Whether it’s steak and potatoes or spaghetti and meatballs, the smell of dinner can be irresistible. Certain species of seabirds have a similar reaction to scent of food. They use a particular odor to track down a meal. But that can be a problem as more plastic trash finds its way into the ocean. Plastic can absorb a scent that should point to prey. And this can trick the birds into eating that plastic, researchers now report.
Plastic is a huge problem for ocean animals, notes Gabrielle Nevitt. She is a zoologist at the University of California, Davis. When animals eat plastic, it can make them sick. It might even kill them. It has not been clear why they have been eating it, though. Especially because plastic doesn’t look like sea-based food.
Nevitt and colleagues started to think about what other senses, aside from sight, are important to ocean animals. To seabirds, such as petrels and albatrosses, “smell is super important,” she says. To find food, they rely on the odor that comes from a chemical called dimethyl sulfide (Dy-METH-ul SUL-fyde), or DMS. It is released into the air and the water when single-celled ocean life called phytoplankton are eaten or crushed. “To us, DMS smells a bit like seaweed or like an oyster,” Nevitt says. To the birds, it smells like dinner.
Studies have shown that phytoplankton and other tiny critters can grow on plastic in the ocean. Scientists call this biofouling. Earlier research had shown that seabirds such as petrels eat a lot of plastic. Nevitt and colleagues wanted to know if there was some connection to that biofouling.
To find out, the researchers put mesh bags of plastic beads into the ocean. They tethered the beads to ocean buoys for three weeks. When they came back to pick them up, the beads were covered in slime. And that slime gave off the scent of DMS. The odor was so strong that petrels and similar seabirds would definitely be able to smell it, the scientists report.
Nevitt and colleagues then used statistics to check the connection among the seabirds, DMS and how much plastic birds ate. Species that hunt using DMS ate much more plastic than did birds that don’t use this scent to find food. The researchers reported their finding November 9 in Science Advances.
This idea that plastic can fool birds into thinking it is food is ominous, says Alistair Dove. He is a marine scientist at the Georgia Aquarium in Atlanta. He was not involved in the new work but studies other animals, such as whale sharks, which might also be affected by food-scented plastic debris.
The new research, is “pretty convincing stuff,” Dove says. “If you want to truly understand what impact we have on ocean life, you have to put yourself in [the animals’] shoes and try to experience the changing ocean the way they do,” he explains. “In this case, the scientists asked ‘what would plastic smell like to a bird?’ And the answer was surprising and informative.”
These odor signals don’t operate in isolation. They work as part of a complex landscape of aromas, a “smellscape,” Dove explains. The next logical step in this research is to look at mixtures of odors that act as cues for food. Some smells block other signals. Some smells make other scents stronger. One important question is whether plastics trap smells important to other filter-feeding animals, such as baleen whales, manta rays and whale sharks, he says.
Sadly, it’s too late to do anything about the plastic that is already in the ocean. All people can do is prevent more plastic from getting in there, Dove says. “It’s going to take all of us — governments, companies, conservation advocacy groups and consumers — to get it done.”
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baleen A long plate made of keratin (the same material as your fingernails or hair). Baleen whales have many plates of baleen in their mouths instead of teeth. To feed, a baleen whale swims with its mouth open, collecting plankton-filled water. Then it pushes water out with its enormous tongue. Plankton in the water become trapped in the baleen, and the whale then swallows the tiny floating animals.
biofouling The attachment of living organisms, such as algae, barnacles and bacterial slime to pipes, ship hulls, buoys and other materials that make contact with the water.
birds Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
buoy A floating device anchored to the bottom of a body of water. A buoy may mark channels, warn of dangers or carry instruments to measure the environment.
chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.
colleague Someone who works with another; a co-worker or team member.
conservation The act of preserving or protecting something. The focus of this work can range from art objects to endangered species and other aspects of the natural environment.
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
filter (in chemistry and environmental science) A device which allows some materials to pass through but not others, based on their size or some other feature. (in physics) A screen, plate or layer of a substance that absorbs light or other radiation or selectively prevents the transmission of some of its components.
marine Having to do with the ocean world or environment.
phytoplankton Sometimes referred to as microalgae, these are microscopic plants and plant-like organisms that live in the ocean. Most float and reside in regions where sunlight filters down. Much like land-based plants, these organisms contain chlorophyll. They also require sunlight to live and grow. Phytoplankton serve as a base of the oceanic food web.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
rays (in biology) Members of the shark family, these kite-shaped fish species resemble a flattened shark with wide fins that resemble wings.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
seaweed Large algae growing in the sea or on rocks below the high-water mark.
sharks A family of primitive fishes that rely on skeletons formed of cartilage, not bone. Like skates and rays, they belong to a group known as elasmobranchs. Then tend to grow and mature slowly and have few young. Some lay eggs, others give birth to live young.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
statistics The practice or science of collecting and analyzing numerical data in large quantities and interpreting their meaning. Much of this work involves reducing errors that might be attributable to random variation. A professional who works in this field is called a statistician.
whale A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins.
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S. Schwartz. This microbe makes a meal of plastic. Science News. April 5, 2016.
C. Samoray. Ocean’s plastics offer a floating fortress to a mess of microbes. Science News. February 9, 2016.