Organic carbon fluxes mediated by corals at elevated pCO2 and temperature

Abstract

Increasing ocean acidification (OA) and seawater temperatures pose significant threats to coral reefs globally. While the combined impacts of OA and seawater temperature on coral biology and calcification in corals have received significant study, research to date has largely neglected the individual and combined effects of OA and seawater temperature on coral-mediated organic carbon (OC) fluxes. This is of particular concern as dissolved and particulate OC (DOC and POC, respectively) represent large pools of fixed OC on coral reefs. In the present study, coral-mediated POC and DOC, and the sum of these coral-mediated flux rates (total OC, TOC = DOC + POC) as well as the relative contributions of each to coral metabolic demand were determined for 2 species of coral, Acropora millepora and Turbinaria reniformis, at 2 levels of pCO2 (382 and 741 µatm) and seawater temperatures (26.5 and 31.0°C). Independent of temperature, DOC fluxes decreased significantly with increases in pCO2 in both species, resulting in more DOC being retained by the corals and only representing between 19 and 6% of TOC fluxes for A. millepora and T. reniformis. At the same time, POC and TOC fluxes were unaffected by elevated temperature and/or pCO2. These findings add to a growing body of evidence that certain species of coral may be less at risk to the impacts of OA and temperature than previously thought.