Alkalinity enrichment stimulates calcification and linear extension in Acropora cervicornis

Environmental change, disease, and a myriad of local stressors have led to worldwide declines in coral cover, demanding that restoration efforts scale with the magnitude of the crisis. Critical to this goal is the industrial-scale propagation of coral fragments. Preliminary evidence from aquarists suggests that elevating seawater alkalinity increases coral growth, and several papers have reported enhanced calcium carbonate deposition. Many questions remain, however, concerning the effectiveness on species targeted for restoration, optimal alkalinity range, and the manner in which growth is affected (e.g., skeleton extension versus density). Here, we investigate the effect of elevated alkalinity on total calcification and linear extension of the Caribbean coral, Acropora cervicornis. Corals were exposed to one of four alkalinity treatments for 33 days using a sodium bicarbonate/sodium carbonate solution. Elevated alkalinity significantly enhanced total calcification, increasing by 125% in the highest treatment. Linear extension was also significantly enhanced during the first half of the experiment (98%), but the effect was no longer detectable after week three when growth slowed in all groups, including the controls. These findings suggest that elevated alkalinity may accelerate coral propagation, representing an affordable and practical tool to enhance production efficiency in land-based coral restoration facilities.