An overview of the Arctic pelagic realm
The growth season of phytoplankton is severely constrained in Arctic Seas by snow and ice cover, low light angles and a relatively short season. The classic view is that phytoplankton production begins in April and ends in early September with a growth curve characterized by a single peak in primary production in late June to early July. Enhanced biological activity in the pelagic zone occurs on the Arctic shelf areas, where the seasonal retreat of the sea ice allows for the formation of ice-edge algal blooms. The melting of sea ice stimulates algal growth as more light enters the sea and the reduction of surface increases vertical stability. Phytoplankton blooms in spring are mainly dominated by diatoms and Phaeocystis pouchetii. The tremendous gradients in the large Arctic estuarine systems cause defined phytoplankton species assemblages, dominated by freshwater, brackish water or fully marine species.
Zooplankton research in Arctic waters can be traced back nearly a century, with the earliest records restricted primarily to the coastal waters. Waters of the continental shelves have now been studied in variable taxonomic detail in the Barents, Kara, Laptev and Chukchi/Beaufort Seas, while the East Siberian Sea, and Canadian Archipelago through northern Greenland have been particularly understudied. Due to their high abundance and ease of capture, the taxonomic composition and life history of the larger more common copepods in the Arctic Ocean is relatively well understood. The same cannot be said for the smallest copepod species that are variably missed by collection techniques, all deep-water species, or the more fragile gelatinous forms.
Historically, effort has concentrated on copepods of the genus Calanus because they appear to dominate zooplankton biomass. As in most oceans, smaller copepod species are actually numerically dominant, yet relatively few studies have used sufficiently fine meshes to fully assess their contribution. Although copepods typically predominate in the basins, there is a broad assemblage of other planktonic groups in the Arctic that are only occasionally reported in full detail. These non-copepod groups in particular hold the greatest promise for discovery of new species and trophic importance because they have been largely ignored or biased against by collection techniques.
Larvaceans (=Appendicularians), for example, have been shown to be abundant in Arctic polynyas and common in the central Arctic. Similarly, important and common predatory groups, such as the chaetognaths, amphipods, ctenophores and cnidarians have received detailed report in only a few surveys. Arctic chaetognaths may represent considerable biomass, and are thought to be important in controlling Calanus populations. Hyperiid amphipods can also be common in Arctic waters, and a similar potential to graze a notable proportion of the Calanus population. The importance of ctenophores and cnidarians in surface and deep waters, and their grazing impacts, are also particularly under-appreciated. The basic biodiversity of all these gelatinous animals is grossly underestimated in polar waters. Based on submersible experience in other oceans, we expect to discover at least twice as many species in most groups as currently described.
Updated: November 2, 2009
