USING SHELL MORPHOMETRICS TO UNDERSTAND OCEAN ACIDIFICATION IMPACTS ON THE CALCIFICATION OF REEF-DWELLING FORAMINIFERA

Anthropogenic fossil fuel emissions since the Industrial Revolution have led to increased concentrations of atmospheric CO₂, with at least one-quarter of emitted CO₂ being absorbed by the ocean. Ocean acidification (OA) refers to the reduction in seawater pH that occurs as a result of CO₂ absorption in seawater. OA results in a lowering of carbonate ion concentration ([CO₃^2-]), which is important to many marine calcifiers that use CO₃^2- to precipitate their shells and skeletons. Foraminifera are one such group of organisms that have demonstrated a response to OA, though many species remain to be examined. These organisms can be used as proxy tools to understand the paleo progression of OA. Samples of the benthic, reef-dwelling foraminifera, Amphistegina gibbosa, were collected from Cayo Enrique, Puerto Rico in 1985 and 2012 while scuba diving. A morphometric measurement, area density (estimated by individual weight/2-D area), was used to approximate shell thickness for each sample population. Scanning electron microscope (SEM) images were used to verify shell-wall thickness and served as a method comparison. Collectively, these results are used to determine long-term changes in foraminiferal calcification and indicate a statistically significant increase in calcification for A. gibbosa since 1985, suggesting an inverse response to OA.