Microplastics are having toxic effects on tiny creatures on the seafloor – and the ripple effect could throw the marine environment out of balance, says University of Auckland research fellow Dr Yuxi You.
Her recent research shows a bamboo worm – Macroclymenella stewartensis – is less active and less able to mix sediment in the seabed when exposed to high levels of microplastics.
“When you go to the estuary, you might not see these tiny animals that live beneath the sediment, but you might notice the casting mounds they leave on the mudflats.
“Despite being well hidden, these creatures are vital for the functioning of the ecosystem.
“They help keep our coastal waters clean and able to support marine life,” says You, from the University’s Institute of Marine Science and Centre for Climate, Biodiversity and Society.
When healthy, the bamboo worm and other tiny creatures burrow in the seafloor, allowing oxygenated water to enter deeper into the sediment. This breathes life into the seabed.
The tiny worms eat organic matter, which regulates the levels of carbon and nitrogen in the sediment and surrounding waters.
When the worms deposit small piles of poo on the seabed, this provides nutrients for microscopic plants that live on the sediments and fuels coastal food webs, says You.
“If microplastics stop creatures on the seafloor performing their vital role of keeping the ecosystem in balance, the risk of algal blooms increases.
“Algal blooms can cause the marine environment to become anoxic, and in an environment with no oxygen, fish and other marine life can’t survive,” she says.
University of Auckland Marine Science Professor Simon Thrush, who supervised You’s research, says healthy marine sediments store carbon, acting as a buffer against climate change.
However, when sediments become unbalanced, they can release greenhouse gases, such as nitrous oxide and methane.
Tiny creatures that help keep the seabed healthy are therefore important for the health of the planet, he says.
“Microplastics are affecting the organisms that live in sediment and they’re part of our biodiversity.
“These organisms are hidden heroes that do a lot for us,” says Thrush.
While You’s study at Leigh Marine Laboratory north of Auckland showed the bamboo worms were less active when exposed to microplastics, it isn’t yet clear why.
It’s possible the worms eat plastic particles, absorb chemicals from plastics that leach into sediment, or have less food available because microplastics reduce the growth of the algae they feed on, she says.
Seabirds and eagle rays feed on worms and other tiny creatures in the seabed, so the harmful effects of microplastics can pass up the food chain, says You.
Thrush says the most common source of microplastics is vehicle tyres, while other major sources include polypropylene and polyester fibres from clothing, and polyethylene from plastic bottles and plastic bags.
People can help tackle the microplastic problem by reducing the amount of plastic they buy, picking up plastic rubbish on the beach, supporting harbour clean up groups, and buying clothing made of natural fibres, he says.
While the amount of plastics pouring into the marine environment has increased, recent research shows some microplastics degrade in sediments over time, he says.
Currently, there are no limits set for safe levels of microplastic pollution in New Zealand – and policies will be needed to manage the problem, Thrush says.
Clean coasts are “precious” to New Zealand communities, says You.
“We benefit from nature, so we need to protect it.
“Most people don’t think about small animals living in the seafloor, but they’re of equal importance to larger animals, such as dolphins and penguins, when it comes to keeping ecosystems healthy,” she says.