13 September 2010

How is coral bleaching at Kusu Island?

It's been three months since we visited Kusu Island. At that time, there were signs of bleaching at Kusu Island as mass bleaching hit all our reefs.Like all our recreational Southern islands, Kusu Island's reeflats had been reclaimed to form man-made swimming lagoons. Over the years, the reefs have crept back into the lagoons. We have a look at them, during an evening low tide.

There were a few colonies with white patches, small and large patches. And I saw a few recently dead colonies as well as dying bleaching corals.
This is a typical view of the reef yesterday. Some corals still have white patches, while others are colourful and seem normal. A lot of the colonies were coated in silty scum. I get the sense that the corals here are less closely packed, and that more of the colonies are covered with silty scum than usual. It's almost as if some of the corals are 'missing'. This is a photo of the Kusu reefs that I took three months ago. Yesterday, I didn't see the same kind of situation. Which suggests that there might have been some colony deaths following the bleaching event.
Some of the Pore coral (Porites sp.) had pale bluish portions that suggest they are affected by some kind of disease. We had seen this at Kusu three months ago, and also at Sisters and Pulau Hantu since the bleaching started. A colony of Pore coral bleaching (left) and another with bluish patches.Another Pore coral colony with small bluish patches. The clusters of branching corals are still there, although many 'branches' seem dead and covered with silty scum.
There seems to be two different kinds of branching corals here. Could the one on the left be a branching Pore coral (Porites sp.) while the one on the right a branching Montipora coral (Montipora sp.)? Some of the Favid corals (Family Faviidae) were not bleaching but their colours seem oddly 'darker' than usual.Among the special corals I saw was one small colony of Sandpaper coral (Psammocora sp.) And a large colony of Lettuce coral (Pavona sp.). I saw small 'balls' of Favid corals, which hopefully suggests there is some regeneration? Chay Hoon saw Galaxy coral (Galaxea sp.). But I didn't see any of these corals that I saw three months ago: Thin disk coral (Turbinaria sp.) or Cauliflower coral (Pocillopora sp.).

I saw only a few leathery soft corals (Family Alcyoniidae) and flowery soft corals (Family Nephtheidae), but these were not bleaching.
I saw a few Frilly sea anemones (Phymanthus sp.), they were not bleaching. I saw many Haddon's carpet anemones (Stichodactyla haddoni) on the seagrassy areas and several had signs of bleaching. There were clusters of several of these sea anemones. I think they are Magnificent anemones (Heteractis magnifica), but I could be wrong. This is a more typical Magnificent anemone, although it is rather droopy and not very magnificent at low tide. I've seen this anemone on this spot over quite some time.There are many Giant anemones (Stichodactyla gigantea) distributed throughout the reefy parts. And many of them held their mouths upturned. But none of them were bleaching.But I didn't see the Snaky sea anemone (Macrodactyla doreensis) and Fire anemone (Actinodendron sp.) that we saw three months ago.

There is a stretch of Kusu that used to be carpeted in zoanthids (Order Zoanthidea). Now this stretch is rather bare, although the zoanthids are still there in much smaller clusters.A cluster of Beaded corallimorphs (Order Corallimorpharia) were rather pale and pastel in shade.This patch of Frilled corallimorphs are also oddly coloured. While bleaching seems to be have stopped and the surviving corals recovering, there seems to be less live coral on the shore. Let's hope the reefs at Kusu Island will eventually recover.

More about bleaching on the Bleach Watch Singapore blog.

We also had a look at the seagrass-seaweed area in the lagoon and were surprised by some unexpected creatures here.

The water at Kusu Island is particularly murky. What is sedimentation and why does it matter? What is causing the murkiness at Kusu? I'm not too sure why. But I do know that there is dredging going on near Kusu Island. This was a large dredger we saw on the way in to Kusu yesterdayCould it be associated with the dredging from Jul 10-Jan 11? And this dredging site is in addition to a much much larger area of dredging and sand mining much closer to Kusu Island that has been going in Apr-Aug 09 and Aug-Dec 09, seemingly related dredging and vibracore sampling in Jun 09, sand mining in Oct 09-Feb 10 renamed dredging and extended to Aug 10.

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