Simultaneous ocean acidification and warming do not alter the lipid-associated biochemistry but induce enzyme...

Ocean acidification and warming affect marine ecosystems from the molecular scale in organismal physiology to broad alterations of ecosystem functions. However, knowledge of their combined effects on tropical-subtropical intertidal species remains limited. Pushing the environmental range of marine species away from the optimum initiates stress impacting biochemical metabolic characteristics, with consequences on lipid-associated and enzyme biochemistry. This study investigates lipid-associated fatty acids (FAs) and enzyme activities involved in biomineralization of the tropical-subtropical starfish Aquilonastra yairi in response to projected near-future global change. The starfish were acclimatized to two temperature levels (27 °C, 32 °C) crossed with three pCO₂ concentrations (455 μatm, 1052 μatm, 2066 μatm). Total lipid (ΣL_C) and FAs composition were unaffected by combined elevated temperature and pCO₂, but at elevated temperature, there was an increase in ΣL_C, SFAs (saturated FAs) and PUFAs (polyunsaturated FAs), and a decrease in MUFAs (monounsaturated FAs). However, temperature was the sole factor to significantly alter SFAs composition. 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. Our results indicate that the lipid-associated biochemistry of A. yairi is resilient and capable of coping with near-future ocean acidification and warming. However, the calcification-related enzymes Ca-ATPase and Mg-ATPase activity appear to be more sensitive to pCO₂/pH changes, leading to vulnerability concerning the skeletal structure.