Beware of bad science reporting: No, we haven’t killed 90% of all plankton

For the past few days, it has been hard to look at social media without coming across a scary-looking report from the Scottish newspaper The Sunday Post. "Scots team’s research finds Atlantic plankton all but wiped out in catastrophic loss of life," reads the breathless headline. The article claims that a survey of plankton in the ocean found that "evidence... suggest(s) 90% has now vanished." The article then goes on to predict the imminent collapse of our biosphere.

There's just one problem: The article is utter rubbish.

The Sunday Post uses as its source a preprint manuscript—meaning it hasn't been peer-reviewed yet—from lead author Howard Dryden at the Global Oceanic Environmental Survey.

There's no denying that our oceans are in trouble—the study notes in its introduction that they have lost 50 percent of all marine life over the past 70 years, and that number is rising at around 1 percent per year. But the Post's article goes further than the preprint, citing plankton counts collected by 13 ships with 500 data points.

Specifically, the article claims that the survey "expected to find up to five visible pieces of plankton in every 10 liters of water—but found an average of less than one. The discovery suggests that plankton faces complete wipe-out sooner than was expected."

Five hundred data points collected from 13 vessels sounds impressive, but David Johns, head of the Continuous Plankton Recorder Survey, describes it as "a literal drop in the ocean." Johns would know—the Continuous Plankton Recorder Survey has been running since 1958 and has accumulated more than 265,000 samples.

The Continuous Plankton Survey has indeed cataloged a loss of plankton over the years—but nothing close to the 90 percent loss claimed by Dryden. "We have noticed long-term changes—northerly movements of plankton species as surface water warms, changes in seasonality in some taxa, invasives, etc.," Johns told Ars by email. "And we work with a wide group of scientists and governmental bodies, providing evidence for marine policy. As a group, we had an email discussion, and no one agreed with this report—and no one had heard of the guy (other than one person, and she was not complimentary at all)."

In addition to the small sample size, the preprint makes no mention of how or when the plankton samples were collected. "If those samples were taken during the day, in surface waters, there is likely lower numbers of zooplankton," Johns explained. "Also, [there is] no mention of what magnification [the researchers] were using. If you were using a low-power microscope, you would struggle to see the small stuff—in warm open ocean Atlantic waters, much of the zooplankton is pretty small, and they might have trouble picking them out."

As noted above, the paper that the Post based its article on has not been peer-reviewed, an apparent theme for Dryden. "It seems he doesn’t really have a scientific profile—none of his work seems to be peer reviewed, which is obviously important when you are making any bold claims," Johns told Ars.

And Dryden is making bold claims. Although he raises the very real problem of ocean acidification, he has appeared to blame the problem on microplastics and not climate change caused by a massive increase of atmospheric CO2 levels. However, in this preprint, Dryden and his co-authors do identify atmospheric CO2 as the driver of ocean acidification, which they warn will result in the loss of 80–90 percent of all marine life by 2045.

In the early days of the pandemic, I was alarmed by the credence given by some in the media to unreviewed studies about COVID-19. It seems we can add marine biology to that list as well.