Corals in murky waters could produce heat-tolerant babies

Coral reefs around the world are in decline, with many reef areas shrinking as increasingly frequent marine heatwaves leave them less time to recover in between. But a new report found that reefs in the East Asian Seas, which includes Singapore, are bucking the global trend, with coral cover holding steady over the past four decades. 

Marine biologist Huang Danwei, deputy head of NUS’ Lee Kong Chian Natural History Museum, said corals which thrive even in harsh environments, such as those that live in the murky waters around Singapore, often have a higher degree of tolerance against marine heatwaves. 

Such corals could produce offspring that are naturally resilient to warmer sea surface temperatures. When these coral babies disperse and settle in neighbouring reefs, it could confer them greater resilience against heat waves, he added.

Mass coral bleaching expected in Mar-May 2027

Mass coral bleaching is likely in Singapore in Mar-May 2027. NParks will be monitoring.

Mass coral bleaching at Kusu Island, Jun 2024

Karenne Tun, group director of NParks’ National Biodiversity Centre said that while recent studies show that repeated bleaching in Singapore has caused relatively low immediate coral death – usually under 10%, and about 5% in the 2024 bleaching event – the reefs are changing and have “flattened” over time. Repeated bleaching and shifts to simpler reefs may affect coral spawning, limiting the  reefs’ long-term resilience even if they appear to recover.

Marine biologist Huang Danwei, deputy head of NUS’ Lee Kong Chian Natural History Museum noted that increased frequency of coral bleaching events means reefs have less time to recover between them. When corals do not recover, the flora and fauna that depend on reef habitats also decline in abundance and diversity.

According to third World Ocean Assessment: “The reefs of today will not be the reefs of tomorrow, and shifting baselines need to be considered when setting objectives, with respect to conservation, restoration and regeneration".

Current efforts include NParks’ 100k Corals Initiative, launched in December 2024 to plant 100,000 corals in Singapore over the next decade and beyond. It is the most extensive coral restoration effort in Singapore to date. Jani Tanzil, facility director of the St John’s Island National Marine Laboratory, noted that in Singapore’s case, where only about 10 sq km of reefs remain, there is no choice but to turn to this last resort of reef restoration to combat their decline.

Recovery at coral garden at East Coast Park

Thanks to Lon, Rui Quan and Dylan for surveying the amazing coral garden that has settled on artificial shores at East Coast Park. 

Photo by Lon Voon Ong.

In 2024, this shore was impacted by mass coral bleaching, the 400tonne Pasir Panjang oil spill and the 5tonne Changi East oil overspill. Oil that landed on this shore was not cleaned as thoroughly because it is not a recreational beach. It's a relief to know the corals and seagrasses here seem to have recovered well in such a short time.

Impact of sedimentation on reef recovery

Singapore waters are known to be murky, and corals have survived in such conditions for several thousand years. But scientists from Nanyang Technological University (NTU) found that mud from land – reclamation or intense rainfall – could smother corals and impede recovery from bleaching events.

Dr Huang Danwei, deputy head of the NUS Lee Kong Chian Natural History Museum, said: “This is the first study to characterise the sediment on coral reefs here in fine detail. This is further direct evidence that land reclamation and run-off from land can drive the loss of corals and lower their resilience against climate change impacts.”

Coral spawning muted in 2025 after mass coral bleaching in 2024

Once a year, on the fourth month, around four days after the fourth full moon of the year, our corals release eggs and sperm all at the same time! Called mass coral spawning, this year's event was 'muted', most likely because of mass coral bleaching in 2024. Scientists say the scale of the event was similar to the spawning in 2017, which occurred months after the 2016 mass bleaching event. 

However, Dr Karenne Tun, group director of NParks’ National Biodiversity Centre noted that while spawning was muted in 2017, it improved significantly in 2018 and 2019. “Thus, we are hopeful that the corals will recover to full fecundity within the next two years if our reefs are not subjected to any further thermal or other stressors,” she added.

