24 June 2020

Terumbu Raya with mass coral bleaching

Dr Jani Tanzil alerted us that mass coral bleaching may have started on our shores since the second week of June. So we are on the look out for this at Terumbu Raya, which lies close to the petrochemical plants on Pulau Bukom.
Living reefs of Terumbu Raya, Jun 2020
I surveyed a short stretch of reef edge facing Pulau Semakau which has many corals of various kinds and sizes. Today, I estimate about 10% of the hard corals that I saw are outright bleaching, with an additional 20% showing stress (paler than usual or with bleaching portions) or with recently dead patches. But many corals were doing alright with no pale or bleaching portions. The situation wasn't as bad as what I saw during mass coral bleaching in 2016.


Here's a glimpse of the corals with Pulau Semakau on the horizon. While a few of the corals were bright white or flourescent yellow, many of the coral colonies were normal or paler than usual, or with small bleaching patches.
Living reefs of Terumbu Raya, Jun 2020
Some of the coral colonies had bleaching or white upper portions while the lower parts seemed alright.
Living reefs of Terumbu Raya, Jun 2020
Here's another colony which had paler-than-usual upper portions while the lower portions seemed normal.
Living reefs of Terumbu Raya, Jun 2020
Here's a compilation of some of the hard corals I saw, with a ruler for further study by others.
The situation today is not as bad as what I saw during mass coral bleaching in 2016 (photo below).
Today, there were many Bubble tip anemones on the reef edge that were bleaching. I also saw one Pizza anemone that was bleaching - these well hidden anemones are usually hard to spot unless they are bleaching. There were several Haddon's carpet anemones on the high shore, most were alright although some had paler centres. I saw two Giant carpet anemones that were alright. And one bleaching Filly anemone.
Most of the zoanthids I saw were alright although I saw a few scattered bleaching ones. I saw a cluster of corallimorphs that were bleaching, and a clumps of leathery soft corals that were bleaching and melted into smaller clumps.
Besides the one above, I didn't see many large leathery soft corals, all were alright.
Pinwheel leathery soft coral (Lobophytum sp.)
I came across a humungous Black-tailed sea hare. It was only later that I realised there was another one near by, from the purple ink in the water.
Here's a video of the sea  hare. Although it is very well camouflaged, its inner flaps have a startling bold pattern!
Black-tailed sea hare (Aplysia dactylomela)
It was great to come across a Burrowing giant clam. It was about 12cm long. Giant clams can also suffer from bleaching, so it was good to see that this one seemed alright.
Burrowing giant clam (Tridacna crocea)
There is usually not much seagrass on this shore. I came across a few small dense patches of seagrasses in some of the large pools left behind at low tide. But most of the seagrasses were sparse, and generally heavily covered with epiphytes. There were scattered clumps of cropped Tape seagrasses.
This submerged reef lies opposite Pulau Hantu and the petrochemical plants on Pulau Bukom, and is next to Pulau Semakau. We didn't come across any fish nets or traps. Which is great because sea turtles are often seen here. Alex our skipper said he saw three during our survey.

Photos by others on this survey

Jianlin Liu


Dayna Cheah



Vincent Choo


Richard Kuah

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