Modelling coral polyp calcification in relation to ocean acidification

[摘要] Rising atmospheric CO₂ concentrations due to anthropogenic emissionsinduce changes in the carbonate chemistry of the oceans and, ultimately, adrop in ocean pH. This acidification process can harm calcifying organismslike coccolithophores, molluscs, echinoderms, and corals. It is expected thatocean acidification in combination with other anthropogenic stressors willcause a severe decline in coral abundance by the end of this century, withassociated disastrous effects on reef ecosystems. Despite the growingimportance of the topic, little progress has been made with respect tomodelling the impact of acidification on coral calcification. Here we presenta model for a coral polyp that simulates the carbonate system in fourdifferent compartments: the seawater, the polyp tissue, the coelenteron, andthe calcifying fluid. Precipitation of calcium carbonate takes place in themetabolically controlled calcifying fluid beneath the polyp tissue. The modelis adjusted to a state of activity as observed by direct microsensormeasurements in the calcifying fluid. We find that a transport mechanism forbicarbonate is required to supplement carbon into the calcifying fluidbecause CO₂ diffusion alone is not sufficient to sustain the observedcalcification rates. Simulated CO₂ perturbation experiments revealdecreasing calcification rates under elevated pCO₂ despite the strongmetabolic control of the calcifying fluid. Diffusion of CO₂ through thetissue into the calcifying fluid increases with increasing seawaterpCO₂,leading to decreased aragonite saturation in the calcifying fluid.Our modelling study provides important insights into thecomplexity of the calcification process at the organism level and helps toquantify the effect of ocean acidification on corals.

[学科分类] 地球化学与岩石