Teeming off Hawaii’s famous beaches is a complex web of life—sharks, turtles, seabirds—that relies enormously on tiny larval fish, the food for many species. In their first few weeks of existence the larvae are at the mercy of currents, still too puny to get around on their own, gathering by their millions in surface “slicks” where currents meet. And it’s here where they’re increasingly meeting a pernicious, omnipresent foe and mistaking it for food: microplastic.

Researchers today published an ominous report showing that these slicks pack 126 times the concentration of microplastic as nearby surface waters, and eight times the density of plastic as the Great Pacific Garbage Patch. Microplastic particles outnumber larval fish in the slicks by a factor of seven to one, and dissections of the larvae reveal that many have plastic in their bellies. The consequences both for these species and the food web as a whole are downright terrifying.

“Seabirds feed on larval fish, adult fish feed on larval fish—it’s a prominent food source,” says NOAA oceanographer Jamison Gove, co-lead author on the new paper in the Proceedings of the National Academy of Sciences. “So that clearly has implications for how plastics can be distributed and quickly get higher up the food chain.”

Gove and his colleagues dissected hundreds of larval fish, and found that 8.6 percent of specimens from slicks—which appear as smooth ribbons on the surface—contained microplastics, more than twice the rate as larvae in nearby non-slick surface waters. Less than 10 percent may not sound like much, but we’re talking about innumerable little larvae out there in the slicks, so that percentage translates into a huge population of tainted organisms.

A larval flying fish (top) and triggerfish (bottom). Their ingested plastics are zoomed in.

Courtesy of Jonathan Whitney/NOAA Fisheries

These larvae don’t yet have fully developed immune systems to deal with ingested microplastics, which is particularly worrisome when you consider that the particles are known to accumulate pathogens like bacteria as they float around the sea. “One possibility is that because larval stages are so vulnerable, eating one piece of plastic could actually potentially kill them,” says NOAA marine ecologist Jonathan Whitney, co-lead author on the paper. It’s possible that far more larvae might be eating microplastics, perishing, and sinking to the bottom of the sea than scientists know.

The larvae might be mistaking plastics for some of their more common foods—other species of plankton that float around on currents. Most of the ingested particles were transparent or blue, the same color as their prey, such as tiny crustaceans called copepods. Nearly all of the consumed microplastics were fibers, from sources like plastic fishing nets, which slough off fibers that resemble the antennae of copepods.

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