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Arctic Ecological Components
Contents:
The Arctic Archipelago is the area of the northern mainland coast and the islands to the north of the coast. The water
depth is generally typical of the continental shelf (< 500 m) and the water is usually open for two to three months during
the summer. For biological purposes, the Arctic Archipelago is divided into two ecoprovinces, five ecoregions, and 21
ecodistricts.
The Arctic Basin is the area north of the Arctic Archipelago, where the water is generally deep (> 2000 m) and
permanently covered by ice. There is low biological productivity in this ecozone: seals and polar bears are the main large
animals. Since there is little shipping activity in this ecozone, it will not be discussed further.
The Canadian Arctic is subject to large variations in the amount of sunlight which falls on the region at different times of year. From
mid-November to late January the sun is not seen above the horizon in the far North; from mid-May to late July the sun does not set. With
little energy input during the dark winter period, temperatures fall to well below freezing. When there is constant heating during the summer,
widespread melting of snow and ice occurs, uncovering the seas and the land surface. This great change in day-length is the main determining
factor in the activity of plants and animals. Plants produce most of their biomass during the long days of summer, and this is when the animals
that depend on them for food do most of their feeding.
As in all complex ecosystems, there are many relationships between species in the Arctic, most of which centre around consumption of one
species by another. The diet of most animals is highly varied, particularly among mammals and birds. For many species, the diet is also
poorly understood. However, it is possible to plot the main food sources of the main groups of animals in the Arctic. A simplified
representation of the Arctic Food Web is shown in Figure 2. 1. In generating this food web, consideration has only been given to the
consumption of living material (known as biomass). The remains of dead organisms (known as detritus) are voraciously consumed by some
organisms (such as the Arctic Fox [which eat carrion from seal kills left by sated Polar Bears], zooplankton [that eat small particles by
filtering them from the water], and benthic invertebrates (that eat small particles by filtering them from the water or picking them off or out of
the sea bottom mud).
The algae that grow on the under-surface of the ice, the phytoplankton, and the macroalgae (which are rooted in the
ocean floor or floating in the water column) produce biomass that feeds an assortment of animals. Together, these plants
are called the Primary producers. Of these plants, the phytoplankton produce the majority of the edible material,
although ice-associated algae are of equal importance in some local areas.
The plants of the Arctic are eaten by small invertebrates in the zooplankton. Together, they are known as the Herbivores.
These animals are primarily crustaceans (mainly amphipods and copepods). Also feeding on the phytoplankton are
some molluscs (mainly benthic bivalves and pelagic pteropods).
There are many species of small invertebrates in the zooplankton that feed on the plant eating crustaceans. These
zooplankton include two groups of crustaceans that are numerous: the pelagic euphausids, often called krill, and the
decapods, including shrimps (some species of which are pelagic when fully grown) and crabs (which are benthic shortly
after hatching). These animals are the Primary carnivores
All of the species of small invertebrates are consumed by large pelagic invertebrates, fish, birds, and mammals. The
pelagic invertebrates are primarily cephalopods (mainly squids) and decapods (mainly large shrimps). The most abundant
fish is the Arctic Cod, but Arctic Char, Cisco, and Whitefish are also present in large numbers (although these return to
fresh water to over-winter). The birds include ducks and geese, auks, loons, and certain others. The mammals include
small toothed whales, and seals. Walrus feed chiefly on bivalves, but also eat some shrimp. All of these groups are the
Secondary carnivores of the Arctic.
At the top of the food web are the Top carnivores: Polar Bears, baleen whales, large toothed whales, and many of the
gulls and birds-of-prey (such as the Peregrine Falcon and Snowy Owl). These predators eat a variety of organisms from
lower levels of the food web. For example, the fish (which are Secondary carnivores) become food for a wide variety of
birds and mammals. Baleen whales sometimes eat them when chasing schools of fish, and often engulf them incidentally
when feeding on zooplankton. Small and large toothed whales and seals hunt them actively. Polar Bears catch them when
opportunity permits (often in shallow waters, including pools on the surface of ice floes that are formed in spring as the
ice melts, and which are connected to the seawater below allowing fish to enter them).
Some birds become prey of certain mammals, primarily the Arctic Fox. Some whales consume birds that are on or just
above the water surface, usually in the course of feeding on zooplankton. Some birds are eaten by other birds: the young
and eggs of many species are eaten by gulls.
