A HITCH-HIKERS GUIDE TO RAPA NUI

A HITCH-HIKERS GUIDE TO RAPA NUI

by Sabine Rech – ESMOI

Even though Rapa Nui is one of the most remote places on earth, plastic litter comes here from several sources. While some stems from high-seas fisheries, other litter comes from the distant continental coasts surrounding the South Pacific.

 

Plastic litter is not inert – many different organisms are growing on it. Some of these organisms may have come from coastal communities thousands of kilometres away. Organisms have already been travelling the ocean on floating stuff (a process that is called “rafting dispersal”) formillions of years. In the past, these travellers arrived on volcanic pumice or on long-living tree trunks. ¿So, why are we concerned about organisms arriving now on plastic litter? The answer is simple: The availability and durability of natural rafts was much more limited. Major rafting events were rather exceptional, occurring after volcanic eruptions or after very big floods on continents. Only the hardiest travellers could survive these very long trips. Nowadays a huge armada of plastic litter is floating in the South Pacific and hundreds of plastic items arrive every day on the coasts of Rapa Nui. And with them undesired stowaways may arrive on the island.

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The Rapa Nui ecoregion comprises a vibrant and colorful ecosystem with a rich diversity of marine animals and plants. Many of those are endemic – they occur nowhere else in the world. But the unique ecosystem is threatened by a global problem: Floating plastic garbage. Loads of plastic litter, large and small, are arriving on the shores of Rapa Nui every day.

Microplásticos en la playa de Rapa Nui. / Microplastics on Rapa Nui beach.

Tapa de Nescafé encontrada en Anakena con colonias adjuntas de Jellyella. / Botella de plástico ensuciada de la playa de Baz de Vizcaya.

Tapa de Nescafé encontrada en Anakena con colonias adjuntas de Jellyella. / Botella de plástico ensuciada de la playa de Baz de Vizcaya.

Today no part of the marine environment is free of plastics, including remote islands like Rapa Nui. The death of seabirds and marine animals byingestion of or entanglement in plastic waste is a harrowing and blatant consequence. Rafting of marine organisms on plastics on the other hand, is a much more inconspicuous phenomenon – that might pose a very serious threat to Rapa Nui´s marine ecosystem. The rafting process has only recently moved in the focus of science and the public – and with it comes a first understanding of the possible consequences.Plastics carry their attached stowaways over vast periods of time and distances, even across oceans, and can reach places that are otherwise isolated from human influence.

 

A recent massive event has shown the immense scope of plastic rafting: Big man-made structures like floating docks or entire boatshave been stranding on US shores for several years now.They got detached from Japanese coasts during the 2011 tsunami. When scientists examined the stranded objects, they made a surprising discovery: The much-travelled rafts harboured a richand thriving community of nearly 300 attached species. To the researcher’s astonishment, they had not only made the transoceanic journey alive, buteven reproduced along the way.While clearly a success story for the travelling biota, their arrival poses a serious threat to their new habitat.Newly arriving species may become invasive and thereby harmlocal biodiversity. “Plastic marine debris … is probably one of the great emerging channels for marine invasions” warns Professor James Carlton of the William College in Massachusetts, who studies the Tsunami debris. He emphasizes the importance of continuously monitoring for the arrival of potential invaders, especially in or near harbours. Although the phenomenon has gained increasing attention in the last years, important questions remained unanswered.

Acumulación de objetos de plástico (en su mayoría incrustados por Jellyella) en la playa de Rapa Nui. / Accumulation
of plastic objects (mostly encrusted by Jellyella) on Rapa Nui beach.

Sabine Rech tomando muestras de una boya varada en una playa mediterránea. / Sabine Rech taking samples from a
stranded buoy on a Mediterranean beach.

Ostras de Magallana invasoras atadas a una suela de zapato en el Golfo de Vizcaya. / Invasive oyster Magallana gigas attached to a
shoe sole in the Bay of Biscay.

How important is plastic rafting on a global scale? And: How does it affect remote islands like Rapa Nui?

Over the past years, the search for answers took me to beaches of theNorth Atlantic, Mediterranean, and South Pacific coasts, examining washed-up objects, collecting, separating, counting, storing and identifying plastics and their stowaways. The result was frightening. I found hundreds of rafts with thousands of attached organisms stranded on the beaches. Biodiversity was rich on the plastic rafts, with a community made up of a variety of species, ranging from algae and tiny moss animals (bryozoans) to fully-grown crabs.

The big question is: Do such plastic rafts really transport non-native biota to remote Rapa Nui? The island is located in the central region of the South Pacific Subtropical Gyre and large amounts of plastic fragments from this current system wash up on its beaches. But, are these fragments actually colonized by rafting organisms?

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Unfortunately – yes. In fact, one-third of all plastics studied on Rapa Nuihad been used as rafts – mainly by colonies of the encrusting bryozoans Jellyella. This moss animal is not native, but it is not an invasive species.  Unlike in other regions, no invaders were found on Rapa Nui´s plastic litter. However, this is no all-clear for Rapa Nui. Dr. Martin Thiel from the Nucleo Milenio Ecologia (ESMOI) explains: “Loads of floating garbage from high-sea fishing and the nearby continents arrive on Rapa Nui’s coasts on a daily basis. Even species that have not yet made it to Rapa Nui can now arrive on this garbage.”The absence of invasive species on the beach plastics is probably due to the generally low number of invasive species in the south-eastern Pacific and the scarceness of important transport mechanisms forthese species, such as international shipping. However – the constant flow of plastics from the sea to Rapa Nui is a potential vector for current and future invasive marine species from the continental coasts. It may just be a question of time until one or more of them survive the long journey and manage to colonize the island´s coasts.

Colonization by invading species becomes more and more likely as the number of plastic objects produced and thrown away increases continuously. At the same time, oceanic conditions are changing due to climate change. This allows invasive species to colonize previously unsuitable habitats. The danger of invasive species rafting on plastics will thereforeprobably increase in the future. A drastic reduction of plastic production and use is needed to protect Rapa Nui and the marine environment in general.

Vista ampliada del patinador de mar Halobates sp. (etapa juvenil) y percebes encontrados en artículos de plástico en las playas de Rapa Nui. / Magnified view of the sea skater Halobates sp. (juvenile stage) and barnacles found on plastic items on Rapa Nui beaches.

Jim Carlton haciendo bioincrustación en una boya
Woods Hole. 
/ Jim Carlton biofouling on a buoy Woods Hole.

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