Additive effects of climate change-related stress factors in Fucus serratus and Fucus vesiculosus

Here we investigated the effects of elevated temperature and low salinity on 2 important tidal foundation species, Fucus serratus and Fucus vesiculosus, to determine how these stressors interact. We conducted a 2-factorial experiment, exposing F. serratus and F. vesiculosus to 15 and 25°C combined with 5 and 25 PSU salinity over a period of 5 wk. The measured endpoints were survival, growth rate, chlorophyll a fluorescence (max. quantum yield and electron transport rate), photosynthetic performance, antioxidant capacity evaluated through superoxide dismutase enzyme activity, and oxidative damages assessed through lipid peroxidation products. Our results showed that exposure to high temperature and low salinity separately had negative effects on both species, but strongest for F. serratus. The combined effects of heat and low salinity were generally stronger than the isolated effects of each stressor, and were additive in most cases, suggesting that the effects of elevated temperature and low salinity can be predicted from single factor experiments. Our study provides valuable insights into the interaction effects of elevated temperature and reduced salinity on 2 important foundation species and highlights the vulnerability of these Fucus species to climate change-induced changes in abiotic factors.