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A study was just released by researchers at Scripps Institute of Oceanography revealing a drastic increase in the amount of plastic adrift in the Pacific Ocean. According to the paper, the amount of plastic in the North Pacific Subtropical Convergence Zone has increased 100-fold over the last 40 years.

But most of the news stories coming out about this discovery are thin on facts about the dangers of plastic. And the research even suggests marine wildlife may be benefiting from the artificial flotsam.

Clearly this increase in trash can't be good. Can it?

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There are very few things in the world that aren't beneficial to some lifeform. Even if you were to, say, spill a mixture of persistent broad-spectrum poisons on an area that killed off 99.9% of all species there, the remaining 0.1% that did survive would benefit from the lack of competition.

The "great garbage patch" is hardly so extreme a phenomenon, but similar effects can be seen there: some species suffer, others benefit. In that sense, it's no different from any other changing habitat.

From a conservation viewpoint, there are two issues here that one might find worrying:

  1. First, novel, extreme or rapidly changing habitats tend to have lower than average biodiversity, at least initially: the few species that thrive in the new environment tend to proliferate at the expense of others, forming a relatively simple (and often not very stable) food web. Of course, over evolutionary timescales we'd expect the surviving species to adapt and diversify and the ecosystem to settle into a more stable state, but that tends to take a long time compared to the human timescale on which such novel habitats are created.

  2. Also, the effects of the "garbage patch", or ecological changes in general, are not limited to the directly changed area. Creating a new habitat in one part of the ocean is one thing; disrupting the ecosystem of the entire ocean is something else, as doing so leaves no unaffected refuge for the species that are harmed.

    For example, fish, birds and marine mammals passing even just occasionally through the patch might end up swallowing plastic and accumulating it in their gut; meanwhile, even for less motile organisms, the patch might act as a population sink, depleting their population density in nearby areas. And if some organisms, such as the sea skaters mentioned in the article you cite, thrive in the patch, the increased population will likely spill into other areas, potentially harming their competitors or prey species.

As for why the news are focusing on the beneficial effects of the garbage to the sea skaters, well, that's what the study that prompted this current batch of news stories was about. It's also seen as newsworthy precisely because it seems so unexpected: we've all heard stories of plastic flotsam harming wildlife, so finding out that some species are actually benefiting from it has some "man bites dog" style news value.

Also, it's a lot easier and more convincing to observe something that is there than something that isn't: we can directly see these insects laying their eggs on the bits of plastic, giving direct and incontrovertible proof of a causal connection. Meanwhile, simply observing that some species used to be more common in the area of the patch than it is now is a lot less direct and informative: we might never be sure just how the patch is harming that species, and it always leaves skeptics an opening to claim that the decline might be caused by other factors. With the sea skates, on the other hand, we're not just observing the effect, but the direct mechanism as well.

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References? especially for the effects of habitat on biodiversity? –  David May 15 '12 at 2:26
    
@David: I'll see if I can dig up some. –  Ilmari Karonen May 15 '12 at 9:54

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