Terrestrial and marine ecosystems

3:4

Ecosystem change and exploration

Are Antarctic ecosystems changing? What are the pressures and threats facing Antarctic ecosystems, and what actions are being taken to reduce them? What are subglacial lakes, what can we learn from them, and how can they be explored?

Warm up

Using your knowledge of climate change from Section 2 and your understanding of south polar terrestrial and marine ecosystems from this section, see if you can guess at the answers to the following questions:

  • What effects might global warming have on terrestrial ecosystems in Antarctica?
  • Why should we be concerned about the ozone hole with respect to south polar terrestrial and marine ecosystems?
  • What effects might global warming have on the marine ecosystem of the Southern Ocean?
  • The Southern Ocean is an important 'sink' for carbon dioxide emissions. How might global warming affect the ability of the Southern Ocean to absorb carbon?
  • As the sea absorbs carbon from the atmosphere, it becomes more acidic (pH decreases). What affects might this process have on the marine ecosystem?

Using your knowledge of the marine food web from the previous section, see if you can guess the answers to the following:

  • How do you think large-scale commercial whaling in the Southern Ocean during the 20th century affected the population of seals?
  • What knock-on effects will this have had on terrestrial ecosystems along the coastline where seals come ashore?
  • What ecological problems are caused on sub-Antarctic islands by the introduction of alien (non-endemic) animals, such as rats, cats, and rabbits?
  • Why should the harvesting of krill be carefully monitored and controlled?

Hopefully you will have been able to make a decent attempt to answer most of the questions raised above: they illustrate some of the important issues facing south polar ecosystems. Because ecosystems themselves are complex, the impacts wrought by human-caused climate change and other human activities are multi-faceted and not always easy to predict. There are also lag effects in which climate changes, or changes in the population size of a particular organism, take time to work their way through the system. Hence the effects of activities like pollution and over-fishing may not be recognised immediately; but by the time impacts are detected, it may be too late to reverse the process. This is why long-term environmental and ecological monitoring is crucial, and why international regulatory bodies (such as The Commission for the Conservation of Antarctic Marine Living Resources) are needed to coordinate preventative action and to ensure that marine resources are used sustainably.

Subglacial lakes represent a different kind of challenge. These bodies of freshwater lying beneath the ice sheets may contain geothermal-based ecosystems similar to those found deep in the oceans along hydrothermal vents and may contain undiscovered species of micro-organisms. However, the exploration of these lakes presents a major technical challenge – not least in designing equipment that can be transported through kilometres of ice and then enter a subglacial lake without contaminating it with bacteria from the surface.

The cold facts:

Ecosystems are always changing and Antarctic ecosystems are no exception. The ice core evidence described in Section 2.3, indicates that there have been significant air temperature fluctuations over Antarctica associated with glacial/interglacial cycles over the past million years or so, and these temperature changes (along with related sea temperature and sea-level changes) have undoubtedly affected the nature and distribution of both terrestrial and marine ecosystems in the south polar region. Because the physical environment is never completely constant, primary production fluctuates, population sizes of organisms adjust, and there are changes in which species have an advantage over their competitors in various places.

So it is normal that ecosystems change and adjust in response to natural environmental and climatic changes. However, add humans to the equation, and the changes seen recently are unprecedented and potentially very destructive. The main impacts of human activity on south polar ecosystems can be grouped according to whether they are due to human alteration of the atmosphere (global warming and ozone depletion) or due to direct exploitation of ecosystems through, for example, over-harvesting and introduction of alien species.

