Antarctica and its Eco-System

 

Prof Craig Franklin – professor of zoology at Queensland University

Dr Peter Carey – director of the SubAntarctic Foundation for Ecosystem Research (SAFER)

 

á       The continent – setting the scene

á       Ice and icebergs

á       The terrestrial eco system

á       The Marine eco system

o      In general

o      Penguins, inc aspects of their physiology

o      Seals

 

i.e. geography, botany, zoology, physiology and iceology (physics?)

 

The continent

 

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Antarctica covered by an international agreement, the Antarctic Treaty System, which covers all land south of 600S. Governs the actions of all people visiting Antarctica.

Ships have to be licensed, no impact on environment

Includes Code for visitors

Antarctica is:

á       The only continent without a permanent human population.

á       The 5th largest continent ( 12 million sq km, 4.59 million sq miles)

However, its Ecosystems are intrinsically linked to the Southern Ocean. The seas surrounding the land mass isolate it from the rest of the worldŐs oceans and keep its temperatures low. Located between 560S and 600S is the Antarctic Convergence, is a fluctuating line where the cold waters of the Southern Ocean meet but donŐt mingle with the relatively warm waters of the subantarctic.  This is the northern limit of the ŇbiologicalÓ Antarctic.

á       Split into E & W Antarctica, separated by the Transantarctic Mountain Range

á       The highest continent, average altitude 2300m, 7500ft. highest point is Mount Vinson 4900m, 16,000ft.

á       The mountainous spine of the Antarctic Peninsular used to be connected to S America

á       The coldest continent (the lowest temperature ever recorded on earth, -90C, -130F was at the Russian Vostok station)

á       The windiest

á       99.6% is covered with glacial ice.

á       2/3 of the planetŐs fresh water is stored on Antarctica

á       Classed as a desert, average of 50mm water equivalent precipitation p.a.

á       One impact of climate change will be to increase the snowfall on East Antarctica because of the increased water content of the warmer air. – reduces the expected rise in sea levels.

á       Climate change isnŐt increasing the worldŐs temperature uniformly and temperatures recorded over the last 50 years shows that only the Antarctica Peninsular has warmed and the rest of Antarctica shows now sign of warming. However, in the last 100 years the temperature increase on the Antarctic Peninsular has been 2 to 3 times greater than the global average of 0.6C. 

Ice

2 basic types of ice

á       Freshwater ice

á       sea ice

Freshwater ice

All ice on land is freshwater ice.

Almost all precipitation on Antarctica falls as snow, seldom melts in the cold conditions. The weight of snowfall on snowfall compresses the flakes and over several years the snow turns to little granulated balls called firn. After a few more years, the firn becomes ice.

When a body of ice starts to move downhill under its own weight, it is a glacier. In Antarctica they are so deep and massive that they are not confined to valleys (as in more temperate parts of the world) but blanket the land on a grand scale to form ice sheets. When these meet the sea, the forces of waves, tides and the relative warmth of liquid water cause bits to break off to form icebergs. 

In large bays, the ice sheet doesnŐt break up when it reaches the coast but continues to flow forward across the surface of the sea, coalescing with others and forming ice shelves, up to 300m thick. (e.g. Ross & Ronne). – see map

The effect of climate change on the Antarctic Peninsular has probably been responsible for the collapse (Larsen B) and reduction of ice shelves on the East side of the peninsular. In turn, the absence of ice shelves means that the glaciers that fed them tumble into the sea more quickly as there is nothing to stop them.

Ice sheets are on land

Ice shelves float on water.

The surface of accumulations of ice follows the surface underneath it, therefore the top of an ice shelf is flat.

Ice shelves are ŇPermanentÓ but bits break off the edge. Largest in 2000 from Ross i.s, size of Belgium,., now broken up, largest piece 250 miles  across. These pieces of ice shelf are called tabular icebergs.

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They may be too large to be pushed around by wind or ocean currents but are pushed forward in bursts by the wave of water that sloshes round the globe with the fluctuating tides. All large icebergs are ŇnamedÓ and their positions monitored.

Other icebergs, bits broken off glaciers, can be all sorts of shapes

PIC x 4                        snowing          -3C, wind 40 knots, -17C wind chill

and change their shapes as they are buffeted by the sea and wind.

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Smooth sides are bits of the iceberg that had previously been under water. 

They may split in half,

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or turn over.

How much of an iceberg do you see above the water? 1/7 or 1/10 if the iceberg has turned over. 

 

Because glacier ice is formed under pressure, much of the air is squeezed out of it. The ice thus takes a long time to melt. Any air remaining in the ice is pressurised and tends to ŇpopÓ when the ice does melt, hence the constant crackling and snapping you hear when near a sea full of ice.

