Our interdisciplinary, long-term project on Arctic benthic macroalgae revealed considerable change of shallow water benthic ecosystems as a consequence of environmental changes. At our Arctic study site at Hansneset, Kongsfjorden, Svalbard, we repeated a quantitative diving study of 1996/98 in 2012-2014 in the shallow rocky sublittoral from 0-15 m depth. The overall seaweed biomass had increased 1.7× and 4.7× at shallow depths (2.5 m), which supported predictions of increased productivity in the Arctic because of climate warming. The standing stock at the biomass maximum at 2.5 m comprised 14.4 kg fresh biomass m-2, a leaf area index (leaf area/sampling area) of approx. 10 and a very high kelp density. Here, the kelp composition included four species, with pronounced dominance of digitate kelp species (Laminaria digitata and/or Saccharina nigripes). Our study showed 1) uplift of kelp biomass maximum from 5 m to 2.5 m depth, 2) decrease in the lower depth limit of dominant brown algae by several m, 3) decrease in biomass of annual species, 4) considerable increase in richness from 20 to 45 species in the intertidal to shallow sublittoral (1 m depth). With respect to the associated fauna, both biomass and production increased, particularly in the shallow sublittoral (2.5-5 m), and a functional change towards the dominance of suspension feeders became apparent. These observed changes are likely a consequence of recent Arctic warming. Lack of landfast sea ice and ice-scouring during winter would reduce physical abrasion and improve irradiance conditions. However, in summer increased sedimentation with reduced phases of clear water conditions has the opposite effect by reducing the radiance and causing less light to reach the deepest part of the kelp beds. Sedimentation had revealed a negative impact on germination and formation of juvenile kelp sporophytes. Moderate grazing could partly counteract the negative effect of sedimentation but not under complete sediment coverage of the recruits (~1 mm thickness). Arctic warming, with increased temperature, less sea ice, but increased sedimentation may cause species-specific differences in sporophyte recruitment, which may lead to “winner” and “looser” species in the kelp forest in Svalbard.