Researchers have discovered microplastics smaller than 300 micrometers in coral skeletons. The team introduced a new method to extract and identify microplastics, which they used on coral samples collected from the Gulf of Thailand. This discovery may provide insights into the ‘missing plastic problem,’ wherein about 70% of the plastic found in oceans is unaccounted for. It appears that corals could serve as a ‘sink’ for microplastics, drawing them from their marine surroundings.
A collaborative research team from Japan and Thailand examined microplastics in coral and found that each part of the coral anatomy — the surface mucus, tissue, and skeleton — harbors microplastics. This significant finding was enabled by a new microplastic detection technique that was applied to coral for the first time.
These results might address the ‘missing plastic problem’ that has confounded scientists, as around 70% of the plastic waste entering the oceans remains undetected. The research team proposes that corals might be acting as a ‘sink’ for these microplastics by absorbing them from the water. Their work has been published in the journal Science of the Total Environment.
While plastics have greatly enhanced conveniences in our daily life, they have also inflicted severe harm to ecosystems, the extent of which researchers are only beginning to comprehend. It is estimated that between 4.8 and 12.7 million tons of plastic enter the oceans each year.
“Plastic pollution is a major concern in Southeast Asia. Annually, nearly 10 million tons of plastic waste are generated, making up roughly a third of the global total,” remarks Assistant Professor Suppakarn Jandang from Kyushu University’s Research Institute for Applied Mechanics (RIAM) and the study’s lead author. “Some of this plastic ends up in the ocean, where it breaks down into microplastics.”
To tackle the problem of plastic pollution in Southeast Asia, RIAM partnered with Chulalongkorn University in Thailand in 2022 to create the Center for Ocean Plastic Studies. This international initiative is led by Professor Atsuhiko Isobe, who also heads the research team responsible for these findings.
The team’s objective was to assess the effects of microplastics on local coral reefs, so they conducted fieldwork on the coast of Si Chang Island in the Gulf of Thailand, an area known for its small reef flats and as a site for anthropological research.
“Corals have three main anatomical layers: the surface mucus, which covers the outer part of the coral; the tissue, representing the inner bodily structures; and the skeleton formed from hard calcium carbonate deposits. Our initial step was to devise a method for extracting and identifying microplastics in our coral samples,” adds Jandang. “We subjected our samples to a series of chemical washes aimed at dissolving each anatomical layer. After each layer was processed, we filtered the contents before moving to the next.”
In total, 27 coral samples belonging to four species were collected and analyzed. The researchers identified 174 microplastic particles in the samples, primarily ranging from 101 to 200 micrometers in size, roughly the diameter of a human hair. Among the identified microplastics, 38% were located in the surface mucus, 25% in the tissue, and 37% in the skeleton. The predominant microplastic types identified included nylon, polyacetylene, and polyethylene terephthalate (PET), making up 20.11%, 14.37%, and 9.77% of the samples, respectively.
This research indicates that corals may function as a marine plastic ‘sink,’ sequestering plastic waste from the ocean in a manner similar to how trees absorb CO2 from the atmosphere.
“The ‘missing plastic problem’ has been a challenge for scientists monitoring marine plastic waste, but this evidence implies that corals could be contributing to that unexplained plastic,” states Jandang. “As coral skeletons remain intact after the corals die, the microplastics they contain could potentially be preserved for centuries, similarly to how mosquitoes are preserved in amber.”
Additional research is still needed to fully understand the implications of these findings on coral reefs and the wider ecosystem.
“The corals we examined in this study are found globally. To gain a clearer understanding of this issue, we need to conduct more extensive global research across various coral species,” concludes Isobe. “We are also unaware of the potential health impacts of microplastics on coral and the larger reef community. There is still significant work to be done to evaluate how microplastics affect our ecosystem.”
