Arctic Sea Ice and the Food Web
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The Arctic is an exotic ecosystem, as fascinating and varied as any place on Earth. In some regions the land is drier than the Sahara, while the ocean's life forms can be as colourful as those in a tropical reef.
The influence of ice and its freezing and thawing is everywhere and affects everything. It is a region of extreme temperatures, nutrients and colours. In the height of summer there is sun 24 hours a day, and in the middle of winter, no sun at all. Towns and roads dot the map in some places, and open wilderness stretches for hundreds and thousands of kilometres.
The summer is boom time—the oceans teem with life, and whales and birds travel from all over the globe to reap the Arctic's riches while the air temperatures are as low as 0 °C. However, the winter is a solemn test of survival, one without sunlight and with temperatures as low as minus 50 °C. In the ocean, the temperature is much less variable; it changes by only a few degrees, and species don't need to go into an over-wintering survival stage or emigrate in order to survive.
The plants and animals that make the Arctic home—and there are many—are all highly adapted to the extreme environment and they are often unique. In the oceans, many species live only in the Arctic, but others have broad ranges throughout the deeper waters of the Atlantic and Pacific. True, there are not nearly as many different species here as there are in a tropical rainforest, but there are more kinds of plants and animals here than you might think—in fact, thousands of them. The species that have adapted to survive in the Arctic have relatively little competition, and can often be found in abundance.
People living in the Arctic are, in some areas, hearing thunder for the very first time in their lives, and encountering new "southern animals" such as robins, for which they have no names in their language. This is because the Arctic climate is warming. In fact, the Arctic is changing faster than any other place on Earth.
The circumpolar region is experiencing its warmest air temperatures in four centuries, and temperatures are increasing at approximately double the global rate. A recent report notes that there has been a 7% reduction in ice cover in just 25 years, and a 40% loss of ice thickness. Scientists predict that the Arctic summer will be mostly ice-free within 30 years if trends continue.
With increased warming, many of the organisms that have adapted so well to the Arctic will be under threat. No-one knows exactly what will happen, but for animals such as polar bears and seals, their habitat—the sea ice—is in grave danger. With the ice gone, the algal community that lives on the undersurface will also disappear, affecting everything else in the food web that depends on it. Scientists don't fully understand the diversity of life of the Arctic Ocean; and it is quite possible that because of climate change, they never will.
Activity 1: Seasonal Arctic Ice Coverage
Review the following reference materials and then answer the questions below.
Animation: Normal Ice Season in Canadian Waters
Map: Minimum and Maximum Sea Ice in Canadian Waters.
1.1 Where is sea ice found in Canada?
1.2 During which months do the maximum and minimum sea-ice extents occur?
1.3 What seasons do these times represent?
1.4 Is there an east–west, ice-free route (passage) through the Canadian Arctic Ocean at any time of the year?
Activity 2: A Unique Ecosystem
Review the following 3D animation, which shows how a unique ecosystem forms underneath Arctic sea ice, and then answer the questions below. Consult the glossary if necessary for an explanation of the terms used.
3D Animation: Sea Ice Ecosystem
Glossary: Sea Ice Ecosystem
2.1 How do drainage channels form in sea ice?
2.2 What enters the tiny holes created by sea water draining out of the ice?
2.3 What feeds on these organisms?
Activity 3: A Phycologist at Work
Watch the following video, in which Canadian Museum of Nature scientist Michel Poulin talks about his research on diatoms in the Canadian Arctic, and then answer the questions below.
Video: Arctic Marine Research (3 min. 4 sec.)
3.1 What is a phycologist?
3.2 What are diatoms?
3.3 What is the name of the instrument lowered into the water from a ship to collect phytoplankton samples?
Activity 4: Arctic Food Web
View the PowerPoint on Arctic marine life and then read the background information for the Arctic food web provided below.
PowerPoint: Arctic Marine Life
You may also look at the photos of example organisms (listed below) in our photo gallery.
4.1 Using the information provided and other material that you can find, draw a diagram of an Arctic Ocean food web. You should include:
• at least four trophic levels
• 10 groups of organisms
• labels for all organisms
• some indication of relative abundance of organisms
• representation of the relationships between organisms.
Background Information for the Arctic Food Web
Sea ice plays an important role in the food web of the Arctic marine ecosystem. The following are some examples of organisms that are part of this ecosystem.
The basis of the food web in oceans depends primarily on microscopic plants called phytoplankton. They usually live in the water, but in the Arctic they are also found in and on the sea ice. One group of phytoplankton includes diatoms. Diatoms are found in almost every aquatic environment. There are so many different types of diatoms that they have not yet been counted; a best guess is more than 100 000 species. Diatoms are microscopic, but they sometimes stick to each other, thus forming clusters or colonies that grow so big that they can be seen floating on top of the water.
