Effects of ocean acidification in relation to diel cycles of seawater pCO2 on early development of Ezo abalone Haliotis dicus hannai

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We investigated the effects of ocean acidification in relation to diel cycles of seawaterpCO 2 levels onthe early development of ezo abalone Haliotis discus hannai in the laboratory. Shell length, mortalityand malformation of larval abalone were examined under different pCO 2 levels with mimicked dielcycle using a CO CO2 manipulation system . Adult abalone were induced to spawn and gametes wereartificially fertil ized in concentrations of 4 400, 800 or 1200 pCO 2 µatm. Sixteen hours post post-fertilization,hatched larvae were exposed to running seawater adjusted to a constant level (400, 800 or 1200 µatmpCO 2) or fluctuating on a diel cycle (400 -1200 or 800 -1600 µatm pCO 2) pCO 2 in 75 h experimentalperiods. There were no significant differences in the mortality rate, malformation rate and shell lengthof larvae among the 400, 800, and 400-1200 µatm pCO 2 treatments. In contrast, the malformation rate was significantly higher in the 1200 and 800 -1600 µatm pCO 2 treatments than in the 400 µatm pCO 2 treatment. Larval shell length in the 800 -1600 µatm pCO 2 treatment was significantly smaller than inthe other pCO 2 treatments. The exposed duration time exceeding the aragonite saturation state wouldbe a critical factor determining the negative impacts on the larval development of abalone.