ANTARCTIC PENGUINS: BELLWETHERS OF ENVIRONMENTAL CHANGE
The following contains a series of images, which with the information contained in their captions, should provide upper class high school students, college students and interested adults with the basic story about how one group of animals is responding, both in a positive and negative way, to climate change.
Every species is adapted to exploit and cope with a set of factors that together determine where on Earth it can live. These factors include physical ones like temperature or rainfall (wetness), or biological ones such as the threat of predation by another organism, infection by parasites or disease microbes, or combinations of physical and biological factors. In the middle of its so-called zoogeographic range (the entire region in which a species normally lives), a species is in balance with the factors important to its existence and its population fluctuates little from year to year. As one nears an outer boundary of that range, however, one or more important factors begin to negatively affect the well being of that species and, depending on variation in the strength of that factor, the animal or plant may exhibit large fluctuations in abundance. Crossing that boundary, the species can no longer exist as that critical factor overcomes the capabilities of the species to cope with it. For instance it may be too hot, or too cold, or too dry or too wet. At different boundaries, say, to the north or to the south, a different factor likely is critical, usually related in some way to climate.
Having been remarkably stable and relatively benign since the end of the last ice age, i.e. the last 10,000 years --- the period, known as the Holocene, when human civilization blossomed --- Earth’s climate now has begun to change rapidly, with the main causes due to human-related factors. The change is so remarkable that geologists now term the era in which we live: the Anthropocene. Human activity in many ways is having a great impact on Earth’s biota, and one way by which this is happening is through climate. As the change in global climate accelerates, and most rapidly at the Poles, species are responding to the change, some more successfully than others, and in different ways at different boundaries of their range. Actually, many species are disappearing in what has become known as the “Sixth Extinction,” i.e. another period similar to that which wiped out the dinosaurs.
To illustrate how species cope with climate, if they can, we’ve chosen as an example the Antarctic penguins.
Any species that occurs in the high latitudes of the South Polar Region has to feel comfortable with ice or have adaptations to deal with it. Only some mites, wingless insects, some microscopic worms, bacteria and a few plants live on the Antarctic continent. The sea ice-covered oceans around the continent, however, are teaming with marine life including lots of vertebrate animals (fish, birds, seals, whales).
The Adélie and Emperor penguin are two vertebrate species that do not occur very far from ocean waters upon which sea ice has been present for at least part of the year. In fact, these penguins are “obligate associates” of sea ice, much like many songbirds are obligate associates of forests. Given that any ice is highly sensitive to changes in temperature (it melts), these two species are likely to be sensitive to climate change through its effect both to sea ice as well as land ice (glaciers, ice shelves, etc.). The Adélie Penguin is probably unique among Earth’s animal inhabitants: not only do we know how it responds to changes in its present environment, but unlike most other creatures we also know how it has responded to habitat and environmental changes for at least the last 35,000 years (detailed below). Unlike Adélies, on the other hand, we know relatively little about how the Emperor Penguin responds to changes in its environment because 1) the species breeds during the dark of winter and therefore is very difficult to study, and 2) they nest on sea ice that periodically melts or breaks up and thus usually they leave no trace of their existence from year-to-year, much less for thousands of years. Nevertheless, they are still highly sensitive to changes in sea ice conditions and offer us some lessons about how any species might respond to changes in climate.
Penguins, however, are sensitive to more than just physical aspects of their environment. Recent research has shown them to be exceedingly sensitive to the availability of their prey as well. Being incapable of aerial flight, by which a bird can move rapidly and scan huge areas, penguins are unable to easily search increasingly larger areas looking for food should it become hard to find. They rely on food in predictable amounts and quality, in predictable places. Thus, the major uncertainties regarding these birds and environmental change are 1) how these penguins will respond to climate change given the destruction of their food web by human fisheries, a factor they have experienced only very recently (only in the last hundred years, as compared with the 2.5 million years of their existence on Earth, i.e. contributing to the Anthropocene); and 2) what will be the consequences of the high rate of climate change going on now, which has occurred only a few times in the history of Earth. The last time a Rapid Climate Change Event occurred was about 12,000 years ago, at the end of the last Ice Age, when Earth’s temperatures rose several degrees in just one or two decades.
