Still no illustrators! Well here’s a hard one…
Climate Story
People say weather is what happens day to day while climate is what happens over thousands of days. But climate times also vary in length.
The sun warms the planet. Its radiance has increased by 25% over the last 4 billion years. Despite everything, the average temperature of the planet hovers above the freezing point of water.
Over a timescale of tens of millions to billions of years, volcanoes emit carbon dioxide and silicate rocks absorb it. If volcanism slows down and the earth cools, the chemical reaction governing the absorption of the carbon dioxide by the rocks also slows down (chemical reactions are dependent on temperature). Then carbon dioxide slowly accumulates in the atmosphere and the planet warms.
New carbon absorbing rocks are also created by volcanism, which is influenced by continental drift. Continental drift also uplifts new rocks from the mantle. It operates on a timescale of tens to hundreds of millions of years.
As plants evolved, they also took a hand in storing carbon dioxide. First they oxygenated the atmosphere, driving most organisms, for whom oxygen was a poison, underground. The plants were single cells floating on the surface of the sea. They took carbon into their bodies through photosynthesis, expelling oxygen as a waste. The carbon from the plants fell as dead plant bodies or animal poop to the bottom of the sea (the “poop pump”), where it remained.
Later, rooted land plants evolved. They pumped carbon dioxide into the soil as part of their strategy to obtain nutrients. This increased the rate of weathering in soil. Soils stored more and more carbon dioxide.
The ocean naturally takes up carbon dioxide from the atmosphere in a simple chemical reaction with water. The deep ocean circulation (the ocean conveyor) stores this carbon dioxide in the deep ocean. One round of the circulation takes 1000-10,000 years.
The placement of continents determines whether the oceans can circulate heat and so even out the temperature of the earth, cooling the tropics (which receive more direct solar radiation) and warming the poles. The narrow basin of the North Atlantic, bounded by continents on each side, lets warm surface water brought by currents from the Pacific and Indian oceans move north, and lets the return flow (at depth) move south toward Antarctica.
There’s more. Over the long term the earth’s temperature is determined by the sunlight falling on it, the position of its land masses, the heat capacity of its oceans and the characteristics of its atmosphere.
The atmosphere lets through the sun’s rays, which strike the earth, while various of its gases absorb the solar energy that is reradiated as heat to space. The gases act like a blanket.
Water vapor is the greatest greenhouse gas. Thus desert days and nights have wide temperature swings (less of a blanket there).
The other (known) gases that absorb heat are carbon dioxide (from combustion, logging, land clearance, animal respiration, plant decay), methane (from coal mining, landfills, rice paddies, cattle, termite mounds, bacterial action, swamps), nitrous oxide (from fertilizer, combustion, denitrifying bacteria), low level ozone (from air pollution and sunlight) and the halocarbons (from fires, bacterial action, chemical manufacture: these are the gases that ate the high altitude ozone shield).
These gases have different molecular weights and absorb infrared radiation at different frequencies. Thus their effect is greater than if they absorbed radiation at the same frequency: a symphony in infrared.
The warming gases are all produced naturally but human activity has become their largest source. The carbon dioxide content of the atmosphere has been measured continuously since the late 1950s from a mountaintop in Hawaii and is now 100 parts per million over the preindustrial level of 280 parts per million. It seems to me that if you know this and accept that carbon dioxide absorbs heat, you must believe in global warming. A hundred parts per million is a large part of 280 parts per million. (In fact, it is the difference between an ice age and an interglacial period.)
The warming gases are not common in the atmosphere and thus human activity can influence their abundance. Their effects are amplified by water vapor, the greatest greenhouse gas. A small warming from carbon dioxide leads to more evaporation from the oceans and more water vapor in the air, therefore a warmer atmosphere, which leads to more evaporation, and a still warmer atmosphere, in an ineluctable positive feedback.
From the steamy Cretaceous Period of 100 million years ago the earth has slowly cooled to our age of continental glaciations. The cooling has several causes: the storage of 8000 billion tons of carbon (10 times that in the modern atmosphere) during the damp, temperate Carboniferous of 300 million years ago; the current position of the continents, which lets massive ice sheets build up on land near both poles; the ongoing storage of methane by bacteria in sea bottom sediments; a moderate degree of volcanism (a volcano is erupting somewhere on earth every day); and an increased biological storage of carbon by higher animals, both in the poop pump of the oceans and on land.
A cooler earth is a dryer one and a drier one lets grasses outcompete trees. Over the last 70 million years grasslands have come to dominate much of the planet. Grassland and grazers accumulate much more carbon in their soils than forests. Grazers help by stimulating new growth and by recycling nutrients: the Great Plains were maintained by buffalo piss. Many of the most productive agricultural soils are former grasslands.
Man with his plow, his axe, his farm animals and his industries releases carbon to the atmosphere.
But back to the story: why the glacial cycles of our relatively low carbon world?
