Abstract
Non-native Vaucheria sp. turfs (Xanthophyceae) have been recently regularly observed in the northern Wadden Sea (south-eastern North Sea) in the lower intertidal and shallow subtidal zone. We investigated how Vaucheria sp . adapts to small-scale site-specific differences in lower intertidal and shallow subtidal zones by evaluating its photosynthetic performance. This was assessed in July and September 2022 by using PAM fluorometry and pigment composition measurements. Vaucheria sp . turfs exhibit site- and season-specific photo-physiological differences, demonstrating high plasticity and distinct acclimation strategies to local light and environmental conditions. In July, Vaucheria populations exhibited stronger stress responses, marked by higher concentrations of photoprotective pigments and enhanced energy dissipation to minimise photodamage under intense light and temperature. In September, turfs showed improved photochemical performance with higher effective quantum yield of PSII, initial slope α, and non-photochemical quenching likely due to accumulated stress and reduced energy availability. This study reveals that Vaucheria sp. turfs may exhibit small-scale site-specific adaptation patterns in response to environmental dynamics, which may explain their increasing occurrence and successful establishment in the Wadden Sea.