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The Future of Coastal Productivity

Paper Reviewed
Villafañe, V.E., Valiñas, M.S., Cabrerizo, M.J. and Helbling, E.W. 2015. Physio-ecological responses of Patagonian coastal marine phytoplankton in a scenario of global change: Role of acidification, nutrients and solar UVR. Marine Chemistry 177: 411-420.

Writing as background for their work, Villafañe et al. (2015) note there is a growing interest in determining the effects and impacts of global change on estuaries, citing the works of Bricker et al. (2008), Bianchi and Allison (2009) and Gillanders et al. (2011), particularly with respect to phytoplankton, given that the tiny plants are responsible for a large share of the primary production in such waters. In light of such interest, the team of four researchers set out to investigate the combined effects of three important factors influencing phytoplankton productivity that are expected to undergo significant change in the not-too-distant future: solar ultraviolet radiation (UVR) exposure, ocean acidification and nutrient content. And in order to achieve this objective, Villafañe et al. exposed natural phytoplankton samples collected from the Chubut River estuary (Patagonia, Argentina) to solar radiation (with and without UVR) under conditions of present-day seawater nutrients and pH, as well as under conditions representing a future scenario of global change (elevated nutrients and reduced pH).

The results of their investigation revealed that marine phytoplankton were "more efficient" under future than current conditions, regardless of solar radiation treatment. Nutrient uptake values, for example, were 1.5 and 5 times higher for nitrate and phosphate, respectively, under future conditions, which let to "higher growth rates (3-fold) and, hence, into higher cell abundances (ca. 6 times)." In addition, they report there was a community shift. Under present-day conditions the phytoplankton community was dominated by small diatoms (ca. 60%) and flagellates, whereas "relatively large diatoms with high growth rates, little or no UVR-inhibition of photosynthesis, and with the potential to cope, at least partially, with acidification via photosynthesis" dominated in the future scenario treatment. In short, they say that large diatoms took "full advantage of both the increase in CO2 and nutrient concentrations" in the future scenario treatment. And as a result of these combined findings, Villafañe et al. conclude that coastal waters in the future "will produce significant increases in primary production, mainly modulated by increases in larger UVR-resistant diatoms that could sequester significant carbon amounts, a process that has already been determined in Patagonian open waters (Bianchi et al., 2009)."

Such findings should be heralded and welcomed, especially in light of the facts that (1) increases in primary production likely will help "sustain important secondary production (including fisheries)," and that (2) there exists "wide consensus that diatoms contribute ~40% of all marine primary productivity in the modern ocean, and they are the major contributors to the export of atmospheric carbon to the deep ocean (Finkel et al., 2010)."

References
Bianchi, T.S. and Allison, M.A. 2009. Large-river delta-front estuaries as natural "recorders" of global environmental change. Proceedings of the National Academy of Sciences, USA 106: 8085-8092.

Bricker, S.B., Longstaff, B., Dennison, W., Jones, A., Boicourt, K., Wicks, C. and Woerner, J. 2008. Effects of nutrient enrichment in the nation's estuaries: a decade of change. Harmful Algae 8: 21-32.

Finkel, Z.V., Beardall, J., Flynn, K.J., Quigg, A., Rees, T.A.V. and Raven, J.A. 2010. Phytoplankton in a changing world: cell size and elemental stoichiometry. Journal of Plankton Research 32: 119-137.

Gillanders, B.M., Elsdon, T.S., Halliday, I.A., Jenkins, G.P., Robins, J.B. and Valesini, S.J. 2011. Potential effects of climate change on Australian estuaries and fish utilising estuaries: a review. Marine and Freshwater Research 62: 1115-1131.

Posted 8 March 2016