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The air in the ice also determines the iceŐs colour. Ice is actually blue, but as our eyes are not very sensitive it only looks that way if we look at a large piece of glacier ice i.e. glacier ice is usually big enough to reflect enough blue light for us to recognise whereas ice in our drinks isnŐt. The bluest ice is often from the base of a glacier because that is under the greatest pressure and has the fewest air bubbles.

Icebergs tend to appear white because we are seeing ice and air bubbles – the air reflects back all the colours of the spectrum which we see as white.

Some icebergs are black/brown because of the rocks and gravel bound up in its ice. This dirty ice comes from the edges of the glacier.

It is possible, though rare, to see green icebergs when algae is bound up within the ice.

Lots of different terms to describe all the different types of ice.

á       Icebergs defined as being at least 5 m above sea level
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á       Much of what we see are Bergy bits which stand between 1 – 5 m above the water

á       Ice < 1m high is a growler, so called because of the noise these chunks made when grinding along the sides of a wooden ship.

á       Smaller still is brash ice. These are the little pieces, some no bigger than a hamster, which crackle the most as they melt in the surround sea water. 

 

Sea Ice

Sea round Antarctica freezes during winter up to 2m thick, effectively doubling the size of the continent. Thick enough to land large planes on.

Breaks up and melts in spring. This freeze/melt cycle has a huge impact on the flora and fauna of the Southern Ocean.

Sea water freezes at -1.9C (28F) because of the salt content. It starts with slush-like grease (or frazil) ice forming on the surface. As this consolidates, it coalesces into pancake shaped pads called pancake ice.  Pack Ice consists of large pieces of floating ice i.e. ice floes. Pack ice is dynamic, it floats around with the wind and currents and is an important habitat for seals and penguins.

When the frozen sea is attached to land & is a solid sheet it is called fast ice. This is very  stable except where it meets the open sea and forms a de facto coastline.

 

EcoSystem

The Antarctic EcoSystem is unique and most of the organisms here are found nowhere else.

Temperature governs the distribution of all life on earth. Temperatures below the freezing point of water are lethal to all but a few organisms. Ice is the problem, bursting cells and dehydrating tissues. Temperatures AntarcticaŐs interior drop to below -80C and the interior is thus virtually lifeless apart from the occasional human!

 

The Terrestrial EcoSystem

Less than 0.4% of the Antarctic continent and surrounding islands is permanently or seasonally free of ice. There is thus a paucity of life on AntarcticaŐs actual land mass.

There are no land based mammals or birds. It is restricted to:

á       2 species of flowering plants, the hair grass (deschampsia Antarctica) and the pearlwort )Colobanthus quitensis)

á       More than 260 species of lichen

á       Red, yellow, green and brown snow algae

á       More than 70 species of mosses

á       Flightless midges

á       Mites

á       Springtails

á       Nematodes (round worms)

 Despite 24 hours of daylight during the summer, the growth rate of plants in Antarctica is very slow, some only grow 0.5mm p.a. so it is crucial not to tread on them.

PIC                  Henryk Arctowski Polish research station, King George Island,

South Shetland islands

Penguin Police

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The Marine EcoSystem

Marine food web

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Because of the low number of species, the web is relatively simple.

1.     primary production – phytoplankton (mainly diatoms)

2.     small zooplankton – e.g. copepods (a crustacean)

3.     large zooplankton – e.g. krill

4.     fish
of the 30,000 different species of fish worldwide, only about 120 are from the waters around Antarctica. There are no sharks and 60% of the fish belong to a single group, the Notothenioidei. In order to live in waters of -1.9 C most Antarctic fish synthesise anti-freeze molecules, special protein carbohydrate compounds that prevent ice from forming in their blood and tissues.

Icefish (Channichthyids are unique among vertebrates and have no red blood cells but carry oxygen dissolved in plasma. Their blood is completely colourless. The lack of red blood cells is possible only in the cold Antarctic waters because of the high oxygen levels and probably evolved as a means of reducing the bloodŐs viscosity.

many of the fish in Antarctica occur near the sea floor and in deep water, including the giant Antarctic toothfishand the larval-looking ellpout, a small bottom dwelling fish that looks a bit like an eel

5.     large fish, penguins, seals

6.     whales, killer whales, leopard seals

food webs usually have 5 or 6 steps from the plants at the base to the predators at the top, however, the Antarctic food web is unusual in that it has several shortcuts where several levels are bypassed. i.e.

Antarctic shortcuts

á       krill (3) feed on (1)

á       baleen whales (5) feed on (3)

The frozen sea water 11 – 3 m thick, provides an important habitat for plants and animals both above and below the surface. Seals and penguins use the sea ice and icebergs as a place to haul out and rest

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Crabeater, Ross and Leopard seals use it as a convenient birthing spot.

