The effects of ocean acidification and upwelling conditions on the growth and calcification of the red abalone (Haliotis rufescens)

Upwelling events along the California coast expose invertebrates to low dissolved oxygen simultaneously with high pCO2 levels that are progressively increasing as a result of rising atmospheric CO2. These multiple stressors could potentially impact the growth and calcification of economically valuable molluscs, such as abalone. To evaluate this threat, juvenile red abalone were maintained over a 4-week period in seawater undersaturated with respect to aragonite and containing 85% dissolved oxygen, which simulated an upwelling event. Seawater conditions were then returned to ambient levels for 3 weeks to determine the ability of the abalone to recover from the potential effects of low oxygen and high pCO2 conditions. Abalone exposed to the treatment had lower shell weights and calcium content per shell than abalone in the ambient group. Shells also appeared much lighter in color following the acidification period. After both groups were returned to ambient conditions, shells of the abalone in the treatment group still weighed less and had lower calcium content than the shells of the ambient group. The amount of weight gained by the abalone during the 3-week ambient period, however, was the same for both groups, suggesting an ability to recover a normal rate of weight gain after exposure. These findings suggest that juvenile red abalone experienced decreased net calcification following exposure to high CO2 and decreased DO. Though abalone were able to recover to normal growth rates, they were not able to accelerate their net calcification to catch up to the shells weights and calcium content of the ambient group, suggesting that they may have thinner or less dense shells following each upwelling event