People often consider remote islands to be vestiges of pristine wilderness. But in stark contrast, the Cocos (Keeling) Islands and Henderson Island are drowning in plastic trash.

A recent study published in the Journal of Hazardous Materials estimates that more than half a million hermit crabs perish in accumulated plastic pollution on the beaches of these heavily polluted remote islands alone each year.

Plastic Trash Coats Beaches

The Cocos (Keeling) Islands, made up of 27 islands, sit 2,760 kilometers (1,715 miles) northwest of Perth in the Indian Ocean.

A quarter-spin of the globe away, uninhabited Henderson Island is located in the Pacific, halfway between New Zealand and Chile.

The atoll, a UNESCO World Heritage Site, is on the western perimeter of the South Pacific Gyre. It’s a major source of the marine trash that coats its beaches.

“The significant quantities of debris on the beaches, and throughout the coastal vegetation, create a significant barrier which strawberry hermit crabs (Coenobita perlatus) encounter during their daily activities,” the paper says.

“This is important for countless other islands worldwide where crabs and debris overlap, as crabs play a crucial role in the maintenance of tropical ecosystems.”

Plastic trash on a beach on one of the remote Cocos (Keeling) Islands in the Indian Ocean. Image courtesy of Lavers et. al., 2019 (CC BY-NC-ND 4.0).

The Marine Debris Problem

Marine plastic trash is a growing concern, with significant plastic accumulation on the high seas. Further, researchers are documenting plastic items at depths of nearly 11,000 meters (36,100 feet).

The paper says plastics account for more than 95% of debris observed “at sea, on beaches and along river banks.”

It turns out, plastic trash can persist in the environment for decades, killing, maiming or sickening wildlife that become trapped or entangled or that mistake it for food.

While marine plastic pollution is widely studied, until now little published research directly links it to species decline and wider environmental damage. Traditional research also typically doesn’t investigates the risk it poses on beaches and in nearby vegetation.

“These results are shocking but perhaps not surprising, because beaches and the vegetation that fringes them are frequented by a wide range of wildlife,” lead author Jennifer Lavers, a marine eco-toxicologist at the University of Tasmania’s Institute for Marine and Antarctic Studies, said in a news release about the study.

“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.”

Map shows the study sites (blue circles) and sampling regions (red). Left: Cocos (Keeling) Islands (North Keeling Island is not shown on inset map); right: Henderson Island. Click here to enlarge. Image courtesy of Lavers et. al., 2019 (CC BY-NC-ND 4.0).

How Researchers Approached the Study: the Process

The research team surveyed beaches on Henderson Island and the Cocos Islands in 2017 and 2019. Researchers were on the lookout for plastic containers that had openings and were positioned at an angle.

Doing so would allow them to figure out how many containers were potential entrapments for crabs. They then counted the number of both living and dead hermit crabs inside those containers.

The researchers then used the survey data to predict total entrapment rates across the islands.

On Henderson Island there were approximately 38 million pieces of trash trapping and killing an estimated 61,000 crabs each year. On the Cocos Islands there were 414 million pieces of trash entrapping 508,000 crabs each year.

That worked out to 239 pieces of trash per square meter on the beaches of Henderson Island. It also worked out to 713 pieces of trash per square meter on the Cocos Islands.

Plastic trash lures hermit crabs by the smell of decaying crabs — and the consequences are clear. In one particularly lethal container on Henderson, the team found 526 trapped hermit crabs.

Importance of Hermit Crabs

Humble hermit crabs are crucial to terrestrial and marine ecosystems. On land, they disperse seeds and create carbon-rich soil micro-habitats by burrowing and collecting leaf litter, which help forests thrive. Their contributions are particularly important on the Cocos Islands and Henderson Island, which lack native ground predators that would otherwise help with those tasks.

The paper also submits that hermit crabs are an important economic resource: the Cocos Islands are home to at least 26 crab species, including several hermit crab species, which could provide an opportunity for wildlife tourism. So a disruption of hermit crab populations could have both ecological and economic effects.

Hermit crabs are common in coastal environments worldwide. The paper hypothesizes that on beaches where the crabs coexist with heavy plastic pollution, there is a risk that they may meet the same fate.

“High concentrations of debris are now being encountered on beaches around the world, many of which are also home to hermit crabs that can be expected to interact with plastic pollution in the same way as those we studied,” Lavers said.

Crabs that became trapped and died inside a plastic drink bottle on one of the Cocos (Keeling) Islands. Image courtesy of Lavers et. al., 2019 (CC BY-NC-ND 4.0).

What The Results Mean, According to this Plastic Pollution Expert

Kristian Syberg, a marine plastic pollution expert at Roskilde University in Denmark, said the hermit crab study provides a comprehensive impact assessment of plastic trash in heavily polluted sites, or hotspots.

“Through this study it is feasible to say that ‘hot-spot’ areas of macro plastic pollution do pose a risk,” Syberg, who was not involved in the study, said.

Syberg said documenting the effect of plastic trash on wildlife populations is very difficult, particularly in remote locations. Nevertheless, he said, “widespread risk from both macro and micro plastics is likely within the next century if current patterns are not changed.”

Some of the 526 hermit crab shells found inside a single plastic container on Henderson Island. Image courtesy of Lavers et. al., 2019 (CC BY-NC-ND 4.0).

Author Grace Dungey wrote this article and originally published it at Mongabay. To fit theRising’s editorial guidelines, our staff has lightly revised this article and republished it with permission.