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

Haynert, Kristin, Schönfeld, Joachim, Schiebel, R., Wilson, B. and Thomsen, J. (2014) Response of benthic foraminifera to ocean acidification in their natural sediment environment: a long-term culturing experiment Biogeosciences (BG), 11 . pp. 1581-1597. DOI 10.5194/bg-11-1581-2014.

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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
5 six month incubation, foraminiferal assemblages were treated with pCO2 enriched
seawater of 430, 907, 1865 and 3247 μatm pCO2. The fauna was dominated by Ammonia
aomoriensis and Elphidium species, whereas agglutinated species were rare. After
6 months incubation, pore water alkalinity was much higher in comparison to the overlying
seawater. Consequently, the saturation state of Òcalc was much higher in the sedi10
ment than in the water column in all pCO2 treatments and remained close to saturation.
As a result, the life cycle of living assemblages was largely unaffected by the tested
pCO2 treatments. Growth rates, reproduction and mortality, and therefore population
densities and size-frequency distribution of Ammonia aomoriensis varied markedly during
the experimental period. Growth rates varied between 25 and 50 μm per month,
15 which corresponds to an addition of 1 or 2 new chambers per month. According to
the size-frequency distribution, foraminifera start reproduction at a diameter of 250 μm.
Mortality of large foraminifera was recognized, commencing at a test size of 285 μm
at a pCO2 ranging from 430 to 1865 μatm, and of 258 μm at 3247 μatm. The total organic
content of living Ammonia aomoriensis has been determined to be 4.3% of dry
20 weight. Living individuals had a calcium carbonate production rate of 0.47 gm−2 yr−1,
whereas dead empty tests accumulated at a rate of 0.27 gm−2a−1. Although Òcalc was
close to 1, some empty tests of Ammonia aomoriensis showed dissolution features at
the end of incubation. In contrast, tests of the subdominant species, Elphidium incertum,
stayed intact. This species specific response could be explained by differences in
25 the elemental test composition, in particular the higher Mg-concentrations in Ammonia
aomoriensis tests. Our results emphasize that the sensitivity to ocean acidification
of endobenthic foraminifera in their natural sediment habitat is much lower compared
to the experimental response of specimens isolated from the sediment.

Document Type: Article
Additional Information: WOS:000334100900008
Keywords: foraminifera, baltic sea, experiments, growth, reproduction, alkalinity, pore water
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
DOI etc.: 10.5194/bg-11-1581-2014
ISSN: 1726-4170
Projects: Future Ocean
Date Deposited: 12 Aug 2013 07:56
Last Modified: 14 May 2014 08:11

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