pH variability at volcanic CO₂ seeps regulates coral calcifying fluid chemistry

Area of Science:

• Marine Biology
• Oceanography
• Climate Change Science

Background:

• Coral reefs are vital ecosystems threatened by ocean acidification (OA).
• Understanding coral calcification mechanisms under changing seawater pH is crucial for predicting reef futures.
• Volcanic CO2 seeps offer natural laboratories to study coral responses to low pH.

Purpose of the Study:

• To investigate the calcifying fluid (CF) chemistry control in corals exposed to varying low pH conditions.
• To assess the relationship between coral abundance and their ability to maintain calcifying fluid homeostasis at CO2 seeps.
• To identify coral species with specialized mechanisms for calcification under ocean acidification.

Main Methods:

• Studied multiple coral species at two volcanic CO2 seep sites in Papua New Guinea.
• Compared coral calcifying fluid (CF) chemistry (pHcf) under low and variable pH with control sites.
• Assessed coral abundance in relation to their pHcf control capacity.

Main Results:

• Corals in highly variable low pH waters showed a greater ability to maintain constant pHcf.
• This pHcf stability was not directly linked to increased coral abundance.
• One species, Montipora foliosa, exhibited complete pHcf homeostasis, potentially influencing abundance in less variable low pH.
• A potential association between ecological success and greater pHcf homeostasis was observed.

Conclusions:

• Coral ability to regulate calcifying fluid chemistry (pHcf) may be linked to ecological success in acidified oceans.
• Variability in seawater pH, not just mean acidity, influences coral's pHcf control.
• Further research across diverse sites and species is needed to confirm the link between pHcf homeostasis and coral resilience to OA.