The Antarctic-wide maps, below, are based on data from NASA, and show the difference in ice extent between winter, when Antarctic sea ice is at its maximum, and late summer, when it is at its minimum (it has melted in the warmer season). In both seasons the ice extends from where waters are warmer than -1.7oC (about 29oF) to the edge of the Antarctic continent, where it is very cold, especially in winter. The Antarctic Polar Front marks the northern (warm) boundary of the Antarctic Southern Ocean; the line labeled “ACC” marks the southern limit of the Antarctic Circumpolar Current, propelled by westerly winds to flow toward the east around the continent, between it and the Polar Front. The southern boundary of this current is where the northern boundary of sea ice occurs, an important detail. Adélie Penguins and all but first-year Emperor Penguins travel no farther north than the limit of winter ice.
Map, above, showing proximity of penguin colonies to areas of persistent open water in the pack-ice covered seas of coastal Antarctica. Between winter (May), when Emperor Penguins begin breeding, and spring (October), when Adélie Penguins begin breeding, the sea ice in the Southern Ocean is very extensive (see previous map) and the openings between ice floes, especially as one travels farther south, become very narrow or disappear all together. Therefore, both species of penguins establish their colonies in areas that are close to polynyas, a Russian term that refers to areas of persistent open water or loose pack ice in otherwise heavily ice-covered seas. Most Antarctic polynyas form when persistent, strong winds sweep off the continent and push away the sea ice; unlike the Arctic there are few polynyas formed by the upwelling of warm water in the Antarctic. This map shows for one section of Antarctica the proximity of penguin colonies (circles = Adélies, triangles = Emperors) to coastal polynyas (light stipling next to the coast; ice shelves are shown in medium shading, and the Antarctic continent in darkest shading).
This image shows what a polynya looks like from a penguins’ perspective. These penguins are standing on an ice floe that is at the edge of a wind-swept polynya. Without the wind acting to keep the polynya ice-free (pushing it away), the penguins would have more difficulty, requiring walking, to find a place to dive into the ocean.
Emperor Penguins breed at locations where the sea ice is locked in place by grounded icebergs, islands or capes. In this view, taken from a helicopter at about 300 m (1000 ft) altitude, the Emperor colony can be seen as a large cluster of dark dots on the ice; the ocean beneath this ice is more than 100 m (300 ft) deep, but shallow enough to ground the icebergs for 100s of years until the wind eats them away.
These Emperors are standing on the sea ice next to a glacier that keeps the ice locked in place. The sea ice, called fast ice (because it remains fast in place) must remain stable from about April until the end of December for them to complete an entire breeding season. If the fast ice is too thin and breaks up too soon, then the eggs or chicks would be swept to sea before they are ready to take care of themselves.
The Emperor Penguin colony at Pt. Géologie is the site of where “March of the Penguins” was filmed. It is among the northernmost of all Emperor Penguin colonies and thus has relatively warm weather compared to most of the rest of Antarctica. In fact, it is near the northern edge of this species’ range; where most Emperor Penguins nest it is much colder. Emperors have been studied for a long time by French biologists associated with the Dumont d’Urville research station nearby at Pt. Géologie.
As shown in this graph (data from Barbraud & Weimirskirch 2001, Nature), the Pt. Géologie colony began a sudden decline in the mid-1970s and has since failed to recover. In part this decrease was due to disturbance from people and their activities, the French government having built their research station right next to the colony (within a few hundred yards!), expanding it from time to time including addition of a large airstrip in the late1980s. Climate change may also be involved, including warming winter temperatures that have resulted in thinner fast ice on which they breed. If its relatively warm and winds are strong, then the fast ice does not get a chance to stay in place; when it finally does solidify, the duration of its presence is shorter than otherwise and it does not get the chance to thicken. Strong Antarctic wind events at times have blown the ice away before the chicks were ready to fledge. An increase in adult survival occurred in the early 1980s (when the decrease in population ceased) when more than 100 killer whales were killed by the Russians in waters just offshore. Why the Russians did that we have no idea; perhaps they felt sorry for the penguins. Apparently, some penguins appear to have moved to more stable ice, and where it is more peaceful not far away. Recently, using high resolution satellite images, nearby Emperor colonies, never before known, have been detected. At Taylor Glacier, another Emperor Penguin colony (studied by Australian biologists) in the same section of coastline but several hundred kilometers to the west, the Emperor Penguin population has not declined much, if at all, during the same time period. This is probably because it’s but one of only two sites where this species of penguin nests on land, and is thus not dependent on the presence of persistent sea ice for their breeding success. In fact, the other colony that has occurred on land, on Emperor Island (Dion Islets) and the northernmost along the western Antarctic Peninsula, moved onto land after the fast ice connected to the island disappeared. A decade or so later, satellite imagery shows that this colony has shifted a few hundred kilometers to the south where there is stable fast ice.