The underside of sea ice is important in providing a habitat for algae growth, a refuge for icefish, and a nursery for krill in the winter.

The most serious impact of climate change and increasing temperatures is a reduction in krill. This is because the sea ice is forming later and retreating earlier, especially around the Antarctic Peninsular and in the SW Atlantic sector of Antarctica. A survey in this region indicates that krill may have dropped by 80% in the past 30 years. This could have serious impact on the Antarctic food web and may explain the decline in some penguin populations. 

 

 

Penguins

 

Leg length – skeleton

 

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Encased for warmth and to make them more streamline in the water

 

Very ancient ancestors > 45 million years ago, were flying birds.  Only penguins form a group in which all members are flightless and completely aquatic

 

Evolved into specialised divers and swimmers e.g.

á       Bodies. Their bodies are bulky but streamlined, inc encasing their legs, adapted for swimming. A penguin has a large head, short neck, and elongated body. The tail is short and wedge-shaped with 14-18 stiff feathers.

á       Their legs are strong with webbed feet and visible claws.

á       Bones The bones of flying birds are filled with air chambers to make them lighter. Penguins bones donŐt have these air cavities and so are much heavier making it easier for penguins to dive underwater.

á       Penguin wings are modified into flippers. The bones are flattened and broadened with a joint at the elbow and wrist to form a rigid, flat flipper that is perfect for swimming.

á       They fly through the water using the same wing-beats and muscles as other birds use for flying though the air. Their flippers provide the power while their webbed feet, tucked in under their tail, are used for steering.

á       Feathers The feathers of most birds grow in lines with gaps of featherless skin in between. Penguin feathers cover all their skin, just like fur. This provides an impregnable coat that prevents water from reaching the skin and enables the bird to stay warm in cold water. Their feathers even cover most of the bill and feet to assist in insulation. The feathers themselves are short and stiff with lots of down at the base which traps air. Penguins frequently come out of the water to preen. This reconditions and replenishes air trapped between feathers.

á       They also have a layer of blubber under the skin to heal conserve their body heat.

á       They are thus able to maintain an internal temperature of a penguin is around 100-102F. The dark feathers also help to absorb heat from the sun. Emperors will huddle close together to conserve heat. The warmer ones on the inside will rotate with the ones on the perimeter so that all are equally protected from the cold. On land, Emperor penguins will tip up their feet, and rest their entire weight on the heels and tail, reducing contact with the cold, icy surface.

To conserve heat, penguins will tuck their flippers close to their bodies and raise them out to release heat.         Also to help with balance when walking.

á       Brood patch. Both males and females have a special break in the insulation, tiny patch of bare skin on their bellies that the egg and chick can nestle against.
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á       All adult penguins are counter shaded; that is they are dark on their back surfaces and white on their underside. The dark side blends in with the dark ocean depths when viewed from above. The light side blends in with the lighter surface of the sea when viewed from below. The result is that predators or prey do not see a contrast between the counter shaded animal and the environment.

Chicks, juveniles, and immature penguins may have slightly different markings than adults.

Many species have distinct markings and coloration.

á       Unlike other birds which moult their feathers continuously, penguins moult in a 2 -3 week period while their new feathers grow. They are not waterproof during this period.

á       They drink sea water and have special glands that extract and excrete excess salt.

 

 

Penguin facts

 

á       17 species worldwide

á       Only 5 species found in Antarctica

á       Adelie – height 18 inches
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á       Gentoo – height 18 inches
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á       Chinstrap – height 29 inches
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á       Marconi – height 28 inches
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á       Emperor – height 45 inches
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á       Live only in the southern hemisphere (Galapagos!)

 

Breeding

Antarctic penguins all nest in colonies, or rookeries, where breeding is synchronised

Rookery is noisy and dirty.

Adults call to each other

PIC                  chinstrap penguin at Half Moon Island

Chicks beg from any adult penguin but will only get food from their own parents

PIC                  gentoo penguin, Chilean research centre, Paradise Harbour

                                                                                                Antarctica Peninsula

Penguins are not always pristine!

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Penguin nest

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Both male and female penguins take an active role in raising the chicks, both incubate the eggs  (except Emperor penguins where the male does all the incubation), feed the chicks and guard the nests. This is essential and chicks that loose a parent to a predator are doomed to starvation or to becoming prey themselves.

 

Then left to fend for themselves and work out how to swim & catch fish.

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Lonely Adelie chick

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MustnŐt approach, stand still, overstayed hour

Mohican haircut

PIC with Penguin Police

 

Skuas – 20 inches long with a wing span of 56 inches. Feed on fish, carrion and penguinsŐ eggs and chicks – but smaller than this one

 

 

Diversion on how other animals in Antarctica teach their young

 

á       Orcas (killer whale) teaching young to catch seals

á       Leopard seal with diver

 

Back to penguins

 

First sight was swimming along the surface .

