Antarctica and itsEco-System

 

Prof Craig Franklin – professor of zoology atQueensland University

Dr Peter Carey – director of the SubAntarcticFoundation 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, theAntarctic Treaty System, which covers all land south of 600S. Governs the actions of all peoplevisiting 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 sqkm, 4.59 million sq miles)

However, its Ecosystems areintrinsically linked to the Southern Ocean. The seas surrounding the land massisolate it from the rest of the worldŐs oceans and keep its temperatures low.Located between 560S and 600S is the Antarctic Convergence, is afluctuating line where the cold waters of the Southern Ocean meet but donŐtmingle with the relatively warm waters of the subantarctic.  This is the northern limit of the ŇbiologicalÓAntarctic.

á      Split into E & W Antarctica, separated by theTransantarctic 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 usedto be connected to S America

á      The coldest continent (the lowest temperature everrecorded 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 equivalentprecipitation p.a.

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

á      Climate change isnŐt increasing the worldŐs temperatureuniformly and temperatures recorded over the last 50 years shows that only theAntarctica Peninsular has warmed and the rest of Antarctica shows now sign ofwarming. However, in the last 100 years the temperature increase on theAntarctic Peninsular has been 2 to 3 times greater than the global average of0.6C. 

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 snowfallcompresses the flakes and over several years the snow turns to littlegranulated balls called firn. After afew more years, the firn becomes ice.

When a body of ice starts to move downhill under its ownweight, it is a glacier. In Antarcticathey are so deep and massive that they are not confined to valleys (as in moretemperate parts of the world) but blanket the land on a grand scale to form icesheets. When these meet the sea, theforces of waves, tides and the relative warmth of liquid water cause bits tobreak off to form icebergs. 

In large bays, the ice sheet doesnŐt break up when itreaches 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 Peninsularhas probably been responsible for the collapse (Larsen B) and reduction of iceshelves on the East side of the peninsular. In turn, the absence of ice shelvesmeans that the glaciers that fed them tumble into the sea more quickly as thereis nothing to stop them.

Ice sheets are on land

Ice shelves float on water.

The surface of accumulations of ice follows the surfaceunderneath 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 piece250 miles  across. These pieces ofice shelf are called tabular icebergs.

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They may be too large to be pushed around by wind or oceancurrents but are pushed forward in bursts by the wave of water that sloshesround the globe with the fluctuating tides. All large icebergs are ŇnamedÓ andtheir positions monitored.

Other icebergs, bits broken off glaciers, can be all sortsof shapes

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

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

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Smooth sides are bits of the iceberg that had previouslybeen 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 or1/10 if the iceberg has turned over. 

 

Because glacier ice is formed under pressure, much of theair is squeezed out of it. The ice thus takes a long time to melt. Any airremaining 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. Iceis actually blue, but as our eyes are not very sensitive it only looks that wayif we look at a large piece of glacier ice i.e. glacier ice is usually bigenough to reflect enough blue light for us to recognise whereas ice in ourdrinks isnŐt. The bluest ice is often from the base of a glacier because thatis under the greatest pressure and has the fewest air bubbles.

Icebergs tend to appear white because we are seeing iceand air bubbles – the air reflects back all the colours of the spectrumwhich we see as white.

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

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

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

á      Icebergs definedas being at least 5 m above sea level
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á      Much of what we see are Bergy bits which standbetween 1 – 5 m above the water

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

á      Smaller still is brash ice. These are the little pieces, some no bigger than ahamster, 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 largeplanes on.

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

Sea water freezes at -1.9C (28F) because of the saltcontent. It starts with slush-like grease(or frazil) ice forming on the surface. As this consolidates, itcoalesces into pancake shaped pads called pancake ice.  PackIce consists of large pieces of floatingice i.e. ice floes. Pack ice isdynamic, it floats around with the wind and currents and is an importanthabitat for seals and penguins.

When the frozen sea is attached to land & is a solidsheet it is called fast ice. This isvery  stable except where it meetsthe open sea and forms a de facto coastline.

