Concentrations of Garbage Patch Plastic Estimated


In the summer of 1972, Scripps Institution of Oceanography, UC San Diego, biological oceanographer Elizabeth Venrick and her colleagues were stuck in the middle of the Pacific Ocean. Specifically, they were stuck in the North Pacific Gyre, an area between Hawaii and California where four currents converge, causing floating debris to cluster. Venrick and the other scientists were there to conduct an ecological study when the ship’s winch broke, stalling their research.

Stuck in the gyre with no science to do, Venrick and her colleagues were resting on the bow of the ship just to pass the time, enjoying the scenery, when they began counting the pieces of plastic flotsam they saw. As their counts got higher and higher, they became concerned. They began keeping a scientific count, recording size, shape, type, and location of each piece of plastic flotsam. By the time their engine was fixed, they had the first scientific record of plastics in what is now known as the “Great Pacific Garbage Patch,” an account Venrick and her colleagues published in Nature in January 1973.

In recent years, this ocean garbage patch has become a symbol of consumer waste, and received a great deal of publicity. Search the web for the term “North Pacific Gyre” and images of endless plastic waste and dead birds with their stomachs full of plastic are among the first items to appear. These pictures are commonly used to attract support for ocean and beach cleanup campaigns.

Miriam Goldstein, a recent Scripps Institution of Oceanography graduate, cited Venrick’s 1973 study in her own paper, a new record of the amount, size, and distribution of plastic in the North Pacific Gyre, published this month in PLOS ONE.
“This issue is something that a lot of people want to take action on, which is great, but in order to be successful, we need a metric to measure these efforts,” said Goldstein, who’s now serving as a Knauss Marine Policy Fellow in Washington D.C. In this paper, she and her coauthors report on visual observations and collections of debris in the North Pacific Gyre
over the course of two cruises, the Scripps Environmental Accumulation of Plastic Expedition (SEAPLEX) on the Scripps research vessel New Horizon in August 2009, and the EX1006 Always Exploring Expedition in October 2010 on the NOAA ship Okeanos Explorer.

From their observations and collections, they found that the average plastic distribution was 0.448 particles per square meter (4.8 per square foot) on their first cruise, and 0.021 particles per square meter (0.22 per square foot) on the 2010 cruise.  Because the collections of debris using fine-mesh nets were so shallow, the concentrations were measured in terms of surface area. The measured concentrations were highly variable, not just between the two cruises but also over the entire area sampled.

“Plastic is very ‘patchy.’ In some areas there is a lot and some have very little. This means that to have an accurate picture [of plastic distribution] you need as many as several hundred samples,” depending on the size of the area one is interested in, Goldstein said.

The results of these cruises highlight the need for substantial quantitative monitoring of debris, just to be able to determine if plastic concentrations are increasing or decreasing over time.

While she was on these research cruises, Goldstein also collected a variety of organisms she found growing on the debris, including some gooseneck barnacles, and preserved them for later analysis. Some months after the cruise, she pulled these samples out for identification, which required her to dissect the barnacles.

“ I thought, well, I’m opening these guys up anyway, I might as well see what they’re eating,” Goldstein said, “And as soon as I opened the first barnacle, out popped a bright blue piece of plastic!”

Surprised, she opened the rest of the barnacles and found many of them had ingested plastic as well.  Since she hadn’t collected the barnacles with any particular experiment in mind, Goldstein didn’t have enough specimens to know how common this phenomenon was.

Goldstein contacted a collaborator, Deb Goodwin, at the Sea Education Association, and asked her to collect some more samples. Soon they had almost 400 specimens, and they found plastic in the intestines of about one-third of them. The results of this study were published in PeerJ in October 2013. This is the first paper that has documented plastic ingestion by invertebrates, as most research so far has been focused on vertebrates such as seabirds, sea turtles, and marine mammals.

In many of the barnacles Goldstein found plastic packaged in fecal pellets, ready to be excreted, which is good news because it means the plastic isn’t blocking their intestines. However, this also suggests barnacles are likely ingesting more plastic than dissections can account for.

“This barnacle study shows that plastic is really widespread and is being ingested by invertebrates. The next step is to find out what this really means, and what the large-scale ecosystem implications are,” Goldstein concluded.

– Mallory Pickett is a master’s student in the lab of chemical oceanographer Andreas Andersson at Scripps Institution of Oceanography, UC San Diego

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