Response of Halimeda to ocean acidification: field and laboratory evidence

Abstract

Rising atmospheric pCO2 levels are changing ocean chemistry more dramatically now than in the last 20 million years. In fact, pHvalues of the open ocean have decreased by 0.1 since the 1800s and are predicted to decrease 0.10.4 globally in the next 90 years. Ocean acidification will affect fundamental geochemical and biological pro- cesses including calcification and carbonate sediment production. The west Florida shelf is a natural laboratory to examine the effects of ocean acidification on arago- nite 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, demon- strates crystal changes in shape and abundance over a 40+ year time span.