A study in 2010, confirmed by a more recent study, projected that as sea ice disappears around the Antarctic continent, which is expected with continued global warming and disappearance of the Ozone Hole (see Changing Antarctic Climate), the northern colonies of Emperor Penguins, north of about latitude 70S, will disappear, similar to that at Emperor Island. This would happen during the next several decades and involve about 50% of present colonies or 40% of the population.
Current distribution of Emperor Penguin colonies according to increments of latitude South. Those shown in red are likely to disappear within the next 50 years due to loss of stable fast ice on which to breed (image from Ainley et al. 2010, Ecol Monographs). See last image in this presentation, below, to see where colonies occur relative to 70o S latitude.
Lessons from Past Environmental Change
Besides knowing how Adélie Penguins are responding to current physical changes in their environment brought on by global climate change, we know a lot about how they responded to past changes, especially as the Earth warmed since the last Ice Age (ending ca 12,000 years ago). That information helps us to predict how these creatures will respond to future climate change. We are beginning to understand, too, how this species responds to alteration of the abundance of its food, which makes it more sensitive to changes in physical habitat.
The reason we know so much about how this species has responded to previous changes in its environment is because its bones are preserved by the cold, dry climate characteristic of high-latitude Antarctica. Elsewhere on Earth the bones of animals disintegrate within decades. This penguin mummy, shown above, is several hundred years old. It has been worn down by the feet of other penguins walking over it and by being sand- and snow-blasted by the wind. The age of these remains can be determined by assessing the amount of a certain form of carbon (carbon-14, or C14) in its tissues; C14 occurs naturally in Earth’s atmosphere and is incorporated into the penguins tissues (and all animals’ tissues) while it is alive. The C14 disappears (turning into more chemically stable C12) over time from tissues at a known, constant rate once the animal dies. If mummies like this one are found along with the bite-sized rocks that Adélie Penguins use for their nests (not too large that the penguins can’t carry them in their bills, and all of the same size), then we know that the mummy’s location was once a breeding colony. Pieces of egg shell can provide additional clues if one digs below the surface. Such “sub-fossil” records (old things not yet turned to stone) tell us that the area has been ice free since at least the oldest dated mummy present; otherwise the penguins and their bone deposits would not occur there.
More than 99% of Antarctic is covered by ice, and coastline, if not ice cliffs, looks like this: sheer cliffs meeting sea ice at their base. Adélie Penguins cannot make their colonies in these locations because they need ice-free land with a supply of small rocks with which to build nests, and although they are very nimble they are unable to climb tall, vertical cliffs. Also, they don’t like to walk very far over ice to find the open water they need for feeding (see above discussion of polynyas). Emperor Penguins could breed here (on the sea ice), but in many places they don’t because the ice breaks out and melts too early in the spring. Because of these factors, suitable nesting habitat for both penguins is very hard to find. In fact, the southern limit of their ranges is defined by the Antarctic coast, which is mostly glacial ice.
Immediately above, is an Adélie Penguin colony, Cape Crozier, which is located at the edge of the continental glacier that covers West Antarctica (the West Antarctic Ice Sheet). This part of the glacier is called the Ross Ice Shelf because it is floating on the sea (like a shelf extending out from the continent); in the image above it rises about 30m or 100ft above the sea surface, and 60m below. It is the largest glacier on Earth, and elsewhere it is much thicker. During the last ice age, Adélie Penguins did not nest here because the front of the Ice Sheet was located much further to the north, covering almost all of the Ross Sea and thus blocking off this Cape. They began to nest here within the last couple of thousand years, ever since the Ice Sheet retreated, enabling a southward extension to the penguins’ breeding range. We know this from the age of the mummies that have been found. The Ice Sheet retreated because pieces broke off, as ice bergs (as shown here), at a rate that was faster than the amount of snow falling in the Antarctic interior and which was maintaining or adding to the ice sheet. In other words ice loss was greater than ice accumulation.
