Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions
Rising atmospheric CO2 is acidifying the world’s oceans, affecting both calcification and dissolution processes in coral reefs. Among processes, carbonate dissolution by bioeroding microflora has been overlooked, and especially its impact on seawater alkalinity. To date, this biogeological process has only been studied using microscopy or buoyant weight techniques. To better understand its possible effect on seawater alkalinity, and thus on reef carbonate budget, an experiment was conducted under various seawater chemistry conditions (2 ≤ Ωarag ≤ 3.5 corresponding to 440 ≤ pCO2 (µatm) ≤ 940) at 25 °C under night and daylight (200 µmol photons m−2 s−1) with natural microboring communities colonizing dead coral blocks (New Caledonia). Both the alkalinity anomaly technique and microscopy methods were used to study the activity of those communities dominated by the chlorophyte Ostreobium sp. Results show that (1) the amount of alkalinity released in seawater by such communities is significant and varies between 12.8 ± 0.7 at ΩArag ~ 2 and 5.6 ± 0.4 mmol CaCO3 m−2 day−1 at ΩArag ~ 3–3.5 considering a 12:12 photoperiod; (2) although dissolution is higher at night (~ 80 vs. 20% during daylight), the process can occur under significant photosynthetic activity; and (3) the process is greatly stimulated when an acidity threshold is reached (pCO2 ≥ 920 µatm vs. current conditions at constant light intensity). We show that carbonate dissolution by microborers is a major biogeochemical process that could dissolve a large part of the carbonates deposited by calcifying organisms under ocean acidification.
KeywordsBiogenic carbonate dissolution Microborers Euendoliths Coral reefs Ocean acidification Seawater alkalinity
We would like to dedicate this paper to our colleague and friend Marlin Atkinson who passed away in 2013. A.T. and P.C. conceived the experimental design. A.T., P.C., and A.C. collected samples and analyzed data. A.T. and P.C. wrote the article and A.C. gave assistance on figure preparations and for formatting. We thank the Plateforme Alizes (IRD Bondy) for SEM access and S. Pyneeandy for her help with measurements of biogenic rates on coral blocks. We thank the Center IRD in Nouméa for its support in the field. Finally, this work was supported by the French Ministry of Ecology (program ‘MIDACOR’, 2011–2014) and the Institut de Recherche pour le Développement. The funding sponsors had no involvement in the present study development (design, collection, analysis, etc.).
Datasets are available from the corresponding author (firstname.lastname@example.org) upon reasonable request, while pending to be deposited on the SEANOE repository.
- Chazottes V, Le Campion-Alsumard T, Peyrot-Clausade M, Cuet P (2002) The effects of eutrophication-related alterations to coral reef communities on agents and rates of bioerosion (Reunion Island, Indian Ocean). Coral Reefs 21:375–390Google Scholar
- Dickson AG, Sabine CL, Christian JR (2007) Guide to best practices for ocean CO2 measurements. PICES Spec Pub 3:1–191Google Scholar
- Golubic S, Friedmann I, Schneider J (1981) The lithobiontic ecological niche, with special reference to microorganisms. J Sediment Res 51:475–478Google Scholar
- Kinsey DW (1978) Productivity and calcification estimates using slack-water periods and field enclosures. In: Stoddart DR, Johannes RE (eds) Monographs on oceanographic methodology, Coral reefs: research methods. UNESCO, pp 439–468Google Scholar
- Kobluk DR, Risk MJ (1977) Calcification of exposed filaments of endolithic algae, micrite envelope formation and sediment production. J Sediment Res 47:517–528Google Scholar
- Morse JW (1983) The kinetics of calcium carbonate dissolution and precipitation. Rev Miner Geochem 11:227–264Google Scholar
- Pierrot D, Lewis E, Wallace DWR (2006) MS Excel program developed for CO2 system calculations. ORNL/CDIAC-105 Carbon Dioxide Information Analysis CenterGoogle Scholar
- Stocker TF, Qin D, Plattner GK et al (2013) Technical summary. In: Climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change. Cambridge, UK and New York, NY, USA: Cambridge University Press, pp 33–115Google Scholar
- Stumm W, Morgan JJ (1996) Aquatic chemistry: chemical equilibria and rates in natural waters. Wiley, New YorkGoogle Scholar
- Tudhope AW, Risk MJ (1985) Rate of dissolution of carbonate sediments by microboring organisms, Davies Reef, Australia. J Sediment Res 55:440–447Google Scholar
- Wu H, Dissard D, Douville E, Blamart D, Bordier L, Tribollet A, Le Cornec F, Pons-Branchu E, Dapoigny A, Lazareth CE (2018) Surface ocean pH variations since 1689 CE and recent ocean acidification in the tropical South Pacific. Nat Commun 9:2543. https://doi.org/10.1038/s41467-018-04922-1 CrossRefGoogle Scholar