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Ocean Acidification's Impact on Planktonic Community Fatty Acids

Reference
Leu, E., Daase, M., Schulz, K.G., Stuhr, A. and Riebesell, U. 2013. Effect of ocean acidification on the fatty acid composition of a natural plankton community. Biogeosciences 10: 1143-1153.
In a paper published in Biogeosciences, Leu et al. (2013) write that "ocean acidification occurs as a consequence of increasing atmospheric CO2 concentrations, and is thought to represent a major threat for some groups of marine organisms," in that polyunsaturated fatty acids or PUFAs - which are essential metabolites that are synthesized only by algae and therefore have to be acquired via their ingestion by all other organisms - may not be as prominent in Arctic plankton in a high-CO2 world as they are nowadays, leading to a degradation of planktonic food quality. But is this really so?

In a study designed to answer this important question, the five researchers studied the effect of ocean acidification of a natural plankton community in the Arctic in a large-scale mesocosm experiment that was carried out in Kongsfjorden (Svalbard, Norway at 79°N), where nine mesocosms of ~50 m3 each were exposed to eight different CO2 levels (from natural background conditions to ~1420 ppm, yielding pH values ranging from ~8.3 to 7.5). And what did they find?

Leu et al. report that "no indications were found for a generally detrimental effect of ocean acidification on the planktonic food quality in terms of essential fatty acids." In fact, they say that from an ecological point of view, "it is remarkable that the overall community response with respect to the relative amount of PUFAs to increased CO2 concentrations was rather positive." And thus they further conclude that "findings about detrimental effects of ocean acidification on single species in laboratory studies (as, for instance, Riebesell et al. (2000) or Tsuzuki et al. (1990)), and even their consequences for grazers (Rossoll et al., 2012) are probably less relevant in a natural situation where other, more CO2-tolerant species take over."

In the end, therefore, Leu et al. state that "the overall availability of essential PUFAs for higher trophic levels seems not to be affected negatively, although the specific fatty acid composition may change." This is because, as they describe it, "the overall amount of essential PUFAs available to the entire community (or at least within a certain size class) is the important measure for the algal food quality," which fact "also holds true for the implications for trophic transfer efficiency and consequences for phytoplankton-zooplankton ratios," as discussed by Brett and Muller-Navarra (1997).

Thus, as a result of these several encouraging observations, it appears that atmospheric CO2 enrichment likely will not lead to a degradation of planktonic food quality in Arctic waters, in contradiction of what many environmental pessimists have ardently postulated.

Additional References
Brett, M.T. and Muller-Navarra, D.C. 1997. The role of highly unsaturated fatty acids in aquatic food web processes. Freshwater Biology 38: 483-499.

Riebesell, U., Revill, A.T., Holdsworth, D.G. and Volkman, J.K. 2000. The effects of varying CO2 concentration on lipid composition and carbon isotope fractionation in Emiliania huxleyi. Geochimica Cosmochimica Acta 64: 4179-4192.

Rossoll, D., Bermudez, R., Hauss, H., Schulz, K.G., Riebesell, U., Sommer, U. and Winder, M. 2012. Ocean acidification-induced food quality deterioration constrains trophic transfer. PLoS ONE 7: e34737.

Tsuzuki, M., Ohnuma, E., Sato, N., Takaku, T. and Kawaguchi, A. 1990. Effects of CO2 concentration during growth on fatty acid composition in microalgae. Plant Physiology 93: 851-856.

Archived 3 September 2013