Response of benthic foraminifera to ocean acidification in their natural sediment environment: a long-term culturing experiment

• Published in: Biogeosciences
• Main Authors: K. Haynert, J. Schönfeld, R. Schiebel, B. Wilson, J. Thomsen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-11-1581-2014; https://doaj.org/article/fc63c9df6e394f6eba1636b066730439

Calcifying foraminifera are expected to be endangered by ocean acidification; however, the response of a complete community kept in natural sediment and over multiple generations under controlled laboratory conditions has not been constrained to date. During 6 months of incubation, foraminiferal assemblages were kept and treated in natural sediment with p CO 2 -enriched seawater of 430, 907, 1865 and 3247 μatm p CO 2 . The fauna was dominated by Ammonia aomoriensis and Elphidium species, whereas agglutinated species were rare. After 6 months of incubation, pore water alkalinity was much higher in comparison to the overlying seawater. Consequently, the saturation state of Ω calc was much higher in the sediment than in the water column in nearly all p CO 2 treatments and remained close to saturation. As a result, the life cycle (population density, growth and reproduction) of living assemblages varied markedly during the experimental period, but was largely unaffected by the p CO 2 treatments applied. According to the size–frequency distribution, we conclude that foraminifera start reproduction at a diameter of 250 μm. Mortality of living Ammonia aomoriensis was unaffected, whereas size of large and dead tests decreased with elevated p CO 2 from 285 μm ( p CO 2 from 430 to 1865 μatm) to 258 μm ( p CO 2 3247 μatm). The total organic content of living Ammonia aomoriensis has been determined to be 4.3% of CaCO 3 weight. Living individuals had a calcium carbonate production rate of 0.47 g m −2 a −1 , whereas dead empty tests accumulated a rate of 0.27 g m −2 a −1 . Although Ω calc was close to 1, approximately 30% of the empty tests of Ammonia aomoriensis showed dissolution features at high p CO 2 of 3247 μatm during the last 2 months of incubation. In contrast, tests of the subdominant species, Elphidium incertum , stayed intact. Our results emphasize that the sensitivity to ocean acidification of the endobenthic foraminifera Ammonia aomoriensis in their natural sediment habitat is much lower compared to the ...