Comparison of the lethal effect of CO2 and acidification on red sea bream (Pagrus major) during the early developmental stages

To compare the acute toxicity of CO2- and HCl-acidified seawater, eggs and larvae of a marine fish, Pagrus major, were exposed to seawater equilibrated with CO2-enriched gas mixtures (CO2=5% or 10%, O2=20.95% balanced with N2) or seawater acidified with 1 N HCl at two pH levels (pH 6.2 (=5% CO2) and 5.9 (=10% CO2)) for 6 h (eggs) or 24 h (larvae). Mortalities of eggs were 85.8% (CO2) and 3.6% (HCl) at pH 6.2, and 97.4% (CO2) and 0.9% (HCl) at pH 5.9, while those of larvae were 61.2% (CO2) and 1.6% (HCl) at pH 6.2, and 100% (CO2) and 5.0% (HCl) at pH 5.9. Thus, previous research on the effects of acidified seawater on marine organisms, as a substitute for CO2, has largely underestimated the toxic effects of CO2