Rocky littoral macroorganisms that live between the high and low water marks were sampled in the summers of 1988 and 2007-2008 in Hornsund Fjord and along the adjacent Sorkappland coast (76-77°N). The same sampling stations and methodology were used to collect the samples. Over the last 20 years, the study area has been exposed to well-documented increases in air and sea temperature, increased windiness, and marked decreases in both the duration and extent of sea ice cover. The study revealed a twofold increase in the number of species found intertidally, a threefold increase in the biomass of macrophytes, and an upward shift in algae occurrence on the coast. Subarctic boreal species occupied new areas, while arctic species retreated. There were no species new to the area in 2007-2008, and all newcomers to the intertidal zone were noted in 1988 in the sublittoral zone. The relative stability of intertidal flora and fauna after 20 years is explained by the fact that the warm Atlantic waters (the main warming agent) are distant from the Sorkappland coast. Current observations show a marked change in the coastal belt biocenosis.

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Climate change has ecosystem‐wide cascading effects. Little is known, however, about the resilience of Arctic marine ecosystems to environmental change. Here we quantify and compare large‐scale patterns in rocky intertidal biomass, coverage and zonation in six regions along a north‐south gradient of temperature and ice conditions in West Greenland (60–72°N). We related the level and variation in assemblage composition, biomass and coverage to latitudinal‐scale environmental drivers. Across all latitudes, the intertidal assemblage was dominated by a core of stress‐tolerant foundation species that constituted > 95% of the biomass. Hence, canopy‐forming macroalgae, represented by Fucus distichus subsp. evanescens and F. vesiculosus and, up to 69°N, also Ascophyllum nodosum, together with Semibalanus balanoides, occupied > 70% of the vertical tidal range in all regions. Thus, a similar functional assemblage composition occurred across regions, and no latitudinal depression was observed. The most conspicuous difference in species composition from south to north was that three common species (the macroalgae Ascophyllum nodosum, the amphipod Gammarus setosus and the gastropod Littorina obtusata) disappeared from the mid‐intertidal, although at different latitudes. There were no significant relationships between assemblage metrics and air temperature or sea ice coverage as obtained from weather stations and satellites, respectively. Although the mean biomass decreased > 50% from south to north, local biomass in excess of 10 000 g ww m−2 was found even at the northernmost site, demonstrating the patchiness of this habitat and the effect of small‐scale variation in environmental characteristics. Hence, using the latitudinal gradient in a space‐for‐time substitution, our results suggest that while climate modification may lead to an overall increase in the intertidal biomass in north Greenland, it is unlikely to drive dramatic functional changes in ecosystem structure in the near future. Our dataset provides an important baseline for future studies to verify these predictions for Greenland's intertidal zone.

Acoustic imaging of seabed morphology and benthic habitats is a fast-developing tool for investigating large areas of underwater environment. Even though single- and multi-beam echosounders have been widely used for this purpose for many years, there is still much to discover, especially in terms of processing water column echoes to detect macroalgae and other scatterers (e.g., fishes, or suspended sediments) that can provide us with important information about the underwater environment and its evolution. In difficult Arctic conditions, acoustic monitoring plays an important role in the investigation of bottom morphology and in imaging habitats. In July 2016, we carried out a multidisciplinary expedition to investigate macroalgae spatial distribution in Isfjorden and to measure significant environmental features (currents, salinity, turbidity) influencing their occurrence. An area of 4.3 km² was mapped using single- and multi-beam sonars along with underwater video recordings, CTD and ADCP measurements. We obtained a unique data set showing variability of acoustic properties among different macroalgae species, supported by very well correlated ground-truth data and environmental measurements. Modern processing techniques were used to analyze water column data signals for kelp detection. This study presents efficient tools for monitoring benthic communities and their environmental context, focusing on macroalgae acoustic characteristics.