MEPS 301:55-66 (2005)  -  doi:10.3354/meps301055

ABSTRACT: The biomass of arctic sympagic (ice associated) amphipods from multiyear ice sampled in September and October 2002 in the Fram Strait between Greenland and Svalbard was approximately 10% lower than in previous recordings (0.4 ± 0.17 g wet mass m^–2). Gammarus wilkitzkii Birula and Apherusa glacialis Hansen were the most numerous species at the 4 ice stations, reaching average densities of 7 ± 6 and 4 ± 3 ind. m^–2, respectively. Along the marginal ice zone, sympagic amphipods are released to the water column and rapidly sink towards the seafloor. Amphipod densities in the surface waters ranged between 0 and 9 ind. m^–2 for the 0 to 25 m water layer and between 0 and 5 ind. m^–2 for the 25 to 50 m water layer. In contrast to our observations in sea ice, the most abundant species in the water beneath the ice was Onisimus glacialis Sars. Laboratory experiments indicated that O. glacialis reaches 100 m water depth within approximately 80 min, and G. wilkitzkii sinks twice as fast. Using hydrographical data, air temperature recordings and simulated trajectories, we estimated the origin and drift route of the investigated ice fields and related their recent and long-term history to our findings. The driving forces for the release of ice amphipods are ice breakup and swell, along with the structural decay of the ice due to intense melting. Comparison of various data sets on the standing stock of sympagic amphipods in the ice north of Svalbard suggests that previous calculations estimating the loss of ice-bound bio-energy in the Fram Strait and Svalbard area are overestimations and apply only to certain climatic regimes. Based on our present understanding of (1) the circulation system and ice drift patterns in the Fram Strait, and (2) the impact of thermo- and hydrodynamics on the sympagic ecosystem along the ice margin, we have identified continental shelves and coastal areas as settling and retention zones for released ice fauna.

KEY WORDS: Arctic ice fauna · Sympagic amphipods · Fram Strait · Retention areas · Sinking velocity