Seawater carbonate parameters function differently in affecting embryonic development and calcification in Pacific abalone (Haliotis discus hannai)

pH or pCO2 are usually taken to study the impact of ocean acidification on molluscs. Here we studied the different impact of seawater carbonate parameters on embryonic development and calcification of the Pacific abalone (Haliotis discus hannai). Early embryonic development was susceptible to elevated pCO2 level. Larvae hatching duration was positively and hatching rate was negatively correlated with the pCO2 level, respectively. Calcium carbonate (CaCO3) deposition of larval shell was found to be susceptible to calcium carbonate saturation state (omega) rather than pCO2 or pH. Most larvae incubated in seawater with omega arag = 1.5 succeeded in shell for-mation, even when seawater pCO2 level was higher than 3700 mu atm and pHT was close to 7.4. Nevertheless, larvae failed to generate CaCO3 in seawater with omega arag < 0.52 and control level ofpCO2, while seawater DIC level was lowered (< 852 mu mol/kg). Surprisingly, some larvae completed CaCO3 deposition in seawater with omega arag = 0.6 and slightly elevated DIC (2266 mu mol/kg), while seawater pCO2 level was higher than 2700 mu atm and pHT was lower than 7.3. This indicates that abalone may be capable of regulating carbonate chemistry to support shell formation, however, the capability was limited as surging pCO2 level lowered growth rate and jeopardized the integrity of larval shells. Larvae generated thicker shell in seawater with omega arag = 5.6, while adult abalone could not deposit CaCO3 in seawater with omega arag = 0.29 and DIC = 321 mu mol/kg. This indicates that abalone may lack the ability to directly remove or add inorganic carbon at the calcifying sites. In conclusion, different seawater carbonate parameters play different roles in affecting early embryonic development and shell formation of the Pacific abalone, which may exhibit limited capacity to regulate carbonate chemistry.