Semi-quantitative macroalgae survey data on lower depth distribution of dominant algal species in Porsangerfjorden

Surveys were performed of lower depth distribution of dominant macroalgal species at Harvika, Holmfjord and Veineset in Porsangerfjorden, northern Norway, between 2 m and 19 m depth in June 2022. This dataset is part of a space-for-time comparison between low-Arctic Porsangerfjorden and high-Arctic Kongsfjorden. The aim was to document differences in kelp forest depth extension and community composition between two Arctic fjord systems at different stages of cryosphere loss to understand how benthic vegetation in the high-Arctic will likely develop in the future. The depth distribution of biomass macroalgae was semi-quantitatively (visually) investigated by scientific divers in four parallel transects off the coastline covering the vertical gradient between 2m and 19m depth. For each replicate a 1x1 m quadrat divided into four 50 x 50 cm subquadrats was placed on the ground or above the kelps at every depth meter along the transect.