This passage is adapted from Matthew Savoca, “The oceans are full of plastic, but why do seabirds eat it?” ©2016 by Matthew Savoca.
Plastic debris can be found in oceans around the world. Scientists have estimated that there are over five trillion pieces of plastic, weighing more than a quarter of a million tons, floating at sea globally. Plastic does not biodegrade, but at sea large pieces of plastic break down into increasingly smaller fragments that are easy for animals to consume. Animals that mistake plastic for a meal may suffer from malnutrition, intestinal blockage, or slow poisoning from chemicals in or attached to the plastic.
Despite the pervasiveness and severity of this problem, scientists still do not fully understand why so many marine animals make this mistake. It has been commonly assumed, but rarely tested, that seabirds eat plastic debris because it looks like their natural prey. However, we propose a new explanation: for many imperiled species, marine plastic debris also produces an odor that the birds associate with food.
Perhaps the most severely impacted animals are tube-nosed seabirds, a group that includes albatrosses, shearwaters, and petrels. Many are at risk of extinction; according to the International Union for the Conservation of Nature, nearly half of the approximately 120 species of tube-nosed seabirds are either threatened, endangered, or critically endangered. As well, these birds are pelagic: they often remain at sea for years at a time, searching for food over hundreds or thousands of square kilometers of open ocean. Although there are many fish in the sea, areas that reliably contain food are very patchy—tube-nosed seabirds are searching for a needle in a haystack when they forage. They may be searching for fish, squid, krill, or other items, and it is possible that plastic debris visually resembles these prey. But we believe that tells only part of a more complex story.
In the early 1970s, Dr. Grubb Jr. showed that tube-nosed seabirds use their powerful sense of smell to find food effectively. Later, Dr. Nevitt and colleagues found that certain species of tube nosed seabirds are attracted to dimethyl sulfide (DMS), a naturally scented sulfur compound. DMS comes from marine algae, which produce a related chemical called DMSP inside their cells. When those cells are damaged—for example, when algae die, or when marine grazers like krill eat it—DMSP breaks down, producing DMS. The smell of DMS alerts seabirds that food is nearby—not the algae, but the krill that are consuming the algae.
Dr. Nevitt and I wondered whether these seabirds were being tricked into consuming marine plastic debris because of the way it smelled. To test this idea, my co-authors and I created a database collecting every study we could find that recorded plastic ingestion by tube-nosed seabirds over the past 50 years. This research showed that species of birds that use DMS as a foraging cue eat plastic nearly six times as frequently as species that are not attracted to the smell of DMS while foraging.
To further test our theory, we needed to analyze how marine plastic debris smells. To do so, I took beads of the three most common types of floating plastic—polypropylene and low- and high-density polyethylene—and sewed them inside custom mesh bags, which we attached to two buoys off of California’s central coast. We hypothesized that algae would coat the plastic at sea, a process known as biofouling, and produce DMS.
After the plastic had been immersed for about a month at sea, we retrieved it and brought it to a lab. There we used a gas chromatograph, specifically built to detect sulfur odors, to measure the chemical signature of our experimental marine debris. Sulfur compounds have a very distinct odor; to humans they smell like rotten eggs or decaying seaweed on the beach, but to some species of seabirds DMS smells delicious!
As proposed, every sample of plastic we collected was coated with algae and had substantial amounts of DMS associated with it. We found levels of DMS that were higher than normal background concentrations in the environment, and well above levels that tube-nosed seabirds can detect and use to find food. Our results provide the first evidence that, in addition to looking like food, plastic debris may also confuse seabirds that hunt by smell.
Question
What does the word chromatograph most likely mean in paragraph 7?
Responses
A a device that measures and analyzes a compounda device that measures and analyzes a compound
B a colorful device that cleans the smell of a compounda colorful device that cleans the smell of a compound
C a calibrated device that is only used under the seaa calibrated device that is only used under the sea
D a calibrated device that is only used on landa calibrated device that is only used on land
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1 answer
The word "chromatograph" in paragraph 7 most likely means:
A. a device that measures and analyzes a compound
This interpretation is supported by the context in which it is used, indicating that the device was designed for measuring the chemical signature of the experimental marine debris.
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