Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
12 May 2009
Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The revised manuscript was not accepted.
Response of Halimeda to ocean acidification: field and laboratory evidence
L. L. Robbins1, P. O. Knorr1, and P. Hallock2 1US Geological Survey, 600 4th St. South, St. Petersburg, FL, 33701, USA
2University of South Florida, College of Marine Science, St. Petersburg, FL, 33701, USA
Abstract. Rising atmospheric pCO2 levels are changing ocean chemistry more dramatically now than in the last 20 million years. In fact, pH values of the open ocean have decreased by 0.1 since the 1800s and are predicted to decrease 0.1–0.4 globally in the next 90 years. Ocean acidification will affect fundamental geochemical and biological processes including calcification and carbonate sediment production. The west Florida shelf is a natural laboratory to examine the effects of ocean acidification on aragonite production by calcareous green algae. Scanning electron microscopy (SEM) of crystal morphology of calcifying organisms reveals ultrastructural details of calcification that occurred at different saturation states. Comparison of archived and recent specimens of calcareous green alga Halimeda spp. from the west Florida shelf, demonstrates crystal changes in shape and abundance over a 40+ year time span. Halimeda crystal data from apical sections indicate that increases in crystal concentration and decreases in crystal width occurred over the last 40+ years. Laboratory experiments using living specimens of Halimeda grown in environments with known pH values were used to constrain historical observations. Percentages of organic and inorganic carbon per sample weight of pooled species did not significantly change. However, individual species showed decreased inorganic carbon and increased organic carbon in more recent samples, although the sample sizes were limited. These results indicate that the effect of increased pCO2 and decreased pH on calcification is reflected in the crystal morphology of this organism. More data are needed to confirm the observed changes in mass of crystal and organic carbon.
Citation: Robbins, L. L., Knorr, P. O., and Hallock, P.: Response of Halimeda to ocean acidification: field and laboratory evidence, Biogeosciences Discuss., 6, 4895-4918,, 2009.
L. L. Robbins et al.
L. L. Robbins et al.
L. L. Robbins et al.


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