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| Mass Coral Bleaching at Kusu Island, Jun 2024 |
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.
Majority of Singapore’s corals have recovered from 2024 bleaching incident: Experts
Zachary Lim Straits Times Apr 14, 2025, 10:20 PM
SINGAPORE – Singapore’s corals, which had been gripped by a mass bleaching event between May and October 2024, have mostly recovered, with an estimated 5 per cent of corals left dead after the incident.
This mortality rate is less severe compared with earlier bleaching events. In the aftermath of the 2016 bleaching event, for example, coral mortality rate was 10 per cent, according to a 2016 scientific report.
The Straits Times had earlier reported that mortality was about 20 per cent in 1998, and 12 per cent in 2010.
Coral scientist Jani Tanzil, the facility director at St John’s Island National Marine Laboratory (SJINML), told ST: “Based on observations during reef surveys, corals tagged and also corals outplanted as part of a reef restoration research project at Kusu Island, most of the corals that had bleached have recovered fully, with mortality rates low.”
Corals get their vibrant colours from microscopic algae called zooxanthellae that live in their tissues. When they get stressed from rising sea surface temperatures, the corals expel the algae and turn ashen white in a phenomenon known as coral bleaching.
These algae supply the corals with nutrients to live, so when bleaching occurs, the coral becomes vulnerable to diseases and may eventually succumb to death.
But recovery is possible if waters cool off shortly after, with a full recovery taking up to 15 years, according to the ARC Centre of Excellence for Climate System Science in Australia.
In April 2024, the US National Oceanic and Atmospheric Administration declared a global bleaching event – the fourth of its kind, where coral reefs around the world were bleached.
Global coral bleaching also took place in 1998, 2010 and 2016. Singapore also experienced mass coral bleaching in those years.
All four global bleaching events took place after an El Nino hit – referring to a climate phenomenon that causes sea surface temperatures to heat up and elevate global temperatures.
The Republic was warmed by El Nino starting from the second half of 2023 to around May 2024.
In May 2024, sea surface temperatures around Singapore started going up. That month, the sea surface temperatures around Singapore ranged between 30.84 deg C and 31.84 deg C, according to the SJINML’s Marine Environment Sensing Network. The highest average monthly temperature here is usually 30.5 deg C.
The ideal water temperature for corals to thrive is between 23 deg C and 29 deg C, according to the National Parks Board (NParks).
According to Dr Tanzil, who is also a marine ecologist at SJINML, water temperatures are now at around 29 deg C.
She added that approximately 30 per cent of the more than 1,000 corals – from about 20 coral species – that were outplanted at Kusu Island suffered some degree of bleaching in June 2024.
However, only about 10 per cent of the affected corals were observed to be severely bleached, with the coral turning almost completely white.
The peak of the bleaching event was in July, 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 SJINML. These southern islands are home to around 250 species of corals.
“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.
However, she noted that there are species differences in bleaching and mortality rates, with species including Pocillopora acuta and Pachyseris speciosa being more vulnerable to bleaching and post-bleaching mortality.
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.
Corals are keystone reef-building animals that support a marine ecosystem, and an estimated one-quarter of marine species depend on coral reefs to survive.
They are also a potential nature-based solution to help mitigate the impacts of climate change, serving as a natural defence against shoreline erosion while providing habitats for a rich array of marine biodiversity.
Efforts are under way to beef up the resilience of the Republic’s reefs, including a project led by Prof Huang and a team of researchers from the National University of Singapore to develop climate-resilient corals. This is one of many projects under the Marine Climate Change Science research programme.
This project involves bioengineering corals to withstand drastic fluctuations in environmental conditions. These corals will host beneficial micro-organisms that can promote coral adaptability and be transplanted to native reefs for restoration.
The 100,000 Corals Initiative was also launched in December 2024. Between 2024 and 2034, 100,000 corals will be progressively planted and grown in Singapore’s waters to beef up its reef cover.
This involves the collection of an adult coral colony from a reef before they are fragmented into smaller grafts known as nubbins. They are then taken to a coral culture facility at NParks’ Marine Park Outreach and Education Centre on St John’s Island before ultimately getting transplanted onto reefs again.
But this is no easy feat, and the process of propagation can take a long time, said Dr Tanzil.
