Towards predicting coral calcification responses to ocean acidification: A combined modeling and experimental approach

Experiments show that ocean acidification is detrimental to coral calcification. Nevertheless, coral sensitivities to OA vary and the mechanism(s) underlying these variable responses are not fully understood. One hypothesis is that ocean acidification affects the ability of coral’s to regulate the pH of fluid at the site of calcification. We developed a numerical model of coral calcification that simulates corals’ pH regulation based on physiochemical principles and predicts the rate of calcification [1]. Here we apply this model to Palauan corals, and seek to test the model’s efficacy by comparing the predicted coral calcification responses with experimental measurements. Four coral cores were collected from two sites of different pH (7.84 and 8.04 respectively). Their bulk annual calcification rates, quantified from average density and extension rate measurements, vary from .83 to 1.39 g cm^-2 year^-1 for the low pH site and from 0.75 to 1.21 g cm^-2 year^-1for the high pH site. The higher bulk calcification rates observed in corals from the low pH site contrasts the expected general decrease in calcification in low pH seawater, and differs from our model prediction. We suspect this apparent discrepancy arises because fast-calcifying corals in low pH water are able to modulate the pH of fluid at the site of calcification. We test this hypothesis using boron isotope measurements from each coral. In addition, a more accurate measurement of instantaneous calcification, considering the number of corallites per measured area and the exact surface area of each polyp’s 3-dimensional calcification site is applied.

[1] Guo, W. (2014). AGU Fall Meeting, Abstract B41B-0033.