WELLINGTON, March 19 (Xinhua) -- Some of the first research into how microplastics are affecting New Zealand fish species has revealed that microplastic fragments can find their way through the gut lining and into muscle tissue, New Zealand's National Institute of Water and Atmospheric Research (NIWA) said in a statement.
Experiments carried out by two masters students from the NIWA and University of Auckland Joint Graduate School in Coastal and Marine Science have shown that some fish species ingest more microplastics than others in the Hauraki Gulf, but that almost 25 percent of all fish sampled had microplastics in their guts.
Microplastics are defined as pieces of plastic less than 5-mm long and are either manufactured to be small or derived from larger plastics that have broken down into smaller pieces. Identifying them in fish gut samples requires specialized laboratory equipment and protocols to ensure all potential sources of contamination are eliminated.
In the study, Devina Shetty focused on six fish species commonly found within the Gulf: snapper, yellowbelly flounder, gurnard, jack mackerel, kahawai and pilchard. Microplastics were found in 70 of 305 fish specimens, which included more than half of the yellowbelly flounder sampled.
"This higher ingestion rate for flounder could be due to microplastics accumulating in marine sediments which makes up more of their diet compared to other species, or it could be because the flounder samples were all obtained from the Waitemata Harbor, which is closer to Auckland as a potential microplastic source," she said.
Veronica Rotman focused on hoki from the West Coast of the South Island, Cook Strait and the Chatham Rise. One or more microplastics were found in the stomachs of 95 percent of the 60 fish examined, with 90 percent of the particles identified as fibers.
Rotman also completed a 10-week tank experiment at NIWA's Northland Marine Research Centre in which snapper were fed a diet containing polystyrene microplastic feed at different concentrations. She found that those fed a higher concentration were more likely to have microplastic in their white muscle tissue.
Rotman also observed significant inflammatory, vascular and structural changes to the intestine with only a low "environmentally relevant" microplastic treatment, suggesting that similar damage is occurring in the wild. The damage to the intestine increased with microplastic concentration, with 60 percent of high treatment fish displaying severe alterations.
While this gut damage didn't lead to any significant effects on growth or mortality in the 10-week experiment conducted, it demonstrates that microplastic has significant negative effects on the fish that eat it.
NIWA fisheries scientist and University of Auckland's Darren Parsons, who oversaw the projects, said there had only been one previous study looking at the effects of microplastics on New Zealand fish species and these studies provided some valuable insight into what has become an issue of huge concern.
"Microplastics are found throughout the world's oceans, even in Antarctica. They pose a unique threat to marine life," said Parsons.
The next steps in this research would be to focus on the microfibers that are the most common type of microplastic found in the ocean, and to conduct more comprehensive experiments to establish the long-term effects of microfibers on fish.
Between 60 to 90 percent of the litter that accumulates on shorelines, the surface and the sea floor is made up of plastic. Each year, an estimated 8 million tonnes of plastic end up in the ocean -- equivalent to a full garbage truck dumped into the sea every minute -- according to a report by the United Nations Environment Programme (UNEP). UNEP launched Clean Seas Campaign in 2017 to push global efforts to tackle single-use plastics and microbeads. Enditem