Background
The authors write that "harmful algal blooms of Prymnesium parvum are global phenomena occurring in marine, estuarine and inland ecosystems," citing Moestrup (1994), Edvardsen and Paasche (1998) and Lundholm and Moestrup (2006), while indicating that P. parvum, commonly known as "golden algae" or "Texas tide," is "a mixotrophic flagellated haptophyte known to produce toxins that may severely impact aquatic organisms," citing Brooks et al. (2010).

What was done
Prosser et al. evaluated "whether pH influences P. parvum bloom development and ambient toxicity," by manipulating pH levels (7, 7.5, 8.5) of in situ experimental enclosures during 21-day pre-bloom development experiments in Lake Granbury, Texas (USA).

What was learned
The ten U.S. researchers report that neutral pH levels preempted P. parvum bloom development, in that "population densities never reached bloom proportions and no ambient toxicity to fish or cladocerans resulted." However, they indicate that "higher pH (8.5) allowed bloom formation to occur" and that it also "resulted in ambient toxicity," while at the other end of the pH spectrum, they say that "reducing pH to 7 and 7.5 did not adversely affect phytoplankton or zooplankton biomass."

What it means
As long as the air's CO2 content continues to rise, we can expect some degree of pH reduction to occur, which should make it more difficult for (1) blooms of P. parvum to occur, and for (2) algal-produced toxins to be released to the surrounding water.

References
Brooks, B.W., James, S.V., Valenti, J.T.W., Urena-Boeck, F., Serrano, C., Berninger, J.P., Schwierzke, L., Mydlarz, L.D., Grover, J.P. and Roelke, D.L. 2010. Comparative toxicity of Prymnesium parvum in inland waters. Journal of the American Water Resources Association 46: 45-62.

Edvardsen, B. and Paasche, E. 1998. Bloom dynamics and physiology of Prymnesium and Chrysochromulina. NATO ASI Series 41: 193-208.

Lundholm, N. and Moestrup, O. 2006. The biogeography of harmful algae. In: Graneli, E. and Turner, J.T. (Eds.). Ecology of Harmful Algae. Springer, Heidelberg, Germany, pp. 23-35.

Moestrup, O. 1994. Economic aspects: 'blooms', nuisance species, and toxins. Systematics Association 51: 265-285.