Microplastics found in marine animals in S'pore's coral reefs, mangroves and seagrass beds: Study

Straits Times

18-05-2025

The animals were dissected and microplastic samples from their organs were collected. PHOTO: CMBS PHOTOGRAPHY TEAM, LEE KONG CHIAN NATURAL HISTORY MUSEUM, NUS
Microplastics were found in the digestive and respiratory organs of the animals. Microplastics found in marine animals in S'pore's coral reefs, mangroves and seagrass beds: Study
SINGAPORE - Microplastics have been found in marine animals across Singapore's coastal areas in a new study, with researchers discovering these plastic bits not just in the animals' digestive tracts, but also in their respiratory organs and bodily fluid.
Microplastics enter the animals not just through the food they consume, but also when they breathe or move through water, said the researchers from the NUS Tropical Marine Science Institute (TMSI).
The study also showed that microplastics are widespread across Singapore's coastal habitats – including mangroves, coral reefs and seagrass beds – and they could potentially be transferred from one organism to the next.
Previous studies had focused mostly on the presence of microplastics – referring to tiny plastic particles smaller than 5mm – in Singapore's environment, said the study's co-principal investigator Neo Mei Lin , a senior research fellow at TMSI.
For example, a recent study had found that 97 per cent of macro- and microplastics on Singapore's shores came from marine-based sources.
The TMSI researchers wanted to find out more about the presence, distribution, abundance and composition of microplastics in local marine organisms. Their study is part of a larger project that examines the impacts and hazards of marine plastics in the coastal environments.
As an emerging field of study, not a lot is known about microplastics and their impacts yet, according to the US National Oceanic and Atmospheric Administration (NOAA).
However, laboratory studies have shown that microplastics and chemicals in plastics may impact animals by delaying their developmental stages, cause problems with reproduction, and may even make it difficult for them to fight off disease, NOAA noted on its website.
In fiddler crabs, microplastics likely accumulate through respiration and direct contact with contaminated seawater.
PHOTO: CMBS PHOTOGRAPHY TEAM, LEE KONG CHIAN NATURAL HISTORY MUSEUM, NUS
Four marine species were selected for TMSI study: the orange fiddler crab (Gelasimus vocans), porcelain fiddler crab (Austruca annulipes), garlic bread sea cucumber (Holothuria scabra) and synaptid sea cucumber (Synaptula recta).
These species 'typically consume and process large amounts of sediments', making them good indicators for researchers to gauge the extent of microplastic pollution in marine sediments, said Dr Neo.
'Their abundant presence indirectly suggests their importance in the ecosystem, and being common across multiple study sites allows us to compare and infer the impact of microplastics,' she said.
Only the guts of the synaptid sea cucumbers were assessed since they lack respiratory trees.
PHOTO: CMBS PHOTOGRAPHY TEAM, LEE KONG CHIAN NATURAL HISTORY MUSEUM, NUS
They are also commonly found in the South-east Asian region, according to study co-author Dr Jenny Fong, who was involved in the study when she was a research fellow at TMSI .
A total of 153 live samples across the four species were collected between November 2021 and May 2022 from mangroves, seagrass beds and coral reefs at seven sites across Singapore.
The sites are Pasir Ris Park, St John's Island, Kusu Island, Small Sister's Island, Pulau Semakau, Changi Beach and Pulau Hantu Besar .
The researchers said they prioritised safety, accessibility and abundance of the target species in choosing these sites, citing the presence of saltwater crocodiles and snakes in other locations as a deterrent.
The animals were dissected and microplastic samples from their organs were collected.
The gills, hepatopancreas – a digestive gland which performs similar functions to the liver and pancreas in humans – and guts of the fiddler crabs were examined.
In the case of garlic bread sea cucumbers, researchers studied its respiratory trees – a branching network of tubes for breathing – guts and coelomic fluid, which is a bodily fluid crucial in transporting nutrients and gases.
Only the guts of the synaptid sea cucumbers were assessed since they lack respiratory trees.
A total of 1,266 microplastic samples were found in these organs.
PHOTO: CMBS PHOTOGRAPHY TEAM, LEE KONG CHIAN NATURAL HISTORY MUSEUM, NUS
A total of 1,266 microplastic samples were found in these organs, which the team carefully analysed and categorised into four shape types – fibres, fragments, films and spheres, listed in order of prevalence. Most particles were less than 1mm in size.
Polymers commonly used in everyday life, such as in plastic bottles, packaging, synthetic textiles and automotive parts, were identified.
'The shapes of microplastics provide hints on the potential sources of plastics... and it tells us what kind of microplastics affect (the animals) the most,' said Dr Neo, who explained that fibres were the most common shape found.
Knowing the most common plastic type helps researchers identify which ones marine animals are likely to ingest, said fellow researcher Ashwini Suresh Kumar, a TMSI research fellow.
'This information could be valuable for policymakers, particularly when considering regulations around additives commonly used during the manufacturing of these polymers, with the aim of reducing bio-accumulation and environmental impact,' she said.
Researchers suggest that in fiddler crabs and garlic bread sea cucumbers, microplastics likely accumulate through respiration and direct contact with contaminated seawater.
The smallest particle, approximately 60 micrometres in size, was found in the respiratory trees of a garlic bread sea cucumber, said Dr Neo.
The hepatopancreas of both fiddler crab species generally had the highest number of microplastics, likely from ingestion as the primary pathway of entry, according to the findings.
With an additional pincer-like claw compared with males, female fiddler crabs exhibit faster and more frequent feeding behaviours – patterns that researchers associate with higher microplastic contamination in their organs.
Synaptid sea cucumbers, which are often seen feeding on the excretion of marine sponges, may ingest microplastics accumulated on these surfaces after the sponges feed by filtering seawater. This suggests that microplastics may be transferred up the marine food chain.
Asked what these findings could mean for the safety of locally grown seafood, Dr Neo said more studies need to be done.
She noted that the guts of contaminated animals are 'typically removed and cleaned before (the animal) goes for sale', adding that 'the sweeping statements of humans eating microplastics need to be carefully discerned'.
'While we do not have any plans to examine the long-term impacts through surveys and sampling, our current work has led us to new research questions such as developing new approaches to studying microplastic distribution in organisms,' she said.
In June 2022 , Singapore launched a national action strategy titled aimed at reducing land- and sea-based sources of plastic waste that end up as marine litter.
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