21 July 2016

Mass coral bleaching at Labrador

Mass coral bleaching is happening at Labrador's rocky shore. We surveyed on a drizzly predawn tide, with permission from NParks.
There are not many live corals on the shore. I estimate about 50% of the hard corals and 40% of the leathery soft corals are bleaching. I 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.


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.
Large coral colonies on the reef edge were 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).
Bleaching hard and soft corals on the reef edge,
taken from the jetty.
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.
A large hard coral colony on the reef edge bleaching.
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.
Portions of this bleaching coral has just died
and is now covered in scummy growth.
But many hard corals we saw on the intertidal flats were NOT bleaching. As during our last survey in July 2015, today, most of the corals on the intertidal were small colonies of Small goniopora coral, Pore coral; most were not bleaching. We also came across some Branching montipora coral, Plate montipora coral and some Disk corals.
But all the Sandpaper corals we saw were bleaching, as well as some other kinds of corals including a few Merulinid corals and one large Trumpet coral colony under the jetty.
Today, Jonathan is using a coral bleaching chart to photograph the corals.
We saw a few leathery soft corals. One small one was alright but another large one under the jetty was bleaching.
We saw a few Frilly sea anemones all bleaching, and did not see any Haddon's carpet anemones among the seagrasses. We did see some clumps of Button zoanthids (no longer as abundant as during our July 2015 survey), and Sea mat zoanthids that were not bleaching.
The reefs at Labrador are home to many animals. Such as the Reef octopus. We saw several on this trip, a common experience on a night trip to Singapore's shores.
Among the prey of octopuses are crabs. And there were quite a few of them on the reef today. Mostly small Swimming crabs. I also saw one Red egg crab.
There were also many small fishes, and reefs are a nursery and shelter for them. Fishes seen include gobies, silversides, a Painted scorpionfish, a Spangled emperor. Jonathan also spotted nudibranchs and other critters.
The seagrasses at Labrador are still doing well, especially those near the gate. There is lush Sickle seagrass, many clumps of Tape seagrass with long leaf blades, and patches of Spoon seagrass. All nice and green, but I didn't see any that were flowering. There was also a good assortment of seaweeds, and some patches of various sponges.
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.

It was good to see that at Labrador, there were no fish nets and not much litter. Labrador shore and the jetty are now permanently closed to the public due to safety issues. Labrador is Singapore's last natural cliff on the mainland. There is work ongoing now to stabilise the cliff.

Our last survey here was in July 2015 when we noticed that the intertidal has become much sandier. The situation remains the same today. For years, next to Labrador, there has been massive reclamation, dredging and other coastal works for the new Pasir Panjang Container Terminal. The shore was also impacted by a huge trench dug into it (called a cofferdam) to relocate service pipelines to Pulau Bukom.
The cofferdam dug into Labrador shore in 2007.
There was also underwater blasting. For example, demolition works took place at Labrador last year (Jun-Oct 2015) to remove the jetty nearby (yellow arrow). According to an MPA Notice "the demolition work will be carried out by crane barge assisted by tug boats. Divers will also be deployed for underwater cutting work." I hope they will not use explosives which will shatter and damage the corals.
These brown corals taken in July 2015 were mostly bleached today.
Hopefully, as the massive construction nearby comes to an end, the seagrasses and other marine life at Labrador can return. It is only through long-term monitoring that we can learn more about what is happening on this shore.

Thanks to Wei Ling and Yi Fei for permission to survey and for coming so early to open the gate and for being with us on our trip. Thank you!

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


Others on this trip: Jonathan Tan, Nicholas Yap, Stephen Beng.

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