Feeding Ecology of the Arctic Ice-Amphipod Gammarus wilkitzkii. Physiological, Morphological and Ecological Studies, Svalbard September 2000

Gammarus wilkitzkii is a presumed omnivorous amphipod that lives in high densities in close association with Arctic pack ice. This dataset consist of 7 rows and 4 species (Apherusa glacialis, Gammarus wilkitzkii, Onisimus nanseni and Onisimus glacialis). The data are derived from a study that tried to illuminate the complexity of food ecology in more detail for G.wilkitzkii and in terms of food detection, food localization, food preference, feeding mechanism, ingestion and digestion. This study combines several experiments, in field and laboratory, with special emphasis on physiology, behaviour and morphology. Sampling took place in September 2000 in the pack-ice north of Svalbard. At three ice stations of each 24 hours duration eight traps baited with different food types were fixed at the ice edge and below the ice. The total number of amphipods caught at all locations was 15. Most of the specimens were attracted by those traps attached at the under-ice surface and baited with rotten polar cod. They belonged to the genera Onisimus. Even though abundance (and biomass) was recorded highest for G.wilkitzkii at all three stations this amphipod was only seldom attracted by baited traps. Compared to previous studies the density and biomass data at this sampling side was remarkably reduced, probably due to recent melting and re-freezing processesand the specific re-colonisation abilities of sympagic amphipods. Since bait experiments resulted in extremely low numbers of attracted amphipods food preference studies were carried out in the laboratory with specimens sampled by SCUBA divers. The most preferred food type was deduced from oxygen consumption rates after exposing the amphipod to homogenates made of plant, animal or detrital material. Fourteen adults (of both sexes) and thirteen juveniles were incubated in a closed bottle set-up for 18 hours. Some experimental set-ups with a wide spectrum of food types including conspecific living and dead amphipods revealed, that G. wilkitzkii rejected none of the food types primarily and ingested even foreign material of no nutritional value. Morphological studies on mouthparts and accessory feeding appendages by means of SEM confirm a more unspecific food ecology of G.wilkitzkii.