Publication Date:
2012-04-17
Description:
Changes in the seawater carbonate chemistry (ocean acidification) from increasing atmospheric carbon dioxide (CO 2 ) concentrations negatively affect many marine calcifying organisms, but may benefit primary producers under dissolved inorganic carbon (DIC) limitation. To improve predictions of the ecological effects of ocean acidification, the net gains and losses between the processes of photosynthesis and calcification need to be studied jointly on physiological and population levels. We studied productivity, respiration, and abundances of the symbiont-bearing foraminifera Marginopora vertebralis on natural CO 2 seeps in Papua New Guinea and conducted additional studies on production and calcification on the Great Barrier Reef (GBR) using artificially enhanced p CO 2 . Net oxygen production increased up to 90% with increasing p CO 2 , with temperature, light and pH together explaining 61% of the variance in production. Production increased with increasing light and increasing p CO 2 , and declined at higher temperatures. Respiration was also significantly elevated (~25%), while calcification was reduced (16-39%) at low pH/high p CO 2 compared to present day conditions. In the field, M. vertebralis was absent at three CO 2 seep sites at pH T otal levels below ~7.9 ( p CO 2 ~700 μatm), but it was found in densities of over 1000 m −2 at all three control sites. The study showed that endosymbiotic algae in foraminifera benefit from increased DIC availability, and may be naturally carbon limited. The observed reduction in calcification may have been caused either by increased energy demands for proton pumping (measured as elevated rates of respiration), or by stronger competition for DIC from the more productive symbionts. The net outcome of these two competing processes is that M. vertebralis cannot maintain populations under p CO 2 exceeding 700 μatm, thus are likely to be extinct in the next century.
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
,
Energy, Environment Protection, Nuclear Power Engineering
,
Geography
Permalink