Internal pH regulation facilitates in situ long-term acclimation of massive corals to end-of-century carbon dioxide conditions

• Published in: Scientific Reports
• Main Authors: Wall, M., Fietzke, J., Schmidt, G. M., Fink, A, Hofmann, L. C., de Beer, D., Fabricius, K. E.
• Format: Text
• Language: English
• Published: Nature Publishing Group 2016
• Subjects: Article; Ocean acidification
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4967918/; http://www.ncbi.nlm.nih.gov/pubmed/27477963; https://doi.org/10.1038/srep30688

The resilience of tropical corals to ocean acidification depends on their ability to regulate the pH within their calcifying fluid (pHcf). Recent work suggests pHcf homeostasis under short-term exposure to pCO2 conditions predicted for 2100, but it is still unclear if pHcf homeostasis can be maintained throughout a corals lifetime. At CO2 seeps in Papua New Guinea, massive Porites corals have grown along a natural seawater pH gradient for decades. This natural gradient, ranging from pH 8.1–7.4, provides an ideal platform to determine corals’ pHcf (using boron isotopes). Porites maintained a similar pHcf (~8.24) at both a control (pH 8.1) and seep-influenced site (pH 7.9). Internal pHcf was slightly reduced (8.12) at seawater pH 7.6, and decreased to 7.94 at a site with a seawater pH of 7.4. A growth response model based on pHcf mirrors the observed distribution patterns of this species in the field. We suggest Porites has the capacity to acclimate after long-time exposure to end-of-century reduced seawater pH conditions and that strong control over pHcf represents a key mechanism to persist in future oceans. Only beyond end-of-century pCO2 conditions do they face their current physiological limit of pH homeostasis and pHcf begins to decrease.