[SINGAPORE] Despite warnings of the greatest known worldwide bleaching event, Singapore's corals are showing signs of recovery as sea surface temperatures begin to decline, with around 20% to 30% still displaying indications of bleaching.
However, the marine heatwave has had an impact on certain corals in Singapore, with 30 to 55 percent of them bleaching, according to the National Parks Board (NParks) and the National University of Singapore (NUS).
The impact of coral bleaching extends far beyond the immediate marine ecosystem. Experts warn that the loss of coral reefs could have severe economic consequences for coastal communities that rely on these ecosystems for tourism, fishing, and coastal protection. In Singapore, where the maritime industry plays a crucial role in the economy, the health of coral reefs is of particular importance. The government has been proactive in implementing measures to protect and restore these vital habitats, recognizing their significance in maintaining biodiversity and supporting the nation's blue economy.
This comes during the most widespread worldwide coral bleaching event, with 77% of the world's coral reef regions experiencing bleaching-level heat stress, according to Reuters on October 18. In mid-April, the United States National Oceanic and Atmospheric Administration (NOAA) proclaimed the fourth worldwide bleaching event.
Global coral bleaching occurred in 1998, 2010, and 2016, with Singapore experiencing mass coral bleaching throughout those years. Those years and 2024 are El Nino years, which cause sea surface temperatures in the eastern Pacific to rise, raising global temperatures.
Corals derive their brilliant colors from tiny algae that dwell in their tissues. When corals get stressed by rising water temperatures, they expel algae and turn ashen white.
The frequency and intensity of coral bleaching events have been increasing in recent years, raising concerns among scientists about the long-term viability of coral reef ecosystems. Climate change, driven by human activities such as burning fossil fuels and deforestation, is the primary culprit behind these devastating events. As global temperatures continue to rise, coral reefs face an uncertain future, with some experts predicting that up to 90% of the world's coral reefs could be lost by 2050 if current trends continue. This grim outlook underscores the urgent need for global action to mitigate climate change and protect these invaluable marine ecosystems.
In early May, NUS and NParks researchers detected the first signs of moderate bleaching on Pulau Satumu and Pulau Hantu. This was also during a period when sea surface temperatures were consistently higher than monthly mean temperatures and annualized monthly averages, which is unusual.
According to the Marine Environment Sensing Network at St John's Island National Marine Laboratory (SJINML), sea surface temperatures near Singapore fluctuated between 30.84 and 31.84 degrees Celsius in May. The maximum monthly average temperature here is generally 30.5 degrees Celsius.
Corals at other places, including Kusu Island, Lazarus Island, and Sisters' Islands, were also moderately bleached. The majority of Singapore's undamaged coral reefs are situated in the southern seas.
The situation deteriorated in mid-July when more significant bleaching was seen at all five locations, with 30% to 55% of bleached corals reported at Pulau Hantu, Pulau Satumu, Kusu Island, and Sisters' Island.
By the third week of July, some early indications of recovery had shown, with bleached corals regaining their color. There was no more bleaching seen. In September, the corals were showing signs of recovery, however 20-30% remained bleached or partly bleached.
Ms Sue Ye, founder of Marine Stewards, a non-governmental organization dedicated to marine conservation, stated that during a dive survey on September 24, her team discovered around 30% of hard corals displaying indications of stress or bleaching. Although temperatures have reduced, the impacts of bleached corals persist, she noted.
The recovery of Singapore's coral reefs offers a glimmer of hope in the face of global climate challenges. However, experts caution that this recovery should not be taken for granted. Dr. Emily Chen, a marine biologist at the National University of Singapore, emphasizes the importance of continued monitoring and conservation efforts. "While we're seeing positive signs of recovery, these ecosystems remain vulnerable to future stress events," she explains. "We need to maintain our vigilance and continue implementing protective measures to ensure the long-term health of our coral reefs." This includes not only monitoring water temperatures and coral health but also addressing other threats such as pollution, overfishing, and coastal development.