Imposed on the increasing radiance of the sun, the position of the continents, the state of the atmosphere and the biosphere, are the angle of the earth’s axis to incoming solar radiation and the earth’s distance from the sun: the Milankovitch cycles. While these cycles don’t affect the total amount of radiation the earth receives, they affect its seasonality. Glaciers grow when summers are short and cool (so snow doesn’t melt) and winters long and moderate (warmer winters mean more snow, which accumulates to become ice); that is, when there is less summer sun and more winter sun in the northern hemisphere (where there is more land at high latitudes for ice to form).
The timing of the Milankovitch cycles seems to correspond with the changes of climate expressed in cores from the Greenland ice sheet, in cores from the deep sea, from other glaciers and ice sheets, and from tree rings.
During a modern glaciation the surface of the planet goes from 10% to 30% ice. The ice forms mostly in the northern hemisphere, but also in Patagonia and New Zealand and wherever there are high mountains. Antarctica remains always covered with ice.
Glaciers take tens of thousands of years to grow and less than ten thousand to die. They seem to be self-limiting, perhaps because they depress the earth’s surface so much (up to half a mile) so any surface melting rapidly brings them down into warmer regions; and perhaps because they cover so much of the earth, whose plants no longer take up carbon dioxide, which then accumulates in the atmosphere, warming the planet.
As the planet warms it begins sucking up more carbon dioxide in its soils and oceans, both from increased biological activity on that newly uncovered 20% of the earth’s surface and because warmer temperatures speed up chemical reactions. This slowly lowers the carbon dioxide content of the atmosphere and sets the stage for the next cooling. These changes are reinforced (or not) by the planet’s position in the Milankovitch cycles.
The small changes in solar radiation during a Milankovitch cycle, and the not-so-small changes in carbon dioxide content of the atmosphere from glacial to interglacial period (about 50%) are amplified by the planet’s water cycle.
Our next glaciation is overdue. Glaciers should have begun forming about 8000 years ago, as the carbon dioxide content of the atmosphere began to fall. There are some signs of this on the rocky surface of northeast Labrador (the center of the last continental glaciation in North America).
But the ice melted. One theory is that deforestation to clear fields by humans in Eurasia 8000 years ago released enough carbon dioxide to stop the fall in atmospheric carbon dioxide and in fact raised it several parts per million.
The cultivation of paddy rice (which releases methane) and the keeping of cattle, as well as human population increases by 5000 years ago, raised it more.
(I should point out that the last long interglacial period, 30,000 years long rather than the more normal 10,000, was 400,000 years ago, when the orbit of the earth around the sun was nearly round, as now.)
Who knows? The numbers work. What is incontrovertible is that burning coal from the beginning of the industrial revolution in the 1700s began to raise the level of carbon dioxide in the atmosphere from its preindustrial level of 280 parts per million. The rise has accelerated lately, from 1.1% a year in the 1990s to 3% a year in 2000-2004. The current level of carbon dioxide in the atmosphere is 389 ppm.
Carbon dioxide shows a peak in the northern hemisphere fall and a trough in the spring. The seasonal variation is explained by the greater amount of land in the North Hemisphere. Plants use up carbon dioxide during the summer, while animals (and many plants) continue to produce it by respiration during the winter.
A warming climate causes many problems. Sea level rises, partly from melting of ice caps and glaciers, partly from thermal expansion of the water. Many continental glaciers, like the West Antarctic Ice Sheet, are grounded on the bottom of the sea. As the sea rises, ever so slightly, the glaciers lose their grip on the sea bottom and surge forward, speeding their collapse (and raising sea levels, in this case, 16-18 feet).
A warmer ocean also melts the glaciers faster where they meet the sea.
A likely estimate for sea level rise is 3-10 feet by 2100. Two feet will drown the Everglades. New Orleans is already a goner. (Because of subsidence, the relative sea level rise at the mouth of the Mississippi is now 4 feet per century.)
A rising sea also raises the heights of inland rivers, which overflow.
Salt water intrudes into coastal aquifers, such as the Magothy under Long Island, making them undrinkable.
Coastal communities build seawalls, move inland or are abandoned.
A warmer climate reduces grain crops in hot climates. Temperatures for growing maize are already marginal in much of the southeastern United States. Farmland moves north, where soils are rocky and poor.
Some regions become drier, some wetter. Reservoirs run out of water or dams must be reinforced. Heavy downpours are increasing in the eastern and middle western United States. A month’s rain comes in a few hours rather than being spread out. This is hard on crops and forests.
Mountain glaciers in the Himalayas and the Andes store winter snowfall and release it into summer springs and rivers. As they melt, summer flow falls and there is little water for people or crops. Similarly, as the winter snowpack in California’s Sierra Nevada melts earlier, summer water becomes more scarce.
Will this happen? Expressing all the known greenhouse gases as carbon dioxide, the current level of carbon dioxide is 430 ppm, a level not reached for a million years. (But carbon dioxide was about 800 ppm in the temperate Carboniferous 300 million years ago.) The last, recent time carbon dioxide was 350 ppm sea level was 80 feet higher.
