Volcanic carbon dioxide vents show ecosystem effects of ocean acidification


The atmospheric partial pressure of carbon dioxide ( p CO 2 ) will almost certainly be double that of pre-industrial levels by 2100 and will be considerably higher than at any time during the past few million years1. The oceans are a principal sink for anthropogenic CO2 where it is estimated to have caused a 30% increase in the concentration of H+ in ocean surface waters since the early 1900s and may lead to a drop in seawater pH of up to 0.5 units by 2100 (refs 2, 3). Our understanding of how increased ocean acidity may affect marine ecosystems is at present very limited as almost all studies have been in vitro, short-term, rapid perturbation experiments on isolated elements of the ecosystem4,5. Here we show the effects of acidification on benthic ecosystems at shallow coastal sites where volcanic CO2 vents lower the pH of the water column. Along gradients of normal pH (8.1–8.2) to lowered pH (mean 7.8–7.9, minimum 7.4–7.5), typical rocky shore communities with abundant calcareous organisms shifted to communities lacking scleractinian corals with significant reductions in sea urchin and coralline algal abundance. To our knowledge, this is the first ecosystem-scale validation of predictions that these important groups of organisms are susceptible to elevated amounts of p CO 2 . Sea-grass production was highest in an area at mean pH 7.6 (1,827 μatm  p CO 2 ) where coralline algal biomass was significantly reduced and gastropod shells were dissolving due to periods of carbonate sub-saturation. The species populating the vent sites comprise a suite of organisms that are resilient to naturally high concentrations of p CO 2 and indicate that ocean acidification may benefit highly invasive non-native algal species. Our results provide the first in situ insights into how shallow water marine communities might change when susceptible organisms are removed owing to ocean acidification.

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Figure 1: Map of CO 2 vent sites north and south of Castello d’Aragonese, off Ischia Island, Italy.
Figure 2: Variation in pH, cover of algae and abundance of species at CO 2 vents south of Castello d’Aragonese.
Figure 3: Sea-grass shoot density and amount of epiphytic CaCO 3 on leaves growing at differing pH levels south of Castello d’Aragonese.
Figure 4: Dissolution of calcified organisms due to naturally acidified sea water.


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We thank the staff of Anton Dohrn Benthic laboratory, Ischia for technical help. J.M.H.-S. was funded by a Royal Society University Research Fellowship and was first shown the gas vent sites by M. Taviani in 2002; R.R.-M. and S.M.T. were funded by the Leverhulme Trust. A. de Simone, A. Ferrara and M. Laurenti helped with field measurements, V. King took photo 4d, and O. Hoegh Guldberg and P. Liss helped improve the manuscript.

Author Contributions All authors were involved with fieldwork and sample analyses. J.M.H.-S. designed the study and wrote the paper along with R.R.-M., M.F. and S.M.T. D.T. analysed gases, S.M. analysed sea-grass epiphytes and seawater chemistry, E.R. and S.J.R. collected intertidal and subtidal data respectively, and M.-C.B. provided sea-grass expertise. All authors discussed results and commented on the manuscript.

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Correspondence to Jason M. Hall-Spencer.

Supplementary information

Supplementary information

The file contains Supplementary Methods with additional references, Supplementary Tables 2 (A,B,C)-4 and Legend to Supplementary Movie 1 (PDF 222 kb)

Supplementary information

The file contains Supplementary Movie 1. Underwater video showing Posidonia oceanica meadow at the CO2 vent site of Castello d`Aragonese (Gulf of Naples, Italy), gas collection from the vents, and Cerithium vulgatum gastropods showing shell dissolution due to the effects of acidified seawater. (WMV 18646 kb)

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Hall-Spencer, J., Rodolfo-Metalpa, R., Martin, S. et al. Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature 454, 96–99 (2008). https://doi.org/10.1038/nature07051

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