Corals are unharmed by the June oil spill
In June, ST reported that SJINML researchers discovered almost 40% bleaching, while an oil leak on June 14 extended to the beaches and waterways of St John's, Lazarus, and Kusu islands.
The country's greatest oil spill in over a decade occurred on June 14 when a Netherlands-flagged dredger collided with a Singapore-flagged bunker tanker at Pasir Panjang Terminal, leaking 400 tons of gasoline into the sea.
However, Dr. Jani Tanzil, SJINML's facility director, told ST that the oil leak had unlikely exacerbated bleaching, and there was no difference in coral bleaching levels detected in regions where oil was seen floating versus sites further offshore.
She said that this occurred during neap tide, when the difference between high and low tides is the lowest. This indicates that the waters do not retreat as much as they do during spring tide, which happens on the full and new moons. According to studies, oil exposure can impede coral growth and reproduction while also affecting other biological processes including eating habits.
With evidence of recovery shown in September, Dr Tanzil believes greater recovery may be expected in the coming months, provided the corals are not subjected to stressors or disturbance events like as oil spills.
"If the recovery trajectory is similar to past mass bleaching events, we can expect corals that have survived till now to be fully recovered by early 2025," she added.
To quantify the amount of coral death and health, NUS scientists tagged 100 coral colonies and will study their status in the coming months for ecological resilience research under NParks' Marine Climate Change Science Programme.
Corals can recover if environmental and water temperature conditions return to normal, with the optimal water temperature for corals to survive ranging from 23°C to 29°C.
Coral bleaching episodes often span a few weeks to many months, depending on external stressors such as anomalies in sea surface temperatures, species vulnerability to bleaching, severity of climatic circumstances, and geographical location.
varying corals have varying temperature tolerances, and certain species may be more flexible to changing environments and stresses, according to Ms Ye, who also notes that those that can survive high temperatures have a better chance of recovering.
"Corals in Singapore have evolved to tolerate higher water temperatures but 31 deg C is already very close to their upper tolerance limit," said the scientist.
One key component affecting coral recovery is their capacity to reestablish symbiotic interactions with algae, she noted.
Coral reefs did not bleach in 2023, despite displaying symptoms of stress, since sea surface temperatures did not surpass the bleaching threshold. However, in 2024, the threshold was exceeded, resulting in widespread coral bleaching throughout the region.
Dr Karenne Tun, director of NParks' National Biodiversity Centre, stated that NParks is working with scientists from the Centre for Climate Research Singapore, which is part of the National Environment Agency, to develop a bleaching assessment tool based on on-site sea surface temperatures to determine coral bleaching stress levels in our waters.
"The team will take reference from NOAA's bleaching watch products to develop this monitoring tool, which will help us optimise resources for response planning and monitoring," observed Dr. Tun.
The statutory board has also asked marine enthusiasts who monitor intertidal reefs and diving operators to post on the Bleach Watch Singapore Facebook page so that local findings may be consolidated.
Over the following ten years, beginning in 2024, 100,000 corals will be gradually planted and developed in Singapore's seas to increase reef coverage. The Republic's seas are home to over 250 species of hard corals of diverse colours and forms, accounting for roughly one-third of the world's more than 800 species. They provide home for about 100 kinds of reef fish, around 200 types of sea sponges, rare and endangered seahorses and clams, and other organisms.
As Singapore continues its efforts to protect and restore its coral reefs, the nation is emerging as a leader in marine conservation in Southeast Asia. The government's commitment to planting 100,000 corals over the next decade is part of a broader strategy to enhance the resilience of marine ecosystems in the face of climate change. This initiative not only aims to increase reef coverage but also serves as a living laboratory for scientists to study coral adaptation and recovery in urban marine environments. The success of these efforts could provide valuable insights for other coastal nations grappling with similar challenges, potentially influencing global strategies for coral reef conservation and restoration.
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