The effects of elevated pCO2 on growth, shell production and metabolism of cultured juvenile abalone, Haliotis iris

Reduced seawater pH and elevated pCO(2) are important considerations in tank-based abalone aquaculture, while sea-based farms may be at risk to ocean acidification reductions in pH. Juvenile Haliotis iris (5-13 and 30-40 mm shell length) were reared in two, 100-day experiments at ambient pH(nbs) (similar to 8.1, 450 latm CO2), pH 7.8 (similar to 1000 latm CO2) and pH 7.6 (similar to 1600 latm CO2). Seawater pH was measured and adjusted automatically by bubbling CO2 into water in replicated flow through tanks. Two separate trials were run, in winter (8.8 degrees C) and summer (16.5 degrees C). Survival and growth were monitored every 30 days, and post experiment measurements of morphometrics and respiration rate undertaken. Growth of shell length and wet weight were negatively affected by reduced pH, with a 2 to 3-fold reduction in growth of both size classes between ambient and pH 7.6 treatments in the summer experiment. For small juveniles, growth reductions were in conjunction with decreases to shell weight, while large juveniles showed greater resilience in shell production. No changes to respiration rate occurred, suggesting that juveniles may maintain physiological functioning while tolerating dissolution pressure or that they are unable to upregulate metabolism to compensate for pH effects. These data show that CO2 driven reductions in pH can impact growth, metabolism and biomineralization of abalone, and indicate that water quality and ocean acidification are of importance in aquaculture of the species.