@ F A C E I TA rc t i c @ F A C E I TA rc t i c @ fa c e _i t _a rc t i c @ The F A C E -I T Pro j e c t www.face-it-project.eu FACE-IT has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 869154. @ No ra _D i e hl No r a D i e hl M a ri ne B o t a ny U ni ve rs i t y o f B re m e n ndi e hl@ uni -b re m e n. de Fig. 2 Experimental set-up using adult sporophytes of L. hyperborea. w = week: w0, w4, w8, w12 = experimental samplings Fig. 1 Dots mark the current distribution of L. hyperborea. Orange line marks AMAP borders. Will L. hyperborea be able to spread throughout the High Arctic under future climatic conditions? Photoperiod and temperature interactions drive the latitudinal distribution of kelps under climate change Nora Diehl1,2*, Philipp Laesekea, Inka Bartsch2, Margot Bligh1,3, Hagen Buck-Wiese3, Jan-Hendrik Hehemann1,3, Sarina Niedzwiedz1, Niklas Plag4,5, Ulf Karsten4,6, Tifeng Shan7 & Kai Bischof1 Background: Due to global rise of temperatures, recent studies predict an expansion of kelps to higher latitudes. One of these is the cold-temperate kelp Laminaria hyperborea. It has been shown in different single-factorial experiments to survive several months of cold temperatures and darkness. Therefore, it is striking that it has not yet spread throughout the high Arctic. Aim: Find strategies how L. hyperborea can to acclimate to past, present and future conditions in the Arctic. Introduction Laminaria hyperborea is a dominant and important European bioengineering species. As ‘season anticipator’, it grows at low temperatures and during the short days of winter and early spring. Long and polar day conditions have been shown to restrict its growth. To investigate the potential ability of L. hyperborea to invade high Arctic sites under future warming scenarios, we conducted a long- term multifactorial experiment using tissue of adult sporophytes from Porsáŋgguvuotna/Porsangerfjord, Finnmark, Northern Norway – a site close to its northernmost distribution margin. Material & Methods Physiological Results & Discussion We quantified the physiological conditions of L. hyperborea and biochemical metabolites, including storage carbohydrates, under polar night, polar day and long day conditions at 0, 5 and 10°C. Cold temperatures in combination with light stressed L. hyperborea, while long polar night conditions did not harm it at any temperature (Fig. 1). Still, samples gained weight under light treatments, due to their physiological modulation to accumulate carbohydrates as reserves for winter (Fig. 2). The physiological results strongly indicate that L. hyperborea is restricted only by the long cold light periods in the Arctic and will benefit from increasing temperatures in summer. The warmer the Arctic becomes, the better L. hyperborea will cope with polar day. New species can have multiple consequences on the functioning of marine ecosystems. The stipe of L. hyperborea is rich in epibiont assemblages, which act, for example, as food source for associated mobile species, such as fish and sea urchins. Hence, the spread of L. hyperborea in the High Arctic will have cascading effects on the entire ecosystem. ©Uli Kunz References Lüning K (1986). New frond formation in Laminaria hyperborea (Phaeophyta): A photoperiodic response. Schaffelke B & Lüning K (1994). A circannual rhythm controls seasonal growth in the kelps Laminaria hyperborea and L. digitata from Helgoland (North Sea). Scheschonk L, Becker S, Hehemann J, Diehl N, Karsten U, Bischof K (2019). Arctic kelp eco-physiology during the polar night in the face of global warming: A crucial role for laminarin. Acknowledgements The authors are grateful to T. Wernberg, K. Filbee-Dexter and their diving team for collecting the kelps. Thank you to A. Wagner for his support in the experimental procedure and to B. Iken for the support in the laboratory. 1 Faculty of Biology and Chemistry & MARUM, University of Bremen, D