 

Need to dive to catch fish which has been studied

Penguin diving behaviour and depth depends on the depth of the penguins' prey, which may vary with season and time of day. Most penguins have very little need for dives of great depth or long duration, since their food is usually found in the shallower depths.

However, Emperor penguins (about 12 kg and 30 kg respectively) have been known to dive to depths of 204 and 534 m for as long as 7.5 and 15.8 minutes.  The ability to dive for long periods increases with body size; this accounts for the Emperor penguin, the largest of all penguins, having the record for deepest and longest dive. The Emperor's record dive has been set at 18 minutes, though usual dive time even for these large birds is around 3 minutes. Emperor penguins can change depth at a rate of 120 m/minute, though judging by the average length of their dives, the depth of most dives is probably not very great. It would be possible for them to perform on-average bounce dives of 180 m, but this would leave the birds very little time for pursuing prey, so most dives are probably much shallower than this.

Emperor penguins were studied at an experimental dive station where they were diving alone under 1.5 m of sea ice and at Cape Crozier rookery where they were diving in groups in open water and appeared to be feeding. Depth recorders were attached to the penguins and recovered after one or two dives. Dives at Cape Crozier were the deepest by far. These dives were vertical plunges usually as a synchronous group of up to 50 birds and ranged in depth from 45 to 265 m. Dives at the dive station never exceeded 40 m. These birds were unfamiliar with the area and were assessing their situation at the remote ice hole while searching for other holes. Emperor Penguins do occasionally dive through ice holes in natural conditions and have been known to swim between holes up to 360 m apart.

Dives over 6 minutes are exceptional for other species for which many observations have been made. In fact, most penguins and other diving birds submerge for only one minute or less. Gentoo, Adelie and Macaroni penguins have been widely studied. Gentoo penguins normally dive for up to 2 minutes, and in the lab, Gentoo penguins and Adelie penguins tolerated forced submersion for a maximum of 7 minutes. Macaroni penguins have been force-dived for durations of 5 minutes.

An experiment done by Green et al. (2003) on Macaroni penguins showed that diving activity was greater in daylight hours. Dives during daylight were deeper (A), of longer duration (B), and more frequent (C).

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Whitehead 1989 focused on the diving depths of Adelie penguins at different stages of chick rearing period at Magnetic Island in eastern Prydz Bay, Antarctica. It was found that no significant differences existed between the maximum depth dived by male or female Adelie penguins. During the early chick rearing period in late December, maximum dive depths ranged from 79 to 175 m. Seventy percent of measurements indicated maximum depths between 109 and 142 m. Only two birds were reported to dive deeper than 150 m. In mid-January, when adults were foraging for early crche-stage chicks, the range of maximum depths was 70-157 m, suggesting slightly shallower dives. Adelie penguin prey species occur mostly within the surface 200 m of the water column; this range is coincident with the range of diving depths recorded in this study, supporting the notion that the range of food items determines the range of penguin diving depths. By late January in the Prydz region, nearly all the ice had broken up and prey species might have reacted by concentrating in shallower waters, resulting in the more limited dive-depths recorded by Adelies during this season.

Whitehead's results suggest that Adelie penguins are fairly deep-diving birds, and only King and Emperor penguins are recorded to greater depths. While Gentoo penguins are nearly 20% heavier than Adelie penguins, it is surprising that Adelie penguins can dive deeper (since it is generally accepted, as stated above, that larger penguins are capable of deeper dives). However, claims have been made that Adelie penguins can dive deeper than Gentoos due to the potential of their swimming muscles for anaerobic capacity.

Loss of oxygen during a dive is probably the most widely studied physiological phenomenon faced by penguins and other diving birds.

Oxygen-saving mechanisms include:

á       Changes in blood flow

á       Slowed heart rate

á       Reduced sensitivity to CO2

Where is oxygen stored in the body?

Principle oxygen stores in the body of a penguin are 1) hemoglobin, 2) myoglobin and 3) lungs and air sacs. Hemoglobin and myoglobin have an interesting relationship; they are functionally related and structurally similar. Myoglobin is a protein that contains a heme group, an organic structure that contains iron. Oxygen binds to the iron in this heme group. Hemoglobin contains four protein subunits, each of which carries a heme group. The iron of hemoglobin's heme group is also the site of oxygen-binding. Myoglobin has a higher affinity for oxygen than hemoglobin .

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These oxygen stores can be enhanced by increasing oxygen carrying capacity of the blood, meaning a greater concentration of hemoglobin and red blood cells (since hemoglobin is contained in red blood cells). The blood volume of the body might also be enlarged. Oxygen carrying capacity of blood and perhaps also blood volume does appear to be greater in diving birds, though there is few comparative data.