Please have a look at the animation of ice sheet retreat, and penguin advance, elsewhere on this website.
There are no penguins currently nesting at this site on Beaufort Island, in the southern, western Ross Sea. However, fossil remains reveal an area that Adélie Penguins used to occupy before the last Ice Age (!), but which they were forced to abandon due to the advance of the West Antarctic Ice Sheet. By dating the penguin remains, we’ve learned that the species has been absent from this location for over 30,000 years. The birds are just now beginning to return owing to an apparent retreat of the snowfield and thus increased access to a snow-free location with lots of stones with which to build nests.
In many parts of the world, glaciers are retreating at increasing rates as a result of global climate change (warming). This particular glacier, shown here, has accelerated its retreat from what it has been since about 8000 years ago (this area was completed covered by glacier during the Glacial Maximum). The glacier is benefiting Adélie Penguins because it has retreated far enough from a very gentle slope to allow the penguins to come ashore to found a colony. The colony here, at Cape Bird, Ross Island, is the light brown area (penguin guano deposits) in the middle ground, with the dark rows being groups of nesting penguins (elevation from where the photo was taken is about 300 m). The upper half of the image shows an ocean that at the time this photo was taken was covered by sea ice.
As glaciers retreat, they also leave piles of gravel, called moraines (little rocks ground from big rocks by the incredible weight and slow but steady movement of the glacier). These deposits supply the stones used by Adélie Penguins to build their nests.
These penguins, above, are nesting on the shores of a bay that is now completely covered by fast ice (Cape Royds, McMurdo Sound). Fast ice is sea ice that is attached to the shoreline and has very few openings through which penguins can dive into the waters beneath. If it becomes too cold and calm, as during the last Ice Age, and this extensive sea ice persists through the summer, then this colony would cease to exist because the penguins would have to spend too much time and energy walking over the ice to get from their nests to open water. In fact, this colony’s population declined rapidly during a recent 5-year period when the fast ice failed to break out owing to a large, grounded iceberg and a lessening of winds. There are still many parts of the Antarctic coast that are too ice-choked to allow penguins to establish colonies. As the Antarctic warms, however, the sea ice in these areas will begin to break up, creating more areas where, if there are some gentle beaches, Adélie Penguins could one day nest.
THE RESPONSE OF PENGUINS TO CURRENT ENVIRONMENTAL CHANGE
Shown here are the changes in colony size of the southernmost penguin colonies in Antarctica (77-78oS latitude). Biologists from LandCare Research (New Zealand) have been counting the penguins nesting in these colonies for 4 decades (these data from Wilson et al. 2001). These colonies are on Ross Island in the southern Ross Sea. The colonies, especially the small ones, have been growing as a result of changes in their environment brought by two important factors.
First, global climate change, especially increased wind strength and warmer winter temperatures, has resulted in thinner sea ice and a more persistent polynya, particularly the one in McMurdo Sound, where two growing colonies are located. By being able to swim to their foraging areas, they can eat their fill of food much more quickly and can bring more food back to their chicks when they return to their nests. Thus, their breeding success has increased and their population within this group of colonies has grown, especially since the mid-1980s.
The second factor that has facilitated the growth of Adélie Penguin colonies in the Ross Sea, and likely other high-latitude areas of the Southern Ocean, is the extraction by whalers of the penguins’ main competitor for food, the Antarctic minke whale. When the numbers of whales increase near a penguin colony, which happens periodically, the penguins find it more difficult to obtain food. That is to be expected, though, as both species are denizens of pack ice and have been together for 3 million years. It could be that where minke whales are especially abundant, that might be one of those factors that limit the number of penguins present. During the last few decades, as sea ice conditions have made life more favorable to Adélie Penguins so has the killing of minke whales by Japanese whalers. This seems to have contributed to the Adélie Penguin increase at the southern limit of their range but also disrupts the foodweb in which both species evolved.
