Abstract
A common, but not universal, effect of ocean acidification on benthic foraminifera is a reduction in the growth rate. The miliolid Archaias angulatus is a high-Mg (>4 mole% MgCO (sub 3) ), symbiont-bearing, soritid benthic foraminifer that contributes to Caribbean reef carbonate sediments. A laboratory culture study assessed the effects of reduced pH on the growth of A. angulatus. We observed a statistically significant 50% reduction in the growth rate (p < 0.01), calculated from changes in maximum diameter, from 160 mu m/28 days in the pH 8.0/pCO (sub 2) (sub air) 480 ppm control group to 80 mu m/28 days at a treatment level of pH 7.6/pCO (sub 2) (sub air) 1328 ppm. Additionally, pseudopore area, delta (super 18) O values, and Mg/Ca ratio all increased, albeit slightly in the latter two variables. The reduction in growth rate indicates that under a high-CO (sub 2) setting, future A. angulatus populations will consist of smaller adults. A model using the results of this study estimates that at pH 7.6 A. angulatus carbonate production in the South Florida reef tract and Florida Bay decreases by 85%, from 0.27 Mt/yr to 0.04 Mt/yr, over an area of 9,000 km (super 2) .