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The Ability of a Seagrass to Buffer the Impacts of Ocean Acidification on a Calcifying Alga

Paper Reviewed
Bergstrom, E., Silva, J., Martins, C. and Horta, P. 2019. Seagrass can mitigate negative ocean acidification effects on calcifying algae. Scientific Reports 9: 1932, doi/10.1038/s41598-018-35670-3.

Writing as background for their work, Bergstrom et al. (2019) say that "seagrasses can act as buffers to ocean acidification (OA) by absorbing large quantities of CO2 and increasing the pH of seawater," such that the increase has "a positive effect on the calcification of co-occurring calcifying algae."

As a test of this hypothesis, the four scientists manipulated the temperature and pCO2 of seawater to examine the physiological responses of two common photoautotrophs from a shallow tropical marine coastal ecosystem in Brazil, the seagrass Halodule wrightii and the calcifying alga Halimeda cuneata.

Results of the short-term (10-day) experiment, in the words of the authors, revealed that "the presence of the seagrass H. wrightii mitigated the negative effect of OA on the calcification of the alga H. cuneata." Under elevated pCO2 conditions, the seagrass was able to maintain relatively high photosynthetic rates, thereby creating seawater conditions that were conducive to the calcification of H. cuneata. More specifically, the calcification rate of H. cuneata was reduced by 72% under OA conditions when the seagrass was not present, whereas it was reduced by only 34% when H. wrightii was present. Thus, the dominant ability of the seagrass to raise the pH of the seawater via photosynthesis "played to the calcifying alga's advantage under OA."

In light of these important findings, Bergstrom et al. write that "the fate of calcifying algae under OA may very well lie in the composition of the accompanying photoautotroph community as well as their associated net community metabolism dynamics." And that fate may well be positive given the likelihood of species to experience physiological tolerance, transgenerational plasticity, phenotypic buffering or plasticity within generations, which combination of factors "will [likely] help maintain population resilience under changing environments" such as OA and/or warming.

Posted 5 June 2019