Some mammals are preyed on by others: seals (mainly the Ringed Seal, but also the Bearded Seal) are the primary food
of the Polar Bear, although it also consumes Walrus. Occasionally these bears also kill Beluga Whales, particularly when
they are stranded on shoals at low tide or in very shallow water. Bowhead Whales and many other species of whales,
dolphins, and seals are eaten by Killer Whales (which also eat large quantities of fish).Many people live off the land in the
Arctic, consuming fish, birds, and mammals. These people also obtain a variety of usable parts from animals, such as
hides, bones, and teeth (and tusks).
Animals tend to be abundant in open water near the ice edge and this is generally the most active biological area in the
Arctic. The bottom of the pack ice is covered with single-celled algae. These algae are eaten by a variety of small
crustaceans, which in turn are consumed by a wide variety of invertebrates, fish, birds, and mammals. These birds and
mammals seek access to the abundant food supply which is under the pack ice. Since birds and mammals must breathe
air, they cannot feed under fast ice and are thus often found feeding and resting in leads and open water near the ice
edge. After the ice in a particular site has melted, the area may continue to be a feeding ground for wildlife if there is a
substantial population of phytoplankton.
Some mammals gather at the ice edge (e.g., Beluga Whale and Narwhal), even though there may be little opportunity for
them to feed there. These mammals wait for the ice edge to melt back and open up migration routes to other feeding
grounds.
Ice occupies coastal areas and most offshore areas. In the western arctic, leads in the ice allow bowhead whales and
beluga whales to migrate eastward in offshore waters. In the eastern high arctic, a series of ice edges forms along major
channels. Marine mammals and birds concentrate at the ice edges to feed and await breakup so that they can move into
summer ranges.
In early spring:
A soft spongy layer of ice with algae growing in it forms on the undersurface of the ice. Amphipods and other
animals graze on this algae. Arctic cod feed on this underice community. Birds and mammals can feed on
under-ice animals in leads, ice edges, and polynyas.
As the ice retreats, zooplankton resume their life cycles and reproduction occurs. The composition of life stages
within the zooplankton community reflects the relative timing of retreat of the ice in various areas.
Ringed seal pups are born in lairs under the ice.
Caribou migrate northward across the ice in the Coronation Gulf area.
Seabirds and waterfowl arrive and feed in whatever open water that is available.
In spring:
Ice is present at least along shorelines, but there are sufficient leads, retreat of ice edges and opening of pack ice
to allow migration of marine mammals,
Migratory marine mammals do not have access to their summering areas. in the west, they are migrating along
leads in Beaufort Sea. In the east, they wait for breakup, at ice edges or along the edge of the shore fast ice.
Ringed seals haul out on the ice to bask in the sun.
Seabirds and waterfowl arrive on nests and lay eggs.
In summer, marine mammals have access to and are found at traditional smmering areas. Belugas make daily trips to the
Mackenzie estuary, and estuaries in the high arctic and Hudson Bay. Walrus spend much time hauled out on traditional
terrestrial haul out sites. Narwhal and harp seals are found throughout their range. Seabirds and waterfowl eggs hatch
and young are reared. Summer is easiest described as the period between spring and fall.
The onset of fall is characterized by:
- The southward migration of breeding care-giving waterfowl and shorebird adults and young. (Non-breeders and
non-care-giving adults may leave in mid summer).
Fall is well underway when:
- Migratory marine mammals move from their summer feeding grounds to wintering areas. Some migrations occur
quickly with the entire population leaving in the space of a week while others are slower and animals may leave in
groups with adult males, juveniles and mothers with calves leaving at different times.
- All seabirds, waterfowl and shorebirds have departed for the south.
- Ice forms in open water at night (it may melt and be broken up during the day).
- The appearance of ice in the open water areas that does not melt.
- The absence of migratory marine mammals. (Some mammals such as walrus can remain in a some areas
year-round as long as there is open water).
- The southward migration of caribou across the sea ice in Coronation Gulf.
Winter is not included in biological seasons because most species are dormant durring the 24 hours of darkness.
The native peoples of the Canadian Arctic are at the top of the food chain and harvest fish, birds, marine and terrestrial
mammals. As such they interact with and influence the ecology. The socioeconomic activities of the indigenous peoples
are discussed in
Click here for more information on Indigenous Peoples
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