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The High Plasticity of a Fleshy Macroalga to Ocean Acidification

Paper Reviewed
Kumar, A., Castellano, I., Patti, F.P., Delledonne, M., Abdelgawad, H., Beemster, G.T.S., Asard, H., Palumbo, A. and Buia, M.C. 2017. Molecular response of Sargassum vulgare to acidification at volcanic CO2 vents: insights from de novo transcriptomic analysis. Molecular Ecology 26: 2276-2290.

Writing as background for their work, Kumar et al. (2017) note that "most of the effects of elevated CO2 and ocean acidification (OA) have been observed in short-term laboratory experiments on a single isolated species," which set up, they say, "hampers the scaling up of the observations to predict the impact in natural environments." However, there are locations in the ocean where the seawater pH is naturally lower than the surrounding environment, such as near volcanic vents where large quantities of CO2 are released into the ocean causing regional declines in seawater pH that are near or lower than values predicted to occur in the future due to OA.

One such site is found off the coast of Ischia Island, Italy, where volcanic vents releasing CO2 have formed two distinct zones of reduced pH (7.8 and 6.7), compared to the surrounding area where the pH value is around 8.1. Interestingly, despite these pH differences, the coastal waters in the area contain large populations of Sargassum vulgare, an important habitat-forming species that contributes to shaping macroalgal communities and trophic dynamics. Thus, it was only natural that Kumar et al. desired to understand "how this macroalga can thrive in lowered pH/high CO2," which curiosity led them to perform a transcriptome analysis on S. vulgare populations, allowing them to compare the global gene expression profiles of this macroalgal species growing under both acidified and normal pH conditions. And what did that comparison and analysis reveal?

According to the authors, only 2.05 percent of all gene transcripts were differentially expressed, among which were some that are involved in a wide range of cellular and metabolic processes. Kumar et al. also report that "no drastic changes were observed" in carbon acquisition and fixation processes. They also say that "relatively few stress genes, including those for antioxidant enzymes and heat-shock proteins, were affected," suggesting that "algae are adopting molecular strategies to thrive in lowered pH conditions." Furthermore, they add that "the cellular signaling components and membrane receptors affected by elevated CO2/decreased pH seem to contribute towards growth, division and development of S. vulgare at the acidified site," where the macroalga "looks healthy and flourishing." Such positive findings led Kumar et al. to thus conclude that, "altogether, the changes induced by acidification indicate an adaptation of growth and development of S. vulgare at the volcanic vents, suggesting that this fleshy alga exhibits a high plasticity to low pH and can adopt molecular strategies to grow also in future more acidified waters." And that is great news that bodes well for the future of this important habitat-forming species!

Posted 21 August 2017