10 



G. J. DIVOKY 



By increasing the stability of the water 

 column. Increased stability of the water 

 column reduces the upwelling of nutrient-rich 

 waters into the euphotic zone. Ice stabilizes 

 the water column primarily by preventing 

 wind-driven movement of surface waters and 

 by forming a layer of meltwater at the surface 

 in the spring and summer (Dunbar 1968). 



Sea Ice Reduces Benthic and 

 Inter tidal Biota 



Benthic flora and fauna can be reduced by 

 the presence of ice in two ways: In shallow 

 water ice can freeze to the bottom for much of 

 the year and prevent the establishment of 

 plant and animal populations; and when ice 

 floes are pushed together, they form under- 

 water ice keels that can scour the bottom 

 when the ice moves. Both of these events not 

 only act directly to decrease benthic popula- 

 tions but also disturb the sediment, making it 

 less suitable for colonization. In areas with 

 heavy ice scour, sessile benthic populations 

 can be greatly reduced, although motile 

 species may move into scoured areas during 

 the ice-free period in summer. In addition to 

 preventing the establishment of sessile 

 benthic animal populations, ice scour also pre- 

 vents the establishment of beds of kelp and 

 eelgrass (Zostera marina), thus decreasing the 

 diversity and productivity of arctic inshore 

 waters. Both kelp and eelgrass beds are im- 

 portant feeding sites for birds in areas south 

 of the region affected by ice scour. 



Sea Ice Allows Terrestrial Predators 

 Access to Breeding Sites 



The formation of ice between the mainland 

 and offshore islands allows the arctic fox (Alo- 

 pex lagopus) and other predators access to the 

 islands used by breeding birds. Foxes can be- 

 come permanently established on islands that 

 have food sources during the period when 

 birds are absent from the island. Often, how- 

 ever, there is little to attract foxes to the is- 

 lands other than breeding birds. Because 

 moats form around many islands before the 

 breeding birds arrive, foxes are primarily a 

 problem when moat formation is incomplete 

 or when the breakup of ice is late. Arctic foxes 

 are found on the pack ice throughout the sum- 

 mer and thus can visit islands that are sepa- 



rated from the mainland by open water but 

 are adjacent to the pack ice. 



Advantages 



Sea Ice Provides a Matrix and 

 Substrate for an Ice-associated Plankton 

 Bloom and an Associated Under-ice Fauna 



The first detailed studies on the blooms of 

 diatoms that occur in the lower levels of ice 

 were done by Appollonio (1961). The impor- 

 tance of this bloom in the energy budgets of 

 arctic and subarctic seas has only recently 

 been realized (Alexander 1974; McRoy and 

 Goering 1974). In areas where ice is present 

 throughout the year, the plankton bloom sup- 

 ports a population of under-ice invertebrates. 

 These populations have been little studied but 

 apparently consist primarily of copepods and 

 amphipods (Mohr and Geiger 1968). Feeding 

 on the invertebrates associated with the ice 

 are two species of fish, polar cod (Arctogadus 

 glacialis) and arctic cod (Boreogadus saida). 

 Andriashev (1968) used the term cryopelagic 

 to describe such fish, which are found in the 

 mid-water zone but also are associated with 

 ice during some part of their life cycle. 



The underside of multi-year ice has 

 numerous ridges and pockets that provide a 

 heterogeneous environment for the under-ice 

 fauna. This environment is protected from 

 disturbance from currents and wave action by 

 ice keels acting as barriers, which also provide 

 shelter from predators in the same manner as 

 a coral reef. The overall effect of the under-ice 

 flora and fauna is to increase the diversity of 

 surface waters in arctic seas by creating an in- 

 verted benthic biota. 



Sea Ice Provides Hauling Out 

 Space for Marine Mammals 



The mammals that inhabit the ice in the 

 Chukchi and Bering seas and their adapta- 

 tions to the pack ice environment were dis- 

 cussed by Fay (1974). Many of these species 

 frequently haul out on the ice, where they pro- 

 vide food in the form of feces, placentas, and 

 carcasses. 



Sea Ice Provides Roosting Sites 



Ice provides a hard substrate that allows 

 seabirds to leave the water to roost. This 



