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Teachers’ notes | Terrestrial and marine ecosystems

3.1 Biogeography of Antarctica

This question is designed to review some basic ecological principles in relation to life in and around Antarctica. In their answers students should show understanding that the productivity of an ecosystem is reflected in the growth rate of the autotrophs; and that, ultimately, if productivity is low there will be little energy available for ‘heterotrophic’ organisms. Other ecosystem characteristics dependent on the level of productivity include the length of food chains and complexity of food webs, the size of populations, the amount of biomass, the rates of nutrient cycling, and the amount of biodiversity. The reasons for the continent’s low productivity are to do with the physical factors: mainly little ice free land, cold temperatures, and little moisture availability. The terrestrial biogeographical zones could be summarised as: the continental interior, the coastal areas, the Peninsula, and the sub-Antarctic islands (listed in order of productivity and biodiversity). The Southern Ocean comprises a marine biogeographical zone, and is far more productive and biodiverse than any of the south polar terrestrial ecosystems.

3.2 The terrestrial environment

This question concentrates on the nature and characteristics of Antarctic terrestrial ecosystems. It is broken down into parts which can be answered by reviewing the previous text and following up some of the suggested weblinks. In the producer/consumer table, students should include organisms such as algae, lichens, and mosses as producers and various invertebrates (e.g. rotifers, tardigrades, and nematodes) as consumers. The second part of the question requires that students do some further research on specific organisms to learn about the characteristics and adaptations that enable them to survive. The third part is more evaluative, asking students to consider what can be gained from studying these ecosystems. Much can be learnt about ecosystem processes in general, since it is easier to isolate specific processes at the small-scale by studying such simple ecosystems; and much can be learnt about how life adapts to climate extremes.

3.3 The marine environment

Question 1 is useful for exposing students to the application of remote sensing technology. The Nasa Earth Observatory website contains a wide range of different kinds of satellite images for a host of different purposes, and students should be encouraged to browse the site. To answer question 1, they must examine the images of ocean chlorophyll concentration (high chlorophyll = high productivity) and describe the global distribution of marine productivity that they observe. The distribution should then be explained in relation to the various factors described in the text – especially nutrient availability in the near surface waters (the ‘euphotic’ zone). Student should be able to explain why (contrary to what might be expected) marine productivity tends to be higher where the seas are colder.

Question 2 is a data response-style question, asking students to interpret the Southern Ocean food web. They should have the food web diagram in front of them for reference when they attempt the answers (and the answers to each sub-question can be relatively short). The Southern Ocean food web is relatively simple in that there are just a handful of key species that support organisms higher up the trophic ladder. This means that it is easier to study certain ecosystem processes (such as predator-prey population dynamics) than would be the case if the web of feeding relationships was more complex. Krill is the major prey species for many other organisms, and from the food web diagram students should identify several of the consumer species that would be affected by a change in the abundance of krill. Because people hunted many baleen whale species to the brink of extinction during the 20th century, the population of seals in particular has increased greatly in recent years because less krill is being eaten by whales. The final part of the question requires that students understand the concept of biomass; and to be aware, for example, that despite the large size of seals and whales in comparison with krill, the total biomass of krill in the Southern Ocean is far greater than the combined biomass of all the organisms that feed on krill. This relates to the concept of the ‘trophic pyramid’ of energy in which typically around 90% of the energy contained in the biomass of one trophic level is used up and dissipated with only around 10% left over for transfer up to the next level.

For question 3, students should learn about three or four species of their choice, concentrating on the adaptations that enable these species to survive the polar conditions (for example the extreme seasonality and perennially cold waters of the Southern Ocean). There is some relevant information in the text, but students will also need to do some of their own research by following up the suggested weblinks.

Question 4 asks students to research a single group of Southern Ocean animals in more detail – for example penguins or seals. Students should use the suggested weblinks to gather information for a fact-file that describes the animals in detail (e.g. number of different species, their distribution, habitats, behaviours, etc.) and any ways that the animals might be threatened by, for instance, climate change or human activities. Examples include Adélie penguin populations threatened by sea ice retreat, or albatross populations threatened by long-line fishing.

3.4 Ecosystem change and exploration

Question 1 is aimed at the concept of ‘sustainable yield’ and the principles used by the The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) when estimating the sustainable yield for krill and other Southern Ocean species. The educational pages of the CCAMLR provide essential background. At the core of the answer should be an explanation of the ‘ecosystem approach’ in which the estimate for sustainable catch of krill (for example) takes into account the implications for other krill predators besides simply the number that must be left in the Southern Ocean for krill to reproduce itself for human consumption.

Question 2 is broad based, asking students to compile information on the many different kinds of threats facing south polar ecosystems and on what is being done (and should be done in the future) to reduce these threats. In their briefing papers, students should pull together concepts and examples from the whole of Section 3 (and their own research), to address issues facing both terrestrial and marine ecosystems. Strong answers will contain specific examples of human impacts on various species, as well as specific examples of steps taken to reduce these, such as the ban on commercial whaling or the quotas for the Patagonian toothfish catch. There should also be discussion of the purpose of the CCAMLR and its policies, as well as discussion of current problems (such as ‘pirate fishing’) and suggestions as to how they might be solved in the future.