 

EcoSystem

The Antarctic EcoSystem is unique and most of theorganisms 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 feworganisms. Ice is the problem, bursting cells and dehydrating tissues.Temperatures AntarcticaŐs interior drop to below -80C and the interior is thusvirtually lifeless apart from the occasional human!

 

The Terrestrial EcoSystem

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

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

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

PIC                  HenrykArctowski Polish research station, King George Island,

SouthShetland 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 isrelatively 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 thewaters around Antarctica. There are no sharks and 60% of the fish belong to asingle group, the Notothenioidei. In order to live in waters of -1.9 C mostAntarctic fish synthesise anti-freeze molecules, special protein carbohydratecompounds that prevent ice from forming in their blood and tissues.

Icefish (Channichthyids are unique among vertebrates and have no red bloodcells but carry oxygen dissolved in plasma. Their blood is completelycolourless. The lack of red blood cells is possible only in the cold Antarcticwaters because of the high oxygen levels and probably evolved as a means ofreducing 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 smallbottom 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 thebase to the predators at the top, however, the Antarctic food web is unusual inthat 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 animportant 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 convenientbirthing spot.

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

The most serious impact of climate change and increasingtemperatures is a reduction in krill. This is because the sea ice is forminglater and retreating earlier, especially around the Antarctic Peninsular and inthe SW Atlantic sector of Antarctica. A survey in this region indicates thatkrill may have dropped by 80% in the past 30 years. This could have seriousimpact on the Antarctic food web and may explain the decline in some penguinpopulations. 

 

 

Penguins

 

Leg length – skeleton

 

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Encased for warmth and to make them more streamline in thewater

 

Very ancient ancestors > 45 million years ago, wereflying birds.  Only penguins form agroup 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 14-18stiff feathers.

á      Their legs are strong with webbed feet and visibleclaws.

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

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

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

á      Feathers The feathers of most birds grow inlines with gaps of featherless skin in between. Penguin feathers cover alltheir skin, just like fur. This provides an impregnable coat that preventswater 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 whichtraps air. Penguins frequently come out of the water to preen. Thisreconditions and replenishes air trapped between feathers.

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

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

To conserve heat, penguins willtuck 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 aspecial break in the insulation, tiny patch of bare skin on their bellies thatthe egg and chick can nestle against.
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á      All adult penguins are counter shaded; that is they aredark on their back surfaces and white on their underside. The dark side blendsin with the dark ocean depths when viewed from above. The light side blends inwith the lighter surface of the sea when viewed from below. The result is thatpredators or prey do not see a contrast between the counter shaded animal andthe environment.

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

Many species have distinctmarkings and coloration.

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

á      They drink sea water and have special glandsthat 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, wherebreeding is synchronised

Rookery is noisy and dirty.

Adults call to each other

PIC                  chinstrappenguin at Half Moon Island

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

PIC                  gentoopenguin, Chilean research centre, Paradise Harbour

                                                                                                AntarcticaPeninsula

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 raisingthe chicks, both incubate the eggs (except Emperor penguins where the male does all the incubation), feedthe chicks and guard the nests. This is essential and chicks that loose aparent 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 thanthis one

 

 

Diversion on how other animals in Antarctica teach theiryoung

 

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 behaviourand depth depends on the depth of the penguins' prey, which may vary withseason and time of day. Most penguins have very little need for dives of greatdepth or long duration, since their food is usually found in the shallowerdepths.

However, Emperor penguins(about 12 kg and 30 kg respectively) have been known to dive to depths of 204and 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 therecord for deepest and longest dive. The Emperor's record dive has been set at18 minutes, though usual dive time even for these large birds is around 3minutes. Emperor penguins can change depth at a rate of 120 m/minute, thoughjudging by the average length of their dives, the depth of most dives isprobably not very great. It would be possible for them to perform on-averagebounce dives of 180 m, but this would leave the birds very little time forpursuing prey, so most dives are probably much shallower than this.

