Marine Megafauna Foundation's Latest Study Into Manta Rays' Consumption of Toxic Microplastic
A new study by Marine Megafauna Foundation (MMF) further highlights the danger that plastic pollution poses to marine megafauna, and finds that the overwhelming majority of plastic and microplastic particles accidentally ingested by manta rays originates from packaging and household items.
The new study, published in Marine Pollution Bulletin, follows previous research into the amount of microplastic present in the waters of Manta Bay, a series of shallow bays off the southern coast of Nusa Penida, Indonesia, where members of the resident reef manta ray (Mobula alfredi) population gather on an almost daily basis to feed. The scientists used visual sorting and chemical analysis to identify which polymers are most commonly present in the material floating on the surface waters of Manta Bay, an important process in understanding what kind of plastics the manta rays are ingesting, how toxic it is to them, and where the plastic comes from.
The researchers found that visual inspection could adequately predict the chemical composition of seven out of 10 visually grouped plastics. The majority of the plastics found in the water came from broken pieces of larger items, and most of them were either transparent, white, blue, or green – all of which are colours that resemble plankton and other natural sources of food for the mantas.
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Ninety-nine per cent of the polymers identified were either polyethylene or polypropylene, commonly used in the manufacture of food packaging and drinks bottles; the remainder of the plastics were comprised of polystyrene and polyester. The compounds vary in their levels of toxicity but can gather other harmful pollutants from the surrounding water and attract microbes that are harmful to manta rays and other marine animals.
'Plastics are not created equal,' said Janis Argeswara, project leader with MMF and lead author of the study. 'We knew that a variety of plastics were floating around manta ray feeding grounds and being consumed by feeding manta rays. To understand the potential damage that these plastics might cause, we need to know what these plastics are made of, especially small-sized plastics, or microplastics.'
In 2015, Indonesia was ranked as the second-worst global producer of marine plastic pollution, although it has taken significant steps to mitigate the problem, including regional bans on plastic bags and common single-use plastics. The plastic that has already entered the marine environment, however, will persist for decades and continue to enter the food chain, posing long-term threats to a wide range of marine animals, especially filter feeders such as manta rays and whale sharks.
'Confirming polymer types of microplastics helps identify their origin, which is important for directing mitigation efforts,' said Dr Elitza Germanov, MMF Senior Scientist and co-author of the study. 'The overwhelming majority of plastics in these critical habitats are made of polymers commonly used in packaging materials and household items. Thus, improved waste management will need to go hand-in-hand with extending the responsibility of producers to reduce the amount of single-use plastics and packaging materials released into local consumer markets.'
The study 'What's in the soup? Visual characterization and polymer analysis of microplastics from an Indonesian manta ray feeding ground' by Janis Argeswara, et al, is published in Science Daily's Marine Pollution Bulletin at https://doi.org/10.1016/j.marpolbul.2021.112427