Elevated CO₂ Has Little Influence on the Bacterial Communities Associated With the pH-Tolerant Coral, Massive Porites...

Ocean acidification (OA) as a result of increased anthropogenic CO₂ input into the atmosphere carries consequences for all ocean life. Low pH can cause a shift in coral-associated microbial communities of pCO₂-sensitive corals, however, it remains unknown whether the microbial community is also influenced in corals known to be more tolerant to high pCO₂/low pH. This study profiles the bacterial communities associated with the tissues of the pCO₂-tolerant coral, massive Porites spp., from two natural CO₂ seep sites in Papua New Guinea. Amplicon sequencing of the hypervariable V3-V4 regions of the 16S rRNA gene revealed that microbial communities remained stable across CO₂ seep sites (pH = 7.44-7.85) and adjacent control sites (ambient pH = 8.0-8.1). Microbial communities were more significantly influenced by reef location than pH, with the relative abundance of dominant microbial taxa differing between reefs. These results directly contrast with previous findings that increased CO₂ has a strong effect on structuring microbial communities. The stable structure of microbial communities associated with the tissues of massive Porites spp. under high pCO₂/low pH conditions confirms a high degree of tolerance by the whole Porites holobiont to OA, and suggest that pH tolerant corals such as Porites may dominate reef assemblages in an increasingly acidic ocean.