Background
The authors indicate that our knowledge about the sensitivity of phytoplankton to ocean acidification is almost entirely based on work conducted on diatoms, coccolithophores and cyanobacteria, while noting that relatively little is known about the responses of autotrophic dinoflagellates, "in particular of toxin producing species (Fu et al., 2010; Hallegraeff, 2010; Kremp et al., 2012)," some of which produce Harmful Algal Blooms (HABs) that may cause mass mortalities of fish, as well as illness - and even death - of marine mammals, seabirds and humans, citing in this regard the work of Anderson et al. (2012) and Graneli and Turner (2006).

What was done
Determined to make new inroads into this little-studied subject, Van de Wall et al. investigated the potential impacts of elevated pCO2 on paralytic shellfish-poisoning toxin (PST), in terms of both its "content and composition in two strains of Alexandrium tamarense (Alex5 and Alex2), which were isolated from the same population at the Scottish east coast of the North Sea (Alpermann et al., 2009; Tillmann et al., 2009)." This they did because "no study thus far," as they put it, had "investigated the impact of elevated pCO2 on toxin production and gene regulation in A. tamarense." And so it was that more specifically - but very briefly - they grew cultures of Alex5 and Alex2 in filtered natural seawater enriched with various metals and vitamins, after which "the culture medium was equilibrated with air containing a pCO2 of 180 ľatm (~Last Glacial Maximum), 380 ľatm (~present day), 800 ľatm (~2100 scenario), and 1200 ľatm (>2100 scenario)," while various sets of measurements were made.

What was learned
The five researchers report that they observed "only minor changes with respect to growth and elemental composition in response to elevated pCO2." But most importantly, they say that "for both strains, the cellular PST content, and in particular the associated cellular toxicity, was lower in the high CO2 treatments." And they additionally found that "Alex5 showed a shift in its PST composition from a non-sulfated analogue towards less toxic sulfated analogues with increasing pCO2." Furthermore, they found that "genes associated to secondary metabolite and amino acid metabolism in Alex5 were down-regulated in the high CO2 treatment," which they felt "may explain its lower PST content."

What it means
"All in all," as they conclude, Van de Waal et al. say their results indicate that "elevated pCO2 will have minor consequences for growth and elemental composition, but may potentially reduce the cellular toxicity of A. tamarense," which would be good news for fish, marine mammals, seabirds and humans.

References
Alpermann, T.J., Beszteri, B., John, U., Tillmann, U. and Cembella, A.D. 2009. Implications of life-history transitions on the population genetic structure of the toxigenic marine dinoflagellate Alexandrium tamarense. Molecular Ecology 18: 2122-2133.

Anderson, D.M., Alpermann, T.J., Cembella, A.D., Collos, Y., Masseret, E. and Montresor, M. 2012. The globally distributed genus Alexandrium: multifaceted roles in marine ecosystems and impacts on human health. Harmful Algae 14: 10-35.

Fu, F.X., Place, A.R., Garcia, N.S. and Hutchins, D.A. 2010. CO2 and phosphate availability control the toxicity of the harmful bloom dinoflagellate Karlodinium veneficum. Aquatic Microbiology and Ecology 59: 55-65.

Graneli, E. and Turner, J.T. 2006. Ecology of Harmful Algae. Springer-Verlag, Berlin, Heidelberg, Germany.

Hallegraeff, G.M. 2010. Ocean climate change, phytoplankton community responses, and harmful algal blooms: a formidable predictive challenge. Journal of Phycology 46: 220-235.

Kremp,A., Godhe, A., Egardt, J., Dupont, S., Suikkanen, S., Casabianca, S. and Penna, A. 2012. Intraspecific variability in the response of bloom-forming marine microalgae to changed climate conditions. Ecology and Evolution 2: 1195-1202.

Tillmann, U., Alpermann, T.L., da Purificacao, R.C., Krock, B. and Cembella, A. 2009. Intra-population clonal variability in allelochemical potency of the toxigenic dinoflagellate Alexandrium tamarense. Harmful Algae 8: 759-769.