an ecologist at the University of California, Davis, has been trying to answer a dismal question: Is everything terrible, or are things just very, very bad?
Rochman is a member of the National Center for Ecological Analysis and Synthesis’s marine-debris working group, a collection of scientists who study, among other things, the growing problem of marine debris, also known as ocean trash. Plenty of studies have sounded alarm bells about the state of marine debris; in a recent paper published in the journal Ecology, Rochman and her colleagues set out to determine how many of those perceived risks are real.
Often, Rochman says, scientists will end a paper by speculating about the broader impacts of what they’ve found. For example, a study could show that certain seabirds eat plastic bags, and go on to warn that whole bird populations are at risk of dying out.’But the truth was that nobody had yet tested those perceived threats,’ Rochman says.’There wasn’t a lot of information.’
Rochman and her colleagues examined more than a hundred papers on the impacts of marine debris that were published through 2013. Within each paper, they asked what threats scientists had studied – 366 perceived threats in all – and what they’d actually found.
In 83 percent of cases, the perceived dangers of ocean trash were proven true. In the remaining cases, the working group found the studies had weaknesses in design and content which affected the validity of their conclusions – they lacked a control group, for example, or used faulty statistics.
Strikingly, Rochman says, only one well-designed study failed to find the effect it was looking for, an investigation of mussels ingesting microscopic plastic bits. The plastic moved from the mussels’ stomachs to their bloodstreams, scientists found, and stayed there for weeks – but didn’t seem to stress out the shellfish.
While mussels may be fine eating trash, though, the analysis also gave a clearer picture of the many ways that ocean debris is bothersome.
Within the studies they looked at, most of the proven threats came from plastic debris, rather than other materials like metal or wood. Most of the dangers also involved large pieces of debris – animals getting entangled in trash, for example, or eating it and severely injuring themselves.