Calcification in Caribbean reef-building corals at high CO levels in a recirculating ocean acidification exposure system.

Projected increases in ocean CO levels are anticipated to affect calcifying organisms more rapidly and to a greater extent than other marine organisms. The effects of ocean acidification (OA) have been documented in numerous species of corals in laboratory studies, largely tested using flow-through exposure systems. We developed a recirculating ocean acidification exposure system that allows precise CO control using a combination of off-gassing measures including aeration, water retention devices, venturi injectors, and CO scrubbing. We evaluated the recirculating system performance in off-gassing effectiveness and maintenance of target CO levels over an 84-day experiment. The system was used to identify changes in calcification and tissue growth in response to elevated CO (1000 μatm) in three reef-building corals of the Caribbean: , , and . All three species displayed an overall increase in net calcification over the 84-day exposure period regardless of CO level (control +0.28- 1.12 g, elevated CO +0.18- 1.16 g), and the system was effective at both off-gassing acidified water to ambient CO levels, and maintaining target elevated CO levels over the 3-month experiment.