In the Southern Ocean, a team of researchers led by the British Antarctic Survey found microplastics in two species of zooplankton: Antarctic krill (Euphausia superba) and salps (Salpa thompsoni), gelatinous invertebrate organisms. The researchers most frequently found microfibers made of nylon. The study was published today in the journal Royal Society Open Science.
In previous studies, Antarctic krill has already been shown in the laboratory to ingest microplastics (plastic particles less than 5 millimeters in size). The current study now provides evidence that two of the most abundant zooplankton species in the Southern Ocean, krill and salps, ingest microplastics in their natural habitat.
“We have already seen the harmful effects that plastic ingestion can have on Antarctic zooplankton in the lab. In this study we show how these animals are vulnerable to plastic in their natural habitat,” Dr. Emily Rowlands, a marine biologist with the British Antarctic Survey and co-author of the study, said in a BAS news release. “The research is particularly important as it supports laboratory experiments and provides new insights into the amounts and types of plastics krill and salps are exposed to in the Southern Ocean.”
Given that microplastics are also omnipresent in the Southern Ocean, from the sea surface to the seafloor, the results are hardly surprising. Antarctic krill probably confuse the microplastic particles with their natural food. Unlike salps, krill select their food, which consists largely of diatoms and is usually between 40 and 300 microns in size. Salps, on the other hand, are not picky and will take anything between 1 and 1000 microns in size.
The researchers chose these two species for their studies because they play a critical role in the Southern Ocean food web. Antarctic krill is the main food source for whales, seals and penguins, while salps are the food source for some fish and larger seabirds.
“Evidence of microplastic consumption in two very high abundance species of the Southern Ocean is concerning. Both of these species are an integral part of the Southern Ocean ecosystem, and we don’t yet fully understand the impact microplastics will have in this environment,” said Laura Wilkie Johnston, a marine biologist at BAS and lead author of the study.
The research expeditions during which the krill and salp samples were collected date back several years: in 2016 off the northern tip of the Antarctic Peninsula and in 2018 near South Georgia. The researchers found microplastic particles in both species, but detected a greater number of particles per individual in krill. Juvenile krill ingested nearly 80 percent more particles compared to near-adults, which the researchers attribute to the fact that young krill eat faster during phytoplankton blooms.
In both species, the extracted microplastic particles consisted mostly of microfibers. About 60 percent of the krill and salps contained nylon (polyamide), which is used in clothing, fishing gear, ropes, and reinforcing car tires. Other synthetic polymers identified by the team included chlorinated polyethylene and rubber. All polymers found have a greater density than seawater and usually remain at the surface for only a short time, indicating that they are more likely to originate from local sources.
In conclusion, the authors write that their findings underscore how sensitive the Antarctic marine ecosystem is to plastic pollution. Because food chains in Antarctica are very short, microplastics are very likely to be passed on to larger predators such as whales, seals, penguins and other seabirds. Furthermore, the ingestion of microplastics by krill and salps could negatively impact the Southern Ocean as one of the largest natural carbon sinks on Earth.
“In addition to being important food sources in the Antarctic marine ecosystem, krill and salps play an important role in slowing down climate change. The Southern Ocean is a hugely important carbon sink and these animals play an integral part transferring atmospheric CO2 into the deep oceans. Interactions with microplastics have the potential to interfere with the amount of carbon these organisms can take down and trap in the deep ocean,” says Dr. Clara Manno, a marine ecologist at BAS and lead scientist on the CUPIDO project.
Julia Hager, PolarJournal
Featured image: Wikipedia/Uwe Kils
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