Changes in Ross and Beaufort Island Adelie Penguin colonies in recent years: graph from Lyver et al. 2014, PLoS ONE).
Even more recently, since about 2004 (see graph above), the numbers of Ross Island penguins have really begun to increase, very sharply. We believe that this is because commercial fishing has arrived in this area, and the target fish species competes for food with the penguins. This fish is called Antarctic toothfish, sold for a high price in restaurants as “Chilean sea bass” (because the name toothfish doesn’t sound as edible). The fish preys mostly on Antarctic silverfish, also a favorite prey of Adélie and Emperor Penguins. This fishery is causing major disruptions to the foodweb. A toothfish-eating Killer Whales (Orca) and toothfish-eating Weddell Seals have had to increase their effort to find food. This is most important to the Killer Whale, because it has few other prey choices, and their numbers are decreasing in the southern Ross Sea. If someone offers you “Chilean sea bass,” asks for something else to eat (and don’t follow the recommendations of the Marine Stewardship Council nor SeaFood Watch).
The graph, above, shows the trend of Adélie Penguin colonies at the northern tip of the west coast of the Antarctic Peninsula (data from Bill Fraser in Ducklow et al. 2007). It is located at the extreme northern (warm) edge of where this species occurs on Earth. The air temperature in this area has been warming rapidly (several degrees in the last 50 years), resulting in sea ice failing to form during an increasing number of winters, as well as increased snow fall (and rain). If sea ice does form in winter, it disappears much more quickly than it used to, that is, the 'sea-ice season' (number of months sea ice is present) is now >3 months shorter than it was 30 years ago. At Anvers Island, the southern most of the three colonies shown in the graph above, the sea ice season now averages only 3 months in length.
Because Adélie Penguins are especially adapted to the cold conditions associated with sea ice and do not compete favorably with other penguins which are less adapted to the cold, the overall population has been declining at this and nearby colonies, and any young produced have chosen to nest farther south where sea ice remains. Eventually, Adélie Penguin colonies along the west coast of the northern Antarctic Peninsula will disappear, leaving only nest stones and mummies behind. Other species of penguins (such as Gentoo or Chinstrap penguins), if fisheries or recovering whale populations do not deplete their prey, may move in to replace the Adélies. If global warming begins to influence the more southern reaches of the Antarctic continent, then the entire world’s population of Adélie Penguins could be at risk.
Besides the loss of sea ice at the northern tip of the Antarctic Peninsula, the warmer atmosphere is holding more moisture there, which in turn results in greater deposits of snow. The Adélie Penguin needs snow-free areas to breed, if only to be able to find stones to build its nests. Heavier snow fall, then, would cause suitable nesting areas for this species to disappear. Penguins in the above image have had to dig out from a spring snow storm.
As temperatures of Earth continue to warm, predicted to reach a critical temperature in the next 20-30 years, eventually all of Antarctica’s sea ice will begin to retreat. As we’ve seen, sea ice is at the core of factors that determine these species’ existence. Adélie and Emperor penguins will continue to live where sea ice exists, and even colonize new locations along the coast where the sea ice becomes more open, and land glaciers retreat. Eventually, however, these penguins will disappear sequentially farther and farther south as the sea ice disappears, and as their prey disappears as humans overfish and alter the foodweb of the Southern Ocean. At the same time, sea level will be rising as the West Antarctic Ice Sheet melts. The rising sea level will cover low lying coast where the penguins otherwise would found colonies. Of course, if this occurs the streets of New York, London, Amsterdam, Calcutta (?) and many other cities will be covered, too. Recent storms, such as the one in 2012 that flooded much of coastal New Jersey and New York, have provided warnings.
Current distribution of Adélie Penguin colonies, with proportion of total colonies or population size partitioned by increments of latitude South. Those shown in red are likely to disappear within the next 50 years due to loss of sea ice and perhaps increased snow fall (see next image).
The yellow circle is 70oS latitude, north of which Adélie and Emperor penguin colonies are the most vulnerable to changes in sea ice owing to climate change. The red dots in the Emperor penguin map show where new colonies have formed near to where existing colonies have decreased or disappeared.
NOTE: We thank the Antarctic programs (and their people) from France, New Zealand and the USA for some of the information in this presentation.