Microplastics are minute polymers that enter ocean ecosystems via cosmetics, clothing, industrial processes and the broken-down remains of larger pieces of marine debris. According to new research, these tiny particles in the water can impair oysters’ ability to grow and reproduce.
“Filter feeding species are among the most impacted by microplastics due to their mode of nutrition: filtering large volumes of water,” says Arnaud Huvet, an invertebrate physiologist at the French Research Institute for Exploitation of the Sea. “We found that microplastics affect the oysters’ reproduction, with consequences to the next generation.”
Past studies have examined the effect of microplastics on mussels, sea cucumbers, sea bass larvae and more. Results range from reduced feeding activity to lost energy and decreased survival rates. Huvet and his colleagues decided to add Pacific oysters to the roster of tested animals because of their prominent role in protecting coastal habitats and their importance in natural food webs, as well as satiating human appetites.
The researchers raised more than 200 oysters in the lab. They subjected half of them to tiny polystyrene particles ranging from two to six micrometers in wide—the size range typically ingested by marine bivalves. After two months, the researchers opened up all of the oysters to count and measure their reproductive cells and to perform artificial fertilization.
Exposure to microplastics did cause significant impacts, Huvet and his colleagues report today in the Proceedings of the National Academy of Sciences. Female oysters in the microplastic tank produced 38 percent fewer eggs compared to the polymer-free shellfish, and the eggs that did form were five percent smaller.
Male reproductive parts suffered, too: Sperm velocity fell by 23 percent. Overall, oysters in plastic-ridden tanks experienced a 41-percent drop in fecundity, and their offspring were 20 percent smaller than those of the uncontaminated animals.
Richard Thompson, a marine biologist at Plymouth University who was not involved in the work, says that the findings advance knowledge about the potential impacts of microplastics on oysters.
However, he cautions against too readily extrapolating the results to the field, because the concentrations of microplastics the authors used in the lab were much higher than those reported in environmental sampling. The authors used concentrations of about 2,000 particles per milliliter of water in their experiments, but some previous work suggests that actual concentrations are closer to one particle per milliliter in the environment.
Using such high concentrations at the start of the experiment is still a useful step, though, because it establishes that microplastics can have an impact if left unchecked.
“Use of high concentrations in ground-breaking studies such as this one is important, since if the experiment showed no effect, this would indicate that concentrations in the environment are relatively safe for marine life,” Thompson says. “There is now a need to repeat the work with lower concentrations that are more representative of those found in the environment.”
In the meantime, many environmental experts already believe it is prudent to limit the amount of microplastics that make their way into oceans. The U.S. government, for instance, recently passed legislation banning microbeads—tiny plastic particles found in many exfoliating face washes, toothpastes, body washes and more.
“An estimated 5,000 to 95,000 microbeads are released into the environment with every single use of personal care products,” Huvet says. “Those flow straight from the bathroom into the sewer system, and once in the environment, they do not biodegrade and are impossible to remove.”
While the U.S. ban on microbeads is a welcome development, much more is needed to curtail the growing problem of plastic pollution worldwide. As Huvet points out, the cumulative quantity of plastic waste available to enter the marine environment is predicted to increase by an order of magnitude by 2025. Microplastics, at least, can be reduced if more countries enact laws banning their use in personal care products.
“Microbeads can easily be replaced by natural exfoliants like apricot shells, which work better anyway,” Huvet says. “We must pay attention to what industries are doing and push back if necessary.”
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