Science in Mind

A new ecosystem: the ‘plastisphere’ adrift in the ocean

Rocky Hadler monitors Neuston net to collect floating plastic for study while students practice celestial navigation with sextants.
Rocky Hadler monitors Neuston net to collect floating plastic for study while students practice celestial navigation with sextants.courtesy of Erik Zettler, Sea Education Association

Scientists have probed the diversity of life in all sorts of ecosystems, from inside our guts to the sediments beneath the ocean floor. Now, a small group of Massachusetts scientists are eyeing a new frontier: the flotilla of tiny pieces of plastic adrift on ocean surf.

A new study describes the “plastisphere”—the microbial communities that hitch rides on confetti-sized bits of plastic that litter ocean waters. The authors discovered a thriving, miniature world aboard the microplastic “reefs,” where communities of bacteria and other microbes create energy from sunlight, reproduce, and prey on one another.

Researchers at three Woods Hole-based institutions worked together to try and better understand what role these tiny bits of plastic played in the larger ocean ecosystem in the study, published in the journal Environmental Science and Technology. Among their discoveries is the surprising finding that the communities are distinctly different from the ones that slosh along in nearby ocean water. And at least one kind of plastic was dominated by a member of a group of bacteria commonly associated with various diseases, including cholera. They could not tell exactly which species was present and plan to do further studies to try and hone in on its identity.

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Plastic marine debris pieces picked from net and drying before archiving Erik Zettler/Sea Education Association

“The thing that impressed me the most is that it is a little world unto itself,” said Linda Amaral-Zettler, an associate scientist at the Marine Biological Laboratory, a research institution based in Woods Hole. “How does it ultimately affect organisms eating it—and ultimately us? We eat shellfish and fish. .. I think there’s a much broader issue here that’s come to our attention.”

To do their work, scientists took two cruises, one that set out eastward from Bermuda in 2010 and another that departed St. Croix in the U.S. Virgin Islands and sailed to Woods Hole in 2012. They threw a net overboard to skim the ocean’s surface and retrieved hundreds of tiny bits of plastic. They performed DNA analysis and used an electron microscope to analyze the life on board, and used a kind of analysis called spectroscopy to figure out the chemical composition of the plastic, which gave hints about the origins of the waste. Different types of plastic are typically used in consumer products. A milk jug may be made of a different polymer than a yogurt container, for example.

A variety of single-celled organisms forming a microbial “reef” on a piece of plastic from the open ocean. Image taken with electron microscope.Erik Zettler/Sea Education Association

The scientists hope that the study can begin to shed light on how plastic contributes to the ocean ecosystem. Plastic has particular properties that make it an interesting ocean substrate—microbes can stick to its surface, and it tends to spend time in coastal waters where runoff and waste enter the ocean. That, combined with the fact that it sticks around in the environment, mean that it might be playing an ecologically significant role in ferrying bacteria around the ocean.

The scientists are currently trying to understand exactly which pathogens might dwell on sea plastic, and why the disease-associated bacteria was so dominant on one sample. Ultimately, they would like to understand what role, if any, those microbes could play in marine and even human health, given that sea creatures might ingest the tiny pieces of plastic.

“Plastic is the major form of debris in the ocean,” said Erik Zettler, associate dean of the Sea Education Association, a nonprofit focused on ocean education based in Woods Hole and one of the authors of the paper. “It has a very long lifespan, not like a piece of wood or a feather that degrades over months and disappears—plastic persists for years, perhaps decades.”

To follow up their work, the researchers are working to find out how plastic caught in ocean gyres gained its unique “plastisphere” in the first place. How did microbial communities so different than the ones in surrounding ocean water take up residence on these tiny plastic islands?

They are tethering bits of plastic in coastal waters to see what kinds of microbes take up residence on the surface of plastic. That could help explain how the particular colonies of bacteria and other microbes latch onto the pieces of drifting trash.

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