Myoglobin is much more concentrated in terrestrial birds than aquatic, based on muscle color. However, the oxygen bound by myoglobin represents only a small part of the total oxygen store and it is likely that in the penguin this supply exhausts much sooner than the actual breath-holding limit. Oxygen reserves in the myoglobin are the first to be exhausted during a dive, and once this oxygen is gone the muscles switch to less efficient anaerobic metabolic pathways. Since myoglobin has a much greater affinity for oxygen than hemoglobin, if any of the remaining blood oxygen stores were exposed to muscle, the oxygen would move from the blood to the myoglobin. Therefore the muscles have to be shut off from other oxygen stores in the body since they would deprive obligate aerobic tissues such as the brain of sufficient oxygen.

The lung and air sac contribution to total body oxygen stores in the penguin is very significant (they contain about 50% of the total oxygen), as opposed to seals that exhale about 50-60% of inspiratory lung volume before diving. Penguins dive right after an inspiration; therefore the diving gas volume relative to body weight of penguins (about 160 cm 3/kg) is much greater than seals which is about 22 cm 3/kg.  

Oxygen saving-mechanisms

Changes in blood flow

A 5 kg penguin has an estimated oxygen reserve of about 250 ml; this would last for 2.5 minutes at resting metabolism. However, penguins have adapted various oxygen-saving mechanisms that allow oxygen in the body to last longer.

Though the majority of penguin dives are essentially aerobic, anaerobic metabolism may be used in some circumstances. Many tissues such as muscle have a capacity to continue anaerobically whereas other tissues, such as the brain, must have a continuous oxygen supply. Accordingly, there are major changes in blood flow during a dive, most importantly being a slowed heart rate and the reduced circulation to muscles. Ponganis et al. (1999) found that cardiac output was restricted in diving King penguins and blood flow was predominantly reduced to the brain, heart and lungs. A reduction in respiratory O 2 stores and a relative increase in muscle O 2 stores appear to be adaptations for deep-diving in King penguins.

Slowed heart rate

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As the dive begins, the penguins heart rate slows. In Adelie and Gentoo penguins, the diving heart rate is about 20 beats per minute. This is independent of the pre-dive rate of about 80-100 beats per minute. Muscles such as the gastrocnemius and pectoralis obtain less blood, while the heart receives a maximum. It was shown in Gentoo penguins that pectoral muscles and toe vessels bleed much more slowly during submersion than when the bird is breathing normally. Heart rates during diving have also been recorded for Humbolt penguins. In this study, no significant reduction in heart rate below resting levels was seen even up to the longest voluntary dives recorded at 50 s (mean dive length was 36.4 s). However, when voluntary dives were forcibly extended by waving hands over the water surface, at 60 s heart rates had fallen dramatically to 78 beats per minute from 119-135 beats/min in shorter dives.

In Macaroni penguins, heart rate was higher than resting before and after dives, falling to a level close to or lower than resting level during dives. According to Green et al. (2003), this response appears to be a trade-off between a classic dive response, which conserves oxygen stores while the animal is deprived of access to air, and the exercise response, which prioritizes blood flow and oxygen uptake to active muscles when exercising. Adjustments in heart rate allow the dive duration to be extended by ensuring full loading of oxygen stores before the dive, then by reducing aerobic metabolism during the dive and ensuring the full and effective use of oxygen stores while submerged.

Reduced sensitivity to CO2

It is also shown that while oxygen concentration drops during a dive, CO2 levels increase correspondingly. Generally, diving birds and mammals are less sensitive to CO2 than land animals, probably due to greater buffering ability of the blood. Reduced sensitivity to CO2 is beneficial in extending the breath hold since CO2 is one of the principle stimuli to terminating an apnoeic episode.

 Anaerobic vs. aerobic dives...Lactic acid buildup and the Aerobic dive limit ADL

Lactic acid

A surge of lactic acid concentration usually occurs after a dive, reflecting an increased flow to tissues previously functioning anaerobically. As blood passes through the tissue, mainly muscle, it picks up large quantities of lactic acid accumulated gradually during the dive. The gradual increase of lactic acid during a dive indicates anaerobic processes in the muscles which are supplied with little blood during the dive but are generously suffused after emerging. However, some increase in blood lactic acid occurs during the dive, which suggests that a small amount of flow continues to the muscle. In fact, this leakage may be considerable compared to the grey seal, Halichoerus grypus. In the penguin during a 5 minute dive the lactate concentration of arterial blood doubles, but in the grey seal there is hardly a noticeable change within the first 5 minutes of submersion .

