Foraminifera promote calcification by elevating their intracellular pH.

Area of Science:

• Marine Biology
• Biogeochemistry
• Paleontology

Background:

• Seawater's high magnesium content inhibits calcite precipitation, a key process for marine organisms like foraminifera.
• Most foraminifera produce low-Mg calcite, implying active magnesium ion removal.
• Some foraminifera species produce high-Mg calcite, suggesting a different calcification mechanism.

Purpose of the Study:

• To investigate the cellular mechanism enabling high-Mg calcite precipitation in foraminifera.
• To determine if pH elevation is a common strategy for calcite precipitation in foraminifera.
• To assess the evolutionary origin and potential impact of ocean acidification on foraminifera calcification.

Main Methods:

• Experimental analysis of foraminifera calcification under varying conditions.
• Measurement of pH at the site of calcification.
• Comparative study across different foraminifera species with varying Mg-calcite content.

Main Results:

• Foraminifera elevate pH at the calcification site by at least one unit, overcoming magnesium inhibition.
• This pH-elevating strategy is employed by both high-Mg and low-Mg calcite-producing foraminifera.
• The mechanism for pH elevation in calcification is ancient, dating back to the Cambrian period.

Conclusions:

• Elevating calcification site pH is a widespread and ancient strategy in foraminifera.
• This physiological mechanism is essential for foraminifera to precipitate calcite in magnesium-rich seawater.
• Ocean acidification poses a significant threat to foraminifera calcification due to their reliance on pH elevation.