Abstract
Ocean acidification and ocean warming compromise the capacity of calcifying marine organisms to generate and maintain their skeletons. While many marine calcifying organisms precipitate low-Mg calcite or aragonite, the skeleton of echinoderms consists of more soluble Mg-calcite. To assess the impact of exposure to elevated temperature and increased pCO(2) on the skeleton of echinoderms, in particular the mineralogy and microstructure, the starfish Aquilonastra yairi (Echinodermata: Asteroidea) was exposed for 90 days to simulated ocean warming (27 degrees C and 32 degrees C) and ocean acidification (455 mu atm, 1052 mu atm, 2066 mu atm) conditions. The results indicate that temperature is the major factor controlling the skeletal Mg (Mg/Ca ratio and Mg-norm ratio), but not for skeletal Sr (Sr/Ca ratio and Sr-norm ratio) and skeletal Ca (Ca-norm ratio) in A. yairi. Nevertheless, inter-individual variability in skeletal Sr and Ca ratios increased with higher temperature. Elevated pCO(2) did not induce any statistically significant element alterations of the skeleton in all treatments over the incubation time, but increased pCO(2) concentrations might possess an indirect effect on skeletal mineral ratio alteration. The influence of increased pCO(2) was more relevant than that of increased temperature on skeletal microstructures. pCO(2) as a sole stressor caused alterations on stereom structure and degradation on the skeletal structure of A. yairi, whereas temperature did not; however, skeletons exposed to elevated pCO(2) and high temperature show a strongly altered skeleton structure compared to ambient temperature. These results indicate that ocean warming might exacerbate the skeletal maintaining mechanisms of the starfish in a high pCO(2) environment and could potentially modify the morphology and functions of the starfish skeleton.