Climate change impacts

The problem of global warming is discussed in Section 2.3. While it is not yet possible to identify a warming trend for the continent as a whole, the Antarctic Peninsula has warmed by over 3°C in the last 50 years. One effect of this warming on the terrestrial ecosystems may be to increase primary productivity and allow certain types of lichens, mosses, and liverworts to expand their geographical range into parts of the Peninsula that were previously too cold or covered by ice. However, the effects on the adjacent marine ecosystem are largely detrimental: the seas around the Peninsula, particularly on the western side, have warmed significantly and this has caused a decline in the extent of sea ice (by around 40% in the area west of the Peninsula). This has caused problems for some penguin populations which breed on, and hunt from, sea ice. Adélie penguin breeding success has declined in areas where sea ice has melted too early in the summer season or where their breeding grounds have become wet due to the increase in snowfall associated with the warmer, moister climate conditions.

Adélie penguins at Rothera Point.
Adélie penguins at Rothera Point.
©British Antarctic Survey, Pete Bucktrout

The following link provides more information about how penguin populations are being affected by climate change:

Of greater concern for the whole Southern Ocean ecosystem is the effect of reduced sea ice on the krill population. Krill shelter and feed beneath and around sea ice during the early part of their life cycle, and as the extent of sea ice has declined in the area around the Peninsula, so too has the regional abundance of krill. This then puts pressure on the populations of the many marine animals that feed on krill, including fish, squid, penguins, seals, seabirds, and whales. Over the next century, it is likely that global warming will result in further sea ice decline in the Southern Ocean, and the problem of declining krill populations could get worse.

You can follow this link back to the main site to review the problem of krill decline and the different marine animals that rely on krill:

Squid, another marine animal that provides food for many other animals in the Southern Ocean food web, is also vulnerable to climate change because as sea temperatures rise, the squid population declines. Other cold adapted species, such as the Mackerel icefish, may be at risk if the Southern Ocean continues to warm.

Learn more about the effects of climate change on south polar ecosystems:

Depletion of stratospheric ozone (see Section 2.4) allows damaging ultra-violet (UV-B) radiation to reach the surface. The effects of this on land and marine organisms are the subject of much research, as illustrated in the photo below. It is has been estimated that phytoplankton abundance has declined by as much as 15% in some areas affected by the ozone hole. Fortunately the Montreal Protocol has been effective in reducing the worldwide emission of ozone depleting chemicals, but the ozone layer over Antarctica will not fully repair itself for another fifty years or more.

Experiment at Rothera Station designed to look at the effects of ultraviolet radiation on Antarctic vegetation. The covers allow different levels of UV light to penetrate.
Experiment at Rothera Station designed to look at the effects of ultraviolet radiation on Antarctic vegetation. The covers allow different levels of UV light to penetrate.
©British Antarctic Survey, Chris Gilbert

Related to the issue of global warming is the role of the world ocean as a carbon sink. It is estimated that nearly a third of all the carbon dioxide emitted by human activities goes into the oceans: through the process of photosynthesis, phytoplankton take in CO2 and some of this carbon becomes locked up in marine sediments as phytoplankton die and sink down to the sea floor. This so called 'biological pump' is a key element of the planet's carbon cycle; and the Southern Ocean makes a large contribution to the total oceanic carbon sink. There is concern, however, that warming of the Southern Ocean could reduce the effectiveness of this sink, causing more of the CO2 emitted by human activity to remain in the atmosphere to contribute to further warming by positive feedback. There is evidence that the Southern Ocean carbon sink has already started to decline because of higher velocity westerly winds that have enhanced upwelling of CO2 from deeper in the ocean. Moreover, CO2 is less soluble in warmer water; and, because of the extra CO2 that the oceans have already absorbed, the acidity of sea water has increased. As ocean water becomes less alkaline, it becomes more difficult for certain types of phytoplankton to form their calcium carbonate shells - if this trend continues many types of phytoplankton will decline in abundance. This in turn, would affect the food supply for consumer organisms operating at higher trophic levels.