Aerobic dive limit (ADL)

The aerobic dive limit (ADL) is the diving duration beyond which post-dive blood lactate levels increase above resting values. ADL has been calculated (cADL) for several penguin species by dividing an estimate of usable body oxygen stores by an estimate of the rate of oxygen consumption (V O 2) while submerged. Many studies have found that 2-50% of observed penguin dives exceeded the cADL. However, the dive:pause ratio in these studies suggests that it is unlikely that so many dives use predominantly anaerobic metabolism. In order for a large proportion of natural dives to be aerobic, the cADL must be greater. If estimates of the usable oxygen stores for penguins are correct, then V O 2 during diving needs to be as low as that recorded from penguins at rest on the water surface for most dives to be within the cADL.

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In a study done by Green et al. (2003), heart rate was used to estimate V O 2 in Macaroni penguins. A suite of physiological and behavior adaptations were found to contribute to the maximizing of cADL while penguins were submerged, including 1) variation of heart rate and circulation, 2) regional hypothermia, and 3) the use of passive gliding during the ascent and descent of dives. This study found that if heart rate is averaged over complete dive cycles, it is an accurate and reliable predictor of V O 2 for the dive cycle. As observed dive durations increased, V O 2 decreased, and hence cADL increased. For all dive durations of up to 138 s (95.3% of all dives), the cADL was greater than the observed dive duration. These results imply that most natural dives within diving bouts by Macaroni penguins are aerobic.

cADL was calculated using V O 2 while resting on water for three other penguins species, though V O 2 was measured using respirometry rather than estimated in the field. In emperor penguins, 96% of dives would be within the cADL, whereas in king penguins and gentoo penguins only 80% of the dives would be within the cADL. Oxygen stores are assumed to be the same for all four species of penguin, so there must be a difference in diving behavior or V O 2 while submerged between species. Food density, distribution and location fluctuate for each species, and are more likely to be the cause of variability in diving performance between species than differences in physiology. Breeding success of gentoo penguins is far more vulnerable than in macaroni penguins to variations in food availability, so it may be that gentoo penguins are under greater pressure to gather enough food to feed their two chicks, leading to a higher proportion of anaerobic dives. Emperor penguins are much bigger than king penguins (and so have greater oxygen stores that allow them to dive to greater depths and for longer durations), and yet their diving performance is similar. A large proportion of foraging dives for both species are to 100-200 m in depth and last up to 5-6 minutes. This indicates that emperor penguins operate well within their physiological limits, whereas king penguins dive to depths and durations that are close to the maximum of their capabilities.

Penguins must cope with extreme changes in hydrostatic pressure as they dive. As a penguin dives to depth, the air sacs, lungs, air space within the middle ear, and gas trapped in the feathers all decrease in size. This is due to Boyle's law of pressure (PV=K). Since hydrostatic pressure is uniform throughout a liquid, the pressure gradient between the internal cavity and the cells and vessels invested in the walls forming the structure would soon become so great that oedema would occur. If the gradient continued to increase, vessels would rupture resulting in internal bleeding. Cavities must be able to shrink in size, sometimes to a considerable extent. Thus the Emperor penguin, diving to its greatest recorded depth of 265 m, would experience a total pressure of 27.5 atmospheres absolute (ATA), which means gas cavities must have shrunk to approximately 1/26 of their original volume.

The partial pressure of gases in the lung and air sacs increases with increased compression, since the solubility of a gas is directly related to partial pressure (Henry's law). As a result, human divers breathing compressed air become vulnerable to inert gas narcosis and decompression sickness. The ratio of gas volume to body size is so great in penguins that they may be more vulnerable than any other diving group as gas exchanges freely between the blood and lungs at depth. In pinnipeds, N 2 uptake is minimized during diving because of small diving lung volumes, lung compression and the forcing of lung air into cartilage-reinforced upper airways. In penguins, however, the volume of air sacs and lungs (respiratory volume) represents a potentially significant reservoir of N 2 and O 2. Calculations based on the diving lung volume of a seal show that if all nitrogen in the lungs were absorbed into the blood the elevation in nitrogen tension could be great, depending on the depth and length of a dive and distribution of blood flow. Since the nitrogen store in the lung of a seal is much less than in a penguin during a dive, it would seem that the penguin would be even more vulnerable. Lung compression is therefore not a feasible mechanism for decreasing N 2 absorption in birds.

