Living under Arctic kelp forests: linking soft-bottom communities to kelp cover in the Canadian Arctic

ABSTRACT: Kelp forests are dominant habitats along Canadian Arctic coastlines. While their extent and productivity are expected to change dramatically due to global warming, their role in supporting Arctic coastal biodiversity remains poorly explored. Leveraging an extensive data set encompassing core samples, video transects, and environmental data, this study explores the patterns and drivers of benthic diversity, particularly focusing on kelp cover, across 4 Eastern Canadian Arctic regions. We show that the widespread soft bottoms in many subtidal coastal Arctic areas are associated with high densities of the kelp Saccharina latissima, often growing in mixed stands with Laminaria solidungula and Alaria esculenta. These kelps enhance the diversity of invertebrate communities thriving in the sediment below, increasing densities in specific groups and promoting subsurface feeding activity. Interregional comparisons indicate that high turbidity conditions typically lead to low macroalgal cover and low invertebrate richness, whereas extensive sea ice cover can favor high macroalgal abundance and unique diverse communities. Conditions of intermediate open-water duration and high water clarity support tall kelp forests, hosting approximately 70% of local rare taxa. Based on these surveys, we provide a list of Arctic invertebrate taxa according to their level of selectivity for kelp forests as habitats. Despite variation among regions, kelp forests enhance biodiversity and drive unique benthic communities in the Canadian Arctic. Due to their ecological significance and potential vulnerability, we recommend efforts to integrate kelp forests into marine protected areas and minimize human-induced damaging activities within or near these habitats.