A world-first study by Australian researchers has found that krill can digest certain forms of microplastic into smaller – but no less pervasive – fragments. The study, published in Nature Communications journal on Friday, found that Antarctic krill, Euphausia superba, can break down 31.5-micron polyethene balls into fragments less than one micron in diameter. The study was conducted in laboratory conditions with new plastics. The lead researcher, Dr Amanda Dawson, who completed the study as part of a PhD with Griffith University, said that it was likely that microplastics in the ocean would be even easier to digest because they had already been degraded by UV radiation. Within five days in a plastic-free environment, all plastics had left the krills’ systems, meaning that microplastics from krill would not accumulate in animals further up the food chain, such as whales. The digested fragments were on average 78% smaller than the original fragments, with some up to 94% smaller. Unfortunately, Dawson said, krill were unlikely to provide a solution to the levels of plastics and microplastics polluting the oceans. “It’s not necessarily helping plastic pollution, it’s just changing it to make it easier for small animals to eat it,” she said. “It could be a new source of plastics for the deep ocean.”
A study by Newcastle University in December found microplastics in the stomachs of deep-sea creatures from 11km deep trenches in the Pacific Ocean. Dawson said microplastics that had been digested by krill were also too small to be detected in most oceanic plastic surveys, meaning the level of microplastics in the ocean could be higher than currently assumed. Co-author Dr So Kawaguchi, a krill biologist from the Australian Antarctic Division, where the experiments were conducted, said the krill had effectively turned microplastics into nano plastics. “It’s a new pathway for microplastics to interact with the ecosystem, and we need to learn more about how microplastics interact with the environment,” Kawaguchi said.
Microplastics are fragments of less than 5mm in diameter. Krill cannot consume anything greater than 2mm in diameter. “They are not going to be able to eat a drink bottle,” Dawson said. The plastics they do consume are broken up by the animal’s gastric mill, which Dawson said functioned like a mortar and pestle. “I would assume that other planktonic crustaceans should be able to do this as well, we just haven’t seen it yet in any laboratory studies,” she said.
It’s not clear whether fibrous microplastics, such as fishing line or threads from clothing, can be digested in the same manner. Fibrous microplastics made up a greater proportion of the microplastics encountered by krill in the wild, Dawson said. A global analysis conducted by US academics last year found that plastic waste was so high as to threaten an “a near permanent contamination of the natural environment.”
Credit: Calla Wahlquist for The Guardian, 12 March 2018.