Mass coral bleaching is happening at Pulau Semakau East. We had a glimpse of this when we surveyed Terumbu Semakau two weeks ago. Mass coral bleaching doesn't seem to be ending on our shores!
We estimate about 70% of the hard corals and 40% of the leathery soft corals are bleaching. We estimate 5-10% of the corals have died recently.
Mass coral bleaching in Singapore is not unexpected. From the NOAA's coral reef watch satellite monitoring, Singapore is in the blue Watch zone. But our corals are still bleaching.
Here's a clip of the mass coral bleaching on the shore today.
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.
Sadly, mass coral bleaching highlights just how many corals are found on this shore. There were many bleaching corals next to similar corals that were not bleaching, like the Merulinid corals in the photos below. Cauliflower corals were still bleaching, we did not see any colonies that were NOT bleaching. But for most other corals, there were both colonies that were bleaching, and those that were not. Brain corals, which are usually all bleached, today I saw a few colonies (about 5%) that were not outright bleaching.
We even saw some small colonies of Acropora corals that were not bleaching.
Sadly, some of the bleaching corals had portions that look like they recently died.
Most of the leathery soft corals we saw were alright, only about 40% were bleaching. But some of those that were not bleaching showed stress, with portions covered in silt or portions covered with peeling 'skin'. There were many Asparagus flowery soft corals that were not bleaching outright, although none were their usual unbleached purply colour.
I went to check the replanted mangroves on the island. Towards the high shore, there were many Pore corals and Branching montipora corals that were not bleaching. Much of the ground remained crumbly rubble and abundantly covered with Feathery soft corals, which were not bleaching.
The mangrove trees looked alright. I didn't see any with no leaves. Although, as usual, the trees are burdened with abandoned nets and other large marine trash.
I didn't see much seagrasses here, just patches of Spoon seagrass and some clumps of Tape seagrass with somewhat cropped leaf blades (about 30cm long). On a positive note, the rest of the team saw two Fluted giant clams, a shark and many other marine critters.
Our last trip here was in Jan 2016 on a rather high tide. The corals were then still mostly alright. 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.
Toward the end of our trip, it started to pour! Fortunately, it lightened up quickly and we even enjoyed a brief rainbow. Let's hope this shore stays safe until we visit again.
Pulau Semakau is NOT the same as the Semakau Landfill. The Landfill was created by destroying all of Pulau Saking, and about half of the original Pulau Semakau by building a very long seawall. Fortunately, the landfill was constructed and is managed in such a way that the original mangroves, seagrass meadows and reefs on Pulau Semakau were allowed to remain. The eastern shore of Pulau Semakau is right next to the seawall of the Semakau Landfill, opposite the petrochemical plants on Pulau Bukom.
It is NOT true that the construction of the Landfill created the marine life found on Pulau Semakau. The marine life was there long before the Landfill was built.
