| Summary: | Coral reefs are a critical building block of the ocean ecosystem, whose health is threatened by ocean acidification (OA) and warming due to increased atmospheric CO2 (Hoegh-Guldberg, 2010; IPCC, 2014). Reliably predicting how coral calcification may respond to OA depends on our understanding of their calcification mechanisms (Ries, 2011; Holcomb et al., 2014; Allison et al., 2014; Gagnon, 2013). But obtaining relevant data on the calcification mechanism is difficult. First, because of coral’s structural arrangement, little is understood about the chemical dynamics inside coral polyps. Second, the speciation, sources, and dynamics of dissolved inorganic carbon (DIC) inside corals remain unresolved because only pH has been measured while a critical second parameter needed to fully characterize the internal carbonate chemistry at the site of coral calcification has been missing (Ries, 2011). Coral calcification processes are affected by changes in ion concentrations due to ocean acidification. Microsensors enable us to measure biological processes in different localities of the coral polyp and we have successfully built pH, CO3 2-, and Ca2+ microelectrodes that are suitable for coral studies with a tip diameter of 10-15 μm. Also this research is the first to combine pH and CO3 2- to calculate DIC inside coral polyp. Two chapters are included in this thesis: chapter 1 focuses on pH and CO3 2-concentrations inside calcifying fluid and chapter 2 focuses on the effects of light on Ca2+ , CO3 2-, and pH dynamics inside coral polyps and different factors that affect the concentration change. In chapter 1, we report the first depth profiles of pH and carbonate ion concentrations ([CO3 2-]) measured inside coral polyps. We observed sharp increases in pH and [CO3 2-] inside the calcifying fluid and very low pH and [CO3 2- ] above it in the coelenteron, supporting the existence of an active process that pumps protons (H+) out of the calcifying fluid. This results in a sharp CO2 gradient from the coelenteron to the calcifying ...
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