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

• Main Authors: Wall, M., Fietzke, J., Schmidt, G., Fink, A., Hofmann, L., de Beer, D., Fabricius, K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Ocean acidification
• Online Access: http://hdl.handle.net/21.11116/0000-0001-C2A1-D; http://hdl.handle.net/21.11116/0000-0005-4FEE-8

The resilience of tropical corals to ocean acidification depends on their ability to regulate the pH within their calcifying fluid (pH(cf)). Recent work suggests pHcf homeostasis under short-term exposure to pCO(2) 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' pH(cf) (using boron isotopes). Porites maintained a similar pH(cf) (similar to 8.24) at both a control (pH 8.1) and seep-influenced site (pH 7.9). Internal pH(cf) 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 pH(cf) 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 pH(cf) represents a key mechanism to persist in future oceans. Only beyond end-of-century pCO(2) conditions do they face their current physiological limit of pH homeostasis and pH(cf) begins to decrease.