According to a report in Nature News, the finding, from a team led by ecologist Charles Trick of the University of Western Ontario in London, Canada, dampens the prospects for schemes to boost the growth of CO2-consuming organisms in surface waters.
"This is a real reminder that while we think we understand what's going on in the environment, we really don't," said Trick. "There's uncertainty with every large-scale experiment we do," he added.
Trick and his colleagues found the neurotoxin domoic acid in samples of seawater from a site in the North Pacific, where iron-fertilization experiments have been conducted.
Shipboard experiments by the team confirmed that adding iron increased production of the toxin by plankton of the genus Pseudonitzschia.
In 2006 and 2007, Trick and his colleagues collected seawater at various depths from a research site south of Alaska.
They found domoic acid in the seawater, from which they also isolated two species of Pseudonitzschia.
The team grew the plankton in on-board incubators, spiking some of the tanks with iron.
The abundance of the plankton and concentrations of domoic acid increased relative to tanks that had no iron added to them.
Adding trace amounts of copper further pushed up the production of domoic acid.
From these results, Trick and his team estimate that proposed large-scale ocean iron enrichment could produce domoic acid in concentrations that might be high enough to shut down coastal fisheries.
"It doesn't surprise me," said David Caron, a marine biologist at the University of Southern California, Los Angeles.
"In the majority of iron-enrichment experiments, Pseudonitzschia has come up in abundance. It's not unreasonable that sooner or later you're going to find domoic acid," he added. (ANI)