Tatters and colleagues varied the amount of dissolved CO2 and the availability of the silicate the diatoms use to make their shells. In a presentation at a recent ocean acidification conference, Tatters reported that the more CO2 and the less silicate, the higher the diatom’s toxin production–more than doubling at the level of dissolved CO2 scientists expect the oceans to reach by 2100. Earlier research by the Hutchins lab found a fourfold increase in toxicity under limited phosphorus and increased CO2 in a related species.
However, Cochlan cautions, what exactly triggers toxic blooms is “the million-dollar question” that hasn’t been answered. Sometimes algae produce more toxins “when they are growing very well,” he says.
Water temperature may also be a factor. Anke Kremp, a researcher at the Finnish Environment Institute, reported in a January 2012 study that eight strains of the toxic dinoflagellate Alexandrium ostenfeldii grew at very different rates under increased acidity and higher temperatures. The amount of toxin in each cell didn’t always increase, but the composition of the toxic compounds consistently changed as temperature and acidity increased.
A. ostenfeldii can make several nasty chemicals, and the overall trend in Kremp’s study was toward more saxitoxin—the most potent compound in its arsenal. Although this may be bad news for the Baltic Sea and other areas plagued by this dinoflagellate, Kremp also noted that the short duration of most lab studies limits what we can know about how toxic algae may evolve over the next century.
Further, NOAA researcher Vera Trainer says that although some species may become more toxic, there may not be a net increase in risk to humans and other consumers of seafood. If the more harmful species become less numerous, she says, “It’s sort of a moot point.” But if they become more toxic and more numerous, she adds, “you’ve got a double whammy.”
These conundrums illustrate how little we know. The different genetic heritages of diatoms, dinoflagellates and cyanobacteria will affect their survival. And in addition to temperature, other physical factors like available light and even large-scale ocean–atmosphere interactions like the El Niño–La Niña oscillation can affect plankton behavior.
“The work is really at an early stage,” says Ulf Riebesell, a professor of biological oceanography at the Helmholtz Center for Ocean Research in Kiel, Germany. But it is fair to say that as algae and other tiny ocean species solve new survival problems, they may force us to do the same.