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

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

An experiment done byGreen et al. (2003) on Macaroni penguins showed that diving activity wasgreater in daylight hours. Dives during daylight were deeper (A), of longerduration (B), and more frequent (C).

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Whitehead 1989 focused onthe diving depths of Adelie penguins at different stages of chick rearingperiod at Magnetic Island in eastern Prydz Bay, Antarctica. It was found thatno significant differences existed between the maximum depth dived by male orfemale Adelie penguins. During the early chick rearing period in late December,maximum dive depths ranged from 79 to 175 m. Seventy percent of measurementsindicated maximum depths between 109 and 142 m. Only two birds were reported todive deeper than 150 m. In mid-January, when adults were foraging for earlycrche-stage chicks, the range of maximum depths was 70-157 m, suggestingslightly shallower dives. Adelie penguin prey species occur mostly within thesurface 200 m of the water column; this range is coincident with the range ofdiving depths recorded in this study, supporting the notion that the range offood items determines the range of penguin diving depths. By late January inthe Prydz region, nearly all the ice had broken up and prey species might havereacted by concentrating in shallower waters, resulting in the more limiteddive-depths recorded by Adelies during this season.

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

Loss of oxygen during adive is probably the most widely studied physiological phenomenon faced bypenguins and other diving birds.

Oxygen-savingmechanisms include:

á       Changes inblood flow

á       Slowed heartrate

á       Reducedsensitivity to CO2

Where is oxygen storedin the body?

Principle oxygen storesin the body of a penguin are 1) hemoglobin, 2) myoglobin and 3) lungs and airsacs. Hemoglobin and myoglobin have an interesting relationship; they are functionallyrelated and structurally similar. Myoglobin is a protein that contains a hemegroup, an organic structure that contains iron. Oxygen binds to the iron inthis heme group. Hemoglobin contains four protein subunits, each of whichcarries a heme group. The iron of hemoglobin's heme group is also the site ofoxygen-binding. Myoglobin has a higher affinity for oxygen than hemoglobin .

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These oxygen stores canbe enhanced by increasing oxygen carrying capacity of the blood, meaning agreater concentration of hemoglobin and red blood cells (since hemoglobin iscontained in red blood cells). The blood volume of the body might also beenlarged. Oxygen carrying capacity of blood and perhaps also blood volume doesappear to be greater in diving birds, though there is few comparative data.

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

The lung and air saccontribution to total body oxygen stores in the penguin is very significant(they contain about 50% of the total oxygen), as opposed to seals that exhaleabout 50-60% of inspiratory lung volume before diving. Penguins dive rightafter an inspiration; therefore the diving gas volume relative to body weightof penguins (about 160 cm 3/kg) is much greater than seals which is about 22 cm3/kg.  

Oxygensaving-mechanisms

Changes in blood flow

A 5 kg penguin has anestimated oxygen reserve of about 250 ml; this would last for 2.5 minutes atresting metabolism. However, penguins have adapted various oxygen-savingmechanisms that allow oxygen in the body to last longer.

Though the majority ofpenguin dives are essentially aerobic, anaerobic metabolism may be used in somecircumstances. Many tissues such as muscle have a capacity to continueanaerobically whereas other tissues, such as the brain, must have a continuousoxygen supply. Accordingly, there are major changes in blood flow during adive, most importantly being a slowed heart rate and the reduced circulation tomuscles. Ponganis et al. (1999) found that cardiac output was restricted indiving King penguins and blood flow was predominantly reduced to the brain,heart and lungs. A reduction in respiratory O 2 stores and a relative increasein 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, thepenguins heart rate slows. In Adelie and Gentoo penguins, the diving heart rateis about 20 beats per minute. This is independent of the pre-dive rate of about80-100 beats per minute. Muscles such as the gastrocnemius and pectoralisobtain less blood, while the heart receives a maximum. It was shown in Gentoopenguins that pectoral muscles and toe vessels bleed much more slowly duringsubmersion than when the bird is breathing normally. Heart rates during divinghave also been recorded for Humbolt penguins. In this study, no significantreduction in heart rate below resting levels was seen even up to the longestvoluntary dives recorded at 50 s (mean dive length was 36.4 s). However, whenvoluntary 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 119-135beats/min in shorter dives.