More about mass coral spawning and this blog post on the 2024 event 

Tanah Merah Ferry Terminal after mass bleaching

Today, a small team returns to survey the amazing coral reef that has settled naturally on the seawalls of Tanah Merah Ferry Terminal.

This shore was impacted by mass coral bleaching last year, and also the 400tonne Pasir Panjang oil spill on 14 Jun 2024. Although we didn't see any bleaching corals, I sense many corals didn't make it.

Japan study: Corals recover faster on artificial structures than on natural reefs

A Japan study compared how quickly bleached corals return to artificial structures versus natural reefs, using 29 years of field data. Within six years, artificial breakwaters recovered to near pre-bleaching levels, while coral cover on natural reefs barely recovered.

A possible explanation is that artificial surfaces are more robust than natural reefs. This suggests combining artificial infrastructure with natural coral reefs could better promote coral regeneration, while also preventing disasters.

Majority of Singapore’s corals have recovered from 2024 Mass Coral Bleaching

Peak bleaching was in July 2024, with about 44 per cent of coral colonies surveyed reported to have been bleached, according to Associate Professor Huang Danwei, deputy head of Lee Kong Chian Natural History Museum. Extensive bleaching was observed at Pulau Hantu, Pulau Satumu, Kusu Island and Sisters’ Islands, according to Coral scientist Jani Tanzil, the facility director at St John’s Island National Marine Laboratory (SJINML).

Mass Coral Bleaching at Kusu Island, Jun 2024

“Most bleached corals that survived the marine heatwave seem to also have recovered by November 2024, with its rate of recovery similar to previous bleaching events – at least for the corals we’ve been monitoring, which are mostly at Kusu Island,” added Dr Tanzil.

On whether the series of oil spills and leaks since June 2024 have affected the recovery of coral reefs around Singapore from the bleaching incident, Dr Tanzil said that the corals have likely “escaped the immediate brunt of it”. However, long-term impacts are still inconclusive.

“(The oil spills) largely occurred not during low tides when corals would be exposed in the splash zone and to the floating oil layer. Speedy clean-up efforts have also mitigated impacts,” she said.

Neptune coastal monitoring system upgraded

The current Neptune system monitors Singapore waters so authorities can respond quickly to incidents such as oil spills and algae blooms (which cause mass fish death). Upgraded sensors will monitor significant wave parameters to support studies on the impact of climate change, said NEA.

Data from the upgraded system will complement the Marine Environment Sensing Network (MESN) said Dr Jani Tanzil, facility director of St John’s Island National Marine Laboratory (SJINML). MESN provides data that in 2024 alerted researchers to mass coral bleaching.

Singapore corals showing signs of recovery amid global coral bleaching event

Amid the largest recorded global bleaching event, Singapore’s corals are showing signs of recovery as sea surface temperatures begin to fall, with about 20 per cent to 30 per cent of them still showing signs of bleaching.

But the marine heatwave has taken its toll on some corals here, with 30 per cent to 55 per cent observed to be bleached in July, the National Parks Board (NParks) and National University of Singapore (NUS) told The Straits Times.

Update on 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 returns to check on the mass coral bleaching that we saw here in Jun 2024.

Today, we estimate less bleaching - 10% of hard corals, few leathery soft coral. But we estimate about 60% of hard corals are dead and there seems to be fewer and smaller leathery small colonies. However, the shore remains very much alive and the team spot special animals.

Oiled East Coast shore: Corals dead, seagrasses okay?

I did a solo check on this shore which was not cleaned after it was impacted by the 400tonne Pasir Panjang oil spill on 14 Jun 2024. The 'House of Horrors' under the bridge in the canal still glistens as the first time I saw a week after the oil spill.

The corals situation seems worse than what we saw a month ago - it seems 90% of the corals are already dead. But seagrasses don't seem to be as severely impacted. There are also still signs of life!

