On the brink of the Arctic: Unusual intertidal sub-Arctic kelp associations in the Porsangerfjord, North Norway

Abstract

The kelps Laminaria digitata and Saccharina latissima are typically sub-littoral species. It is therefore surprising to find large intertidal kelp beds dominated by these two species in the inner Porsangerfjord, North Norway. The areas of the nine intertidal kelp beds ranged from 0.01 to 3 km2 and covered a total area of 8.3 km2. Both species had a prostrate growth form with short stipes, usually less than 10 cm long, independent of the length of the lamina. The laminae of L. digitata and S. latissima measured 77.0 ± 35.2 cm and 99.4 ± 41.0 cm (mean ± 1 SD), respectively. The associations occurred in sheltered areas with a muddy bottom on wide, flat areas of moraine. The areas are completely drained at low tide. The holdfasts were attached to small pebbles sunk in the mud. The mean biomass density of the two dominant kelp species was 4.1 ± 1.8 kg m−2. The mean biomass of all the algal species in the association was 6.1 ± 2.2 kg m−2. A total of 32 species were identified in the association, of which 16 species were annuals and 16 were perennials. All the species found in the kelp associations are also found in the Arctic. The prostrate growth form of L. digitata and S. latissima, the topography and substrate of the intertidal zone, low summer temperatures, low desiccation and protective sea ice during winter are possible factors contributing to the formation of these unusual intertidal kelp associations.