More than half a million hermit crabs died after becoming trapped in plastic debris on two remote island groups, prompting concerns that the deaths could be part of a global decline in the species.
The groundbreaking study found that 508,000 crabs died on the Cocos (Keeling) Islands archipelago in the Indian Ocean, along with 61,000 on Henderson Island in the South Pacific. Previous studies have found high levels of plastic pollution at both sites.
Researchers from the University of Tasmania's Institute for Marine and Antarctic Studies (Imas), the Natural History Museum in London, and the community scientific organization Project Dos Manos, found that one or two crabs per square meter of beach were being wiped out by litter. .
They surveyed sites on the Cocos and Henderson Islands for open plastic containers, with the opening tilted upward in a way that prevents the crab from leaving, and counted the number of crabs caught in each. They then extrapolated their results across 15 other islands in the Cocos archipelago.
The problem was exacerbated as hermit crabs used the scent of recently deceased crabs to track available shells, leading to multiple crabs being trapped in the same area; in one case, 526 crabs were found in a single plastic container.
Dr. Alex Bond, Senior Curator of the Natural History Museum and one of the report's researchers, said: "The problem is quite insidious, because it only takes one crab to start it."
"Hermit crabs don't have a shell of their own, which means that when one of their compatriots dies, they give off a chemical signal that basically says there is a shell available, which attracts more crabs ... essentially this is a horrible chain reaction."
Hermit crabs are an important part of tropical environments as they disperse seeds and aerate and fertilize the soil, so their decline could have a significant impact on surrounding ecosystems.
The Cocos Islands and Henderson Island are highly polluted, with pieces of debris measuring 414 m and 38 m respectively, found on their beaches and in nearby vegetation.
Bond said the potential of plastics to cause damage to land was underrecognized: “In the ocean, it becomes entangled and ingested by wildlife; on land it acts as a trap, as we have seen, but it can also be a physical barrier for species that move on the ground ”.
Imas researcher Dr. Jennifer Lavers, who led the study, said: “These results are shocking but perhaps not surprising, because the beaches and surrounding vegetation are frequented by a wide range of wildlife.
"It is inevitable that these creatures interact with and be affected by plastic pollution, although ours is one of the first studies to provide quantitative data on such impacts."
The research team says their findings show the need for urgent research on the death rate of hermit crabs around the world.