01 June 2010

Coral bleaching on our Southern shores?

It was heartbreaking to be away from the oil spill affected areas the last three days.
But we were committed well before the spill to trips to our Deep South. Alas, another tragedy seems to be unfolding there.

Our Southern shores include many submerged reefs. We visited three southern reefs over the last three days and observed coral bleaching on all of them. In some parts of these reefs, only one or two colonies were bleached, while the others seemed fine.
In other parts, more were bleached.
And in some, only one was NOT bleached.
In other parts, almost all of the hard corals were bleached.
These bleached mushroom corals are still alive. They have lost their colour because they have lost their symbiotic algae that provides them nutrients which they produce through photosynthesis. This usually happens when the corals are stressed. More about coral bleaching.
Large boulder Pore corals (Porites sp.) are commonly seen on our reefs. Many of these large colonies seemed as usual.
But many large boulder Pore corals were bleaching or pinkish or pale.
As for the Anemone corals (Goniopora sp.) some were slightly less colourful while others were completely white.
Favid corals (Family Faviidae) are also very commonly seen on our reefs. Many I saw were pale or white.
A great deal of these ringed Favid corals were white or flourescent yellow. The one on the left has the usual colour.
Some Favid corals were bright pink, or had bright yellow portions. And some were completely white.
Favid corals can form large boulders. Many were pale pink, yellow or had white patches.
Disk corals (Turbinaria sp.) are also common on our reefs. They did not seem to be doing well. Of the encrusting kind, some were spotted with pink while others were completely white.
I saw a really white Carnation coral (Pectinia sp.). The one on the left is what a normal one would look like.
Ringed plate coral (Pachyseris sp.) are not common on our shores, and some seem to pale but not white, while others were completely bleached. I saw only a few Lettuce coral (Pavona sp.) and most seemed normal.
Torch anchor coral (Euphyllia glabrescens) is not commonly seen. Alas, one of the colonies I saw was bleaching.
Most of the Acropora corals (Acropora sp.) I saw seemed alright. These branching corals are homes to many small animals, which were observed by James and Kok Sheng during our recent trip to Kusu Island.
Although one was rather pale, most were the usual dark colour.
Some plate Montipora corals (Montipora sp.), however, didn't seem to be doing too well, although many were OK.
The branching Montipora corals (Montipora sp.) that are usually found on the higher shore seemed alright. Their usual brown with white tips.
Many of the Pebble corals (Astreopora sp.) seen had pink or white patches.
It was heartbreaking to see a completely white Astreopora colony.
Crinkled sandpaper coral (Psammocora sp.) is usually blue. All those I saw were pale beige or yellowish. Though none were totally white. Fan worms are usually found in these corals.
The brain corals (Family Mussidae) I saw were pale or rather flourescent yellow.
Many of the pale or white corals had pinkish patches. Mei Lin told me that a pink colour may mean the corals are suffering from some disease.
Hard corals produce mucus to get rid of bad stuff. On one reef, we saw many large boulder corals producing copious amounts of slime.Many of the leathery soft corals (Family Alcyoniidae) I saw also seemed 'off colour'. Instead of the usual muted pale yellows and orange, some were more 'flourescent'. A feature which Marcus pointed out, doesn't photograph very well.
Some leathery soft corals were also appearing to produce 'slime'.
Closer look at the 'slime'.
Some other reef creatures also seemed off colour. I saw an unusually pink Frilly sea anemone (Phymanthus sp.).
And my first time seeing a sickly yellow Giant carpet anemone (Stichodactyla gigantea). I had sadly seen Haddon's carpet anemones (Stichodactyla haddoni) in this colour during the mass deaths at Chek Jawa in 2007.
Fortunately, the Giant clams we've seen are not bleached. Mei Lin says these animals can bleach too. Like hard corals, soft corals and some anemones, Giant clams also have symbiotic algae which undergo photosynthesis and shares the nutrients produced with the host clam.
I have also heard that there is extensive bleaching going at Tioman right now. While Jeff blogged earlier about massive coral bleaching reported in the Andaman Sea side of Thailand, covering Phuket, Surin abd Phi Phi.

The last mass bleaching event we had in Singapore was in 1998. From the Coral Reefs of Singapore website:
The 1998 coral bleaching event As with coral reefs around the world, Singapore reefs suffered a mass bleaching event in June 1998. Sea temperatures around Pulau Hantu and St John's were elevated by 1-2 deg C from March to June 1998. 50-90% of all reef organisms in Singapore were affected, particularly the hard corals, soft corals and anemones. The bleaching effect extended till 6m, the lower growth depth limit for coral growth locally. Sea temperatures returned to normal in August 1998. A study of the stressed colonies was undertaken during this period. 10 out of 35 coral colonies died from the stress, and the genera Sinularia and Euphyllia were most affected. Other colonies showed various signs of stress, such as growth of turf algae and silt accumulation, leading to partial mortality.
From the trips we made over the last week, my very rough and uneducated impression is that there was only a little bleaching on Kusu Island, somewhat more on Pulau Tekukor, and more extensive bleaching in the southern most reefs which we visited. I'm not sure why this is so.

The bleaching is worrying.

I was relieved, however, to see that the water in the south is so far clear of signs of oil spill. As we headed home today, the wake is still white.

Update on 3 Jun: Karenne Tun has just shared photos of bleaching at Pulau Hantu and Raffles Lighthouse on facebook.

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What is coral bleaching?


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