Mass coral bleaching at Pulau Semakau (North)

The team surveys the rich reefs of Pulau Semakau (North). They encounter Giant clam, large sea stars, large snails and other interesting marine life.

We estimate about 20% of hard corals were bleaching and are relieved to see very little recent death, with many large colonies at the reef edge still healthy. Unfortunately, seagrasses remain sparse. Kelvin also flew the drone for unique overviews of the situation.

Mass coral bleaching at Tanah Merah Ferry Terminal

Today, a small team returns to survey the amazing coral reef that has settled naturally on the seawalls of Tanah Merah Ferry Terminal. There were lush seagrasses on the shore next to the Ferry terminal. 

Sadly, we saw signs of oil on the shores and also extensive mass coral bleaching (about 30%) and coral deaths (about 20%). But otters were seen and the seagrasses seem alright.

Reefy Changi with some coral bleaching

A small team check out the delicate 'reefy' garden under the Changi Boardwalk. 

The sea fans and sponges were doing very well! The team spot seahorse, nudibranchs and other interesting marine life. Unfortunately, we noticed some mass coral bleaching. 

Mass coral bleaching at Pulau Semakau (East)

At a not-so-low-tide before dawn, we survey Pulau Semakau next to the Semakau Landfill and near petrochemical plants on Pulau Bukom.

Despite its location, this shore has living reefs with giant soft corals, giant sea anemones and we saw 2 Giant clams! Unfortunately, it is impacted by mass coral bleaching. We estimate 50% of hard corals  and 70% of leathery soft corals were bleaching. Kelvin also flew the drone and will have valuable insights into the situation.

Mass coral bleaching and oil spill impact at East Coast coral garden and seagrass meadows

Heartbreak as we survey the reef that has settled at a seawall on the other side of Tanah Merah Ferry Terminal next to the East Coast PCN. We estimate 90% of the corals here are bleaching or highly stressed, and about 50% already have dying/dead portions. 

One of our nicest seagrass patches is growing at the mouth of a canal here and fortunately, they seem alright for now. Oil is still very present on this shore which is not cleaned as it is not a recreational beach. We also had a quick look at the shore opposite NSRCC, which is being cleaned.

Ubin living rocky shores with some bleaching

There are living rocky shores next to Pulau Ubin jetty. We started at Thomson's rock and was rather disappointed that it was rather bare of sponges, and the sea fans around it were mostly half dead.

Could the huge fish farm located just off the shore (dark blob on the right) have something to do with this? Fortunately, sea fans were doing much better closer to the jetty. Sadly, we saw coral bleaching.

Mass coral bleaching at Cyrene, no oil spill impact

A small team decided to survey Cyrene on a less than ideal tide on the last of the low spring tide cycle. Because Uncle Tony ODempsey shared with us this chart. Which suggests the oil escaping from the accident site spent some time over Cyrene. Thanks to Uncle Tony for this important information.

Fortunately, we didn't come across any smell or signs of oil on the shore. Ian did a great drone overview of the shore too. We saw dugong feeding trails, Knobbly sea stars, Giant clam and other marine life commonly seen here. But sadly mass coral bleaching seems to be getting worse here. We estimate about 50% of hard corals and 70% of leathery soft corals are bleaching. On our last visit here on 10 Jun 2024, the estimate was15% of hard corals were showing signs of stress and about 10% outright bleaching. While about 40% of soft corals were showing signs of stress and about 30% outright bleaching.

Mass coral bleaching and oil spill impact on a restricted East Coast Park site

Corals, seagrasses, mangroves have settled on artificial shores at East Coast Park! Thanks to NParks for obtaining permission for us to survey this restricted site.

Because the site is closed to the public, it appears that oil has not been removed from this shore. We saw much impact from the 400tonne Pasir Panjang oil spill on 14 Jun 2024. Mass coral bleaching is also ongoing here. We estimate that up to 80% of corals were bleaching.