The amphipod scavenging guild in two Arctic fjords : seasonal variations, abundance and trophic interactions

Abstract

Scavenging amphipods are important for the circulation and dispersal of organic material in the marine environment. Despite their dominance in the scavenging guild and importance in the food web, little is known about Arctic amphipods and their feeding preferences. We studied the amphipod scavenging guild using baited traps for one full year to increase our understanding of its seasonal variations. Two Arctic fjords with contrasting hydrographical conditions were studied: Adventfjorden, which is influenced by Atlantic water inflow, and Rijpfjorden, which is dominated by cold Arctic water masses. The species composition clearly differed between the 2 fjords. Onisimus caricus, followed by Anonyx laticoxae, were the dominant species in Adventfjorden. In Rijpfjorden, the species diversity was higher, particularly for Anonyx spp. In both fjords, a clear depth zonation in species distribution was detected, with a seasonal dynamic in species composition. A seasonal pattern in catch sizes was observed in both fjords. The timing of this pattern varied, likely because of the climatic differences between the fjords. Lipid content, lipid classes and fatty acid composition were analyzed for A. nugax, O. caricus, O. litoralis, O. nanseni and O. glacialis, and stable isotopes were also analyzed for the all these species except O. glacialis. A clear difference in the fatty acid and stable isotope composition was found among species. O. glacialis and O. litoralis were primarily omnivorous-herbivorous, while the other species were predominantly carnivorous. O. nanseni and A. nugax preyed extensively on calanoid copepods (Calanus spp.) whereas O. caricus did not.