The longer the better: the effect of substrate on sessile biota in Arctic kelp forests

Abstract

Kelps are ecosystem engineers and thus enhance biodiversity and subsidize food webs in nearshore areas. Numerous studies describing diversity and abundance of biota associated with kelp have focused on sub-tropical and temperate waters while kelp forests at high latitudes, where kelp is predicted to expand in distribution, remain mostly unexplored. Kelp forests contribute significantly to regional biodiversity, and associated fauna and the kelp themselves play ecologically important roles as habitat and feeding areas. Here, we report patterns in diversity, abundance and seasonal dynamics of fouling organisms associated with different regions of Saccharina latissima and nearby substrates (including stones of the barren ground). The study was conducted in Kongsfjorden, a high Arctic fjord on the west coast of Spitsbergen; and samples were taken five times between September 2013 and January 2015. Trends in species richness of epifauna were similar for stones and holdfasts: higher in winter (due the presence of rare species), and lower in spring and autumn. Species richness and abundance demonstrated a clear tendency to increase in accordance with substrate stability. Stones housed the most diverse biota compared to living substrates. Holdfasts demonstrated similar patterns in species composition and abundance as stones due their close spatial arrangement and presence of demersal larvae in most of fouling organisms. Similarly, assemblages on blades in prostrate kelp forests are influenced by the species inhabiting stones of the barren ground. Both biotic and abiotic factors, including habitat stability and proximity to source populations, contribute to these spatial and temporal patterns in faunal abundance and diversity.