Coral reef calcifiers buffer their response to ocean acidification using both bicarbonate and carbonate

Area of Science:

• Marine Biology
• Oceanography
• Climate Change Science

Background:

• Ocean acidification (OA), driven by increased CO(2) absorption, reduces seawater carbonate ion concentration ([CO(3)(2-)]) and increases bicarbonate ion concentration ([HCO(3)(-)]).
• Coral reefs are vulnerable to OA, which affects the calcification rates of corals and associated calcifying algae.

Purpose of the Study:

• To investigate the individual and combined effects of [CO(3)(2-)] and [HCO(3)(-)] on the calcification of the coral Porites rus and the alga Hydrolithon onkodes.
• To determine the roles of [CO(3)(2-)] and [HCO(3)(-)] in coral and algal calcification under light and dark conditions.

Main Methods:

• Experimental manipulation of [CO(3)(2-)] and [HCO(3)(-)] in seawater over a 15-day incubation period.
• Measurement of calcification rates for Porites rus and Hydrolithon onkodes during both day and night cycles.

Main Results:

• [CO(3)(2-)] significantly influenced both light and dark calcification in Porites rus, while [HCO(3)(-)] primarily affected light calcification.
• [CO(3)(2-)] and [HCO(3)(-)] both significantly impacted Hydrolithon onkodes calcification, with [CO(3)(2-)] showing the strongest correlation.
• The study demonstrated that increased [HCO(3)(-)] can partially mitigate the negative impacts of reduced [CO(3)(2-)] on coral and algal calcification.

Conclusions:

• Coral and algal calcification responses to ocean acidification are complex, involving both carbonate and bicarbonate ions.
• Bicarbonate ions may play a crucial role in supporting calcification and photosynthesis under future ocean acidification scenarios.
• These findings support conceptual models for predicting coral reef calcification under changing ocean chemistry.