|Mass bleaching seen in June 2010|
on a submerged reef off Pulau Semakau
What is coral bleaching?
Coral are colonies of tiny animals called polyps. Each polyp lives inside a little hard skeleton. The huge colony is made up of the skeletons of countless polyps.
The polyps of all reef-building hard corals harbour microscopic, single-celled algae (called zooxanthellae). The polyp provides the zooxanthellae with shelter and minerals. The zooxanthellae carry out photosynthesis inside the polyp and share the food produced with the polyp. Corals generally have white colour skeletons, which is believed to assist in photosynthensis by reflecting light onto the zooxanthellae.
The 2010 mass coral bleaching event was widespread in Asia affecting reefs in Malaysia, Indonesia, Thailand, forcing the closure of tourist dive sites.
In a media report, James Guest shared that the 2010 bleaching event at its peak in June affected 60% of Singapore corals. But there were signs by September 2010 that the situation had eased with corals regaining their colour.
More about coral bleaching on the Bleach Watch Singapore blog and more about bleaching events on the wildsingapore news blog and our own field trips to document coral bleaching in Singapore.
During a 2010 bleaching episode, James Guest's team studied three coral reef sites. At one in Indonesia that had not bleached previously, corals responded typically to warmer water. There, fast-growing branching coral species—such as Acropora—suffered severe die-offs. But at two sites in Singapore and Malaysia that had bleached in 1998, this pattern was reversed, with normally susceptible Acropora colonies appearing healthy while massive slow-growing corals, such as Porites were heavily damaged.
Biodiversity Crew@NUS blog. James Guest, until recently, a Lee Kuan Yew post-doctoral research fellow with the Marine Lab at the University of Singapore, published the paper in PLoS ONE.
James told N. Sivasothi enthusiastically that he hopes these stunning images “provides a bit of hopeful news among the general climate change doom and gloom!”
In media reports about the study, James Guest says additional work is needed. "We don't know whether the unusual resistance in the branching corals was due to the host coral or the symbionts or both," he says. They are starting additional studies to learn more about the specific type of zooxanthellae inhabiting the coral that adapted and to try to study the phenomenon in the laboratory. He also cautions that higher water temperatures could still affect the composition and health of reefs. Finding evidence of adaptation "does not mean that the global threat to reefs from climate change has lessened," he says.
Read more in the paper: James R. Guest, Andrew H. Baird, Jeffrey A. Maynard, Efin Muttaqin, Alasdair J. Edwards, Stuart J. Campbell, Katie Yewdall, Yang Amri Affendi, Loke Ming Chou. Contrasting Patterns of Coral Bleaching Susceptibility in 2010 Suggest an Adaptive Response to Thermal Stress. PLoS ONE, 2012; 7 (3): e33353 DOI: 10.1371/journal.pone.0033353