In Macaroni penguins,heart rate was higher than resting before and after dives, falling to a levelclose 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 diveresponse, which conserves oxygen stores while the animal is deprived of accessto air, and the exercise response, which prioritizes blood flow and oxygenuptake to active muscles when exercising. Adjustments in heart rate allow thedive duration to be extended by ensuring full loading of oxygen stores beforethe dive, then by reducing aerobic metabolism during the dive and ensuring thefull and effective use of oxygen stores while submerged.

Reduced sensitivity toCO2

It is also shown thatwhile oxygen concentration drops during a dive, CO2 levels increasecorrespondingly. Generally, diving birds and mammals are less sensitive to CO2than land animals, probably due to greater buffering ability of the blood.Reduced sensitivity to CO2 is beneficial in extending the breath hold since CO2is one of the principle stimuli to terminating an apnoeic episode.

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

Lactic acid

A surge of lactic acidconcentration usually occurs after a dive, reflecting an increased flow totissues previously functioning anaerobically. As blood passes through the tissue,mainly muscle, it picks up large quantities of lactic acid accumulatedgradually during the dive. The gradual increase of lactic acid during a diveindicates anaerobic processes in the muscles which are supplied with littleblood during the dive but are generously suffused after emerging. However, someincrease in blood lactic acid occurs during the dive, which suggests that asmall amount of flow continues to the muscle. In fact, this leakage may beconsiderable compared to the grey seal, Halichoerus grypus. In the penguin during a 5 minute dive thelactate concentration of arterial blood doubles, but in the grey seal there ishardly 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 levelsincrease above resting values. ADL has been calculated (cADL) for severalpenguin species by dividing an estimate of usable body oxygen stores by anestimate of the rate of oxygen consumption (V O 2) while submerged. Manystudies have found that 2-50% of observed penguin dives exceeded the cADL.However, the dive:pause ratio in these studies suggests that it is unlikelythat so many dives use predominantly anaerobic metabolism. In order for a largeproportion of natural dives to be aerobic, the cADL must be greater. Ifestimates of the usable oxygen stores for penguins are correct, then V O 2during diving needs to be as low as that recorded from penguins at rest on thewater surface for most dives to be within the cADL.

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In a study done by Greenet al. (2003), heart rate was used to estimate V O 2 in Macaroni penguins. Asuite of physiological and behavior adaptations were found to contribute to themaximizing of cADL while penguins were submerged, including 1) variation ofheart rate and circulation, 2) regional hypothermia, and 3) the use of passivegliding during the ascentand descent of dives. This study found that if heart rate is averaged overcomplete dive cycles, it is an accurate and reliable predictor of V O 2 for thedive cycle. As observed dive durations increased, V O 2 decreased, and hencecADL increased. For all dive durations of up to 138 s (95.3% of all dives), thecADL was greater than the observed dive duration. These results imply that mostnatural dives within diving bouts by Macaroni penguins are aerobic.

cADL was calculated usingV O 2 while resting on water for three other penguins species, though V O 2 wasmeasured using respirometry rather than estimated in the field. In emperorpenguins, 96% of dives would be within the cADL, whereas in king penguins andgentoo penguins only 80% of the dives would be within the cADL. Oxygen storesare assumed to be the same for all four species of penguin, so there must be adifference in diving behavior or V O 2 while submerged between species. Fooddensity, distribution and location fluctuate for each species, and are morelikely to be the cause of variability in diving performance between speciesthan differences in physiology. Breeding success of gentoo penguins is far morevulnerable than in macaroni penguins to variations in food availability, so itmay be that gentoo penguins are under greater pressure to gather enough food tofeed their two chicks, leading to a higher proportion of anaerobic dives.Emperor penguins are much bigger than king penguins (and so have greater oxygenstores that allow them to dive to greater depths and for longer durations), andyet their diving performance is similar. A large proportion of foraging divesfor both species are to 100-200 m in depth and last up to 5-6 minutes. Thisindicates that emperor penguins operate well within their physiological limits,whereas king penguins dive to depths and durations that are close to themaximum of their capabilities.

