Arctic fjords host a diverse seaweed community forming the base of the benthic foodweb and providing habitat and shelter for a vast diversity of associated fauna. Seaweed model species as well as seaweed communities are intensively studied with reference to their general adaptive and functional traits, as well as their responses to global environmental change. Our long-term project ats Svalbard aims at a holistic understanding of seaweed ecosystem function spanning from the environmental control of gene expression to energy flow through trophic levels. Research is currently focusing on the sugar kelp Saccharina latissima and the wing kelp Alaria esculenta as abundant model species under a set of combined stressors such asthe combined stressors elevated UV-B radiation and temperature or increased sedimentation and grazing. In addition the responses of seaweeds to increased CO2 are addressed. In the frame of this global change scenario species-specific acclimation patterns are studied aton the physiological levelbase and species competition at the community level. Both approaches intendin order to predict shifts in the competitive strength of habitat engineeringa respective species, potentially resulting in a changing seaweed community. Comparative community analyses conducted in 1996-98 and 2012-2014 indicate a considerable change in seaweed biomass, a change in kelp depth limits and a change in species richness at low depth at the study site off Hansneset/Kongsfjord, Spitsbergen, but no obvious biodiversity change all possibly correlated to the recent warming of winters. The seaweed biomass maximum was shifted from 5 to 2.5m depth and overall biomass increased. Future surveys are needed to separate climate related signals against a background of high interannual variability.