Some good news from the 2010 Singapore coral bleaching event

It was heartbreaking to see the mass coral bleaching on Singapore reefs in 2010, particularly since our reefs experienced a similar bleaching event in 1998. I was glad that there was some good news from the 2010 event. Not only about Singapore reefs but globally!

Mass bleaching seen in June 2010
on a submerged reef off Pulau Semakau

In a recent paper, James Guest found that corals in Singapore and Malaysia that previously experienced severe bleaching in 1998, unexpectedly survived the 2010 event! The paper provides solid field evidence that certain corals in Singapore and Malaysia can cope with higher water temperatures.

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.

Fleshy polyps of a living coral showing signs of bleaching.

When there is massive loss of zooxanthellae in a hard coral colony, the polyps become colourless and the underlying white skeleton shows through. Thus patches of the colony appear pale, white or 'bleached'. The polyps are still alive and the hard coral is not dead (yet).

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.

Contrasting coral bleaching patterns during 2010. Bleached Acropora colonies from (A) Pulau Weh, north Sumatra, Indonesia where patterns in bleaching susceptibility were normal. Reversals in bleaching susceptibility gradients in (B) Singapore and (C) Tioman Island, Malaysia, where healthy Acropora colonies were found adjacent to bleached encrusting, foliose and massive colonies: corals which are usually relatively resistant to bleaching.

I first heard about the paper from N. Sivasothi on the 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