Hermit crabs are mistaking plastic for shells and the problem has killed more than half a million of the crustaceans, a new study by the Natural History Museum has found.
The creatures do not make their own shells but instead move from discarded shell to discarded shell as they grow. They are not used to plastic in their environment so do not know to avoid it.
Once they crawl into a piece of plastic debris, the crabs frequently get stuck and starve to death.
Researchers said that if even just one crab mistakes some plastic debris for a shell, this can cause a “gruesome chain reaction”, as when one dies it emits a signal alerting others there is a new shell. This causes scores of crabs to come scurrying across the island and fall into the plastic trap.
The team carried out several surveys across a range of sites to ascertain of how many containers there were, including how many were open, how many were in a position likely to trap crabs, and how many contained trapped crabs.
The results recorded 61,000 crabs trapped in debris on Henderson Island and 508,000 on the Cocos (Keeling) islands. This equated to 1-2 crabs per m2 of beach falling foul of debris, a significant percentage of the population.
Around 570,000 hermit crabs become entrapped in debris on two tropical islands – the Cocos (Keeling) Islands in the Indian Ocean and Henderson Island in the Pacific.
Dr Alex Bond, Senior Curator in Charge, Birds, The Natural History Museum, said, “The problem is quite insidious really, because it only takes one crab.
“Hermit crabs do not have a shell of their own, which means that when one of their compatriots die, they emit a chemical signal that basically says ‘there’s a shell available’ attracting more crabs who fall into the containers and die, who then send out more signals that say there are more shells available.
“Essentially it is this gruesome chain reaction.”
The results come from a first of its kind study led by the Institute for Marine and Antarctic Studies (IMAS) at the University of Tasmania and including researchers from London’s Natural History Museum as well as the Two Hands Project community science organization.
IMAS researcher Dr Jennifer Lavers, who led the study said, “These results are shocking but perhaps not surprising, because beaches and the vegetation that fringes them are frequented by a wide range of wildlife.
“It is inevitable that these creatures will interact with and be affected by plastic pollution, although ours is one of the first studies to provide quantitative data on such impacts.”
The study is published in the Journal of Hazardous Materials.