It is unknown how a penguin avoids nitrogen narcosis or decompression sickness. The respiratory system in birds is very different from that of mammals. The bulk of the gas contained in the respiratory system of penguins is in the air sacs, the non-respiratory part of the system. The opposite is true for mammals. It has been shown that gas exchange in Adelie and Gentoo penguins continues between the lungs and the air sacs during deep dives. A possible conclusion is that most penguin dives are too short for a significant amount of nitrogen to be absorbed. Ponganis et al. (1999) found this to be true in Adelie and gentoo penguins during simulated dives to depth. Their dives were of short duration and shallow to avoid the risk of elevated N 2. However, King and Emperor penguins frequently make dives to depths of 200 m and 400 m, and a few mechanisms have been proposed to deal with the pressure changes associated with these deep dives. Severe bradycardia and reduction in cardiac output could reduce cumulative uptake of N 2 during dives. In addition, a pressure-induced restriction of gas exchange might occur. Histological examination of lungs in Emperor penguins have demonstrated thickened blood-air barriers and increased blood capillary volumes as well. It is postulated that, at depth, engorgement of blood capillaries might fill the parabronchal air capillaries, preventing or reducing gas exchange. The lowering of cardiac output would also limit the total amount of N 2 absorbed due to low pulmonary flow and the small volume of distribution.  

Ponganis et al. (1999) also found low venous P N2 during and after submersions. This is consistent with the idea that during periods of increased pressure (during ascent and surface tachycardias), blood P N2 should be reduced due to increased flow, increased volume of distribution and N 2 exchange into the respiratory system. Their conclusion is that king penguins have probably adapted to deep dives by a reduction in respiratory O 2 stores, a relative increase in muscle O 2 stores, and a reduction in respiratory N 2 uptake, possibly secondary to either reduced cardiac output or a pressure-induced restriction of pulmonary gas exchange. Similar adaptations probably function in emperor penguins, which display similar diving patterns but of nearly twice the depth and duration.

Hydrostatic pressure has a pronounced effect on the biochemical function of enzymes and transport proteins. Pressure may perturb protein and membrane function though a number of mechanisms where changes in volume may be involved such as 1) ligand binding efficiency, 2) catalytic rates, 3) structural stability and 4) membrane fluidity. These changes can also lead to perturbations in metabolic rate via perturbations in rates of enzymatic catalysts, ion transport, and hormone, neurotransmitter and neuromodulator binding. Croll et al. (1992) suggests that diving mammals and birds may have evolved specialized enzyme systems that are insensitive to changes in pressure, and that insensitivity to pressure is a preadaptation for diving birds and mammals.

Ponganis et al. (1999) evaluated blood N 2 uptake and the role of respiratory volume (air sacs/lungs) as a N 2 and O 2 reservoir in deep-diving penguins. It was found that compared to shallow-diving penguins, these penguins have a lesser reliance on the respiratory oxygen store for extended breath-holding and also a reduced uptake of nitrogen at depth.

It is assumed that, like fur seals and sea otters, penguins depend on their pelt for insulation. Penguin feathers are narrow and short, the central axis is solid, and distribution is dense (11-12/cm 2). Based on temperature gradients between skin and core, when the bird is in air the feathers account for 80% of the insulation and the rest is due to blubber.. Unlike blubber, feathers during swimming lose their insulative properties as air is swept out. Also, as the penguin descends the air is compressed and the insulative layer is reduced in thickness.

What happens to penguin body temperatures during diving?

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It has been found that abdominal temperatures show a progressive decline during most dive bouts. Similar decreases in body temperatures have been observed for king penguins and emperor penguins. Many scientists have put forth the suggestion that this decline in abdominal temperatures may be due to the ingestion of cold food while underwater or conduction to cold seawater from exposed surfaces on the feet and flippers. However, data from king penguins shows that lowered abdominal temperatures are somehow facilitated. Abdominal temperatures of king penguins may fall to as low as 11 C during sustained deep diving. These temperatures are 10 to 20 C below stomach temperature, suggesting that the low abdominal temperatures are not the result of ingesting cold food . It is proposed that these temperature reductions lead to lowered metabolic rates in diving birds through the effects of cold temperatures on metabolically active tissues and reduced thermoregulatory costs. In diving birds, a lowering of abdominal temperatures and metabolic rate is suggested to be sufficient to bring most natural dives observed in the field within the cADL (see Physiological Constraints: Asphyxia). Slower metabolism of cooler tissues resulting from physiological adjustments associated with diving may help to explain why penguins can dive for such long durations, and the ADL (aerobic dive limit) of penguins may be prolonged by this temperature-induced metabolic suppression that is independent of stomach-cooling.

Macaroni penguins showed a progressive decrease in abdominal temperatures during periods of diving interspersed with surfacing; this is probably the result of many smaller decreases associated with individual dives that simply accumulate. The abdomen may not have sufficient time to return to its initial temperature during the surface interval between dives, and the overall decrease in temperature may be the result of accumulation of these cycles. This pattern was also found in emperor penguins, where abdominal temperature started to decrease as soon as a dive began and continued to decrease until the animal surfaced. Upon surfacing, abdominal temperature immediately increased until the dive commenced. However, the increase at the surface was not sufficient to match the decrease while diving, so there was a net effect of progressive decline in abdominal temperature during diving bouts.

