MEPS 636:63-75 (2020)  -  DOI: https://doi.org/10.3354/meps13228

ABSTRACT: Ocean acidification has been investigated extensively in scleractinian corals, but studies on different life stages of the same species are lacking. We investigated the response of recruits of the temperate coral Oculina arbuscula to increased CO₂ concentrations, a species whose adults show significant tolerance to elevated concentrations of CO₂. Specifically, we exposed small colonies (5-12 mm diameter) to 475, 710, and 1261 ppm CO₂ for 75 d in the laboratory to address the hypothesis that, like adults, the health of O. arbuscula recruits is not affected by increased CO₂ concentrations. Calcification rates were monitored regularly during the experiment, while mortality, respiration rates, photosynthetic rates, algal symbiont densities, and soluble protein were quantified at the end. As predicted, CO₂ concentration did not impact survival, algal densities, or soluble protein concentrations in O. arbuscula recruits. In contrast, both calcification rates and photosynthesis:respiration ratios tended to be lower at higher CO₂. Comparing the results of this study on recruits with published studies on adults suggested that both life stages exhibit a similar non-linear response to CO₂ concentration, whereby recruits may be unable to counter the increased energetic cost of calcification that occurs at the highest CO₂. Based on these results and environmental monitoring showing that mean pCO₂ is increasing by ~2.4% yr^-1 in the waters off Georgia, USA, we conclude that O. arbuscula recruits may begin to exhibit depressed calcification rates within the current century if CO₂ emissions are not reduced.

KEY WORDS: Ocean acidification · Temperate corals · Physiology · Calcification · Recruitment