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Scuba diving in the Antarctic is the closest thing on Earth to walking
in space. When the water temperature drops to 0.4 degree C, an unprotected
diver would lose consciousness and die after only a few minutes’ exposure.
For my dive in Admiralty Bay, King George Island, 100 kilometres off the
Antarctic Peninsula, I don several layers of woollen underwear and socks,
a one-piece neoprene dry suit, a hood, boots and three-fingered gloves.
All of my body heat is reflected back at me, and it is a sauna inside; my
armpits become damp, and my forehead, which is not covered by the rubber
hood, drips with perspiration. Immediately I understand the discomfort that
a seal or a penguin, insulated by blubber, must feel on a warm day.

I waddle to the beach and sit on a whale vertebra to prepare the rest
of the equipment. This is an ordeal. The metal tank and regulators are too
cold to touch comfortably with my bare hands, yet I can’t operate them while
wearing the bulky, three-fingered gloves. Edson Rodrigues, my diving buddy
from the Brazilian Antarctic station, holds the tank while I slip into its
backpack. The tank weighs 30 kilograms and I must hunch forward in order
not to fall backwards.

Edson also connects a low-pressure hose to the dry suit and inflates
it. On the chest of the suit is a control panel with buttons for inflation
and the release of air. A skilled diver, with weights properly balanced,
can operate these like the buttons on an elevator. I rub Vaseline on the
seals around my wrists, ankles and neck, and put on the gloves, flippers
and mask. Edson will not accompany me on the dive but will wait on shore.
A tether is attached to the air tank, and I drape it over the palm of my
right hand. He will tug on it periodically to signal me; if I fail to respond,
he will pull me to shore.

COMFORTING COLD

The blessed cool and the weightlessness are an enormous relief as soon
as I enter the water. It actually feels good to be in this sea that is so
cold it would be excruciating to bare skin. But when I immerse my head,
the band of exposed forehead above the mask gives me a momentary blinding
headache, and the seals around my wrists, ankles, and neck begin to leak
slowly. This is a temporary discomfort; soon the woollen underwear sops
up this water and warms it to close to body temperature.

I plan to descend to about 15 metres to collect the tiny amphipods that
skitter over the ocean floor and hide beneath boulders that have been dropped
by passing icebergs. Since I am studying the pathologies of these crustacean
relatives of shrimps, I want representative samples of both diseased and
healthy animals. A baited trap would attract only those amphipods with strong
appetites, which are inevitably the healthy ones. A trawl net would favour
the slow and sick animals that couldn’t escape, biasing the sample toward
the unhealthy ones. So I use a simple hand-held net, purchased in a tropical
fish store in New York. The 50 kilograms of diving equipment, worth thousands
of dollars, is all configured simply to bring this simple net within reach
of these tiny prey.

Only a few dozen people have gone before me into this realm. Until the
late 1950s, when humans first began scuba diving in Antarctic waters, this
seafloor was beyond the reach – and the ken – of the few humans who visited.
Even now, we dive only in the shallowest and most hospitable areas of the
Antarctic continental shelf. Most of this dark and cold ocean floor has
never been witnessed.

Underwater visibility is 20 to 30 metres. Flocculent streamers of brown
organic matter, a mixture of penguin guano and the one-celled algae known
as diatoms, hang from the surface of the water. Even through the muffling
hood, I hear a sea filled with popping and snapping sounds. From what? Crustaceans?
Perhaps. But most of the sounds seem to be coming from two icebergs stranded
on the seafloor ahead. I swim next to one of them. It is releasing puffs
of fine, silty sediment, scraped from the base of Stenhouse Glacier, into
the clear water. As it melts in the summer sea, the iceberg emits columns
of bubbles. I steady myself by placing a hand on the small berg, and it
rolls over, almost hitting me on the head. Edson tugs in alarm, but I signal
back that all is well.

Ice is the dominant environmental factor of the Antarctic’s shallow-water
marine communities. Not only does it abrade the ocean floor, scraping away
bottom-dwelling, or benthic, organisms and mixing layers of sediment, it
also affects salinity, temperature, currents and the amount of light that
penetrates the sea. The seafloor beneath me is a plane of glacial silt and
sand, punctuated by occasional boulders. Icebergs have ploughed furrows
in the soft bottom. Most of the rocks have one or two Antarctic limpets
grazing on them.

