Tolerance Of Allogromiid Foraminifera To Severely Elevated Carbon Dioxide Concentrations: Implications To Future Ecosystem Functioning And Paleoceanographic Interpretations

摘要

Increases in the partial pressure of carbon dioxide (pCO_2) in the atmosphere will significantly affect a wide variety of terrestrial fauna and flora. Because of tight atmospheric-oceanic coupling, shallow-water marine species are also expected to be affected by increases in atmospheric carbon dioxide concentrations. One proposed way to slow increases in atmospheric pCO_2 is to sequester CO_2 in the deep sea. Thus, over the next few centuries marine species will be exposed to changing seawater chemistry caused by ocean-atmospheric exchange and/or deep-ocean sequestration. This initial case study on one allogromiid foraminiferal species (Allogromia laticollaris) was conducted to begin to ascertain the effect of elevated pCO_2 on benthic Foraminifera, which are a major meiofaunal constituent of shallow- and deep-water marine communities. Cultures of this thecate foraminiferan protist were used for 10-14-day experiments. Experimental treatments were executed in an incubator that controlled CO_2 (15000; 30000; 60000; 90000; 200000 ppm), temperature and humidity; atmospheric controls (i.e., ～375 ppm CO_2) were executed simultaneously. Although the experimental elevated pCO_2 values are far above foreseeable surface water pCO_2, they were selected to represent the spectrum of conditions expected for the benthos if deep-sea CO_2 sequestration becomes a reality. Survival was assessed in two independent ways: pseudopodial presence/absence and measurement of adenosine triphosphate (ATP), which is an indicator of cellular energy. Substantial proportions of A laticollaris populations survived 200000 ppm CO_2 although the mean of the median [ATP] of survivors was statistically lower for this treatment than for that of atmospheric control specimens. After individuals that had been incubated in 200000 ppm CO_2 for 12 days were transferred to atmospheric conditions for ～24 h, the [ATP] of live specimens (survivors) approximated those of the comparable atmospheric control treatment. Incubation in 200000 ppm CO_2 also resulted in reproduction by some individuals. Results suggest that certain Foraminifera are able to tolerate deep-sea CO_2 sequestration and perhaps thrive as a result of elevated pCO_2 that is predicted for the next few centuries, in a high-pCO_2 world. Thus, allogromiid foraminiferal "blooms" may result from climate change. Furthermore, because allogromiids consume a variety of prey, it is likely that they will be major players in ecosystem dynamics of future coastal sedimentary environments.