Antarctic Marine Ecosystem

Quick links

1. introduction
2. lesson objectives
3. vocabulary
4. 'story'
   • physical factors and the Antarctic food web
   • vertical structure of the open ocean and phytoplankton production
   • the Antarctic marine food web
5. summary
6. vocabulary review
7. self test
8. student activity

Introduction

This web page will familiarize students with the Antarctic marine ecosystem. Students will learn how physical conditions affect what kinds of plants and animals live here and how they interact with one another

grade level: 7th thru 9th

for the teacher: Further information on the Antarctic may be found at these resource sites:

• http://lima.nasa.gov/antarctica/ -- NASA Landsat Image Mosaic of Antarctica
• http://geography.about.com/library/cia/blcantarctica.htm -- general geographic information
• http://lima.usgs.gov/documents/LIMA_overview_map.pdf-- large very detailed map [loads slowly]
• NOVA Online | Warnings from the Ice -- good general overview on Antarctic, links to additional student activities
• Who Eats Who in the Antarctic? -- instructional module, good activities
• revised Alfred Wegener Institute: http://www.awi.de/en

for everyone:

This web page uses JavaScript to provide several extra functions.

1. Words which appear as underlined maroon text (e.g. phytoplankton) will pop-up a definition box when you move your mouse over them. Try it!
2. The pictures on this page are 'thumbnail' images. Click on the picture to the larger version.
3. Once you've answered the self-test, you can immediately find out the percentage you answered correctly by pressing the 'Score it' button.
4. The detailed answer sheet shows you your answer and the correct answer for each question. It also provides a link back to the point in the text which discusses the material for the question.

Lesson
Objectives

The objectives of this lesson are:

1. Students will be able to identify physical factors that affect the interrelationships among living things in an Antarctic ecosystem.
2. Students will be able to identify members of the Antarctic food web and their interrelationships.
3. Students will be able to construct an Antarctic food web and show how the members are related to one another.

Vocabulary
new words

Story

Physical factors and the Antarctic food web

The Antarctic ecosystem is highly influenced by physical factors such as weather & climate, ice, and ocean currents. In the Antarctic Ocean, the extent of ice cover affects competition between species of phytoplankton, the primary producers. The outcome of this competition affects competition between zooplankton species, which are primary consumers. Colder winters mean greater ice cover than warmer winters. colder winter favor larger phytoplankton, like diatoms. Diatoms are the preferred food of krill, which are in turn eaten by many other animals in this food web. So when winters are very cold and there is a lot of ice, almost every group in the food web does better because more food energy is transferred from lower to higher feeding or trophic levels.

When conditions are reversed, and milder winters occur, more of the ice melts and different species of phytoplankton have an advantage for growth and reproduction.

Warmer winters favor smaller phytoplankton such as cryptophytes. Unfortunately, these are not consumed as well by krill, so less of the food energy from cryptophytes gets into the food web. A big population of cryptophytes means a smaller population of diatoms since the two species compete for nutrients. Smaller diatom populations mean less food for krill. Less krill means less food for vertebrate predators.

Image courtesy of ecoSCOPE.

In the past 50 years, winters that have extensive sea ice development have been less frequent, leading to reduced krill populations. It's not hard to see that in the Antarctic, the food web is affected by climate factors.

Scientists disagree as to whether the warming trend of the past 50 years is part of a long-term cycle of warming and cooling of the earth or an effect that has been accelerated by human activities. In the current century the burning of fossil fuels has greatly increased the amount of carbon dioxide in the atmosphere. It is well known that carbon dioxide gas is a principal warming agent in the atmosphere. If the observed warming trend is part of a global pattern that continues unchecked, the consequences could be disastrous not only for the Antarctic, but for the entire planet.

Vertical structure of the open ocean and phytoplankton production

The vertical structure of the ocean is determined by the density of water, which, in turn, is determined by temperature and salinity.

• Salinity refers to the concentration of dissolved salts in water.
• The higher the salt concentration, the denser the water.
• The colder the water, the denser it is.

Phytoplankton need light and nutrients for growth and reproduction. A problem exists since the light source comes from the top, the nutrient source is from the bottom, and photosynthesis can take place only in the euphotic zone. Turbulent motion caused by such factors as wind stress at the surface or internal waves below creates a mixed layer at the surface. The mixing brings up nutrients from deeper water into the euphotic zone where phytoplankton can use the energy of sunlight and available chlorophyll to grow and reproduce.

When strong winds continue to blow, the turbulence created by waves makes the mixed layer deeper. At the bottom of the mixed layer there is a change in density called a pycnocline. This separates the lighter water of the mixed layer above from the denser water below. The pycnocline is important to phytoplankton and to primary productivity because it prevents nutrients from getting to the mixed layer where phytoplankton can use them. During the Antarctic winter, cooled surface water moves deeper and the wind produces turbulence.

