Seawater carbonate parameters function differently in affecting embryonic development and calcification in Pacific...

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 (Ω) rather than pCO₂ or pH. Most larvae incubated in seawater with Ω_arag = 1.5 succeeded in shell formation, even when seawater pCO₂ level was higher than 3700 μatm and pH_T was close to 7.4. Nevertheless, larvae failed to generate CaCO₃ in seawater with Ω_arag ≤ 0.52 and control level of pCO₂, while seawater DIC level was lowered (≤ 852 μmol/kg). Surprisingly, some larvae completed CaCO₃ deposition in seawater with Ω_arag = 0.6 and slightly elevated DIC (2266 μmol/kg), while seawater pCO₂ level was higher than 2700 μatm and pH_T 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 Ω_arag = 5.6, while adult abalone could not deposit CaCO₃ in seawater with Ω_arag = 0.29 and DIC = 321 μmol/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.