Sympagic macro-fauna from multiyear sea-ice near Svalbard

Abstract

The object of the present investigation was to map the distribution and abundance of sympagic fauna (= ice fauna) (>350 μm) within the perennial sea ice zone near Svalbard and to study relations between the sympagic fauna and the age and history of its ice substrate. The sampling took place in July/August 1986 and September 1988 using SCUBA-operated sampling gear (suction samplers, plankton nets with especially designed frames for sampling at the sea-ice/seawater interface, and underwater cameras). The amphipods Apherusa glacialis, Onisimus sp., and Gammarus wilkitzkii were the most conspicuous sympagic species both years. Scattered individuals of the amphipods Gammaracanthus loricatus, Weyprechtia penguis and the polychaete Harmathoinae indet. were also recorded. A. glacialis was the most numerous and contributed near 65% of the collected specimens in both years, with a maximum density exceeding 2000 individuals/m2. However, G. wilkitzkii was on average larger, and contributed most to the biomass (1986: 80%; 1988: 77%). The average biomass of sympagic fauna in 1986 and 1988 was estimated to be 4.7 g/m2 and 8.3 g/m2 respectively. Biomass values reported here are ten to hundred times higher than what is found within the seasonal sea ice zone. Autochthonous sympagic species, like A. glacialis, Onisimus sp. and G. wilkitzkii, have a permanent association with ice. The seasonal sea ice zone will thus have to be recolonized every year resulting in lower densities compared to multiyear ice. It is suggested that the speed of the ice leaving the Polar Basin through the Fram Strait is too high for the sympagic fauna to remain its position in the sea ice zone. The result is an annual loss in the order of 7*105 tons of sympagic fauna from the perennial sea ice zone.