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Ocean Trash Is a Lifesaver for Insect

8 May 2012 7:10 pm
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Anthony Smith; (inset) Miriam Goldstein/Scripps Institution of Oceanography, UC San Diego

Plastic ahoy! Halobates sericeus lay their eggs onto plastic bits of human trash (inset).

In the event of a shipwreck, a sailor's best friend is a floating barrel. For one species of insect, it's bobbing plastic. New research reveals that the spindly-legged Halobates sericeus has begun to lay its eggs on not only bobbing pieces of pumice and other ocean debris but also on floating garbage in the Pacific Ocean. The behavior may be giving the insect an edge in a tough environment—but it may also have negative consequences for the ecosystem as a whole.

Luckily for H. sericeus, there's more than enough trash to go around—at least in a region of the Pacific Ocean often dubbed the "Great Pacific Garbage Patch." Strong ocean currents pool floating, usually plastic, waste into this wide expanse of relatively calm seas that is centered roughly halfway between Hawaii and California. Still, it's no dump, says study co-author Miriam Goldstein, a marine ecologist at the University of California, San Diego. Most plastic that accumulates here tends to be small, usually tiny particles of polystyrene and other buoyant plastics no bigger than a popcorn kernel, making it nearly impossible to see from the deck of a boat.

But some scientists suspect that even these tiny pieces of plastic can throw aquatic life for a loop. Goldstein discovered that nearly by accident. She and a colleague were perusing a collection of small debris skimmed from the North Pacific Ocean when they noticed something strange: Eggs. Some aquatic creature had plastered one to two bright orange eggs about the size of a grain of rice onto several of the pieces of plastic—something these researchers had never seen before. The culprit, Goldstein found, was H. sericeus, a marine cousin of water striders.

Intrigued, Goldstein and colleagues decided to dig deeper. The team compared samples of debris collected from the same region of the Pacific in the 1970s and 1980s to other flotsam gathered more recently. As expected, this plastic soup has grown a lot thicker. Over several decades, the concentration of garbage in the patch grew by two orders of magnitude, reaching densities of about one piece of trash per 10 cubic meters of surface water, the group reports online today in Biology Letters. And the concentration of Halobates eggs seemed to rise in tandem with this plastic.

What that means for the insects isn't clear, Goldstein says. Unlike all but a handful of bugs, Halobates spend their entire lives at sea. But they still need to lay their eggs on something solid. In the past, they've opted for chunks of buoyant volcanic pumice or even bits of wood, both of which are rare on the open ocean. Now, with more floating nurseries to choose from, the bugs could be in for a population explosion, she says.

And that could have subtle but important consequences for the insect's entire ocean community, Goldstein suggests. The insects, for instance, likely make quick meals for many marine crabs, which themselves raft on floating debris in the North Pacific. And those invertebrates could, theoretically, be able to feast on the new prey, finding themselves with an unexpected surplus of food. "This is an ecosystem that doesn't have many nutrients," she says. "There's a lot of things there that are hungry all the time."

Greater numbers of bugs could also deplete populations of the plankton they feed on, throwing a wrench into the ecosystem, Goldstein adds. The actual fate of H. sericeus and its associates may still be unclear, but the findings are still potentially worrisome, says Giora Proskurowski, a chemical oceanographer at the University of Washington, Seattle. The effects of waste on larger animals, including birds with stomachs full of plastic, have garnered significant attention, he says, but "when you start altering [whole] populations, … that's when you get these true impacts."

The study is "a great example of some of the impacts [of plastic] that we are just becoming aware of," says Kara Lavender Law, a research oceanographer who studies accumulations of plastic in the open ocean at the Sea Education Association in Woods Hole, Massachusetts. And studies of waste bobbing at the ocean's surface only scrape, well, the surface, she says. Other plastics—including the material used to make soda or water bottles—sink, potentially influencing life on the sea bottom. "The fact that we have all these little bits of plastic floating around, and we don't know what happens to them is concerning," she says.

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