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| Mass coral bleaching in Singapore's Terumbu Bemban in Jun 2010 |
From media articles consolidated in wildsingapore news
When were the previous global bleaching events?
The first global bleaching event was in 1998, during a strong El Nino that was followed by an equally very strong La Nina. A second one occurred in 2010. During these previous global events in 1998 and 2010, every major ocean basin experienced bleaching. This year's El Nino is expected to peak between October and January and could turn into one of the strongest on record. The last 'super El Nino' was in 1997-98.
Why are global bleaching events of concern?
While corals can recover from mild bleaching, severe or long-term bleaching is often lethal. Bleached corals are more vulnerable to stressors such as disease that can kill them. In 1998, the biggest bleaching event in history led to the death of 16% of the world’s coral reefs.
This bleaching event, which began in the north Pacific in summer 2014 and expanded to the south Pacific and Indian oceans in 2015, is hitting U.S. coral reefs disproportionately hard. NOAA estimates that by the end of 2015, almost 95 percent of U.S. coral reefs will have been exposed to ocean conditions that can cause corals to bleach.
Since the early 1980s the world has lost roughly half of its coral reefs. Hoegh-Guldberg said the current event was directly in line with predictions he made in 1999 that continued global temperature rise would lead to the complete loss of coral reefs by the middle of this century.
“It’s certainly on that road to a point about 2030 when every year is a bleaching year … So unfortunately I got it right,” he said.
The difference between this year's bleaching event and others before it is not just the extremity of sea temperatures, but how long they have persisted for. Corals can recover from bleaching if the temperature relents.
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.
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).
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| Some polyps in this colony are still brown, while others have lost their colour. |
Why do corals bleach?
Factors believed to cause bleaching include: temperature fluctuations (too high or too low), excessive exposure to ultraviolet light, excessive sedimentation in the water, changes in salinity and disease. It is generally believed that bleaching is related to unusual prolonged temperature increases in the seawater. Hard corals harbouring zooxanthellae live close to the upper limit of temperature tolerance. Thus a temperature increase of even 1-2 degrees centigrade can result in bleaching. It is believed that global warming will lead to massive bleaching.
From the NOAA Press Release
Are Singapore's corals affected by global coral bleaching?
Sadly, yes. More about these effects are documented in the Singapore Bleach Watch blog.
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| Mass coral bleaching on Singapore's Terumbu Pempang Tengah, Jul 2010 |
We can help our corals by minimising other stresses on them as they face global mass coral bleaching. This mean reducing pollution, sedimentation, physical damage.
You can also help by documenting and sharing any sightings of coral bleaching in Singapore. You can do so on the Singapore Bleach Watch facebook page, or email me at hello@wildsingapore.com.
