We report results from an oyster hatchery on the Oregon coast, where intake waters experienced variable carbonate chemistry (aragonite saturation state , 0.8 to . 3.2; pH , 7.6 to . 8.2) in the early summer of 2009. Both larval production and midstage growth (, 120 to , 150 mm) of the oyster Crassostrea gigas were significantly negatively correlated with the aragonite saturation state of waters in which larval oysters were spawned and reared for the first 48 h of life. The effects of the initial spawning conditions did not have a significant effect on early-stage growth (growth from D-hinge stage to , 120 mm), suggesting a delayed effect of water chemistry on larval development.

Abstract. The concentration of CO2 in the atmosphere is projected to reach twice the preindustrial level by the middle of the 21 st century. This increase will reduce the 2 concentration of CO3-of the surface ocean by 30% relative to the preindustrial level and will reduce the calcium carbonate saturation state of the surface ocean by an equal percentage.Using the large 2650 m 3 coral reef mesocosm at the BIOSPHERE-2 facility near Tucson, Arizona, we investigated the effect of the projected changes in seawater carbonate chemistry on the calcificafion of coral reef organisms at the commtmity scale. Our experimental design was to obtain a long (3.8 years) time'series of the net calcificafion of the complete system and all relevant physical and chemical variables (tem•rature, salinity, light, nutrients, Ca 2+, pCO2, TCO2, and total alkalinity). Periodic additions of NaHCOz, Na2CO•, and/or CaC12 were made to change the calcium carbonate saturation state of the water. We found that there were consistent and reproducible changes in the rate of calcificafion in response to our manipulations of the saturation state. We show that the net community calcificafion rate suggests that saturation state or a closely related quantity is a primary environmental factor that influences calcffication on coral reefs at the ecosystem level. We compare the sensitivity of cal½ification to short-term (days) and long-term (months to years) changes in saturation state and found that the response was not significantly different. This indicates that coral reef organisms do not seem to be able to acclimate to changing saturation state. The predicted decrease in coral reef calcification •een the years 1880 and 2065 A.D. based on our longterm results is 40%. Previous small-scale, short-term organismal studies predicted a calcification reduction of 14-30%. This much longer, community-scale study suggests that the impact on coral reefs may be greater than previously suspected. in the next century coral reefs will be less able to cope with rising sea level and other anthropogenic stresses.

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