If you go to the beach, you’re likely to see some form of plastic pollution scattered in the waves or sprinkled among the sand grains. A bottle cap fragment here, a transparent piece of packaging there. But researchers have identified a new, and perhaps more permanent type of plastic pollution, one that incorporates itself right into the rocky shoreline: “plasticrust,” a veneer of plastic encrusted right onto wave-licked rocks.
Ignacio Gestoso, a marine ecologist at the MARE-Marine and Environmental Research Center on the Portuguese island of Madeira, first noticed the strange crusts on the volcanic island’s shoreline rocks in 2016. The light blue films were plastered onto the rock like old chewing gum grafted onto a sidewalk. Gestoso and his colleagues took some photos and quick samples, but figured the sighting was a one-off. The next year, the researchers saw that the crusts were still there. Early this year, they returned to the spot to find more area covered in the mysterious substance, now in multiple colours. So, the team decided to take measurements and collect more samples to see what they were dealing with.
By randomly sampling rocky areas of the shoreline, the researchers found that over three years, the crusts had gone from a single sighting to covering nearly 10 percent of the rocks’ surfaces. Chemical analysis of the stuff revealed that it was polyethylene, an extremely common plastic often used in single-use packaging and food containers.
“[The crusts] likely originated by the crash of large pieces of plastic against the rocky shore, resulting in plastic crusting the rock in a similar way algae or lichens do,” Gestoso told Earther.
But plasticrust may have more immediate impacts. On Madeira, the plasticrust is gradually replacing natural biological crusts and films on the rocks—surfaces that inter-tidal animals like barnacles and snails adhere to and feed from. Gestoso’s team found that an algae-eating species of winkle sea snail was nearly as abundant on the plasticrusts as it was on normal surfaces, suggesting that the molluscs might not avoid plasticrusts, but graze on the algae that settle right on top. That raises the possibility that they’re ingesting some of the plastic in the process.