The results of Handrich et al. (1997) show that during deep dives, temperatures in certain body regions of freely foraging penguins can decrease much more dramatically than in the stomach, which is cooled predominantly by the ingestion of cold prey. These temperature decreases, leading to a depressed metabolism, may give penguins an overall energetic benefit during foraging trips, helping to explain the extraordinary diving performance of king penguins and other marine endotherms. This energy saving may be analogous to torpid periods in hibernators.

Seals

Seals can be broadly divided into

á       Phocids, which have no external ears and can only flollop along on land like giant slugs
include the Ross seal, the crabeater seal, the leopard seal and the Weddell seal which inhabit the icy waters round Antarctica, and the Southern Elephant seal which inhabits the shoreline
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male, only 5 years old , will grow another 0.5 m to 5 m and will weigh 3000kg
crabeater seals donŐt actually eat crabs, but krill and their teeth have been modified to filer food from the sea.
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á       Otariids, which do have external ears, strong forelimbs and can rotate their hind flippers forward and support some of their body weight on these limbs. This enables them to move very swiftly on land. The Antarctic Fur Seal belongs to this group. (as do sea lions)

Both the Fur Seal and the southern elephant seals were hunted almost to extinction in the 1800s, the former for their fur and the latter for the fine oil that could be produced from their blubber. Both species are now fully protected and their populations have recovered. e.g. in 1933 it was estimated that there were only 60 living on Bird Island in South Georgia, whereas today the population exceeds 65,000.

Physiology

Southern Elephant Seals can dive over 1 mile beneath the surface of the sea to catch fish and squid. Weddell seals are known to go almost ½ miles deep.

Special physiology is needed for a mammal to function without breathing for up to an hour at a time. This is achieved by storing lots of oxygen and using it conservatively. Seals donŐt hold their breath when they dive, instead most of the oxygen previously breathed in is stored in their blood and muscles.

The volume of blood in a Weddell seal is 20% greater relative to their body size, than that of a human, and their blood can also hold 3 times more oxygen per unit volume. In addition, seals can drop their heart rate from 100 beats per minute at the surface to fewer than 10 beats per min when submerged.

The greatly reduced blood flow is redirected to service only priority areas such as the brain and heart. There are no muscles in their extremities, the muscles that power their flippers are within their body mass and connected to the flippers via tendons thus also conserving heat.

Summary

Antarctica is a beautiful, unique and fragile environment, privileged to visit.

It is fragile and 1/3 of its wildlife features on the IUCN (World Conservation Union) list of threatened species.

Threats from

á       Sealing – already discussed

á       Whaling – International Whaling Commission set up in 1946. since the mid 1980s the Japanese have been hunting and killing Minke whales in the Southern Ocean as part of a scientific study to assess the feasibility of a sustainable harvest. In discussion, in which Prof Franklin tried to be impartial, he did admit that the study could be carried out by just taking tissue samples from the whales. There is pressure to allow hunting of the baleen whales, all of which are on the IUCN Red List of Threatened Species.

á       Fishing – most fishing in the Southern Ocean is by longline. Some of these lines are over 62 miles long and contain thousands of baited hooks. Although they are effective in catching large fish, sea birds are also caught. In trying to take the bait while on the surface they get caught, pulled under and drowned. Over 100,000 birds are killed in this way each year.  Measures are being introduced to reduce the number of sea bird deaths but these are not adopted by illegal fishing operations. These are also threatening the Patagonian and Antarctica toothfish.

á       Invasion of alien species. -  in recent years, non native microbes, plants and animals are appearing and establishing themselves. They are likely to upset the delicate balance of the Antarctic ecosystem.
itŐs likely that these alien species have been brought to Antarctica by humans e.g. in the water in shipŐs ballast tanks. Ships visiting Antarctica are therefore asked not to discharge their ballast water in Antarctic waters as it will have certainly come from other oceans. The footwear of passengers is also thoroughly disinfected between landings.
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á       Ozone depletion – the destruction of the ozone layer and the resulting increased levels of UVB are damaging the ecosystem and some phytoplankton are decreasing productivity by up to 12%.
International agreement on the phasing out of CFCs etc has been very successful and there is an apparent slowing in the growth of the ozone hole.

á       Global warming – already highlighted

The future of the Antarctic ecosystem depends not only on what happens on Antarctica itself but also changes to the environment in the northern hemisphere. The more people who are aware of the problems, the more chance there is of protecting what is left.

Prof Franklin feels this very strongly and spends his summer holiday each year teaching us on cruise ships in the hope that we will spread the message about this wonderful environment and the need to protect it. I hope I have!