Scientists in Japan have discovered plastic permanently fused to pieces of coral rubble, creating an unusual material they have called “plasticoral.” The finding raises concerns about chemical pollution, habitat degradation and another possible pathway for plastics to enter marine ecosystems.
Researchers from the University of the Ryukyus discovered five pieces of plasticoral on three beaches on Japan’s Okinawa Island during a marine litter survey in August 2024. Unlike ordinary plastic waste that may simply rest on rocks or coral, the plastic in these samples had melted and adhered permanently to the porous structure of coral rubble.
The researchers believe the plastic may have been melted by a beach fire, although further investigation is needed to confirm how the material formed.
The team described plasticoral as a type of plastiglomerate. Plastiglomerates are materials formed when melted plastic becomes fused with natural materials such as rocks, wood or other debris. However, researchers said the Okinawa samples were unusual because the melted polymers had flowed into and conformed to the intricate, porous skeleton of the coral rubble.
Laboratory analysis showed that four of the samples were made from polyethylene, a widely used plastic found in products including bottles and packaging. The fifth sample consisted of polypropylene, which is commonly used in food containers, bottle caps and other products.
Both types of plastic are widespread in marine environments and can soften or deform when exposed to high temperatures.
The researchers are particularly concerned about what happens when plastic is burned. Burning plastic can release hazardous substances, including dioxins and fine particles. Heating and burning can also cause plastics to break apart into smaller particles, potentially increasing the amount of microplastic entering the surrounding environment.
Although the plasticoral was found on beaches rather than on living coral reefs, scientists said its formation could still have ecological consequences. Coral rubble can provide shelter and habitat for small invertebrates while algae and sponges can grow on its surfaces. These organisms can, in turn, form part of habitats used by fish and other marine life.
When plastic melts onto coral rubble, it may alter the natural surface and reduce its ability to function as a habitat.
The discovery also highlights the growing presence of plastic in marine ecosystems. Large quantities of plastic have accumulated in the world’s oceans while microplastics have been detected across a wide range of environments.
The researchers said plasticoral could potentially become part of a longer-lasting geological record of human plastic pollution, particularly in tropical reef environments. They suggested that such materials could represent an early stage in the transformation of temporary plastic litter into persistent deposits.
The team plans to work with other researchers and members of the public to identify and document plastic pollution, including additional examples of plasticoral.
The discovery adds another dimension to growing scientific concern over how plastic waste interacts with natural materials and ecosystems, particularly in coastal and marine environments.