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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 20 | Copyright
Biogeosciences, 15, 6167-6183, 2018
https://doi.org/10.5194/bg-15-6167-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Oct 2018

Research article | 23 Oct 2018

The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

Craig S. Young and Christopher J. Gobler Craig S. Young and Christopher J. Gobler
  • Stony Brook University, School of Marine and Atmospheric Sciences, Southampton, NY 11968, USA

Abstract. Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In six of seven experiments, exposure to elevated pCO2 levels ( ∼ 1700µatm) resulted in depressed shell- and/or tissue-based growth rates of bivalves compared to control conditions, whereas rates were significantly higher in the presence of Ulva in all experiments. In many cases, the co-exposure to elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification-only treatment. Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates, and growth rates of bivalves were significantly correlated with Ω in six of seven experiments. Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Ω.

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Photosynthetic activity and/or nitrate assimilation by the macroalgae Ulva buffered carbonate chemistry and yielded enhanced growth of bivalves by mitigating the harmful effects of elevated CO2 levels. This benefit was not limited to acidified conditions, as evidenced by increased bivalve growth in the presence of Ulva within ambient CO2 treatments. The ability of macroalgae to buffer carbonate chemistry may be increasingly important for calcifying organisms vulnerable to ocean acidification.
Photosynthetic activity and/or nitrate assimilation by the macroalgae Ulva buffered carbonate...
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