You can learn more about the problem of acidification of the oceans at the links below:

Direct exploitation of ecosystems

The main ways that humans damage ecosystems are through habitat destruction, fragmentation, pollution, over-harvesting, and introduction of alien species. In the south polar region, habitat destruction and fragmentation of habitat are not significant, but the other three are. Global warming and ozone depletion are the results of atmospheric pollution on a global scale, and there are more localised situations where human activities along the Antarctic coast or on the sub-Antarctic islands have left waste (e.g. disused whaling and mining operations) or caused oil spills (e.g. the 1989 Bahia Paraiso shipwreck on the Antarctic Peninsula which spilled 200 000 gallons of oil).

Learn more about British Antarctic Survey policies to reduce pollution, clean up waste, and reduce other human impacts:

Over-harvesting of marine resources in the Southern Ocean (along with the possible future impacts of climate change) presents the greatest long-term threat to the marine ecosystem. One of the most well known examples is the whaling industry during the 20th century. Some whales, notably the Blue Whale, were hunted nearly to extinction; and the dramatic decline in the population of baleen whales in general has had far reaching effects on the whole ecosystem. Large-scale commercial whaling was finally banned in 1982 by the International Whaling Commission, and in 1994 the seas around Antarctica were declared a Whale Sanctuary. Due to this protection, whale populations are recovering, but most species remain far less numerous than they were before commercial whaling began. For instance the Blue Whale population was probably about 250 000 in pre-whaling times; but today they are only numbered in the hundreds.

With less competition from whales for krill (and after it became a protected species under the Environmental Protocol of the Antarctic Treaty), the population of fur seals has surged. This has had the knock-on effect of causing damage to terrestrial ecosystems on sub-Antarctic islands. Data collected by BAS scientists on Signy Island (South Orkney Islands) have shown that numbers of fur seals coming ashore each year at Signy have increased from just hundreds during the 1970s to over 20 000 during the 1990s. The seals damage vegetation (and the associated invertebrate fauna) through trampling and by eutrophication as their excrement loads the local terrestrial ecosystems with nutrients. This example illustrates one way in which terrestrial and marine ecosystems are interlinked, as well as how removal of one group of organisms in a food web has ramifications elsewhere.

Fur seals at Bird Island Station, South Georgia.
Fur seals at Bird Island Station, South Georgia. In some places large gatherings of seals can damage terrestrial ecosystems.
©British Antarctic Survey, Pete Bucktrout

Because modern fishing methods are so efficient, there is a danger throughout all of the world's oceans of over-harvesting; and therefore there is a need to identify what the sustainable yield is for particular species and to introduce quotas to ensure that a large enough population of a given species remains in the ecosystem to be able to reproduce itself. For the Southern Ocean, this is done by The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) which was established in 1982 as part of the Antarctic Treaty System.

Learn more about the activities of CCAMLR:

Management of the harvesting of krill is of critical importance for the long-term health of the Southern Ocean ecosystem because so many other organisms rely on it as a food source. Krill is harvested commercially mainly for fish food and animal feed; although it can also be processed and sold for human consumption, often used in Japanese food for example. The CCAMLR manages the annual allowable krill harvest not just for krill sustainability but also to ensure that enough krill remains available to ensure viable populations of the various species that rely upon it. The CCAMLR also sets quotas (total allowable catch) for fish in the Southern Ocean, and it regulates fishing methods to reduce 'by-catch' (the term for the accidental catch of other, 'non-target' species). For example, fishing with baited hooks on long lines has had a serious impact on the Wandering Albatross population. As seabirds (e.g. albatrosses and petrels) dive for the bait, they can become tangled on the lines and drown. This type of fishing could be killing about 100 000 albatrosses every year.

Learn more about the decline in albatross populations:

Unfortunately there is a lot of illegal and unregulated fishing in the Southern Ocean because it is so difficult to enforce and police CCAMLR regulations over such a large area. This is particularly problematic for the sustainable management of commercially valuable species such as the Patagonian toothfish (sometimes sold under the name 'Antarctic sea bass'). The fish resources of the Southern Ocean may come under more pressure in the future if fish stocks are not managed properly in other parts of the world ocean.

