MEPS 432:53-67 (2011)  -  DOI: https://doi.org/10.3354/meps09138

ABSTRACT: Culturing experiments were performed with the benthic foraminifer Ammonia aomoriensis from Flensburg Fjord, western Baltic Sea. The experiments simulated a projected rise in atmospheric CO₂ concentrations. We exposed specimens to 5 seawater pCO₂ levels ranging from 618 µatm (pH 7.9) to 3130 µatm (pH 7.2) for 6 wk. Growth rates and mortality differed significantly among pCO₂ treatments. The highest increase of mean test diameter (19%) was observed at 618 µatm. At partial pressures >1829 µatm, the mean test diameter was observed to decrease, by up to 22% at 3130 µatm. At pCO₂ levels of 618 and 751 µatm, A. aomoriensis tests were found intact after the experiment. The outer chambers of specimens incubated at 929 and 1829 µatm were severely damaged by corrosion. Visual inspection of specimens incubated at 3130 µatm revealed wall dissolution of all outer chambers, only their inner organic lining stayed intact. Our results demonstrate that pCO₂ values of ≥929 µatm in Baltic Sea waters cause reduced growth of A. aomoriensis and lead to shell dissolution. The bottom waters in Flensburg Fjord and adjacent areas regularly experience pCO₂ levels in this range during summer and fall. Increasing atmospheric CO₂ concentrations are likely to extend and intensify these periods of undersaturation. This may eventually slow down calcification in A. aomoriensis to the extent that net carbonate precipitation terminates. The possible disappearance of this species from the Baltic Sea and other areas prone to seasonal undersaturation would likely cause significant shifts in shallow-water benthic ecosystems in the near future.

KEY WORDS: Benthic foraminifera · Biometry · Test dissolution · Carbon dioxide · Baltic Sea