30 June 2010

Bleaching at Sentosa

A very small team checks out Sentosa's natural shores just before dawn.
We start on the shores behind Underwater World.

There are some seagrasses here, which seem to be alright. And a stretch of sandy shores with a few Haddon's carpet anemones (Stichodactyla haddoni) which seem healthy today. But we can't find the Common sea stars (Archaster typicus) that are usually here. Probably because the tide is still too high. There were lots of crabs in the water, including several Moon crabs (Matuta lunaris) that seem to be getting ready to mate.
I saw this Blue spatula sponge (Lamellodysidea herbacea) that seems to be bleaching. But most of the sponges I saw today seemed to be as usual.
Our main focus, however, are the reefs found on the western shore of Sentosa. As we make the trek there, we notice there is a great deal more sand on what is usually a very pebbly shore that gives us a good 'foot reflexology' workout. I wonder where all the sand came from? There is lots of Spoon seagrass (Halophila ovalis) with big leaf blades growing on the low water mark on the now more sandy shore. We also saw some Cake sand dollars (Arachnoides placenta) here, as we have in the past.
Finally we reach the western shore. This shore is overlooks Labrador Nature Reserve (the forested area to the right of the photo), and the massive reclamation project to build a new container terminal at Pasir Panjang.
Bleached corals are immediately visible. Almost all the big coral colonies were bleached, while there were more smaller ones that were not bleached.
There are not many corals on this shore, although in some parts, there are more colonies crowded near one another. In this photo, a leathery soft coral that seems alright, a boulder hard coral that is bleaching slightly and a plate coral that looks like it's already dead.
Most of the hard corals seen on Sentosa are Favid corals (Family Faviidae). And most of the large Favid coral colonies were completely white.
Some were yellowish white.
While other large Favid coral colonies were only just starting to bleach.
I saw a few small colonies of Favid corals that seem to be their normal colours. They were seen at both the low water and mid-water mark.
Pore hard corals (Porites sp.) are also common on this shore. Not all were bleached though most showed signs of bleaching.
There were several small colonies of Sandpaper coral (Psammocora sp.) and all of them seem to be bleaching to some extent.
In a bleached Sandpaper coral, I noticed a huddle of tiny hermit crabs. And little holes peppered in the stark white coral which might be barnacles that burrow into living corals. Things I might not have noticed if the coral were its usual colour.
Not all the Disk corals (Turbinaria sp.) were bleaching. Although in a large one it seems the upper section had already died out while the lower section seems alright.
At first I thought the Small goniopora corals (Goniopora sp.) were alright because they were not white. But most colonies are greenish yellow, when they are usually more pinkish purple.
Although most were bleached completely white, it was heartening to see a few large leathery soft corals (Family Alcyoniidae) that were still unbleached.
I saw only one mushroom coral, this Mole mushroom coral (Polyphyllia talpina) which was unfortunately bleaching. I also only saw one Cauliflower coral (Pocillopora sp.) which was also completely white.
A first bleaching encounter which I have not seen during our recent field trips: many clusters of bleaching feathery soft corals.
Here's a closer look at some of these animals which are quite common on Sentosa especially. They are usually a darker purplish brown with a pale centre.
Many of the Frilly anemones (Phymanthus sp.) were bleached completely white. Although there were some that were still normal looking. The bleached creatures are so much easier to see, so I wonder if I am over-estimating the bleaching as I fail to see those which are not bright white.
I saw a bunch of corallimorphs (Order Corallimorpharia) and they seem alright. Unlike the ones I saw at Pulau Hantu recently which were starting to bleach.
There are lots of Tape seagrass (Enhalus acoroides) on this side of the shore. But even the hard corals among the seagrasses were bleached white.
I didn't really look much at other animals today, but who can ignore the very large, very scary, but also quite lovely Giant reefworm (Eunice aphroditois). It is quite harmless and is usually more surprised by us than visa versa and will disappear instantly into its hiding place if it is alarmed.
Tang Ling and Wee Hock joined us for this trip and told us they saw an octopus eating a crab! Wow, that's awesome!

This shore is ringed by natural cliffs which are home to many special plants which are no longer common elsewhere on Singapore.
Among the very special trees on this shore is the Critically Endangered Nyireh (Xylocarpus rumphii) which grows below the high water mark and thus considered a mangrove tree. Although it seems to prefer growing on rocky cliffs which sadly are uncommon in Singapore. The only other big trees are found on St. John's Island.
When I last looked at the Sentosa trees in April, they had small fruits. Today I didn't see any fruits. Alas, I noticed the 'curling' leaves are still seen on both trees. I do hope the trees will overcome whatever is causing their leaves to curl up so alarmingly.

Another special tree that I only recently realised was growing wild on Sentosa is the beautiful and Critically Endangered Delek air (Memecylon edule) which is also seen on Chek Jawa. Today, the tree is both flowering and fruiting!As we ended the trip, we noticed there is also a great deal of sand on this western shore.

While it was quite depressing to see the already sparse coral on this shore suffering from bleaching, not all were bleached completely white.
We estimate about 80% of the corals were bleaching today. Hopefully, the corals can recover and Sentosa's natural reefs can begin to grow again.


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