Arctic field experiment shows differences in epifaunal assemblages between natural and artificial substrates of different heterogeneity and origin

Many studies have the aim of increasing our knowledge on settlement and colonization of epifauna. Despite broad interest these important processes have proved to be very complex and there are still issues which need more attention. Experiments presented here, performed in the Arctic, aim to explore colonization of epifauna on hard substrates in relation to: (1) site, (2) depth, and (3) substrate characteristics (i.e. heterogeneity and biotic/abiotic origin). Three different substrate types (pebbles, empty Buccinum undatum shells and artificial shells made of granite) were prepared and deployed on the seabed in four Arctic sites (two at Spitsbergen 78°N, two in Northern Norway 69°N) for one year. After recovery, epifaunal assemblage structure, species richness, abundance, and Shannon-Wiener diversity of each substrate was estimated, subjected to a three-factor fixed experimental design and analysed using permutational multivariate analysis of variance (PERMANOVA). As hypothesized, site (i.e. colonizer species pool, local environmental conditions) explained most of the variation, and proved to be most influential factor in determining epifaunal assemblage structure. However, where the spatial scale of investigation was lower, as at Spitsbergen where study sites were in close vicinity (2 nm apart), factors that varied with depth (e.g. macrofaunal cover) predominated. The study indicated that epifaunal assemblages are influenced to a different degree at various sites. Depending on the region (Spitsbergen or Northern Norway), the substrate surface area or substrate type were the least important factors, but still made some contribution. Results suggest also that among substrate features surface heterogeneity is of high importance, higher than its biotic/abiotic character. In most of the cases rough surfaces of artificial shells supported the highest species richness, abundance and diversity.