| Summary: | This thesis comprises firstly of method development, using a newly developed remotely operated vehicle carrying an underwater hyperspectral imaging camera (mini-ROV-UHI) for identification and mapping of brown, green and red macroalgae in a kelp forest in the Arctic and for ice algae in sea ice habitats. Secondly, this thesis aims to determine the health state, growth, and photobiology of macroalgae during the Polar Night and of microalgae growing under sea ice during spring. The thesis consists of three scientific papers. Paper 1 describes the mini-ROV-UHI to identify and map green, red, and brown macroalgae during the Polar Night. The mini-ROV-UHI lowers the technological threshold of use and information gathering for biologists working in extreme environments. This system is easy to transport, assemble, operate, and deploy (by two people) from shore, keeping the operational costs low. In Paper 2, we investigated the photobiological and health state of the macroalgae in Kongsfjorden. We observed new lamina growth in January, indicating that the growth of the studied macroalgae species starts during the Polar Night. Furthermore, the studied species were able to photosynthesise (converting light energy into chemical bonded energy) under artificial light during Polar Night. They have a slow functioning photosynthesis apparatus, needing more light to saturate photosynthesis. Lastly, in Paper 3, we used the mini-ROV-UHI system to study the light climate and algal biofilm under sea ice in the Northern Barents Sea (near Kvitøya). We measured the light transmitted through the ice (as radiance), as well as the light absorbed by ice algae representing the light usable for photosynthesis. The ice algal biofilm had a patchy distribution, dominated by diatoms that are evolutionary adapted to low light but were acclimated to the light conditions measured.
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