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Spatial community shift from hard to soft corals in acidified water

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Anthropogenic increases in the partial pressure of CO2 ( p CO 2 ) cause ocean acidification, declining calcium carbonate saturation states, reduced coral reef calcification and changes in the compositions of marine communities1. Most projected community changes due to ocean acidification describe transitions from hard coral to non-calcifying macroalgal communities2; other organisms have received less attention, despite the biotic diversity of coral reef communities. We show that the spatial distributions of both hard and soft coral communities in volcanically acidified, semi-enclosed waters off Iwotorishima Island, Japan, are related to p CO 2 levels. Hard corals are restricted to non-acidified low- p CO 2 (225 μatm) zones, dense populations of the soft coral Sarcophyton elegans dominate medium- p CO 2 (831 μatm) zones, and both hard and soft corals are absent from the highest- p CO 2 (1,465 μatm) zone. In CO2-enriched culture experiments, high- p CO 2 conditions benefited Sarcophyton elegans by enhancing photosynthesis rates and did not affect light calcification, but dark decalcification (negative net calcification) increased with increasing p CO 2 . These results suggest that reef communities may shift from reef-building hard corals to non-reef-building soft corals under p CO 2 levels (550–970 μatm) predicted by the end of this century3, and that higher p CO 2 levels would challenge the survival of some reef organisms.

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Figure 1: Aerial photograph, map of the acidified area (red rectangle in Supplementary Fig. S1) and transect profiles of the acidified area.
Figure 2: Change in water depth and seawater carbonate chemistry.
Figure 3: Net photosynthesis rates of cultured S. elegans plotted against p CO 2 .
Figure 4: Net calcification rate of cultured S. elegans plotted against p CO 2 .

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Change history

  • 28 March 2013

    In the version of this Letter originally published online, the e-mail address for the corresponding author should have been: This error has now been corrected in all versions of the Letter.

  • 23 April 2013

    In the version of this Letter originally published online, in the legend for Fig. 1b, the contour lines for the distribution of hard corals were swapped. This error has now been corrected in all versions of the Letter.


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We would like to thank T. Nishino, M. Yamaguchi and the members of the Tokyo University Marine Expedition Club for assisting with the field survey, Y. Imahara (Kuroshio Biological Research Institute) for identification methodology of soft coral and H. Tomaru (Graduate School of Science and Technology, Chiba University) for analyses of ion concentrations. We acknowledge J. D. Reimer (Transdisciplinary Research Organization for Subtropical Island Studies, University of the Ryukyus) for checking and editing the English. This research was financially supported by a Sasakawa Scientific Research Grant and a Grant-in -Aid for Scientific Research on Innovative Areas (Strategy for Ecosystem Symbiosis and Coexistence with Human Beings under Multiple Stresses).

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S.I. designed the study and compiled the manuscript with the help of all other co-authors. S.I. performed the field survey, collected soft coral samples, and performed the culture experiments. H. Kayanne supported the planning operations and conducted the field survey with S.I. and S.Y., who analysed seawater chemistry together with S.I. H. Kurihara designed the CO2-enriched culture experiment.

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Correspondence to Shihori Inoue.

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The authors declare no competing financial interests.

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Inoue, S., Kayanne, H., Yamamoto, S. et al. Spatial community shift from hard to soft corals in acidified water. Nature Clim Change 3, 683–687 (2013).

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