Mass coral bleaching at Kusu Island

This rich reefs of Kusu Island lies just opposite the Central Business District, less than half an hour away by fast boat.

A small team do a health check specifically for mass coral bleaching which was expected and seems to have started to affect some of our shores. We estimate about 20% of hard corals were outright bleaching while about 40% of soft corals were bleaching or very stressed. Kelvin took drone views that with amazing details help assess the extent of mass coral bleaching.

As usual, the rest of the team spot all the interesting animals. Kelvin spotted the Yellow-lipped sea krait from the jetty! The jetty is also encrusted with cave corals, sea fans and other marine life that flourish out of the sun. They spot octopuses, squid, fishes, crabs and more.

Collage of photos by the team.
Links to their albums at the end of the blog post.

The reef edge at the Northern lagoon is still densely covered in hard corals - including many kinds not commonly seen. Most seemed alright, with only about 20% outright bleaching, and an additional 5% showing stress - pale or pinkish. Even delicate branching corals and plate corals seemed fine. There was a patch of Branching montipora corals that was still brown. Often, a bleached coral would be seen right next to a perfectly healthy one. 

About 40% of the Leathery soft corals here were bleaching or showing signs of severe stress - very pale or yellowish. Because these are rather large and abundant, they do give the impression of widespread bleaching.

Kelvin took awesome drone views with amazing details help assess the extent of mass coral bleaching.

Corals have settled inside the Northern lagoon. Today, although large patches of the Branching montipora corals growing near the higher shore were dead, there are still some in the lower shore that were brown and not bleaching. Some colonies had recently dead patches with remaining areas bleaching. While others were still brown with only small pale patched. On the dead portion of a large coral that was pale with stress, there were tiny corals that were still okay.

Here's video of the corals inside the northern lagoon, and on the reef edge outside the northern lagoon. High res photos of all cnidarian sightings on wildsingapore flickr.

We started the survey well before dawn. While some went to survey the shore under the jetty, I headed for the reef edge outside the southern lagoon. Which I have not seen for many years. There are a lot of small to medium-sized Leathery soft corals here and about 40% were bleaching or showed signs of stress. I saw many Asparagus flowery soft corals and they were all bleaching. 

Past the lights at the temple, I came across a small dense patch of Branching montipora corals. They were pale but seemed alright. This edge isn't as reefy as the northern lagoon, but has many interesting corals. Most that I saw seemed alright. Only a few were bleaching outright with large dead patches. Corals that in the past were the first to bleach were still hanging on.

Other cnidarians can also bleach, so I looked out for those too. The only anemone that I saw bleaching was a Fire anemone. I saw one Leathery sea fan, many Frilly anemones, some Giant carpet anemones, some corallimorphs, none were bleaching. There are still many Magnificent anemones, none bleaching - I have never seen these anemones bleach even in full blown mass bleaching events. There are many Sea mat zoanthids and most were pale, some even greenish. Only a few were their usual brown. 

The situation today is not as bad as what we saw here in Jul 2016 during the last Global Mass Coral Bleaching event. But if we are not yet at peak bleaching, it could just be the beginning. The NOAA prediction for the Singapore Strait doesn't seem to suggest a sharp worsening in the weeks ahead. Let's hope for the best!

What is the future of Kusu Island?

The rich reefs of Kusu Island of today are slivers of massive reef flats that were reclaimed less than one human lifetime, 50 years ago. Today, all these vast reef flats have been reclaimed, leaving very narrow margins outside the seawall that can only be accessed by non-divers at the very lowest tides. Check out the Historical maps of Singapore by NUS Libraries site where you can actually overlay the various maps over time and use a slider to see the changes. 

Kusu Island was in fact originally a tiny outcrop where the temple now is. And during the annual Kusu Island pilgrimage, devotees would land by sampan. As captured by this iconic photo by Ivan Polunin, from "Once upon an island: A rare peek into our past" Scenes of old Singapore through the lens of the late naturalist Ivan Polunin. Wallace Woon, Straits Times 20 Sep 2023.

Last month, it was announced that the reefs outside the northern lagoon of Kusu Island would be part of Singapore's second national Marine Park at Lazarus South-Kusu Reef. It is good to cherish and protect what we have left. More on Singapore's second marine park: past, present and future.

In fact, the Singapore Blue Plan 2018 recommended the cluster of Kusu, Lazarus and St. John's Islands  for elevated protection status.

The Blue Plan highlights that Lazarus, St. John’s, and Kusu Islands are established sites for coral nurseries as their shoreline offers ideal sheltered areas for growth of corals. Designating these islands as No-fishing Areas can bolster their rehabilitation. Protecting a larger cluster of islands means 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


Kelvin Yong Part 1


Part 2


Part 3 Drone views


Marcus Ng


Tammy Lim



Others on this survey: Jonathan Tan