High pCO₂ promotes coral primary production.

Area of Science:

• Marine Biology
• Oceanography
• Climate Change Science

Background:

• Coral reef research has primarily focused on calcification impacts of ocean acidification (OA).
• Limited understanding exists regarding OA effects on coral photosynthesis and respiration, key metabolic processes for acclimatization.
• Coral metabolic flexibility is crucial for adapting to environmental changes.

Purpose of the Study:

• To investigate the metabolic flexibility of coral species under high CO2 conditions.
• To assess the impact of natural CO2 seeps on coral photosynthesis and respiration rates.
• To determine if enhanced metabolic rates confer resistance to thermal stress.

Main Methods:

• Field measurements of net oxygen flux (photosynthesis and respiration) for 12 coral species.
• Data collection at three natural CO2 seeps in Papua New Guinea between 2016 and 2018.
• Comparison of metabolic rates at ambient and high pCO2 levels (approx. 1200 µatm).

Main Results:

• Metabolic rates, measured by net oxygen flux, were generally higher at elevated pCO2.
• Increases in photosynthesis exceeded those in respiration, indicating enhanced Symbiodiniaceae productivity in hospite.
• Species-specific variability in metabolic response was observed.
• This metabolic flexibility did not enhance coral resistance to extreme thermal stress, with mortality observed under high CO2 and bleaching conditions.

Conclusions:

• Ocean acidification can stimulate coral productivity and metabolic flexibility, potentially enabling some species to thrive in high CO2 environments.
• The metabolic benefits of OA do not confer resistance to thermal stress, highlighting a critical vulnerability for coral reefs.
• The combined impacts of OA and global warming are predicted to cause significant coral diversity loss despite OA's localized productivity benefits.