Shoreline Scavenger Shows Gene-Level Effects After Eating Plastic Foam

Researchers at Kyushu University in Japan have found that wharf roaches — common shoreline scavengers that act as a natural "cleanup crew" on beaches — show measurable biological changes after eating expanded polystyrene, or EPS, a lightweight foam that is a major component of marine plastic pollution. The study, published in Marine Pollution Bulletin, used multi-omics analysis to examine gene activity and gut microbes in the digestive tracts of wharf roaches (Ligia species) that had ingested the foam.

The team, led by Professor Emeritus Yuji Oshima of Kyushu University's Faculty of Agriculture, first tested whether eating EPS affected the roaches' survival. Foam-fed roaches lived for an average of 27.8 days compared with 31.6 days for unfed control animals, a difference the researchers said was not statistically significant. Oshima said earlier fieldwork had shown that wharf roaches chew EPS and excrete it as much smaller fragments, suggesting the animals can help turn large pieces of foam into microplastics, and that the team wanted to find out whether swallowing foam comes at a biological cost for these shoreline scavengers.

Gene expression in the digestive tracts of EPS-fed roaches showed higher activity in three detoxification enzymes — cytochrome P450, UDP-glucuronosyltransferase and sulfotransferase — along with a gene involved in DNA repair, while several digestive enzyme genes were expressed at lower levels. Overall gut microbial diversity did not differ between the two groups, but three types of methane-producing archaea and one family of bacteriophages showed up only in the EPS-fed roaches.

Oshima said the foam-fed animals appeared healthy and had lifespans similar to the controls, but their guts showed differences in the expression of genes involved in chemical defense — showing that "no visible harm" does not necessarily mean "no biological effect." He said further work is needed to determine whether these gene-expression changes lead to functional effects in the animals, and that the findings underline the importance of managing EPS waste more carefully.