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Plastic debris killing half a million crabs on remote islands

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.

•Around 570,000 hermit crabs become entrapped in debris on two tropical islands.
•Accumulating debris is likely to seriously impact hermit crab populations.
•Entrapment is likely widespread on islands worldwide causing global species decline.

An estimated 570,000 hermit crabs have been killed on the Cocos (Keeling) Islands in the Indian Ocean and Henderson Islandin the Pacific after being trapped in plastic debris. 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. Whilst considerable attention has been given to plastic pollution in the marine environment, little research has so far been done into the risk that marine pollution poses to wildlife.

The researchers, who previously revealed that Cocos and Henderson islands are littered with millions of pieces of plastic, found that piles of plastic pollution on beaches create both a physical barrier and a series of potentially deadly traps for hermit crabs.

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.

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.'

High concentrations of plastic debris are now being found on beaches worldwide, many of which are also home to hermit crabs that can be expected to interact with plastic pollution in the same way as those studied.

IMAS researcher Dr Jennifer Lavers, who led the studysaid, ‘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 thefirst studies to provide quantitative data on such impacts.’

Hermit crabs play a crucial role in the health of tropical environments by aerating and fertilising soil, and dispersing seeds and removing detritus, as well as being a key part of the marine ecosystem. It is feared that comparable hermit crab losses on a global scale would have important implications for ecosystems.

Dr Bond, added, ‘We don’t really know how many hermit crabs are living on these islands, but the simple thing is that on Cocos there are now half a million fewer hermit crabs than there would be otherwise’

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.’

The team state that the global mortality of hermit crabs is undocumented and likely to be substantial requiring urgent investigation. The study Entrapment in plastic debris endangers hermit crabshas been publishedopen accessin the Journal of Hazardous Materials.

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This study also included researchers from the Two Hands Projectand the plastic survey on the beaches of Cocos (Keeling) Islands was assisted by Sea Shepherd’s Marine Debrisand the Tangaroa Blue Foundation.The Natural History Museumexists to inspire a love of the natural world and unlock answers to the big issues facing humanity and the planet. It is a world-leading science research centre, and through its unique collection and unrivalled expertise it is tackling issues such as food security, eradicating diseases and managing resource scarcity.

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