More than half a million hermit crabs have been killed by becoming trapped in plastic debris on two remote islands, researchers said.

Scientists conducted surveys across a range of sites on the Cocos (Keeling) Islands in the Indian Ocean, where they recorded 508,000 trapped crabs, and Henderson Island in the Pacific, where 61,000 were found.

The numbers falling foul of debris such as plastic bottles is equivalent to one to two crabs per square metre of beach, a significant percentage of the population.

Shells

The problem is likely to be widespread on islands worldwide, seriously affecting hermit crab populations, the researchers said.

The study was led by the Institute for Marine and Antarctic Studies (IMAS) at the University of Tasmania and included researchers from London’s Natural History Museum and the Two Hands Project community science organisation.

The researchers have previously revealed that Cocos and Henderson Islands are littered with millions of pieces of plastic.

Now their research has found that the piles of plastic pollution on island beaches create both a physical barrier for the crabs to navigate and a series of potential deadly traps.

Hermit crabs do not have a shell of their own, instead seeking out available empty shells.

Cost

Because dead crabs trapped in the plastic debris send out a chemical signal to others of their species advertising an available shell, more are attracted to the deadly trap in a “gruesome chain reaction”, the experts said.

Dr Alex Bond, from 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.”

He added: “We all need to consider our actions, especially in relation to the purchase of single use plastic products as we are proving time and time again that the cost of this convenience is immense.”

Impacts

High concentrations of plastic debris are being found on beaches worldwide, where hermit crabs could be expected to encounter the same problems as on the islands studied.

Hermit crabs play an important role in tropical environments by aerating and fertilising soil, dispersing seeds and removing detritus, and are also a key part of marine nature systems.

Losses of hermit crabs on a global scale would cause problems for ecosystems, the researchers warn.

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 has been published open access in the Journal of Hazardous Materials.

This Author

Emily Beament is the PA environment correspondent. Image: warrenski.