Invasive Plastic Hitchhikers

Posted by Jonathan Waterman in Ocean Views on October 15, 2012

Hitchhikers on a plastic ball collected Sunday October 14. Photo by Matt Ecklund

We’re ten days and 690 nautical miles out from the nearest land in California.  In that time, we’ve conducted 21 net deployments to collect and analyze plastic.  We’ve counted a total of 3,190 pieces of plastic, most of it in the North Pacific subtropical gyre.  Here in this gigantic eddy-like “trap,” the concentration of floating plastic has increased exponentially.

We’re finding grain-size and quarter-size pieces of plastic in the net cod ends.  Occasionally nets have counts as low as ten—versus counts of 1,372 pieces.  Why? 

Because of the gyre’s patchiness, some places are loaded with plastic and others are not.  On calm days, often times the plastic can be seen floating by the ship, other times the sea looks clear and free of plastic until you filter it and discover plastic pieces that are invisible to the human eye.

One project (among many onboard) is to count microscopic plastics that aren’t normally tallied with the larger and more visible pieces in the neuston net due to the fact that they pass out of the mesh net as it’s being towed.  To measure these, a liter of seawater is dyed pink and vacuumed through a micrometer-sized filter mesh. 

The dye doesn’t stick to plastic, therefore, the pieces can be seen clear of other microbial life and counted through a microscope.  Over the last week, microscopic plastic counts have ranged from 56 to 224 pieces per liter of seawater.

One of the greater mysteries being studied onboard is how pieces of floating plastic act as a host or “island” to creatures large and small, from crabs to zooplankton to microbes.   Past studies have shown, for instance, how surface-level plastic gives the water strider insect (Halobates sericeus) a platform on which to lay its eggs.

The hypothesis is that the favorable nature of this “plastisphere” for many species could cause a quantum shift in life across the ocean ecosystem.  After all, Halobates (or thousands of other species) feed upon the zooplankton and in turn, become part of the food chain for birds, fish and turtles.  Yet, until plastics arrived in the gyre, the population of Halobates was naturally limited by what little floating material it could lay its eggs upon.

Until recently, rafting insects and other ocean organisms relied only upon driftwood—coconuts, trees, or an occasional stray buoy.  Now these rafters have miniature ocean island chains of floating plastic to travel upon, according to one scientist on board. 

Mike Gil, from the University of Florida, has joined this cruise holding the equilibrium theory of island biogeography as a framework for his investigation of floating debris.  This 45-year-old theory proposes that the larger an island, the more species it will hold, and Mike points out that floating plastic qualifies as islands.  He is hoping to compare large and small floating objects and come up with accurate resident species counts.

And like most of the crew, Mike is fascinated with the amount of species-rich biomass bearding the objects we’ve been pulling aboard.  When quizzed about the number of species, let alone family taxonomy, he wisely won’t even hazard a guess.  As for what we’ve seen, several crabs—up to 1.5 inches wide—were living on a four-inch ball; a three-foot-wide buoy is weighed down by twice its weight in barnacles and worms; a small car’s tire and rim, heavy with algae and organisms, is plainly embossed “Made in Japan.”

Two buoys we pulled onboard were also marked with Japanese characters, one reading “Nichimou” (the name of a fishery industry complex), the other pronounced “Do Nan” which means the equipment came from Hokkaido, the northernmost island of Japan, 3,360 miles west of our present position.

So as small plastic pieces from around the Pacific Rim countries are mixing with larger debris from Japan, a non-scientist sailor like myself feels safe in saying that we have entered the tsunami debris zone.   But I return to Mike to get the bigger picture.

“We’re potentially seeding the ocean with a transport mechanism to take invasive species across the ocean,” Mike says.  “Species invasions can have devastating effects on natural ecosystems.”  Since conservation biologists believe in preserving the biodiversity of species, he is concerned about biodiversity being compromised by foreign hitchhikers.  “It is possible that plastic litter could increase species invasions to new coastlines.”