Facing climate change: physiological and biochemical responses of European kelp species to ocean warming

In coastal ecosystems, large brown macroalgae are important foundation species, growing on rocky shores from temperate to polar regions. They form marine forests, also known as kelp forests, which are among the most productive coastal marine ecosystems in the world. Kelps are of high ecological and economic value, however, climate change poses a great threat to these ecosystems. Warming has vast implications on marine forests and their global biogeographic patterns, but also other drivers affect kelps and strong interactive effects are observed.
The aim of this study was to gain a deeper understanding of the inter- and intraspecific acclimation processes of kelp species to abiotic conditions along large spatial and environmental gradients. The thermal tolerance of the broadly distributed kelp Saccharina latissima towards marine summer heatwaves across latitudes and its biochemical and morphological variability across its entire distribution range in Europe was investigated. Seasonal and inter-annual differences in the susceptibility of S. latissima to marine heatwaves in summer were revealed and the impact of potential interactions of marine heatwaves in summer paired with hyposalinity or enhanced nutrient availability was analyzed. The combined effect of different temperatures and salinities on physiological and biochemical response variables was also investigated in young Laminaria solidungula sporophytes.
In conclusion, this thesis presents important information on the functional variability of two kelp species with different distributional ranges. Both studied species exhibit different sensitivity towards drivers related to environmental change. Furthermore, intraspecific variation must not be underestimated. The observed changes in the kelp populations of Europe, thus, cannot exclusively be ascribed to temperature variation but to an interplay of various abiotic and biotic factors. These findings contribute further knowledge to support future approaches to the conservation of marine forests.