Marine life in the Great Barrier Reef are at risk of plastic exposure due to high levels of microplastics found in the water, a new study has found.
A three-year study of plastic waste in the Reef by James Cook University and the Australian Institute of Marine Science (AIMS) found a total of 533 synthetic and semi-synthetic plastic items.
The team, based at AIMS, conducted 66 surface seawater samples next to the SS Yongala shipwreck site, southeast of Townsville, between September 2016 and September 2019.
The samples were collected by neuston tows, a net that skims the surface of the water, and then analysed, with the team finding 92 per cent of micro-sized fragments and fibres to be microplastics.
This comes ahead of AIMS Annual Summary Report of Coral Reef Condition 2021/22 report, released on August 3, that revealed “In 2022, widespread recovery has led to the highest coral cover recorded by the Long-Term Monitoring Program in the Northern and Central Great Barrier Reef”, showing an ability to begin recovery after disturbances such as mass bleaching.
Impact on marine life
James Cook University’s Professor Mark Hamann, who was part of the study, said the impact of microplastics on marine life varies amongst different critters.
“When we start looking at these plastic fragments, they become so small that pretty much anything large enough with a mouth to eat them is going to eat them,” he told Hope 103.2.
If an animal consumes a piece of plastic, the impact will also vary depending on their size.
“If a large animal eats a piece of plastic and that plastic is smaller than the width of their digestive tract, chances are that plastic will pass all the way through.
“It may leach out chemicals when it’s passing through; we don’t really know that, it’s something we suspect.
“The other thing that happens… if an animal is eating plastic that is the same size or similar size to their digestive tract, it increases the chance of that plastic getting stuck or clogged within the digestive process and then it starts to back up and that’s where you get the problems.”
“If you get large amounts of rainfall, we get a spike in the number of plastics in the water samples collected,” – Professor Mark Hamann, James Cook University
How microplastics end up in the ocean
Microplastics are small pieces of plastics from around 5mm down to less than a millimetre in size, Professor Hamann said.
“Microplastics are the small pieces that are usually visible to the naked eye,” he said.
These can end up in the ocean in several ways, according to Professor Hamann, with one being rainfalls.
“What we found was there was really large patterns where if you get large amounts of rainfall, we get a spike in the number of plastics in the water samples collected.”
He said this indicates that a lot of these plastics are coming out of land systems, such as agriculture, urban settings, stormwater drains or even debris washing out into the ocean.
Lead author of the study Michaela Miller, and JCU PhD candidate, said plastic also ends up in the ocean when there is increased wind speed and river output as a result of extreme weather events.
“(This includes) Cyclone Debbie in 2017 and big flood events like the one we had in 2019 up here in Townsville,” she told Hope 103.2.
Another source for microplastics in the oceans comes from broken-down ropes, Professor Hamann said.
“They break down into small fibres and those fibres end up in the rivers and the oceans.”
This can include mooring buoys, anchors, anchor ropes, nets or ropes people use in other land-based areas.
“If an animal is eating plastic that is the same size or similar size to their digestive tract, it increases the chance of that plastic getting stuck or clogged within the digestive process,” – Professor Mark Hamann, James Cook University
What can be done?
Prevention is the best solution to this problem, according to Professor Hamann.
“If we think about the volume of water in the ocean and the amount of plastic, it’s very, very hard to get microplastics out of the ocean, no matter how hard you try.
“But if we can set up systems, event systems that haven’t been thought of yet, to try and remove plastics from the waterways before they get out into the ocean, that’s where the steps need to be taken.”
“If we think about the volume of water in the ocean and the amount of plastic, it’s very, very hard to get microplastics out of the ocean… But if we can set up systems,” Professor Mark Hamann, James Cook University
This begins by working out where the plastics are coming from, whether that be urban systems, stormwater drains, agricultural systems or sewage treatment plants and other places, he said.
“Then we can target mitigation to each of those different components and therefore slowly reduce the imports into the ocean,” Professor Hamann said.
Monitoring programs can also be helpful, he said, although they won’t eliminate the problem.
“They help us work out the frequency and the magnitude of the problem.”
The research team are now looking at the biological impacts of microplastic pollution to find out what animals are eating the plastic and what consequences that will bring.