Arctic sea ice as feeding ground for amphipods - food sources and strategies

The amphipod species Gammarus wilkitzkii, Apherusa glacialis, Onisimus nans eni and O. glacialis live permanently associated with the Arctic sea ice. Q ualitative and semi-quantitative investigations of gut contents and faeces showed that all four species use detritus as the main food source. Detrital lumps from the underside of sea ice had the same item composition as amphi pod gut contents and faeces. Crustacean remains and ice algae were addition al food items, but overall they were quantitatively less important. All spe cies are omnivorous; however, differences in gut contents, behavioural obse rvations and functional-morphological studies of the mandibles suggest a di fferentiation within this feeding strategy. G. wilkitzkii is a detritivorou s-carnivorous-necrophagous-suspension-feeding species and shows the most co mplex feeding strategy. O. nanseni and O. glacialis are predominantly detri tivorous-necrophagous, whereas A. glacialis is characterised as a more herb ivorous-detritivorous species. By using a variety of the available food sou rces under Arctic sea ice, the amphipods are well adapted to the under-ice habitat and are less influenced by temporal and spatial variations. Further more, the wide food spectrum of all four species reduces the intra- and int erspecific competition in a habitat where certain food sources are limited or only seasonally available.