IMPACT OF ELEVATED pCO2 on SURVIVAL AND TEST STRUCTURE OF BENTHIC FORAMINIFERA

We tested the impact of predicted increases in surface ocean pCO₂ on the survival and test microstructure of a suite of benthic foraminiferal species from a range of geographical regions and water depths. Ocean acidification is likely to affect the majority of marine organisms and may have a particularly strong influence on those that produce calcium carbonate. Foraminifera are among the most ubiquitous marine calcifying organisms and are an important link the marine food web. The response of benthic foraminifera to ocean acidification may vary depending on the environmental conditions of their habitats – for instance, shallow-water taxa may respond differently than deep-water taxa, and infaunal taxa may be adapted to high-pCO₂ / low [CO₃^2-] pore-water microenvironments. Species from three different regions (temperate Atlantic, 80m; temperate Pacific, 430m; and tropical Florida reef, 1.5m to 8m) were exposed to ambient and two elevated pCO₂ conditions for a period of up to six weeks. Elevated atmospheric pCO₂ was maintained using a feedback controlled infrared CO₂ sensor, and carbonate chemistry parameters (alkalinity, dissolved inorganic carbon) were determined at five time points throughout the incubation period. Specimens were harvested after one week, two weeks and six weeks. Foraminiferal survival and cellular energy levels were assessed using Adenosine Triphosphate (ATP) analysis and test microstructure was evaluated using high resolution SEM. We observed little direct impact of elevated pCO₂ on the survival of the temperate (Bolivina argentea, Bulimina marginata) and tropical (Amphistegina gibbosa) foraminiferal species used in our study. However, reproduction by A. gibbosa was affected; the mean number of offspring of this reef species was lower under elevated pCO₂ than under ambient pCO₂ . None of the other species studied reproduced in any of the three treatments (elevated pCO₂ or atmospheric controls). The test microstructure of A. gibbosa from high pCO₂ treatments displayed areas of dissolution, but the other species did not show this response. Future work must determine the ecological effects of such changes in test microstructure and whether entire life cycles can be sustained in such environmental conditions. Supported by NSF OCE- 0725966 to JMB and DCM.