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

Area of Science:

• Marine Biology
• Oceanography
• Climate Change Science

Background:

• Rising atmospheric carbon dioxide (CO2) lowers ocean pH, a process known as ocean acidification.
• Calcifying marine organisms, including foraminifera, are vulnerable to these changes.
• The specific effects of ocean acidification on foraminiferal shell volume and density remain under-investigated.

Purpose of the Study:

• To investigate the impact of ocean acidification on the calcification of large benthic foraminifera (LBF).
• To determine if reduced calcification affects shell volume, shell density, or both.
• To differentiate the effects of pH and temperature on foraminiferal growth parameters.

Main Methods:

• Culturing of Amphisorus kudakajimensis, a type of LBF.
• Exposure to varying pH conditions (pH 7.7-8.3).
• Analysis of shell volume and density in response to pH changes.

Main Results:

• Ocean acidification significantly affects both the quantity (shell volume) and quality (shell density) of foraminiferal calcification.
• pH and temperature influence calcification through different mechanisms, impacting processes like Ca2+-ATPase activity and carbonate saturation state (Ω).
• Under the IPCC RCP8.5 scenario, combined ocean acidification and warming are projected to severely impact tropical reef foraminiferal carbonate production by 2100.

Conclusions:

• Ocean acidification poses a dual threat to foraminifera by altering shell volume and density.
• Differential impacts of pH and temperature on calcification and photosynthesis are key.
• Future climate change scenarios predict substantial reductions in reef carbonate production due to these stressors.