Ocean acidification effects on calcifying macroalgae

An increase in pCO sub(2) in surface ocean waters causes an increase in bicarbonate ions (HCO sub(3) super(-)) and protons (H super(+)) and a decrease in carbonate ions (CO sub(2) super(2-)), thereby decreasing the pH and the saturation state of the seawater with respect to CO sub(3) super(2-). These changes in ocean chemistry (termed ocean acidification) are expected to have negative impacts on marine calcifying organisms. Due to a recent strong increase in the number of studies investigating the responses of calcifying marine macroalgae to elevated pCO sub(2), this review aims to present the state of knowledge on the response of calcifying macroalgae to ocean acidification alone and in combination with global and local stressors. We discuss the physiological responses of calcifying macroalgae to elevated pCO sub(2) within the contexts biogeography, taxonomy, and calcification mechanisms. Calcifiers generally show sensitivity to overgrowth and outcompetition by noncalcifying algae when grown under elevated CO sub(2) conditions, and this trend could be amplified under conditions of high inorganic nutrients.