21 August 2016

Corals weeping at Raffles Lighthouse

For our last predawn survey for 2016, we checked out mass coral bleaching at Raffles Lighthouse. It was heartbreaking to see corals weeping.
Hard corals may produce slime in reaction to rain
(which we had lots of this morning).
Pulau Satumu, the location of Raffles Lighthouse, has the best reefs in Singapore. We could see the corals bleaching immediately from the jetty.
Today, we estimate about 10-30% of hard corals are bleaching, while about 10-20% of leathery soft corals were bleaching. About 20% of the hard corals have died recently. Thanks to Nick for organising the trip as part of his survey of sea anemones and related animals in Singapore.

Here's a video of the mass coral bleaching I saw today.
Mass coral bleaching at Raffles Lighthouse, 21 Aug 2016
Mass coral bleaching in Singapore should be ending. From the NOAA's coral reef watch satellite monitoring, Singapore is in the blue Watch zone. It sure is taking a long time for our corals to recover. I hope they can recover before they die. Sigh.

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 photosynthensis by reflecting light onto the zooxanthellae.
The intertidal shore still thickly covered with a variety of
hard and soft corals. Most of them not bleaching.
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. 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.
Bleaching corals on the eastern shore of Pulau Satumu.
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. 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.
A storm hit us just after we started.
Bleaching subtidal corals on the northern shore.
But fortunately, just rain and no lightning. So Nick and I continued to check out the shore for sea anemones. We found some Banded bead anemones, some Frilly anemones. But no Pink-spotted bead anemones. We also saw some Giant carpet anemones. I didn't see any bleaching anemones. But Kok Sheng saw a bleaching Pizza anemone. And some of the large patches of Sea mat zoanthids were very pale. Later on, we found some strange sea anemones in the lagoon!
Pulau Biola is just off Pulau Satumu.
The intertidal shore is still thickly covered with corals and looks somewhat similar to what I saw on my last trip here in May 2013 for the Mega Marine Survey. But many large patches, particularly of the branching corals, look like they recently died. In some, almost the entire colony is recently dead with only the tips alive and still bleaching.
Among the special finds for me was a small Fluted giant clam. The rest of the team saw more giant clams including a Burrowing giant clam.
I thought this was a sea anemone, but it turned out to be a Reef octopus, sheltering in its burrow during the rain.
Kok Sheng saw a Bamboo shark! While Chay Hoon found interesting snails. The rest of the team also had other interesting finds.

Bamboo Shark at Raffles Lighthouse (Pulau Satumu) from Loh Kok Sheng on Vimeo.

Sadly, trash ends up even on remote shores like Raffles Lighthouse.
While Russel shared this photo of a TV among the corals.

We arrived just before sunrise. On the way, we could see the flashing of the lighthouse from a very long distance away. Here's more about the Raffles Lighthouse and other lighthouses in Singapore. During Maritime Week, the Maritime and Port Authority (MPA) usually organises free trips to Raffles Lighthouse for the public. Look out for announcements on the MPA facebook page.
Today is the last predawn low spring tide for 2016. We get a break in September and October until the evening low spring tides resume in November. I really do hope our coral reefs are doing better when we resume intertidal surveys then.

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

Posts by others on this trip

Others on this trip: Loh Kok Sheng, Toh Chay Hoon, Ivan Kwan, Heng Pei Yan, Nick Yap.

On the same day, Lisa Lim and Richard Kuah led the rest of the team on a survey of Pulau Hantu and they also saw mass coral bleaching there. While they did not see many corals bleaching on the intertidal, they did see subtidal corals bleaching. Lisa says: "The corals found in the water around the jetty's area were bleaching and we estimated 30% to 40% of bleaching corals."

Richard says: "Coral bleaching is still on going at certain parts of the island and we estimated 30% of the corals are affected."

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