Penguins must cope withextreme changes in hydrostatic pressure as they dive. As a penguin dives todepth, the air sacs, lungs, air space within the middle ear, and gas trapped inthe 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 pressuregradient between the internal cavity and the cells and vessels invested in thewalls forming the structure would soon become so great that oedema would occur.If the gradient continued to increase, vessels would rupture resulting ininternal bleeding. Cavities must be able to shrink in size, sometimes to aconsiderable extent. Thus the Emperor penguin, diving to its greatest recordeddepth 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 theiroriginal volume.

The partial pressure ofgases in the lung and air sacs increases with increased compression, since thesolubility of a gas is directly related to partial pressure (Henry's law). As aresult, human divers breathing compressed air become vulnerable to inert gasnarcosis and decompression sickness. The ratio of gas volume to body size is sogreat in penguins that they may be more vulnerable than any other diving groupas gas exchanges freely between the blood and lungs at depth. In pinnipeds, N 2uptake is minimized during diving because of small diving lung volumes, lungcompression and the forcing of lung air into cartilage-reinforced upperairways. In penguins, however, the volume of air sacs and lungs (respiratoryvolume) represents a potentially significant reservoir of N 2 and O 2.Calculations based on the diving lung volume of a seal show that if allnitrogen in the lungs were absorbed into the blood the elevation in nitrogentension could be great, depending on the depth and length of a dive anddistribution of blood flow. Since the nitrogen store in the lung of a seal ismuch less than in a penguin during a dive, it would seem that the penguin wouldbe even more vulnerable. Lung compression is therefore not a feasible mechanismfor decreasing N 2 absorption in birds.

It is unknown how apenguin avoids nitrogen narcosis or decompression sickness. The respiratory systemin birds is very different from that of mammals. The bulk of the gas containedin the respiratory system of penguins is in the air sacs, the non-respiratorypart of the system. The opposite is true for mammals. It has been shown thatgas exchange in Adelie and Gentoo penguins continues between the lungs and theair sacs during deep dives. A possible conclusion is that most penguin divesare too short for a significant amount of nitrogen to be absorbed. Ponganis etal. (1999) found this to be true in Adelie and gentoo penguins during simulateddives to depth. Their dives were of short duration and shallow to avoid therisk of elevated N 2. However, King and Emperor penguins frequently make divesto depths of 200 m and 400 m, and a few mechanisms have been proposed to dealwith the pressure changes associated with these deep dives. Severe bradycardiaand reduction in cardiac output could reduce cumulative uptake of N 2 duringdives. In addition, a pressure-induced restriction of gas exchange might occur.Histological examination of lungs in Emperor penguins have demonstratedthickened blood-air barriers and increased blood capillary volumes as well. Itis postulated that, at depth, engorgement of blood capillaries might fill theparabronchal air capillaries, preventing or reducing gas exchange. The loweringof cardiac output would also limit the total amount of N 2 absorbed due to lowpulmonary flow and the small volume of distribution.  

Ponganis et al. (1999)also found low venous P N2 during and after submersions. This is consistentwith the idea that during periods of increased pressure (during ascent andsurface 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 areduction 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 reducedcardiac output or a pressure-induced restriction of pulmonary gas exchange.Similar adaptations probably function in emperor penguins, which displaysimilar diving patterns but of nearly twice the depth and duration.

