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Henderson atoll: an expedition to the uninhabited island harbouring 38 million pieces of plastic
The uninhabited Henderson Island is one of the Pitcairn Islands, in the middle of the Pacific Ocean. Despite its isolation, the beaches of this atoll are thought to harbour one of the highest densities of plastic found anywhere in the world.
In June Dr Alex Bond, senior curator in charge of birds at the Museum, will travel to Henderson Island to investigate the impact of this plastic tide on the local wildlife, from the sea birds that are eating it to the hermit crabs that are using it as a home.
Where is Henderson Island?
Positioned halfway between Peru and New Zealand, Henderson Island is a raised coral atoll sitting in the middle of the South Pacific Gyre. This is a roughly circular system of ocean currents that runs between the western coast of South America and the eastern coast of New Zealand.
The currents concentrate the rich nutrients that run off the land, but in recent decades it has become more apparent that they are also accumulating much of the trash and debris that makes its way into the South Pacific. This means that Henderson Island has found itself in a hotspot for plastic pollution.
Henderson Island is one of the Pitcairn Islands, and has no permanent settlement on the outcrop. It lacks of many of the invasive species that have decimated wildlife populations on other remote islands. For a long time it was thought that Henderson Island was one of the few remaining island ecosystems free from the majority of human impacts.
Henderson Island in the Pacific was designated a UNESCO World Heritage Site in the 1980s due to its near-pristine state © Angela K. Kepler/Wikimedia Commons
That was until an expedition in 2015 revealed that the beaches are actually covered in an exceptional amount of plastic debris. The team, which included Alex and his colleague Dr Jennifer Lavers, had found that there was an estimated 38 million pieces of plastic, at an astonishing density of 672 items per square metre.
In a 2017 paper published in the Proceedings of the National Academy of Sciences documenting the state of the island, they wrote:
'The density of debris was the highest recorded anywhere in the world, suggesting that remote islands close to oceanic plastic accumulation zones act as important sinks for some of the waste in these areas.
'As global plastic production continues to increase exponentially, it will further impact the exceptional natural beauty and biodiversity for which remote islands have been recognised.'
Splendid isolation in the Pitcairn Islands
Henderson Island is part of the Pitcairn Islands group, which is a British Overseas Territory.
While the island is now uninhabited, Polynesians are known to have arrived on the island around 1,000 years ago, but limited resources led to them abandoning the outcrop after just a few hundred years.
Amongst the rubbish on Henderson researchers have found the tracks of turtles as they search for nesting sites © Melva Evans
The relatively flat island is now covered in a tangled scrub forest. Of the 51 flowering plants found there, 10 are endemic, meaning that they are found nowhere else in the world.
These forests are also home to many invertebrates, up to a third of which are unique, as well as four endemic birds: the Henderson lorikeet, fruit-dove, reed warbler and crake. The remoteness of the coral atoll has also seen it become an internationally important breeding site for many species of sea birds.
Henderson Island is so ecologically important that it was designed as a UNESCO World Heritage Site in 1988.
According to the organisation, 'As one of the last near-pristine limestone islands of significant size in the world, Henderson Island retains its exceptional natural beauty with its white, sandy beaches, limestone cliffs, and rich and almost undisturbed vegetation.
'With its vast numbers of breeding seabirds, the island is an outstanding example of a raised and forested oceanic coral atoll with its fundamental features intact.'
Warning signs
This assessment of the island, however, is in stark contrast to what was seen in 2015.
Alex and Jennifer found that the 'white, sandy beaches' were in fact covered in trash, mostly plastic. By studying a small section they estimated that over 17 US tons of debris littered the beaches, the highest density recorded anywhere in the world. This is just a fraction of the plastic waste produced globally.
Much of the plastic pollution on Henderson Island comes from industry, but also includes many other common items such as plastic shoes © Melva Evans
'The 17.6 [US] tons of anthropogenic debris estimated to be present on Henderson Island account for only 1.98 seconds' worth of the annual global production of plastic,' the 2017 study concluded.
'As global plastic production continues to increase exponentially, it will further impact the exceptional natural beauty and biodiversity for which this island and many other UNESCO World Heritage Sites have been recognised.'
On this new expedition, Alex and Jennifer hope to discern what these impacts on the local wildlife might be.
For example, Hermit crabs on Henderson Island are known to use plastic containers instead of shells. What effect this is having on the crustaceans, how they live in these human-made homes and the risk they may face from the chemicals the plastics leach, is still unknown.
The team will also look at the impact on the birds that nest there. They will also attempt a small beach clean-up to not only assess the feasibility of such actions but also study the rate at which new plastic is washed back onto the beaches.
The expedition is being supported by generous assistance from The Pew Trusts, Valpak, the Zoological Society of London, Blue Belt Programme (UK government), Architectural & Community Planning Inc, Schwab Charitable, Toughsheet Environmental and the Howell Conservation Fund, with the aim of studying and raising awareness of global ocean plastics and promoting the Pitcairn Island Marine Reserve.
