The Health and Productivity of Diatoms in Acidified Seawater

Crawfurd et al. (2011) state that diatoms are very important for the productivity of the world's oceans, as they contribute about 45% of global marine primary production (Mann, 1999); and they therefore say it is essential to understand how diatoms and other marine phytoplankton will respond to the higher aqueous CO₂ and lower pH conditions that will prevail in their surface waters in the near future, as a result of the dissolution of anthropogenic CO₂ in them.

Against this backdrop, Crawfurd et al. grew over 100 generations of the diatom Thalassiosira pseudonana in seawater maintained in equilibrium with air of either current (ambient) CO₂ concentration or expected end-of-the-century (twice-ambient) CO₂ concentration (380 or 760 ppm) - which produced pH values of 8.1 and 7.8, respectively - for a period of three months, after which they evaluated a number of the species' physical and physiological characteristics.

Overall, in the words of the five UK researchers, "there were very few effects on T. pseudonana of long-term culture at different pCO₂ and pH." In fact, they report that "growth rates were identical in cultures supplied with 780 or 360 ppm CO₂," and they note that "similar results have been reported for other diatom species," citing the studies of Tortell et al. (1997), Tortell (2000), Kim et al. (2006) and Shi et al. (2009 ).

In light of their several findings and the analogous results of several other scientific teams, Crawfurd et al. conclude in the final sentence of their paper that "if all diatoms respond in a similar fashion to T. pseudonana, acidification of this magnitude in the future ocean may have little effect on diatom productivity."

Additional References
Kim, J.-M., Lee, K., Shin, K., Kang, J.-H., Lee, H.-W., Kim, M., Jang, P.-G. and Jang, M.-C. 2006. The effect of seawater CO₂ concentration on growth of a natural phytoplankton assemblage in a controlled mesocosm experiment. Limnology and Oceanography 51: 1629-1636.

Mann, D.G. 1999. The species concept in diatoms. Phycologia 38: 437-495.

Shi, D., Xu, Y. and Morel, F.M.M. 2009. Effects of the pH/pCO₂ control method on medium chemistry and phytoplankton growth. Biogeosciences 6: 1199-1207.

Tortell, P.D., Reinfelder, J.R. and Morel, F.M.M. 1997. Active uptake of bicarbonate by diatoms. Nature 390: 243-244.

Tortell, P.D. 2000. Evolutionary and ecological perspectives on inorganic carbon acquisition in phytoplankton. Limnology and Oceanography 45: 744-750.