Faecal pellet production by Arctic under-ice amphipods - transfer of organic matter through the ice/water interface

The underside of Arctic sea ice is inhabited by several autochthonous amphi pod species (Apherusa glacialis, Onisimus spp., Gammarus wilkitzkii). The a mphipods graze on ice-bound organic matter, such as ice algae, detritus and ice fauna, and release faecal pellets into the underlying water column, th us forming a direct link between the sea ice and the pelagic ecosystems. Ex periments on faecal pellet production rates showed species-specific differe nces, which were related to size of the animals. The smallest species, A. g lacialis, produced the highest mean number of pellets (15.4 pellets ind.(-1 ) d(-1)), followed by Onisimus spp. (2.7 pellets ind.(-1) d(-1)) and the la rgest species, G. wilkitzkii (1.1 pellets ind.(-1) d(-1)). Relative carbon content of the pellets was very similar in all species (21.2-22.6% dry mass ). Juvenile amphipods (Onisimus spp., G. wilkitzkii) produced more pellets with less POC than adults. Based on field determinations of the POC concent ration in the lowermost 2 cm of the sea ice (mean: 36.4 mg C m(-2)) and mea n amphipod abundances (A. glacialis: 33.8 ind. m(-2), Onisimus spp.: 0.5 in d. m(-2), G, wilkitzkii: 9.4 ind. m(-2)) in the Greenland Sea in summer 199 4, the amount of POC transferred from the ice to the water by faecal pellet production was estimated (0.7 mg C m(-2) d(-1) or almost 2% of ice-bound c arbon). Since this process probably takes place in all ice-covered Arctic r egions as well as during all seasons, grazing and pellet production by unde r-ice amphipods contributes significantly to matter flux across the ice/wat er interface.