeared healthy and fully pigmented, while most colonies of massive coral were severely bleached.
“Mass coral-bleaching events, caused by a breakdown in the relationship between the coral animals and their symbiotic algae, are strongly correlated with unusually high sea temperatures and have led to widespread reef degradation in recent decades,” Guest said.
“The severity of these events varies considerably but until now we’ve seen one consistent trend: certain types of coral tend to be more resistant to bleaching than others. This has led to the prediction that hardier, slow-growing massive species will replace less hardy, fast-growing branching species on reefs in the future.
“But during the 2010 event the normal hierarchy of species susceptibility was reversed in some places. Corals at our Indonesian study site in Pulau Weh, Sumatra, followed the usual pattern, with around 90 percent of colonies of fast-growing species dying. But the pattern was the opposite at study sites in Singapore and Malaysia, even though sea-temperature data showed that the magnitude of thermal stress was similar at all sites.
“This suggests that the thermal history of these sites may have played an important role in determining the bleaching severity in 2010.
“When we looked at archived sea-surface temperature data and past bleaching records we found that the locations that had a reversed hierarchy of susceptibility and less severe bleaching in 2010 also bleached during 1998,” Guest said. “In contrast, the site that had a normal bleaching hierarchy and severe bleaching did not bleach in 1998. The most parsimonious explanation, therefore, is that coral populations that bleached during the last major warming event in 1998 have adapted and/or acclimatised to thermal stress.”