Publication Date:
2024-03-15
Description:
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 Porites sp. and Stylophora pistilata, exposed to high pCO2(or low pH) conditions and to observe possible changes in physiologically related parameters as well as skeletal isotopic composition. Fragments of Porites sp. and S. pistilata were kept for 6-14 months under controlled aquarium conditions characterized by normal and elevated pCO2 conditions, corresponding to pHTvalues of 8.09, 7.49, and 7.19, respectively. In contrast with shorter, and therefore more transient experiments, the long experimental timescale 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 pCO2 (low pH) conditions. Both species showed similar trends of delta11B depletion and delta18O enrichment under reduced pH, whereas the delta13C results imply species-specific metabolic response to high pCO2 conditions. The skeletal delta11B values plot above seawater delta11B vs. pH borate fractionation curves calculated using either the theoretically derived deltaB value of 1.0194 (Kakihana et al., Bull. Chem. Soc. Jpn. 50(1977), 158) or the empirical deltaB value of 1.0272 (Klochko et al., EPSL 248 (2006), 261). However, the effective deltaB must be greater than 1.0200 in order to yield calculated coral skeletal delta11B values for pH conditions where omega arag 〉1. The delta11B vs. pH offset from the literature seawater delta11B vs. pH fractionation curves suggests a change in the ratio of skeletal material laid down during dark and light calcification and/or an internal pH regulation, presumably controlled by ion-transport enzymes. Finally, seawater pH significantly influences skeletal delta13C and delta18O. This must be taken into consideration when reconstructing paleo-environmental conditions from coral skeleton
Keywords:
Alkalinity, total; Animalia; Aragonite saturation state; Benthic animals; Benthos; Bicarbonate ion; Biomass/Abundance/Elemental composition; Buoyant weighing technique according to Davies (1989); Calcification/Dissolution; Calcification rate; Calcification rate, standard deviation; Calcite saturation state; Calculated using CO2SYS; Calculated using seacarb after Nisumaa et al. (2010); Carbon, inorganic, dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Chlorophyll per zooxanthellae; Chlorophyll per zooxanthellae, standard deviation; Cnidaria; Coast and continental shelf; Containers and aquaria (20-1000 L or 〈 1 m**2); Continuous Flow Isotope Ratio Mass Spectrometry (CF/IRMS); Element analyser isotope ratio mass spectrometer (EA-IRMS); EPOCA; EUR-OCEANS; European network of excellence for Ocean Ecosystems Analysis; European Project on Ocean Acidification; Experimental treatment; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Growth/Morphology; Growth rate; Growth rate, standard deviation; HOBO Pendant Temp/Light Data Loggers (Pocasset, MA, USA); Image analysis; Laboratory experiment; Light:Dark cycle; MC-ICP-MS Thermo-Finnigan Neptune; Measured; OA-ICC; Ocean Acidification International Coordination Centre; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); pH; pH, Electrode; Porites sp.; Protein per surface area; Protein per surface area, standard deviation; Radiation, photosynthetically active; Red Sea; Salinity; Single species; Species; Stylophora pistillata; Temperate; Temperature, water; Zooxanthellae, per protein content; Zooxanthellae per protein content, standard deviation; Zooxanthellae per surface area; Zooxanthellae per surface area, standard deviation; δ11B; δ11B, standard deviation; δ13C, dissolved inorganic carbon; δ13C, standard deviation; δ18O, standard deviation; δ18O, water
Type:
Dataset
Format:
text/tab-separated-values, 258 data points
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