These two events combine to deepen the mixed layer. The turbulence reaches so deeply that it brings nutrients up into the euphotic zone. At the same time, phytoplankton from the top layer are carried down out of the euphotic zone, where photosynthesis cannot occur.

At the end of winter, the process reverses as the surface water becomes warmer. The mixed layer becomes shallower and phytoplankton are trapped for longer periods in the euphotic zone with an abundance of upwelled nutrients. (Neither phytoplankton nor nutrients can sink down due to the pycnocline therefore they are held in the less dense water above the pycnocline). The increase in light and warmth, with plentiful availability of nutrients produce the spring bloom as phytoplankton grow and reproduce at peak rates.

The Antarctic marine food web

Phytoplankton and zooplankton
Phytoplankton are the primary producers in the Antarctic marine food web. They provide food for animals at all trophic levels from tiny zooplankton, like krill, to the largest blue whales. In winter, when phytoplankton is not available, krill feed on ice algae on the underside of the pack ice. Grazers, like zooplankton and some fish are the primary consumers in this food web. Zooplankton, such as krill, are eaten by many fish, birds, and mammals. Krill is a small (~5 cm. long) shrimp-like crustacean. So much krill is produced in the Antarctic, that its biomass is estimated to be greater than that of the world's human population. Krill is a critical species in the Antarctic marine food web because animals of all higher trophic levels depend on it. Since they feed exclusively on krill, Baleen whales would be most threatened by a decrease in the krill population. This is a real possibility since its high protein content makes krill a valuable target for commercial fishing.

Squid and small fish
Squid and small fish as well as whales feed directly on krill. Of the estimated 100 million tons of squid in the Antarctic, about 1/3 is consumed by whales, seals, and sea birds. Squid is also harvested commercially for food, bait, and other uses.

Fish
There are between 120 and 200 species of fish in the Antarctic. Most of them feed on krill and on one another. Many have developed special adaptations to survive in the extreme cold. These adaptations include reduced metabolic rates and molecules called glycopeptides in their body fluids. These molecules act like antifreeze by keeping body fluids liquid at temperatures below freezing.

Penguins
There are 5 major species in the Antarctic including Adélie, Emperor, and Chinstrap penguins. The emperor penguins, the largest, are the only species that depend on the ice for breeding and rearing their chicks. Penguins feed on krill and fish. In turn, they are preyed upon by leopard seals and killer whales.

Seals
Four species of seals inhabit the Antarctic.

• Weddell seals feed on squid and fish.
• Crabeater seals feed on krill. They may be the largest group of all seals in the world and probably consume more krill than whales do. Crabeater seals are preyed upon by killer whales.
• Leopard seals prey on penguins and small seals as well as on krill, squid, and fish.
• Ross seals are seldom observed, very little is known about them. They feed mostly on squid and fish. No known predators.

Sea birds

• Skuas are both predators and scavengers. they feed on carcasses and eggs as well as on living penguin chicks. The skuas distract the parent penguins, then disembowel the living chicks with sharp, hooked beaks.
• Snow petrels feed on zooplankton in polynyas and sometimes on food regurgitated by penguins.
• other... A large variety of birds frequently visit the Antarctic. Many prey on krill, fish, and squid.

Whales

• Orcas feed on penguins, seals, and fish near the surface. Also known as 'killer whales', they occasionally attack other whales such as sperm whales. Orcas occupy the highest position in the food web... nobody messes with them, except man!
• Sperm whales feed on fish and squid in deep water. A toothed whale, it finds prey in the deep by using echolocation. Occasionally sperm whales are preyed upon by orcas.
• Minke whales are the smallest of the Baleen whales. They are the most numerous of the whale species. They feed on krill and are preyed upon by Japanese and Norwegian whalers for supposedly 'scientific purposes'.
• Blue whales are the largest animal on earth. Blue whales feed on krill. They are preyed upon by man and by killer whales.

Summary

In the Antarctic, living things and their relationships in the food web are greatly influenced by the physical environment. This includes such factors as the annual extent of ice cover, currents, winds, temperature, and other weather & climate conditions.

The food web itself is a relatively simply one, consisting of many species in very few trophic levels. The primary producers in the Antarctic food web are phytoplankton. The primary consumers are zooplankton. A key species of zooplankton is krill, on which animals of all other trophic levels depend,some directly, others indirectly.

Vocabulary
review

Self test

Now that you have read through the material on this page, how about a little quiz to confirm that you've learned the major points about the Antarctic marine ecosystem?

Student activity

Additional lessons

Administrivia:

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