25 June 2016

Mass coral bleaching at Pulau Tekukor

Mass coral bleaching is happening at Pulau Tekukor. This rocky shore doesn't have many corals. Our last visit here was at the beginning of the last mass coral bleaching in May 2010.
The survey team estimates about 50% of the hard corals we saw were bleaching, 50% for leathery soft corals and 10% for sea anemones. I was glad to see lush patches of seagrasses, and the team saw a Fluted giant clam that was not bleaching. Alas, the team also came across a dead sea turtle.

Mass coral bleaching in Singapore is not unexpected. From the NOAA's coral reef watch satellite monitoring, Singapore is in the yellow Watch zone. Where we should be prepared for mass coral bleaching.

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 photosynthesis 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).
Without the food provided by the lost zooxanthellae, the polyps will be stressed and prone to diseases. Skeleton production and reproduction are also affected.
This leathery soft coral is 'peeling', probably a stress response.
Hard corals harbouring zooxanthellae live close to the upper limit of temperature tolerance. Thus a temperature increase of even 1-2 degrees centigrade can redult in bleaching. It is believed that global warming will lead to massive bleaching.
About 50% of this Merulinid coral that I saw was bleaching.
The other half were nice and brown. 
But prolonged bleaching can kill corals and seriously damage large sections of a reef. 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.
Once the cause of bleaching is removed, however, polyps may eventually regain zooxanthellae (which live freely in the water) and thus recover their health. About 50% of the leathery soft corals I saw were bleaching.
As usual, bleaching reveals hard corals more clearly to me. I saw several of these encrusting hard corals that look like Plate montipora corals. All those I saw were bleaching. 
I also saw a few Disk corals, most were bleaching. I only saw one small Brain coral and it was bleaching. Hard corals that were not bleaching included most of the Pore corals and Small goniopora corals.
Much of the eastern rocky shore is still covered with Button zoanthids. There are some bleaching patches. About 90% of the Sea mat zoanthids that I saw were bleaching.
There are many many Frilly sea anemones on this shore. Only about 10% of the Frilly sea anemones that I saw were bleaching. But does that mean that many Frilly anemone that bleached have already died? And I'm only seeing those that have not died yet?
The next most abundant animals on the shores are Black long sea cucumbers and Giant carpet anemones, only a few of the Giant carpet anemones that I saw were bleaching. There was also a good variety of seaweeds and sponges on the shore.
Here's a bleaching Giant carpet anemone, and Kok Sheng found this bleaching Snaky anemone. He and the team also found Leathery sea anemones, alas, also bleaching.
These look like bleaching Banded bead anemones.
These look like bleaching Posy anemones.
The western shore of Pulau Tekukor is part of the Sisters' Islands Marine Park. I was delighted to see a large lush patch of seagrasses growing here. You can see the Sisters' Islands overlooking this shore.
Here's a video clip of the seagrass meadows. The western shore has been developed, with a seawall and jetty. Pulau Tekukor used to be an ammunition dump which was closed in the 1980s.
Seagrasses at Pulau Tekukor
There were nice healthy looking Sickle seagrass and Spoon seagrass growing here. There are also spinkles of seagrasses on the eastern shore.
The eastern side of the shore remains untouched as a natural rocky cliff. This kind of habitat is now rare in Singapore.
Among the interesting plants I saw was a Tembusu treelet growing on the cliff! There were also many Raffles pitcher plants.
This shore has many natural rocky features including big rock formations and natural pebble beaches. Quite scenic! But really hard on the foot, foot reflexology whether you want it or not.
As usual, there is trash on the shore. But not a lot considering that this shore is not cleaned on a regular basis. Perhaps we should organise a clean up now and then. I was glad we did not come across any nets or traps on the shore.
The rest of the team found awesome animals such a Fluted giant clam that was NOT bleaching, several Tiger cowries and more.

Alas, they also came across a dead sea turtle. Here's photos they shared of it. It appears to be a Green turtle. There were no visible external injuries. RIP poor turtle.

High res photos of mass coral bleaching in Singapore for free download on wildsingapore flickr

Posts by others on this trip

Other on this trip: Juria Toramae and Mr Kuet.


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