Salinity and temperature tolerance of the invasive alga Undaria pinnatifida and native New Zealand kelps: Implications for competition

Invasive species are generally believed to be more tolerant to varying abiotic conditions than native species. Here, we report the combined effect of temperature (5, 15, 20 and 25 °C) and salinity (33, 24, 18, 12 and 6 S A ) on the performance of the invasive kelp Undaria pinnatifida and two native kelp species ( Lessonia variegata , Ecklonia radiata ) from Tauranga Harbour, New Zealand (37°38′S, 176°10′E, 2014). Vegetative blade discs were exposed to temperature and salinity treatments in a 10-day laboratory experiment, and the physiological response was assessed employing photosynthetic (Fv/Fm, ETR max ) as well as biochemical parameters (chlorophyll a , xanthophylls and antioxidant pool size). U. pinnatifida sustained a high photosynthetic quantum yield in most treatments, with a negative synergistic effect on photosynthetic yield observed at 25 °C and low salinities (12, 6 S A ). E. radiata died in salinities below 18 S A , except at 5 °C and L. variegata was highly susceptible to elevated temperatures (20, 25 °C). Antioxidant pool size showed species-specific responses to the experimental conditions, being most resilient in U. pinnatifida . Overall, U. pinnatifida displayed broader tolerance to the experimental salinity and temperature conditions than native kelps. The abilities to cope with a wide range in abiotic factors and to thrive in estuarine conditions might contribute to higher competitive strength compared to native kelps leading to its invasion success, especially with regard to ocean warming.