MIGRATING LIMPETS

The Antarctic limpet is one of the few benthic organisms that is able
to cope with the caprices of scraping ice. The limpets retreat to the safety
of cracks and fissures at the slightest hint of ice bumping their rock.
This is an elaborate version of characteristic limpet behaviour. All limpets,
even tropical ones, are well known for their territoriality, returning to
the same spot each morning after a night of grazing. Limpets also migrate
according to the seasons. In the winter, when the sea is considerably warmer
than the air, they move to deeper water and wait out the cold. But during
the summer they slide into the intertidal zone and, for brief periods, even
live above the high-tide mark. Coated with a mucous that inhibits the formation
of ice crystals, they can withstand exposure to freezing air . Their pay
off is the abundant algae and lichens that coat the intertidal rocks, which
are exploited by no other grazing animal. But the exposed limpets are easy
prey for Dominican gulls, which pluck them from the rocks and swallow them
whole.

As I swim over the seafloor, a flurry of tiny amphipods of various species
are grazing on the algae beds growing on the rocks below me. Some are Bovallia
gigantea, which, despite their name, are only 2 or 3 centimetres long. They
stand poised on their rear four pairs of legs, tails tucked underneath abdomens,
heads elevated and antennae brushing the water. This is their characteristic
alert posture. A stark silhouette against the bright light from above, I
must resemble a seal or penguin. I release a few bubbles of air from my
suit and slide down onto the soft plain, stirring up a puff of sediment.
The amphipods scurry beneath a rock. I nudge the rock aside and sweep the
net in the depression it leaves. The net quickly fills with the little creatures;
turning it inside out, I place the amphipods in a transparent zipped bag.
Alarmed at being lifted into open water, they dance on the bottom of the
bag, trying to return to the seafloor.

Releasing more air from the suit, I ease down the undulating mud slope
to a depth of 10 metres. At this depth, beyond the reach of the gouging
pack ice, the Antarctic continental shelf changes its appearance. The soft
bottom gradually loses its ice scars and becomes a plain etched by the tracks
of for-aging animals. The deepest furrows are made by asymmetrical sea
urchins. Covered with short, soft spines, they look like mice made of calcium.
At first the spines seem to be rising and rotating in confusion, but in
fact all are netted to the same simple nervous system and working toward
a common purpose: pushing the urchin through the edible mud like a bulldozer.
An armoured, animate gut: what wonderful economy in a realm where resources
are few.

The gloomy plain ahead invites me to swim deeper, to 15 metres. I am
now beyond the reach of even the heaviest winter pack ice. Unlike the shallow
sea, this is a realm of relative stability; of near constant temperature
and with a steady rain of silt and nutrients from above. Here nemerteans
(1-metre-long, marine worms) lie on the surface of the mud. Each is striated
with hundreds of annulations, the tracings of the muscles that push it peristaltically
through the ooze. A wad of them, the size of a basketball, congregate in
a prolonged communal copulation. Nemerteans are gregarious at feeding time
as well. Hundreds of them will heap atop a dead seal or other carrion on
this sterile plain. But they are also hunters, equipped with a proboscis,
10 centimetres long, that shoots a dart into their prey. On occasion they
have been known to overpower and eat fish.

At these depths the ooze is alive with the crustacean Serolis polita,
a flat isopod the size of a thumbnail. Although abyssal species of Serolis
– those that live at depths below 2000 metres – are found as far north
as the Bahamas, the genus probably originated in Antarctica. Their flat,
segmented carapace, arched legs and two-lobed compound eyes, each mounted
on a high ‘turret’, give them the appearance of extinct trilobites. Every
Serolis is an ecosystem unto itself and is colonised by bryozoans (aquatic
polyps that resemble mosses); algae; fungi in the shape of white stars;
and by hydrozoans that look like red chalices. Serolis passes its life in
cold slow motion and sheds its shell only once or twice a year. Its encrusting
organisms, however, are denied the luxury of slow development, and must
complete their life cycles to the schedule set by their host. In a few months
they colonise, grow, and reproduce, before being sloughed off with the shell.

