Seawater temperature and buffering capacity modulate coral calcifying pH.

Area of Science:

• Marine biology
• Biogeochemistry
• Climate change science

Background:

• Scleractinian corals precipitate carbonate skeletons by increasing pH and dissolved inorganic carbon (DIC) in their calcifying fluid.
• Corals possess mechanisms to regulate calcifying fluid chemistry, suggesting potential acclimation to ocean acidification.
• The degree to which coral regulation can adapt to decreasing ocean pH remains insufficiently understood.

Purpose of the Study:

• To investigate the relative influence of physiological regulation versus environmental seawater conditions on coral calcifying fluid chemistry.
• To model the impact of projected ocean warming and acidification on coral calcifying fluid pH.
• To assess the susceptibility of coral calcification to future ocean changes.

Main Methods:

• Development of a numerical model to simulate coral pH and DIC regulation.
• Analysis of the interplay between enzymatic proton pumping, carbon influx, and fluid exchange.
• Quantitative reproduction of calcifying fluid pH variations in natural Porites coral colonies.

Main Results:

• Seawater temperature and buffering capacity are the primary drivers of pH elevation in coral calcifying fluid, explaining most observed variability.
• Physiological regulation contributes to variability but remains relatively stable despite changing seawater conditions.
• A projected 0.16 unit decrease in Porites calcifying fluid pH by 2100 due to ocean warming and acidification was predicted.

Conclusions:

• Coral calcification is highly susceptible to future ocean warming and acidification.
• Seawater conditions, rather than physiological regulation, exert dominant control over coral calcifying fluid chemistry.
• While supporting coral-based pH proxies, findings emphasize the need to account for multiple influencing factors beyond seawater pH.