Distribution, abundance, and ecological importance of marine sympagic fauna in the Arctic

Sympagic (under-ice) fauna is important to the food web of the northern ice-covered oceans, and it functions as a link in the energy transfer from primary production (ice algae, phytoplankton) to seabirds and marine mammals. The most conspicuous sympagic organisms are one- to two-year-old polar cod (Boreogadus saida) and amphipods belonging to the species Gammarus wilkitzkii, Apherusa glacialis, Onisimus nanseni, and Onisimus glacialis, but other crustaceans (copepods, mysids, isopods, amphipods), foraminifers, rotatorians, nematodes, polychaetes, chaetognaths, pteropods, and appendicularians have also been found. Biomass values up to 20—40 g (wet weight) rrT2 of ice undersurface have been recorded, but values of 0 .1 -1 0 g m- - are more common, and the mean value in Arctic multi-year ice is probably of this order. Both grazers and predators are present in the sympagic fauna.
Autochthonous sympagic animals of both sexes and in all developmental stages (juveniles, immature individuals, mature individuals) occur in the ice habitat. They are not normally benthic or pelagic, and may be adapted physiologically (e.g.. with high tolerance to brine) and morphologically (e.g., with spiny appendages enabling the animals to cling to the ice). Examples of autochthonous animals are G. wilkitzkii and the mysid Mysis polaris.
Allochthonous sympagic animals are found temporarily in the ice, and may occur as nekton, plankton, or benthos. They may actively seek out the ice habitat for shelter or food, or may be passively transported by hydrodynamic action. Examples of allochthonous animals are A. glacialis, Parathemisto libellula, calanoid copepods, and B. saida.
The composition and abundance of the sympagic fauna are especially dependent upon the age, structure, and history of the ice habitat; water depth; and origin of surrounding water masses. Generally, old, stable drift ice from the Polar Basin contains more autochthonous sympagic animals than does newly frozen ice on the margins of the Arctic. Ice above shallow water usually contains more animals than does ice above deep water.