5. Conclusion
In this novel Arctic time series, we report considerable changes in kelp forest dynamics over the past 25 years in Kongsfjorden on Svalbard which are likely the result of global climate change. At our study site kelp demography, biomass and species dominance along the depth transect were influenced by the prevailing counteracting environmental drivers related to Arctic warming (Schlegel et al., 2023). In contrast to proposed assumptions (Assis et al., 2022; Krause-Jensen et al., 2012; Krause-Jensen & Duarte, 2014) we observed a decrease of depth expansion of the investigated kelp forest despite its release from ice scouring pressure and shading by thick sea ice coverage. The documented retreat of the kelp forest to the uppermost depth level reflects the decline of key engineer species exposed to coastal darkening with potentially large impacts on all associated higher trophic levels. As kelp communities represent complex marine ecosystems our investigation aims to serve as an example study that quantifies the negative consequences of increasing glacier loss (Geyman et al., 2022) to facilitate future predictions for wider stretches of Arctic coastline. We propose that in Arctic fjord systems influenced by strong melt water runoff, kelp forest communities will decline further as long as glaciers retreat and coastal darkening intensifies. The effects of the rapidly shrinking Arctic cryosphere on marine primary producers and their highly valuable ecosystem services are extensive and will continue in a changing future Arctic.