Terrestrial
Life
With its unforgiving and extreme conditions, Antarctica represents
a region where life approaches its environmental limits. Terrestrial
life must survive in the few, isolated pockets not continually covered
by ice and snow. The McMurdo Dry Valleys of southern Victoria Land
are of particular interest.
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Lichens
and Algae
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Surprisingly enough, Antarctica is home
to at least 200 species of lichens, over 100 species of mosses
and liverworts, more than 30 species of macrofungi, two species
of flowering plants and many species of algae.
The relationships between these plants
and those on the surrounding continents have interested botanists
for almost 150 years, and it is only now, after a great deal
of specimen-collecting and detailed taxonomic study, that
the relationships are finally becoming clear.
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There, scientists find
extremely basic ecosystems with organisms showing remarkable adaptations.
All aspects of life are studied, from the bacterial organisms living
on sandstone outcroppings to microscopic worms, called nematodes,
that live in the gravelly, dry soil.
One of the most unusual plant habitats
on Earth is in Antarctica: in areas formed from large-grained
sandstone, most obviously in Victoria Land, the outer skin
of the rocks themselves has been colonized by plants.
These plants live within the rock, growing
between the sand grains and forming separate layers of algae,
fungus and lichen.
Just enough light penetrates the rock
for photosynthesis to occur for a short period each year when
melt water is available.
Acids excreted by the plants eventually
dissolve the rock and the outer skin breaks off, leaving an
obvious dark mark where the algal cells remain.
The growth rate of these plants is so
slow that some may well be many thousands of years old.
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The Dry Valleys, unlike
most other ecosystems, are dominated by microorganisms, mosses,
lichens, and relatively few groups of invertebrates; higher forms
of life are virtually non-existent. Organisms have, over eons of
evolution, developed mechanisms to survive under conditions of desiccation,
extreme cold temperatures and with limited food or light for photosynthesis.
These organisms are unique and only exist in the frozen Antarctic
continent.
All ecosystems are dependent
upon liquid water and shaped to varying degrees by climate and material
transport, but nowhere is this more apparent than in the McMurdo
Dry Valleys. In very few places on this planet are there environments
where minor changes in climate so dramatically affect the capabilities
of organisms to grow and reproduce.
Biological studies in
the dry valleys have revealed life forms that have colonized rocks,
soils, glaciers, glacial meltwater streams, and lakes. Bacteria,
fungi, algae, mosses protozoa, tardigrades, rotifers, and nematode
worms are the most common types of organisms encountered. Algae
and lichens are found growing inside sandstone rocks, in which these
endolithic microorganisms are living in a relatively stable environment
with high humidity and protected from the rigors of the external
world. Lichens are found on rock surfaces, from the valley floors
to the summits of some mountains. The dry-valley soils, once thought
sterile, contain numerous bacteria, fungi, and algae. In damper
soils along meltwater streams, mosses are found. Small holes and
ponds on the surface of glaciers also provide a habitat for algae
and other organisms transported by wind.
 The
only plants that are relatively "luxuriant" in Antarctica
are found in the northernmost parts of the Antarctic Peninsula and
some sub-Antarctic islands. They include mosses lichens grasses
liverworts, and a few ferns. The animals native to Antarctica include
a few species of ducks, a pipet, flies, midges, moths, beetles,
and earthworms, nearly all of these occurring on the Antarctic Peninsula
and certain islands. Also found are microscopic protozoa, rotifers,
and tardigrades, which inhabit moist soils and mosses.
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How
Do Organisms Survive in an Environment of Extremes?
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You'll have to look hard to find any
insects in Antarctica, but you might see a springtail jumping
among vegetation or find a group of tiny mites under a stone.
Despite their size, these insects, and
the slightly larger ones on the sub-Antarctic islands, are
the subject of much research by US, British, French, Italian
and South African scientists.
Many are able to make antifreezes which
allow them to survive temperatures as low as -28 °C.
When frozen into ice, some can put their
metabolism into a special state to survive the lack of oxygen.
They also show a remarkable ability to
survive drying out without long-term damage to their cells.
The lack of species diversity makes these
invertebrate communities among the simplest anywhere, so they
provide ideal models for understanding how ecosystems work.
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