Ca-ATPase and Mg-ATPase enzyme activities of the tropical-subtropical starfish Aquilonastra yairi under ocean acidification and warming in the laboratory

Enzyme activities involved in biomineralization were determined in the tropical-subtropical starfish Aquilonastra yairi from the culture stock of the ZMT-MAREE laboratory in response to projected near-future global change. To investigate the physicochemical alteration of starfish induced by elevated seawater pCO2 and temperature, starfish of the species A. yairi (342 specimens, size 3-11 mm in diameter, culture stock) were reared in aquaria system under controlled experimental environment conditions at ZMT-MAREE. The starfish were acclimatized to two temperature levels (27 °C, 32 °C) crossed with three pCO2 concentrations (455 µatm, 1052 µatm, 2066 µatm). Protein concentration was determined using the Bradford assay method (Bradford, 1976). Furthermore, Ca-ATPase and Mg-ATPase activities were measured according to protocols initially developed by Chan et al. (1986), Busacker and Chavin (1981) and modified by Prazeres et al. (2015). Positive parabolic responses of Ca-ATPase and Mg-ATPase enzyme activities were detected at 27 °C with elevated pCO2, while stable enzyme activities were observed at 32 °C with elevated pCO2. The calcification-related enzymes Ca-ATPase and Mg-ATPase activity appear to be sensitive to pCO2/pH changes, leading to vulnerability concerning the skeletal structure.