Mean fresh weight of macroalgae collected at Hansneset, Kongsfjorden, Spitsbergen in 2012, 2013 and 2021

Macroalgal fresh biomass was surveyed at Hansneset, Blomstrand in Kongsfjorden, Svalbard, from the infralittoral fringe down to 15 m depth in summer 2012, 2013 and 2021. This dataset is part of a time series currently spanning over 25 years including the following three time points: 1996/98 (Hop et al., 2012; doi:10.1515/bot-2012-0097), 2012-14 (Bartsch et al., 2016; doi:10.1007/s00300-015-1870-1) and 2021 (Düsedau et al., in prep.). Our goal was to document changes in Arctic kelp forests dynamics in an Arctic fjord system influenced by glacial melt by repeatedly sampling the same site in a standardized manner. As ocean temperatures in the Arctic have risen substantially and underwater light climate continuously deteriorated over this time period we observed alterations in the seaweed community, especially kelps as major coastal foundation species. This data contains the mean fresh weight [kg/m²] of a number of species sampled within replicate quadrats (Replicate) at different water depths (Depth [m]) over different years at Hansneset, Kongsfjorden, Svalbard. Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible so they are listed here with the WORMS code for Laminariales. Historically these kelps were considered Laminaria digitata.