Slow rates of development and growth and concomitant longevity are typical
of Antarctic marine invertebrates. Serolis polita doesn’t reach sexual maturity
until it is three years old. Bovallia gigantea males take 18 months to mature;
females take 40 to 42 months. An Antarctic limpet, in the unlikely event
that it is not snatched by a gull or eaten by a sea star, has the potential
to live for a hundred years. Some species of Antarctic sponges may survive
for several hundred years in the still and unchanging depths of the continental
shelf.

After 30 minutes I have arrived at the farthest point of my dive, a
ridge of rock that rises from the floor of Admiralty Bay. A hard bottom
makes all the difference. Unlike the unconsolidated silt, it is festooned
with living things. This rock is valuable real estate, a place from which
sponges, tunicates, soft and hard corals, and bryozoans can project their
siphons, mouths and tentacles into the nutritious water. They in turn provide
habitats for all manner of invertebrates and fish.

At this depth, the seafloor appears grey and gloomy. But when I turn
on my light, the beam is like a paintbrush: everywhere I sweep it I see
splashes of colour. The 10-centimetre-diameter anemones, which basically
consist of a mouth (that doubles as an anus) fringed by tentacles, are orange.
White brachiopods, 5 centimetres long, attached to the seafloor by red stalks,
reach into the water. The two halves of their shells have an ‘overbite’,
and are striated with hundreds of growth rings. The drooping soft corals,
which look like long catkins, are bright yellow. Each is a colony of thousands
of tentacled polyps embedded in a flexible protein matrix. Each polyp, although
only a fraction of a centimetre wide, is morphologically identical to an
anemone and, like an anemone, presents its mouth to the sea.

There are even a few foliating red and green algae at this depth, and
aquatic lichens paint the rock face a deep purple. These plants barely survive
here; like the mosses and bundle grasses that grow beneath the cover of
springtime ice and snow, they must photosynthesise in dim, filtered light.
They ‘scavenge’ light from the sea, just as the animals with which they
share this rock scavenge organic material. Red sea urchins browse on the
algae, prising it from the rocks with a rosette of spiny teeth. Bristled
polychaete worms insinuate themselves into this living terrain, sometimes
entering the siphons of the sponges and tunicates themselves.

A giant Antarctic isopod, 10 centimetres long, walks through the rock
garden on its six pairs of legs. Segmented, its shell dorsally keeled with
flared margins, it looks as if it has been chiselled from rock. Another
giant, an eight-legged sea spider with a leg span of about 20 centimetres,
is standing on pointed legs in the ooze at the base of the promontory. Its
rust-coloured skin is crinkled by colonies of hundreds of bryozoans.

These creatures are misnomered; despite a superficial resemblance to
spiders, they are only distantly related to them. They are in fact unlike
any other group of arthropods and comprise their own subphylum, the Pycnogonida.
The pycnogonids seem to be all legs; what little body they have consists
of a head, a short neck bearing four eyes on a tubercle, and six cylindrical
posterior segments. These segments are so short that parts of the gut and
the female reproductive tract extend into the legs. This pycnogonid seems
to move in hesitant slow motion on its tiptoes. These animals aren’t built
for the chase, but neither are their prey – sedentary organisms such as
sponges, corals and bryozoans.

All pycnogonids have a large, extended mouth known as a proboscis. The
proboscis is so massive and complex, relative to the minuscule body, that
it is endowed with its own ganglion of nerves – in effect, a secondary
brain. Many species of pycnogonid use their proboscises to suck up the tissues
and fluids of their prey in a prolonged and lethal kiss, and some also
have paired claws, known as chelicerae, which are used to prise off tissue
and pass it to the mouth.

