Response of Halimeda to ocean acidification: field and laboratory evidence
Other literature type
Robbins, L. L.
Knorr, P. O.
(issn: 1726-4189, eissn: 1726-4189)
Rising atmospheric <i>p</i>CO<sub>2</sub> 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 <i>Halimeda</i>
spp. from the west Florida shelf, demonstrates crystal changes in shape and
abundance over a 40+ year time span. <i>Halimeda</i> 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 <i>Halimeda</i> 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 <i>p</i>CO<sub>2</sub> 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.