Mass coral bleaching on Pulau Hantu, but no oil spill impact

Although Pulau Hantu lies just across the petrochemical plants on Pulau Bukom, there are living reefs and even mangroves here. The full team visit to check up for oil spill impact and mass coral bleaching.

Good news: no sign of oil spill impact on Pulau Hantu! But mass coral bleaching is ongoing here. We estimate about 20% of hard corals were full on bleaching and another 20% of hard corals were stressed (pale, odd colours). About 10% of soft corals were full on bleaching and another 20% slightly stressed (pale). Kelvin also flew the drone for a special overview of this rich shore.

No sign of impact from the 400tonne Pasir Panjang oil spill on 14 Jun 2024! Ironically, I am glad to see 'clean' litter on Pulau Hantu. I didn't come across oil on the litter or marine debris, and there was no smell of oil (compared to what we encountered yesterday on an East Coast Park shore that was impacted). There is also only a light load of litter on this island that is NOT cleaned regularly - maybe because it's not on a ferry route?

As usual, the rest of the team make all the special finds! Kok Sheng saw the lionfish again! Richard spotted the Burrowing giant clam that Che Cheng first saw on another trip. Three different Magnificent anemones were seen! There were also lots of other colourful fish and marine life.

Collage of photos by the team.
Links to their albums below.

We are specifically checking for the expected mass coral bleaching which seems to have started to affect some of our shores. Most of the hard corals in the island's intertidal area are boulder shaped, with a few larger colonies. Most that I saw seemed normal, some with pale patches, only about 5% out right bleaching white. I saw one that was not only bleaching but had recently dying tissue (greyish, smells bad) - this is the next stage of mass bleaching that I dread.

I looked at corals that in the past bleached first: Cauliflower corals (some already with dead patches), Brain corals, Anchor corals (a large cluster had mostly dead corallites), Trumpet corals were all bleaching, while most Sandpaper corals were okay. The dense Branching montipora corals in the lagoon were pale but hanging on.  Most of the Flowery disk corals were bleaching, but other plate forming corals were okay. Uncommon corals like Lettuce coral were okay.

The western reef edge remains rich with dense corals of all kinds!

At the reef edge, there are lots and lots of mushroom corals! Lots of the Circular mushroom corals were fullon white bleaching. But to be fair, when they are not bleaching, they are not so obvious and we saw clusters that were fine. All the other kinds of  'long' mushroom corals were alright, with only very few bleaching. Kok Sheng saw 6 Sunflower mushroon corals - fortunately all fine.

The large colonies of Goniopora corals at the reef edge were mostly okay, with some showing stress. While the large colonies of Galaxy corals were pale but not outright bleaching.

There have always been many medium-sized leathery soft coral various kinds here. Today, most were alright, although about 10% were full on bleaching and another 20% slightly stressed (pale, more yellowish than usual or 'melting' with holes in the middle). I also saw many Asparagus flowery soft corals - most were pale, one was bleaching. High res photos of all cnidarians sightings on wildsingapore flickr.

Other cnidarians can also bleach, so I looked out for those too. Many large colonies of Sea mat zoanthids were very pale, I only saw a few all brown ones. Most other zoanthids were okay although I saw a small clump bleaching. There were also small bleaching anemones tucked in rocky areas. A few Giant carpet anemone were very pale (one had tiny 'Nemos'), the rest I saw were okay. I saw one Fire anemone and it seemed fine, I saw one bleaching Frilly anemone. 

Kelvin's awesome drone footage gives such great detail of the bleaching going on at the reefiest intertidal part of Pulau Hantu. See all his drone footage in this album.

It seems Singapore is currently at peak bleaching threat (Alert 2). The NOAA prediction for the Singapore Strait suggest that the situation will ease in the weeks ahead. Down to Alert 1 and then further down to Warning. Let's hope for the best! 

On the seawall facing the petrochemical plants, mangroves have settled naturally (without planting)!

The mangroves are still doing well. There are tall mature trees growing on the seawall (with some rare species), some medium to tall ones on the shore. Most of the trees were flowering or producing propagules. 

There is now very little sign of seagrasses in the northern lagoon. Where long lush Tape seagrass used to grow, these are now scattered most with very short cropped leaves (10cm). Very few had longer leaves, even then not more than 30cm. Even Spoon seagrasses are hardly seen in the lagoon. I saw more Spoon seagrass under the Hantu kecil jetty outside the seawall.

What is the fate of Pulau Hantu?

Pulau Hantu and all the terumbus west of it are slated for massive reclamation outlined recently in the Long-Term Plan Review. Singapore's submerged reefs are often out of sight under the high tide and thus forgotten.

The Singapore Blue Plan 2018

Pulau Semakau and nearby islands and submerged reefs have been recommended by the Singapore Blue Plan 2018 for Immediate Conservation Priority. The Blue Plan recommends the intertidal and subtidal marine areas of Pulau Semakau and adjacent Pulau Hantu, and Pulau Jong to be designated Marine Reserve.

The Blue Plan highlights that Pulau Semakau and its associated patch reefs comprise many ecosystems: coral reefs, mangrove areas, intertidal sandflats, seagrass meadows, and coral reefs. The subtidal area of Pulau Jong is larger than the terrestrial area. Pulau Hantu is a popular dive site has seen increasing interest in the past decade due to biodiversity awareness. If protection is accorded to these three islands, zonation plans for use can be implemented to manage tourism and human impacts.

DOWNLOAD the Plan, SUPPORT the Plan! More on the Singapore Blue Plan 2018 site.


Photos by others on this survey

Che Cheng Neo


Loh Kok Sheng


Tammy Lim


Richard Kuah


Rachael Goh


Kelvin Yong Part 1


Part 2


Drone footage


Muhd Nasry


Chay Hoon