Through photosynthesis, these microscopic plants consume carbon dioxide while releasing oxygen and producing carbohydrates. Elements in the water such as nitrogen, phosphorus and sulphur attach to these carbohydrates and convert them into organic compounds that provide food for tiny plant-eating creatures called zooplankton, as well as other marine invertebrates.
See some diatoms.
Isopods are a very diverse group of animals. They include sowbugs, which can often be seen in basements or gardens. The isopods that live in the Arctic Ocean are mostly carnivorous and feed on dead whales, fish and squids; they may also be active predators of slow-moving prey such as sea cucumbers, sponges and other animals that live on the ocean floor.
See an isopod.
Amphipods are small, shrimp-like animals. The majority of amphipods in the Arctic live in holes in the sea ice and on the underside of pack ice. Amphipods are eaten by fish such as Capelin and Arctic Cod, which are very important in the diet of other fish, marine mammals and seabirds. Some seabirds, such as the Arctic Tern, also feed on amphipods, as do young seals.
See an amphipod.
The cockle is a bivalve, which is a group of animals that have two halves to their shell, joined together by a ligament. Other examples of bivalves include clams, scallops, mussels and oysters. Arctic cockles are preyed upon by fish, walruses, bearded seals and several duck species. About 140 Arctic bivalve species are currently known.
See a cockle.
Nudibranchs are commonly referred to as sea slugs. They are carnivores that live on the sea floor. Depending on the group, they feed on sea anemones, sponges, bryozoans and other animals.
See a nudibranch.
Sea cucumbers are animals that generally use their special tube feet to trap food particles, such as dead and decaying matter, from the sea-floor sediment. Many also use their branchial tree to trap particles suspended in the water. They are related to sea stars and sea urchins, which have the same radial symmetry in which their bodies are divided into five segments: their body has five lines running down it, sea stars usually have five arms, and urchins have five rows of tube feet.
See a sea cucumber.
Sea anemones are animals that are sometimes mistaken for plants. They usually remain attached to hard surfaces such as shells or rocks, but some of them burrow into the sea floor. Anemones are most diverse in the tropics, but are found in the Arctic Ocean as well, in particular on the continental-shelf sea floor.
See a sea anemone.
Eleven sea urchin species are known to live in the Arctic Ocean. They usually live on hard surfaces, and feed by scraping off algae and encrusting animals with their five teeth. The teeth are located in a complex organ called an Aristotle's lantern that is on the underside of their shell.
See a sea urchin.
Most sea stars are carnivores whose favourite food is bivalves. They have a unique feeding method: they use their tube feet to pry open the two halves of a bivalve and then they insert their stomach inside it! Their stomach then releases enzymes that slowly digest the animal within its own shell.
See a sea star.
Arctic Cod (Boreogadus saida) are fish that eat mainly shrimp, amphipods and copepods. They are eaten by a variety of other large fish, as well as many seabirds and most Arctic marine mammals. They spend much of their time associated with sea ice and remain in Arctic waters throughout their life cycle. This fish is a key component of the Arctic food web because it is the link in the food chain between small amphipods and higher vertebrates such as seabirds and marine mammals.
See an Arctic Cod.
Walruses (Odobenus rosmarus) overwinter in areas of pack ice where the ice is thin enough (less than 20 cm thick) to allow them to break through and maintain breathing holes, but thick enough to support the weight of groups of these large animals. Walruses prefer to eat bivalves such as clams, mussels and cockles, which they suck from the shells. They also consume many other kinds of invertebrates, including nudibranchs, sea cucumbers and other soft-bodied animals.
See some walruses.
Ringed seals (Pusa hispida) are the most abundant seal species in the Arctic. They use the ice for breeding, moulting and resting, and rarely, if ever, move onto land. They maintain their cone-shaped breathing holes by clawing the forming ice with their front claws. These seals can be found under ice up to 7 m thick. Before surfacing, a seal may blow bubbles into the hole to test for predators. As snow drifts over the hole, a space is hollowed out to provide some protection from cold and predators, and to give birth to pups. Ringed seals have a varied diet composed primarily of shrimp-like crustaceans and small fish such as Arctic Cod.
See a ringed seal.
Belugas (Delphinapterus leucas) are commonly found in ice-covered waters where they use open water at ice-edges, leads and polynyas to surface for breathing. These whales feed on crustaceans and small fish such as Arctic Cod. Like those of narwhals and bowheads, Arctic beluga populations stay in the Arctic year-round.
See a beluga.
The polar bear (Ursus maritimus) is dependent on sea ice for most of its needs, and as a result, is often regarded as a marine mammal. Factors that influence the distribution, movement, duration and structure of sea ice have a major impact on the population ecology of polar bears, whose diet consists mainly of ringed and bearded seals. They will catch and consume, on average, about one seal every six and a half days. Polar bears also occasionally feed on whales and young walruses.
See a polar bear.