Mapping macroalgae beds and environmental factors for understanding the impact of climate change in the Arctic - a case study from Isfjorden (West Spitsbergen)

Macroalgal beds are an important component of the coastal zone in Arctic regions. They provide habitats for a vast number of associated invertebrates and fishes and high amount of fresh organic carbon. Distribution of macroalgae is essential for estimating the overall productivity of the Arctic area and for understanding processes occurring at the sea-shore interface. Moreover, macroalgae are sensitive to environmental changes. They can be good indicators of the health and evolution of an ecosystem. Changes in environmental factors (temperature, salinity, turbidity, current velocity) may limit or influence their spatial distribution and health. In July 2016, we carried out a multidisciplinary expedition to investigate macroalgae spatial distribution in Isfjorden and to measure significant environmental features influencing their occurrence. This survey was a first part of a 2-year monitoring project in Isfjorden and covered 3 sampling areas inside the fjord, two on the south and one on the north. During the expedition an overall area of 4.3km² was mapped using single- and multi-beam sonars. Modern processing techniques were used to analyze water-column data signals for kelp detection and to create a map of their spatial distribution related to bottom morphology and confirmed by ground-truth data. Along with acoustic studies, we collected many underwater video recordings through all the depths in the euphotic zone. ADCP measurements in each sampling zone were carried out and 85 CTD profiles were collected. We found considerable differences in kelp species abundance and distribution on the bottom between the northern and the southern parts of the fjord, where environmental conditions are significantly different. The southern part is influenced by salty, transparent shelf waters while the northern one is under the influence of glaciers that bring fresh water with dense sediment suspension. We would like to present not only the results of our work but also the methodology, as efficient data collection is crucial in difficult polar conditions.