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Ocean Acidification Impacts on a Marine Diatom

Paper Reviewed
Jacob, B.G., Dassow, P.V., Salisbury, J.E., Navarro, J.M. and Vargas, C.A. 2017. Impact of low pH/high pCO2 on the physiological response and fatty acid content in diatom Skeletonema pseudocostatum. Journal of the Marine Biological Association of the United Kingdom 97: 225-233.

Diatoms contribute a significant portion of the downward flux of particulate organic matter into the deep ocean. Consequently, these marine phytoplankton are of interest to scientists, who have begun to study their response to ocean acidification, including Jacob et al. (2017). Working with Skeletonema pseudocostatum, the five researchers evaluated the effects of CO2-driven ocean acidification on semi-continuous cultures of this coastal diatom.

In accomplishing this objective, Jacob et al. collected S. pseudosostatum from Yaldad Bay, southern Chile, and acclimated the specimens in the laboratory for ten generations under normal (~8.15) or reduced (~7.65) seawater pH. Thereafter, they cultured the diatoms for an additional six generations while monitoring their growth and development. And what did their study reveal?

In the words of the authors, "CO2-driven acidification had no significant impact on growth rate, chlorophyll-a, cellular abundance, gross photosynthesis, dark respiration, particulate organic carbon and particulate organic nitrogen between CO2-treatments, suggesting that S. pseudocostatum is adapted to tolerate changes of ~0.5 units of pH under high pCO2 conditions." What is more, although total fatty acids were significantly higher under ambient pCO2 conditions, the amount of polyunsaturated fatty acids was not significantly different among the two seawater pH treatments.

The importance of this latter observation was not lost on Jacob et al., who note that polyunsaturated fatty acids (PUFA) represent an important proxy for food quality in the marine food web. The lack of change in PUFAs in the diatoms in this study thus indicate that "the nutritional quality in terms of essential fatty acids remains unchanged," which findings the authors add "are consistent with other studies showing no detrimental effects of high pCO2 on the nutritional quality in terms of essential fatty acids." Consequently, ocean acidification does not appear to negatively impact this diatom. And that is good news for the marine food web, upon which this species serves as a foundation.

Posted 28 February 2019