Populations of large benthic foraminiferans (LBFs) that inhabit coral reef platforms are major producers of calcium carbonate (CaCO3) in reef ecosystems. This study documented the population density of living intertidal LBF populations at One Tree Reef (OTR), southern Great Barrier Reef, in a community dominated by Marginopora vertebralis and Baculogypsina sphaerulata. Densities of 7.7 × 103 M. vertebralis individuals (ind.)/m2 and 4.5 × 105 B. sphaerulata ind./m2 were estimated for these populations in May 2011. We applied remote-sensing technology to determine reef-scale estimates of suitable Foraminifera habitats and used these to estimate overall stocks of LBF populations on the intertidal algal flat at OTR of ca. 2800 metric tons. The growth rate of M. vertebralis was determined in a laboratory study, and the data were used to calculate the annual CaCO3 production of the reef flat by the LBF population. The response of M. vertebralis to ocean warming was investigated using 3-week incubations at temperatures ranging from ambient sea surface temperature to +6°C. There were significant decreases in growth and concomitant CaCO3 production in 6°C warmer water, which resulted in shell dissolution of M. vertebralis. These results indicate that climate-driven ocean warming projected for the region will result in significant decreases in CaCO3 production in overall foraminiferan populations, although species-specific effects should be further investigated.