Hydrostatic pressure hasa pronounced effect on the biochemical function of enzymes and transportproteins. Pressure may perturb protein and membrane function though a number ofmechanisms where changes in volume may be involved such as 1) ligand bindingefficiency, 2) catalytic rates, 3) structural stability and 4) membranefluidity. These changes can also lead to perturbations in metabolic rate viaperturbations in rates of enzymatic catalysts, ion transport, and hormone,neurotransmitter and neuromodulator binding. Croll et al. (1992) suggests thatdiving mammals and birds may have evolved specialized enzyme systems that areinsensitive to changes in pressure, and that insensitivity to pressure is apreadaptation 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 comparedto shallow-diving penguins, these penguins have a lesser reliance on therespiratory oxygen store for extended breath-holding and also a reduced uptakeof nitrogen at depth.

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

What happens topenguin body temperatures during diving?

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

Macaroni penguins showeda progressive decrease in abdominal temperatures during periods of divinginterspersed with surfacing; this is probably the result of many smallerdecreases associated with individual dives that simply accumulate. The abdomenmay not have sufficient time to return to its initial temperature during thesurface interval between dives, and the overall decrease in temperature may bethe result of accumulation of these cycles. This pattern was also found inemperor penguins, where abdominal temperature started to decrease as soon as adive 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 temperatureduring diving bouts.

The results of Handrichet al. (1997) show that during deep dives, temperatures in certain body regionsof freely foraging penguins can decrease much more dramatically than in thestomach, which is cooled predominantly by the ingestion of cold prey. Thesetemperature decreases, leading to a depressed metabolism, may give penguins anoverall energetic benefit during foraging trips, helping to explain the extraordinarydiving performance of king penguins and other marine endotherms. This energysaving may be analogous to torpid periods in hibernators.

Seals

Seals can be broadlydivided into

á      Phocids, whichhave 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 Weddellseal which inhabit the icy waters round Antarctica, and the Southern Elephantseal 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 beenmodified to filer food from the sea.
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á      Otariids, whichdo have external ears, strong forelimbs and can rotate their hind flippersforward and support some of their body weight on these limbs. This enables themto move very swiftly on land. The Antarctic Fur Seal belongs to this group. (asdo sea lions)

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

Physiology

Southern Elephant Sealscan 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 isneeded 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. SealsdonŐt hold their breath when they dive, instead most of the oxygen previouslybreathed in is stored in their blood and muscles.

The volume of blood in aWeddell 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 tofewer than 10 beats per min when submerged.

The greatly reduced bloodflow 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 flippersare within their body mass and connected to the flippers via tendons thus alsoconserving heat.

Summary

Antarctica is abeautiful, unique and fragile environment, privileged to visit.

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

Threats from

á      Sealing –already discussed

á      Whaling –International Whaling Commission set up in 1946. since the mid 1980s theJapanese have been hunting and killing Minke whales in the Southern Ocean aspart 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 thatthe 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 onthe IUCN Red List of Threatened Species.

á      Fishing –most fishing in the Southern Ocean is by longline. Some of these lines are over62 miles long and contain thousands of baited hooks. Although they are effectivein catching large fish, sea birds are also caught. In trying to take the baitwhile on the surface they get caught, pulled under and drowned. Over 100,000birds are killed in this way each year. Measures are being introduced to reduce the number of sea bird deathsbut these are not adopted by illegal fishing operations. These are alsothreatening the Patagonian and Antarctica toothfish.

á      Invasion of alienspecies. -  in recent years, nonnative 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 humanse.g. in the water in shipŐs ballast tanks. Ships visiting Antarctica aretherefore asked not to discharge their ballast water in Antarctic waters as itwill have certainly come from other oceans. The footwear of passengers is alsothoroughly disinfected between landings.
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á      Ozone depletion– the destruction of the ozone layer and the resulting increased levelsof UVB are damaging the ecosystem and some phytoplankton are decreasingproductivity by up to 12%.
International agreement on the phasing out of CFCs etc has been very successfuland there is an apparent slowing in the growth of the ozone hole.

á      Global warming– already highlighted

The future of theAntarctic ecosystem depends not only on what happens on Antarctica itself butalso changes to the environment in the northern hemisphere. The more people whoare aware of the problems, the more chance there is of protecting what is left.

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