Physiological and isotopic responses of scleractinian corals to ocean acidification

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Krief, Shani, Hendy, Erica J., Fine, Maoz, Yam, Ruth, Meibom, Anders, Foster, Gavin L., Shemesh, Aldo
• Format: Text
• Language: unknown
• Published: 2012
• Subjects: Ocean acidification
• Online Access: http://infoscience.epfl.ch/record/177141; https://doi.org/10.1016/j.gca.2010.05.023

Uptake of anthropogenic CO2 by the oceans is altering seawater chemistry with potentially serious consequences for coral reef ecosystems due to the reduction of seawater pH and aragonite saturation state (Omega(arag)) The objectives of this long-term study were to investigate the viability of two ecologically important reef-building coral species, massive Ponies sp. and Stylophora pistillata, exposed to high pCO(2) (or low pH) conditions and to observe possible changes in physiologically related parameters as well as skeletal isotopic composition. Fragments of Ponies sp. and S. pistillata were kept for 6-14 months under controlled aquarium conditions characterized by normal and elevated pCO(2) conditions, corresponding to pH(T) values of 8.09, 7.49, and 7.19, respectively. In contrast with shorter, and therefore more transient experiments, the long experimental time-scale achieved in this study ensures complete equilibration and steady state with the experimental environment and guarantees that the data provide insights into viable and stably growing corals. During the experiments, all coral fragments survived and added new skeleton, even at seawater Omega(arag) < 1, implying that the coral skeleton is formed by mechanisms under strong biological control. Measurements of boron (B), carbon (C), and oxygen (O) isotopic composition of skeleton, C isotopic composition of coral tissue and symbiont zooxanthellae, along with physiological data (such as skeletal growth, tissue biomass, zooxanthellae cell density, and chlorophyll concentration) allow for a direct comparison with corals living under normal conditions and sampled simultaneously. Skeletal growth and zooxanthellae density were found to decrease, whereas coral tissue biomass (measured as protein concentration) and zooxanthellae chlorophyll concentrations increased under high pCO(2) (low pH) conditions. Both species showed similar trends of delta B-11 depletion and delta O-18 enrichment under reduced pH, whereas the delta C-13 results imply species-specific ...