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The Impact of Ocean Acidification on Phytoplankton Fatty Acid Production

Paper Reviewed
Wang, T., Tong, S., Liu, N., Li, F., Wells, M.L. and Gao, K. 2017. The fatty acid content of plankton is changing in subtropical coastal waters as a result of OA: Results from a mesocosm study. Marine Environmental Research 132: 51-62.

Wang et al. (2017) set out to examine the impacts of ocean acidification on the production and trophic transfer of algal fatty acids in a marine mesocosm experiment involving two diatoms (Phaeodactylum tricornutum and Thalassiosira weissflogii) and one coccolithophore (Emiliania huxleyi).

The experiment was conducted in the Center of Wuyuan Bay (24.52°N, 117.18°E) at the Facility for Ocean Acidification Impacts Study, Xiamen University, Xiamen, China. Three mesocosms were set up under normal seawater pCO2 conditions (400 µatm) and three under ocean acidification conditions with a pCO2 level of 1000 µatm. Then, every two days after Day 10 of the experiment, the phytoplankton were sampled for fatty acid determination, which lasted until the end of the 33-day experiment.

In discussing their findings, Wang et al. report that concentrations of saturated fatty acids remained high in phytoplankton grown under both acidified and non-acidified conditions. In contrast, they note that "polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA) increased significantly more under elevated pCO2," which combined findings led the authors to conclude that "these selected phytoplankton species have a relatively high tolerance to acidification in terms of fatty acid production." Furthermore, they state that "the observed higher contents of PUFA and MUFA in late exponential phase under elevated pCO2 indicate increased nutritional value for zooplankton and higher trophic levels."

Indeed, as discussed in the Introduction of their paper, Wang et al. report that essential fatty acids, such as PUFAs, "are critical constituents in the diets of zooplankton and higher trophic levels (Jónasdóttir et al., 2009)," adding that "feeding on algae rich in PUFA markedly increases zooplankton growth rates (Müller-Navarra, 1995; Müller-Navarra et al., 2000), highlighting the important roles that phytoplankton PUFA have in the marine food web (Kainz et al., 2004)."

What is more, Wang et al., note that "diets rich in PUFA are essential for egg production in copepods (Jónasdóttir et al., 2009) as well as in fish growth and reproduction (Watanabe, 1982; Bell et al., 1986; Henderson and Tocher, 1987)." Consequently, it would appear that the impacts of ocean acidification on these three phytoplankton species, as well as on the entire marine food web upon which these primary producers are based, are positive, having little indication of the negative impacts predicted by ocean acidification alarmists.

References
Bell, M.V., Henderson, R.J. and Sargent, J.R. 1986. The role of polyunsaturated fatty acids in fish. Comparative Biochemistry and Physiology B 83: 711-719.

Henderson, J.R. and Tocher, D.R. 1987. The lipid composition and biochemistry of freshwater fish. Progress in Lipid Research 26: 281-347.

Jónasdóttir, S.H., Visser, A.W. and Jespersen, C. 2009. Assessing the role of food quality in the production and hatching of Temora longicornis eggs. Marine Ecology Progress Series 382: 139-150.

Kainz, M., Arts, M.T. and Mazumder, A. 2004. Essential fatty acids in the planktonic food web and their ecological role for higher trophic levels. Limnology and Oceanography 49: 1784-1793.

Müller-Navarra, D.C. 1995. Evidence that a highly unsaturated fatty acid limits Daphnia growth in nature. Archiv fur Hydrobiologie 132: 297-307.

Müller-Navarra, D.C., Brett, M.T., Liston, A.M. and Goldman, C.R. 2000. A highly unsaturated fatty acid predicts carbon transfer between primary producers and consumers. Nature 403: 74-77.

Watanabe, T. 1982. Lipid nutrition of fish. Comparative Biochemistry and Physiology B 73: 3-15.

Posted 18 February 2019