TOLERANCE OF BENTHIC FORAMINIFERA TO SEVERELY ELEVATED CARBON DIOXIDE CONCENTRATIONS: IMPLICATIONS TO FUTURE ECOSYSTEM FUNCTIONING AND PALEOCEANOGRAPHIC INTERPRETATIONS

Increases in atmospheric carbon dioxide will significantly affect a wide variety of fauna and flora. Because of tight atmospheric-oceanic coupling, marine species are also expected to be affected by higher [CO₂]. Experiments were conducted to ascertain the effect of elevated [CO₂] on benthic foraminifera, which are a major meiofaunal constituent of marine communities. Cultures of the “naked” (non-fossilizable) salt marsh foraminifer Allogromia laticollaris were subject to augmented [CO₂] for 10-14 days. Replicated experiments were done in an incubator that controlled CO₂ (1.5%, 3%, 6%, 9%), temperature and humidity. Just before experiment terminations, the pH of the seawater medium was measured. Present-day atmospheric controls (i.e., 0.037% CO₂, 370 ppm) were executed simultaneously. Survival was assessed in two independent ways: pseudopodial presence/absence and measurement of adenosine triphosphate (ATP), which is an indicator of cellular energy. Results indicate that A. laticollaris survived 9% CO₂ although the average [ATP] per individual was lower than that of atmospheric controls. After specimens that had been incubated in 9% CO₂ for 11 days were transferred to atmospheric conditions overnight, their [ATP] approached those of controls. Incubation in 9% CO₂ also resulted in asexual reproduction in many adults. Interestingly, [CO₂] of 1.5% and 3% resulted in increased [ATP], with subsequent decreases in [ATP] after transfer to atmospheric conditions. In sum, these soft-bodied foraminifers are able to tolerate, and perhaps thrive, during elevated carbon dioxide concentrations and concomitant pH decreases that are expected from global change. Thus, allogromiid foraminiferal “blooms” may result from global change. Because these allogromiids consume a variety of prey, including bacteria and their biofilms, unicellular algae, and small metazoans, it is likely that they will be major players in ecosystem dynamics of future coastal sedimentary environments.