Abstract
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.
Highlights
Increasing levels of atmospheric carbon dioxide from anthropogenic emissions have led to higher CO2 concentrations in the surface seawaters of the oceans, changing seawater chemistry (Caldeira and Wickett, 2003; Doney et al, 2009)
There was an increase in coral cover at the Dobu seep (37.93%) compared to the Dobu control sites (26.06%), largely due to a fivefold increase in cover of massive Porites spp., from 4.13% at the Dobu control site to 21.41% at Dobu seep
We show that massive Porites corals that occur in high abundance at low pH/high pCO2 seep sites in Papua New Guinea (PNG) host robust bacterial communities that are stable across a broad range of environmental pH levels
Summary
Increasing levels of atmospheric carbon dioxide from anthropogenic emissions have led to higher CO2 concentrations in the surface seawaters of the oceans, changing seawater chemistry (Caldeira and Wickett, 2003; Doney et al, 2009). Over the last 200 years, the average pH of global surface seawater has been reduced by ∼0.1 units. Porites Microbiome Robust to CO2 to ∼8.1, and based on current CO2 emissions modeling, pH is predicted to decrease by a further 0.2–0.4 units by 2100. This decrease will lead to changes in ocean chemistry not seen for the past 23 million years (Rhein et al, 2013). Seawater pH fluctuates (especially on coral reefs) with season, depth and productivity (Joint et al, 2011), the reduction in baseline pH levels, termed ocean acidification (OA), represents a growing concern for global ocean ecosystems (O’Brien et al, 2016)
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