Changes in coral microbial communities in response to a natural pH gradient

Area of Science:

• Marine Biology
• Oceanography
• Microbiology

Background:

• Ocean surface pH has decreased by 0.1 units since pre-industrial times, with projections indicating a further drop of up to 0.4 units by 2100.
• Ocean acidification poses a significant threat to marine organisms, especially corals, due to their calcium carbonate skeletons.
• Previous research primarily focused on laboratory settings, leaving a gap in understanding coral responses to natural acidification gradients.

Purpose of the Study:

• To investigate the impact of natural ocean acidification on coral microbial communities and physiology.
• To examine changes in microbial diversity and endosymbiotic dinoflagellates (Symbiodinium spp.) in corals exposed to volcanic CO2 vents.
• To compare findings with previous laboratory-based studies on ocean acidification effects.

Main Methods:

• Studied two Mediterranean coral species, Balanophyllia europaea and Cladocora caespitosa, near volcanic CO2 vents off Ischia, Italy.
• Monitored microbial community diversity and physiological parameters of Symbiodinium spp. along a natural pH gradient (pH(T) 7.3-8.1).
• Analyzed coral responses in situ to a real-world ocean acidification scenario.

Main Results:

• Coral microbial community composition remained largely unaffected by the natural pH gradient in both studied species.
• Corals at lower pH sites exhibited only minor physiological changes.
• No microbial pathogens were detected in the coral samples from the acidified areas.

Conclusions:

• Ocean acidification, even at naturally occurring vent sites, may not drastically alter coral microbial communities or cause severe physiological damage.
• The coral holobiont demonstrates a degree of resilience to current levels of ocean acidification.
• Findings suggest that laboratory-controlled studies may overestimate the negative impacts of ocean acidification on some coral species.