06 August 2016

Mass coral bleaching at Terumbu Pempang Laut

Mass coral bleaching is happening at Terumbu Pempang Laut.
There are not many corals on this rocky submerged reef. We estimate about 20-30% of the hard corals are bleaching. About 20-40% of the leathery soft corals were bleaching. We estimate 20-30% of the corals have died recently. On a positive note, the Fluted giant clam on the shore is still alive and well.  And I saw furrows that look like dugong feeding trails.


Terumbu Pempang Laut is one of our largest submerged reefs and located near industrial islands such as Jurong Island and Pulau Bukom.
Shouldn't mass coral bleaching in Singapore be ending? From the NOAA's coral reef watch satellite monitoring, Singapore is in the blue Watch zone. But our corals are still 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.
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).
Hard corals harbouring zooxanthellae live close to the upper limit of temperature tolerance. Thus a temperature increase of even 1-2 degrees centigrade can redust in bleaching. It is believed that global warming will lead to massive bleaching. Once the cause of bleaching is removed, however, polyps may eventually regain zooxanthellae (which live freely in the water) and thus recover their health. 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.
Here's a clip of mass coral bleaching on Terumbu Pempang Laut.
Mass coral bleaching at Terumbu Pempang Laut, 6 Aug 2016
Today, I did see many corals that were not bleaching. But I sense that there are fewer hard and soft corals compared to our last survey in May 2015. Many Merulinid corals had bleaching patches, some with patches of recently dead tissue, these range from 20-60% of the colony.
There were many Pore corals and most were not bleaching. But many had also recently dead patches.
I saw two small Cauliflower corals that were bleaching with patches that recently died. I saw a few Anemone corals  and Small goniopora corals that were alright. I didn't see any other kinds of corals.
I saw two small colonies of Acropora corals, one was bleaching and half dead. This kind of coral is home to the Bandit coral crab, which needs to live in a coral. So if the coral dies, so do the animals that rely on it.
I saw many large colonies of leathery soft corals and about 20% were bleaching. But many also had large holes -- recently dead portions that have rotted away?
I saw a few Flowery soft corals that were not bleaching, but also appear to have holes in them. Much of the rocky shore was covered with Button zoanthids which were alright.
Sea anemones harbour zooxanthellae and thus can also bleach. I also saw a few Frilly sea anemones and they were all alright. I saw several Haddon's carpet anemone and Giant carpet anemones and one Fire anemone, all of them not bleaching. One of the Giant carpet anemones had an anemonefish.
We are relieved to see the Fluted giant clam near the arrival spot is still there and not bleaching. We saw it first in Jun 2014.
Much of the sandy area in the middle of the reef flat, as well as some of the rocks, was covered by a growth of fine black filamentous stuff, possibly cyanobacteria?
There were many patches of seagrasses but they were all heavily covered in epiphytes. These include Spoon seagrass (small and large leaf blades), Sickle seagrass and even some Noodle seagrass.
Most of the Tape seagrass had cropped leaf blades, but some patches growing in the rocky areas had longer leaf blades.
I also saw furrows that appear to be dugong feeding trails. The last time we saw dugong feeding trails here was in May 2012.
Thanks to Heng Pei Yan for flying the drone. She spotted sharks and rays swimming around the reef edge.

I saw one disabled fish trap and there were some floats that look like they mark fish traps in deeper water. I also saw a deep hole (red arrow) with a big pile of coral rubble  (blue arrow) next to the hole. A sign of a recent boat strike.
While there is not much we can do when our corals start bleaching, we can do a lot to stop other stresses that impact our reefs so the corals are in better health and don't succumb after bleaching.

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



Terumbu Pemang Laut is one of the existing natural shores that may be impacted by the landuse plan by the Ministry of National Development released in Jan 2013 in response to the Populations White Paper with a 6.9 million population target. The dotted margined blue areas are "Possible Future Reclamation".
The other shores impacted by this plan include Pulau Hantu, Terumbu Pempang Darat, Terumbu Pempang Tengah and Pulau Jong and Terumbu Semakau.
Singapore's submerged reefs are often out of sight under the high tide and thus forgotten. Let's hope Terumbu Pempang Laut stays safe until we can visit again.

Photos by others on this trip


Others on this trip: Lisa Lim, Loh Kok Sheng, Heng Pei Yan.

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