RT Journal Article T1 Short-term response to light after the polar night in the Arctic kelps Alaria esculenta and Saccharina latissima A1 Cobos-Mateo, Pablo A1 López-Gordillo, Francisco Javier A1 Roza, Patricia A1 Wulff, Angela A1 Smerdou, Carlos K1 Biología marina K1 Cambios climáticos K1 Ártico K1 Algas marinas-Fisiología K1 Algas marinas-Composición K1 Fotobiología AB The current absence of ice in early spring in a number of Arctic fjords allows sunlight to penetrate the water column about two months earlier than it used to be when a thick ice cover was present. This can potentially change the growth dynamics of permanent seaweed forests. To elucidate the ability of seaweeds to take advantage of this early available light, growth, photosynthetic performance, and biochemical composition has been analyzed in two major forest-forming algal species, Alaria esculenta and Saccharina latissima, from Kongsfjorden (Svalbard) collected in early February, and incubated in dim light and dark conditions. For A. esculenta, new tissue appeared during the last weeks of the polar night, so that the new and old tissues coexisted in the same individuals and were compared. Dim light triggered positive growth rates. The onset of light led to rapid (1 h) increase in the optimum quantum yield (Fv/Fm) in the new tissue of A. esculenta, while the old tissue and S. latissima increased their maximum photosynthetic electron transport rate (ETRm). The new tissue accumulated 3 to 5 times more internal nitrate than the old tissue, but it showed lower content of photosynthetic pigments. Dim light promoted changes in stored carbohydrates in A. esculenta while the total C:N:P ratios remained stable in both species. Furthermore, S. latissima responded to light by decreasing its ∂13C values, indicating some activation of its carbon concentrating mechanism. Overall, dim light showed the potential to trigger photosynthetic metabolism and growth as early as February. PB Elsevier YR 2025 FD 2025-06 LK https://hdl.handle.net/10630/39160 UL https://hdl.handle.net/10630/39160 LA eng NO Pablo Cobos, Francisco JL. Gordillo, Patricia Roza, Angela Wulff, Carlos Smerdou, Short-term response to light after the polar night in the Arctic kelps Alaria esculenta and Saccharina latissima, Marine Environmental Research, Volume 210, 2025, 107298, ISSN 0141-1136 NO This research was funded by the Ministry of Science, Innovation and Universities project PID 2021-127865NB-I00, and the Research Vice-rectorate of the University of Malaga. Funding for Open Access charge: Universidad de Malaga/CBUA. DS RIUMA. Repositorio Institucional de la Universidad de Málaga RD 11 abr 2026