A coralline alga gains tolerance to ocean acidification over multiple generations of exposure


Crustose coralline algae play a crucial role in the building of reefs in the photic zones of nearshore ecosystems globally, and are highly susceptible to ocean acidification1,2,3. Nevertheless, the extent to which ecologically important crustose coralline algae can gain tolerance to ocean acidification over multiple generations of exposure is unknown. We show that, while calcification of juvenile crustose coralline algae is initially highly sensitive to ocean acidification, after six generations of exposure the effects of ocean acidification disappear. A reciprocal transplant experiment conducted on the seventh generation, where half of all replicates were interchanged across treatments, confirmed that they had acquired tolerance to low pH and not simply to laboratory conditions. Neither exposure to greater pH variability, nor chemical conditions within the micro-scale calcifying fluid internally, appeared to play a role in fostering this capacity. Our results demonstrate that reef-accreting taxa can gain tolerance to ocean acidification over multiple generations of exposure, suggesting that some of these cosmopolitan species could maintain their critical ecological role in reef formation.

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Fig. 1: Growth of CCA populations after two to six generations of exposure to present-day and ocean acidification treatments.
Fig. 2: Growth of CCA after seven generations grown under present-day and ocean acidification treatments (controls), versus those transferred to these novel treatments following treatment with the opposite mean pH for six generations.
Fig. 3: Geochemical measurements of coralline algal calcite in each generation.

Data availability

Data are available at dryad: https://doi.org/10.5061/dryad.pzgmsbcfq.

Code availability

Examples of R code used for analysis and figure creation are available at: https://zenodo.org/record/3564869#.XemBMegzaUk. Raman code is available at: https://zenodo.org/record/3563461#.XeithpMzbOQ.


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We thank A.-M. Nisumaa-Comeau, G. Ellwood and J. P. D’Olivo for laboratory assistance; V. Schoepf and S. McCoy for comments on a previous version; and R. Townsend from the Western Australian Museum for training in species’ identification. M.T.M. was supported by an Australian Research Council (ARC) Laureate Fellowship (no. FL120100049) and C.E.C. and T.M.D. by the ARC Centre of Excellence for Coral Reef Studies (grant no. CE140100020). S.C. was supported by an ARC Discovery Early Career Researcher Award (no. DE160100668). C.E.C. was also supported by a Rutherford Discovery Fellowship from The Royal Society of New Zealand Te Apārangi (no. RDF-VUW1701).

Author information




C.E.C. and S.C. conceived and ran the experiment and wrote the manuscript. C.E.C. ran the statistical analysis and conducted boron isotope measurements. M.T.M. conceived the experiment and provided vital laboratory equipment, facilities and resources. T.M.D. conducted Raman spectroscopy. E.L., B.M., K.G., F.P. and Q.D. all ran the experiment and measured seawater carbonate chemistry. All authors edited the manuscript, provided intellectual input and agreed to its submission.

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Correspondence to C. E. Cornwall.

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The authors declare no competing interests.

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Peer review information Nature Climate Change thanks Jan Fietzke and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Growth of coralline algae in all treatment combinations.

Growth of coralline algae in all treatment combinations exposed to 2 to 6 generations to experimental treatments. PC = present-day constant, PF = present-day fluctuating, OC = ocean acidification constant, OF = ocean acidification fluctuating. Populations from high variance (Tallon) and low variance (Shell Island) shown here. Median and quartiles presented in boxplots. N = 6 per treatment and generation combination.

Extended Data Fig. 2 Total area covered by coralline algal recruits by the end of each generation.

Total recruit area at the end of each generation (41–52 days) averaged across each population and variability treatment combination. Note significant effect of mean seawater pH, generation, and their interaction. Median and quartiles presented in boxplots. n = 24 per treatment and generation combination.

Extended Data Fig. 3 Total area covered by coralline algal recruits by the end of generation 8.

Total area covered by coralline algal recruits by the end of generation 8 (61 days). Note significant effect of low pH on recruitment and expansion on only the pH 7.70 constant pH treatment from parents transferred from the pH 8.00 constant treatments. Median and quartiles presented in boxplots. n = 12 per treatment and generation combination.

Extended Data Fig. 4 Geochemistry of generation 8 individuals.

Geochemistry of generation 8 individuals. δ11B (pHcf proxy), FWHM (Ωcf proxy) and magnesium content measured using Raman spectroscopy of generation 8 individuals either transferred into the opposite mean pH for one generation, or kept as controls within their original treatment. Median and quartiles presented in boxplots. n = 12 per treatment and generation combination.

Extended Data Fig. 5 Growth of coralline algae against FWHM.

Growth of coralline algae plotted against their FWHM (Ωcf proxy), showing that those with faster growth have lower Ωcf. Points represent means of treatment by generational combinations, that is n = 6 each.

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Supplementary Figs. 1–3 and Tables 1–11.

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Cornwall, C.E., Comeau, S., DeCarlo, T.M. et al. A coralline alga gains tolerance to ocean acidification over multiple generations of exposure. Nat. Clim. Chang. 10, 143–146 (2020). https://doi.org/10.1038/s41558-019-0681-8

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