SPONGY SIPHONS

The sponges on this promontory are mostly white and tan; a few, dirty
yellow. Some form crusts and adopt the shape of the rock on which they are
growing. Their smooth surfaces are pocked with siphons through which they
filter plankton and other organic material. Others stand freely, cupping
the water and catching the nutrients falling from above. Sponges are colonies
of cells that are barely consolidated as organisms; they have no discrete
organs, and the division of labour among their cells is rudimentary. Yet
this lack of cell specialisation endows the sponges with great powers of
regeneration. One can mash the tissues of a living sponge through a coarse
cloth, and the resulting broth of cells will reassemble into another sponge.

The tunicates, nacreous and pale, also seem part of the fabric of the
rock. As adults, they have the appearance of sponges, with single siphons
and the tough protein and cellulose outer ‘tunic’ that gave them their name.
But a large evolutionary gap separates them from the sponges. Tunicates
have a gut, nervous system and circulatory system, including a heart. More
remarkable, their larvae resemble tadpoles, complete with a dorsal nerve
cord and a rudimentary backbone called a notocord. This trait places them
in the Chordata, the same phylum as fish, amphibians, reptiles, birds –
and mammals.

Amid all of this diversity, certain groups that are ubiquitous in other
seas are missing: decapod crustaceans, which include crabs and shrimp, and
the cirripedes, the familiar barnacles that adorn rock faces in all the
oceans of the world except the Antarctic. It is easy to understand why barnacles
fare poorly in Antarctica. As adults they are filter-feeding animals that
are permanently cemented to an object, such as a rock or piece of wood,
and are necessarily confined to shallow, sunlit waters where plankton abound.
But this is the zone in the Southern Ocean that is scraped by ice.

The lack of crabs, prawns, and shrimp is more of a mystery. One reason
for their absence is the isolation of the continent by the Southern Ocean
and the West Wind Drift. Decapod crustaceans are shallow-water organisms
that tend to broadcast an abundance of eggs and larvae into the planktonic
swarm. Many shallow-water colonists simply couldn’t survive the ocean crossing,
either as larvae or as adults. However, their close relatives – and therefore
strong competitors – the isopods and amphipods, which crept along the ocean
floor and emerged on the Antarctic continental shelf, found the crossing
less perilous.

I can visit these depths for only 30 minutes before the leaky suit and
the cold set me shivering. I inflate my vest and signal Edson to pull me
in. Gliding from behind an iceberg, I nearly collide with a Weddell seal.
She shows no fear, just curiosity. There is no suggestion of aggression.
I swim toward her. She backs off, but not far, and settles to watch again.

Back at the station, I stand in the shower of generator-heated glacial
meltwater for half an hour. Then I eat two plates of black beans and rice,
and I am still shivering.

David G Campbell is the Henry R Luce Professor of Nations and the Global
Environment at Grinnell College, Iowa. This article is an abridged extract
from The Crystal Desert, an account of three summers (from October to March)
he spent in Antarctica between 1982 and 1987. The book, which is not illustrated,
is published next week by Secker and Warburg in hardback at £17.99.
It is available from Reed Book Services, PO Box 5, Rushden, Northants NN10
9YX (Tel: 0933 410511). copyright David Campbell 1992.

* * *

Learning to live without icy insides

Although water, like light, is a precious and limiting resource for
Antarctic animals, it becomes deadly when it turns to ice. Because water
expands when it freezes, cells (which are mostly water) tend to rupture
when ice crystals form inside them.

Antarctic terrestrial invertebrates employ three general strategies
to adapt to the cold. The tardigrades (eight-legged arthropods that live
in aquatic or moist environments) simply dehydrate; ice can’t form where
there is no water.

The larval midges submit to the cold and freeze, a tactic that would
kill most other animals. They survive because ice crystals form in the spaces
between the cells, not inside them.

Mites less than a millimetre long, and springtails (primitive wingless
arthropods that can flip themselves into the air like fleas off a cat’s
back) employ a more sophisticated strategy to survive the winter temperatures.
They produce biological ‘antifreezes’ such as sugars and polyhydric alcohols,
which permit their body fluids to remain liquid at subfreezing temperatures
– a process known as supercooling.

But a supercooled fluid is a hair-trigger medium, in which ice can instantly
precipitate around a nucleating particle such as a fleck of mineral dust.
Therefore springtails and mites prepare for winter by fasting, evacuating
their guts of any debris.