Coastal species form new communities on floating debris

Coastal organisms, such as crabs, barnacles and seaweeds, are not able to live in the open oceans and high seas. They need surf, rocky shores or sandy beaches to provide the living conditions and food they require. Up until now, that is. 

Marine scientists have recently found that coastal species can use floating plastic debris to survive in the open ocean. The organisms can potentially travel, by rafting on pieces of plastic, to areas that are thousands of kilometers from their natural homes. The scientists call these communities of floating coastal species “neopelagic,” signifying that these are new communities which are found in the open oceans.

In a commentary published today in Nature Communications, scientists report on the communities of coastal species growing on floating debris in the North Pacific Subtropical Gyre, more commonly known as the “Great Pacific Garbage Patch.”

“The issues of plastic go beyond just ingestion and entanglement,” said Linsey Haram, lead author of the article and former postdoctoral fellow at the Smithsonian Environmental Research Center (SERC). “It’s creating opportunities for coastal species’ biogeography to greatly expand beyond what we previously thought was possible.”

Plastic pollution emanating from continental coasts is driven by oceanic currents and eventually may collect in regions where rotating currents, or gyres, trap the floating debris. There are at least five plastic-infested gyres, or “garbage patches” in the world’s oceans. 

The North Pacific Subtropical Gyre, between California and Hawai’i, is the largest of the garbage patches, consisting of an estimated 79,000 metric tons of plastic floating in an area of over 610,000 square miles. Although the debris contains nets, buoys, plastic bottles and assorted litter, much of the waste consists of microplastics that are too small to be seen with the naked eye. 

The drifting plastics carry along coastal species from their natural home regions but, until recently, confirmed sightings of these organisms living on plastic in the open ocean were rare. 

During the first year of COVID, a team of sailors from Ocean Voyages Institute, a nonprofit organization that clears up plastic pollution while on sailing expeditions, collected a record-breaking 103 tons of plastic debris from the North Pacific Subtropical Gyre. Mary Crowley, founder of Ocean Voyages Institute, sent some of the plastic samples to SERC’s Marine Invasions Lab, where Haram analyzed the species that had colonized them. 

Haram, now a fellow at the American Association for the Advancement of Science, found many coastal species – including anemones, hydroids and shrimp-like amphipods – not only surviving, but thriving, on the marine plastic. The idea that coastal communities can live successfully away from coastal waters has led marine scientists to a paradigm shift in thinking.

“The open ocean has not been habitable for coastal organisms until now,” said SERC senior scientist Greg Ruiz, who heads the Marine Invasions Lab where Haram worked. “Partly because of habitat limitation – there wasn’t plastic there in the past –and partly, we thought, because it was a food desert.”

Clearly, both ideas will need to be re-evaluated. And now, the scientists foresee new problems relating to the presence of these coastal species in the open oceans. The open ocean has plenty of its own native species, that also colonize floating debris. The arrival of new coastal organisms could disrupt these ocean ecosystems that have remained undisturbed for millennia.

“Coastal species are directly competing with these oceanic rafters,” Haram said. “They’re competing for space. They’re competing for resources. And those interactions are very poorly understood.”

Another problem relates to the potential impacts that drifting coastal species could have if they made landfall on faraway coastlines and became invasive. Scientists have already seen that floating debris from the Japanese tsunami in 2011 carried organisms all the way from Japan to North America. Species that invade new coasts in this way could damage natural communities and disturb the ecological balance.

“Those other coastlines are not just urban centers … That opportunity extends to more remote areas, protected areas, Hawaiian Islands, national parks, marine protected areas,” Ruiz said.

The authors still do not know how common these “neopelagic” communities are, whether they can sustain themselves or if they even exist outside the North Pacific Subtropical Gyre. But the world’s dependence on plastic continues to increase. Scientists estimate cumulative global plastic waste could reach over 25 billion metric tons by 2050. 

With fiercer and more frequent storms likely in future, thanks to climate change, the researchers expect even more of that plastic will get pushed out to sea. Colonies of coastal rafters on the high seas will likely only become larger and more widespread. This long-overlooked side effect of plastic pollution, the authors said, could soon transform life on land and in the sea.

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By Alison Bosman, Earth.com Staff Writer