Coralline algae are important ecosystem engineers worldwide. Especially in the Arctic, they are facing a variety of environmental impacts caused by global change. Sebastian Teichert, Nora Voigt and Max Wisshak now published a first evaluation of these impacts on the Mg/Ca ratio in the coralline algal skeleton. Over a time interval of 40 years, they showed that atmospheric CO2 concentration seems to be the most important factor, followed by water temperature and light availability. For details, please read their paper in Polar Biology: https://doi.org/10.1007/s00300-020-02767-3