Learn more about the problems of 'pirate fishing' by reading the 'Focus on Fish' downloads and following the links contained in the Under Pressure section:

The introduction of alien species has mainly been a problem on the sub-Antarctic islands (which are not too cold for some introduced species to survive). For example, cats were introduced on some islands to try to control the population of introduced rats and mice; but, as is so often the case with alien species introductions, this had the unintended outcome of reducing the population of seabirds, such as petrels, that nest on land.

Two alien species on South Georgia: a dandelion and hoverfly.
Two alien species on South Georgia: a dandelion and hoverfly. The introduction of a pollinating insect along with an alien species of flower could lead to the rapid reproduction and dispersal of both, at the expense of endemic vegetation and insects.
©British Antarctic Survey, Peter Convey

Exploration of subglacial lakes

One of the most interesting discoveries about Antarctica in recent decades is that there are about 150 'subglacial' lakes existing beneath the East and West Antarctic Ice Sheets. These bodies of freshwater underneath the ice exist because geothermal heat emanating from inside the Earth melts basal ice (and the thickness of the ice insulates the underlying glacier bed from the extremely cold air temperatures at the surface). Many of these lakes are probably connected by subglacial channels, making up a vast subglacial hydrological network. The lakes vary in size, the largest being Lake Vostok which has an area of about 14 000km2 (roughly the size of Lake Ontario), a length of about 200km, and a depth of as much as 500m. It is located beneath the Russian Vostok Station, lying more than 4km beneath the ice. The dimensions of the lakes are known through remote sensing technology (using radar, seismic waves, and satellite imagery).

It is possible that these subglacial lakes contain ecosystems reliant on geothermal heat, as opposed to sunlight, similar to ecosystems in the deep sea associated with hydrothermal vents. There are plans to drill all the way through the ice to sample water from subglacial lakes, and to design probes (robots) which can enter the lakes to take photographs, search for organisms, and collect samples of water and sediments. Major technical challenges include designing equipment than can be transported through kilometres of ice without being damaged as well as remaining completely sterile so that nothing from the surface is introduce into the subglacial water to contaminate it. Lake Ellsworth located under the West Antarctic Ice Sheet with an area of 18km2 (about the size of Lake Windermere in the English Lake District) may be the first subglacial lake to be sampled because the logistics of setting up a facility and transporting the equipment are less challenging than is the case in East Antarctica.

Any life found in the subglacial lakes will have to be adapted to extremely harsh conditions: permanent darkness, high pressure, low nutrient availability, and cold water of about -3°C. (Under pressure, the freezing point of water is lower than 0°C.) Exploration of Antarctic subglacial lakes could lead to discoveries of previously unknown micro-organisms as well as revealing more about how geothermal-based ecosystems work. There is also the fascinating prospect that the environment beneath Antarctic ice offers an 'analogue' (meaning a comparable environment) to what scientists know about the ice covered moon of Jupiter – Europa. Thus, exploration of Antarctic subglacial lakes will also make a contribution to the search for extra-terrestrial life: the drilling, robotic, and sampling technologies that are being developed for Antarctica may one day be used on Europa.

Learn more about Antarctica's subglacial lakes and the technical challenges of exploring them:

Student activities

1. When estimating the total allowable catch of krill and other Southern Ocean species, the CCAMLR takes a whole 'ecosystem approach' rather than looking only at the sustainable yield of the species itself. Write a paragraph or two to explain what you understand by an 'ecosystem approach' and why you think the CCAMLR takes this approach.

The educational pages on the CCAMLR website will help you:

2. Using the text above and any of the suggested links within this section, write a briefing paper to describe:

  • What the main threats to south polar ecosystems are
  • What actions are currently being taken to address these threats
  • What further steps are needed to protect and conserve south polar ecosystems and their wildlife

>> 4:0 Geopolitics of Antarctica

 

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