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Abstract:
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.
