Decrease in volume and density of foraminiferal shells with progressing ocean acidification

Azumi Kuroyanagi,Atsushi Suzuki,Takahiro Irie,Osamu Sasaki,Hodaka Kawahata,Reishi Takashima,Hiroshi Nishi,Shunichi Kinoshita,Kazuhiko Fujita

doi:10.1038/s41598-021-99427-1

Abstract

Rapid increases in anthropogenic atmospheric CO2 partial pressure have led to a decrease in the pH of seawater. Calcifying organisms generally respond negatively to ocean acidification. Foraminifera are one of the major carbonate producers in the ocean; however, whether calcification reduction by ocean acidification affects either foraminiferal shell volume or density, or both, has yet to be investigated. In this study, we cultured asexually reproducing specimens of Amphisorus kudakajimensis, a dinoflagellate endosymbiont-bearing large benthic foraminifera (LBF), under different pH conditions (pH 7.7–8.3, NBS scale). The results suggest that changes in seawater pH would affect not only the quantity (i.e., shell volume) but also the quality (i.e., shell density) of foraminiferal calcification. We proposed that pH and temperature affect these growth parameters differently because (1) they have differences in the contribution to the calcification process (e.g., Ca2+-ATPase and Ω) and (2) pH mainly affects calcification and temperature mainly affects photosynthesis. Our findings also suggest that, under the IPCC RCP8.5 scenario, both ocean acidification and warming will have a significant impact on reef foraminiferal carbonate production by the end of this century, even in the tropics.

Highlights

Rapid increases in anthropogenic atmospheric CO2 partial pressure have led to a decrease in the pH of seawater
Our results demonstrate that shell weight, volume, and density are all positively associated with seawater pH (Table 1 and Fig. 1)
The pH 7.9 condition showed different results for each parameter: there was no statistically significant difference in shell density compared to the pH 7.7 condition, in shell weight compared to the control condition, or in volume compared to either the control or pH 8.3 conditions (Fig. 1)

Summary

Introduction

Rapid increases in anthropogenic atmospheric CO2 partial pressure have led to a decrease in the pH of seawater. Foraminifera are one of the major carbonate producers in the ocean; whether calcification reduction by ocean acidification affects either foraminiferal shell volume or density, or both, has yet to be investigated. Amphisorus kudakajimensis, formerly classified as Marginopora kudakajimensis, is a dinoflagellate endosymbiont-bearing LBF belonging to the Soritinae (high-Mg calcite) This species is common in shallow lagoon environments and accounts for 10% of the inorganic carbon production of protected lagoon communities[12,16]. To examine the effect of ocean acidification on foraminiferal shell calcification and apply this to the estimation of past and future environmental changes in coral reefs, we cultured asexually reproducing specimens of A. kudakajimensis under different pH conditions and determined their shell volume and density using microCT

Methods

Results

Conclusion