Feedback processes are in play. Eastern forests are accumulating carbon much more quickly than 20 years ago; that is, their growth has speeded up. More carbon dioxide in the atmosphere makes it easier for the trees to photosynthesize (they lose less water obtaining carbon). A hopeful sign: but the trees will soon run out of nitrogen, an essential nutrient.
Forests throughout the western United States and Alaska are collapsing from a century of poor management, drought and an infestation of bark beetles. Drought and crowding stresses the trees. Winter temperatures no longer fall low enough to kill the beetles’ larvae and warm long summers let the beetles breed continuously for several months. Crowded stressed trees are not able to mobilize their defenses against the beetles. As these forest collapse and burn they release billions of tons of carbon dioxide to the atmosphere. Similar problems may affect the boreal forests (which may in any case be cleared for agriculture).
Moving societies north will require a lot of energy, which will put more carbon dioxide in the atmosphere.
Warming is most pronounced in polar regions. As the sea ice melts, the ocean absorbs heat from the sun, melting more ice, and the glaciers that touch the sea (as in Alaska and Greenland).
As the tundra warms, and the permafrost below it thaws, the soil releases carbon dioxide and methane. Methane now bubbles up through Siberian lakes all winter keeping them from freezing. As the permafrost around them melts, the lakes expand, then drain away as the land beneath them thaws, leaving the bare ground to warm in the sun, and release methane (perhaps 400 billion tons are stored in the tundra).
Off the northeastern coast of Siberia, methane is bubbling up from the sea from underwater clathrates, lattices of water and ice in which the methane is held by cold and pressure. The amount of methane held in underwater clathrates is enormous. Those under shallow seas will be released by a small increase in temperature of the water (of the order of 1° Centigrade).
A warming climate may shut down the Gulf Stream, part of the deep ocean circulation. Warm tropical water from the Indian and Pacific oceans is pulled north around Africa by the sinking of cold salty water around Iceland and Greenland. The warm water loses evaporated moisture to the Eurasian plains as it moves north, to the Pacific as easterly trades blow it across the Isthmus of Panama. It becomes salty and more dense. When it reaches a sufficient density of coldness and saltiness around the latitude of Iceland, it sinks into the oceanic abyss, helping drive the deep ocean circulation.
As the water moves north out of the tropics it also freshens from fresh water from rivers and melting ice. This lessens its density. If the density of the water is sufficiently reduced, it won’t sink. About every 1500 years over the last 100,000, the sinking has slowed and the earth’s climate has become colder, windier and more dry. A complete halt to the sinking and a disruption of the deep ocean circulation (which keeps the sea oxygenated) would be a disaster.
If we do nothing about the accumulation of greenhouse gases in the atmosphere we may be in for a wild ride.
Who knows? It may be interesting.
Friday, May 28, 2010
Wednesday, May 12, 2010
Biology Comics
Lyme Disease
Lyme disease is caused by a spirochete bacterium of the genus Borrelia that lives in some small mammals ((white-footed mice, chipmunks, meadow voles) and some birds (robins, grackles, house wrens) without causing them distress. Such animals are reservoir species for the disease. White tailed deer are not a reservoir species.
However the tick of the genus Ixodes that spreads the spirochete has deer for one of its hosts. So the ticks are called deer ticks.
Eggs laid by mature female ticks hatch into larvae (tiny ticks) in early spring. The larvae feed on a small animal, preferably a white footed mouse, but a chipmunk, a bird, a frog or a human will do. The larvae need a blood meal to mature into the next insect stage, a nymph. Feeding lasts a few days. After its meal, the larvae drops off its host, winters over in the leaf litter and the next spring sheds its cuticle to become a nymph.
Nymphs also need a blood meal to mature and also feed preferentially on white footed mice, but again will feed on any animal with blood. Nymphs, as a result of their first blood meal, are more likely to be infected with the spirochete that causes Lyme disease than larvae. Many climb high enough in the vegetation to bite people. Their activity in southern New England and New York State peaks in early summer.
By fall the nymph sheds its skin to become an adult. Adults are able to climb still higher in the vegetation, from where they attach themselves to any animal that brushes against them. Their preferred (or most common) host is deer. The blood meal from the deer or a human lets them develop sexually and survive until spring, when the female lays her eggs and dies.
Lyme disease was here when the Native Americans inhabited the continent (some Puritans seem to have contracted it) but was uncommon. It also exists (with similar ticks carrying it) in Eurasia. Peter Kalm, a Swedish botanist, remarked on the abundance of ticks in the eighteenth century New Jersey forest. Of course Peter Kalm didn’t wear shorts in the woods.
Deer ticks in the Northeast today prefer young forest and forest edges. They probably became much less common around human habitations as the landscape was cleared and settled. The virtual elimination of white tailed deer in the Northeast by 1900 may also have helped break the transmission of the disease to humans.
As northeastern farms were abandoned in favor of better farmland in California or Ohio and as northeastern industries used up their natural resources or failed during the first half of the twentieth century, the land emptied of people and grew back to young woodland, ideal habitat for ticks and deer. Much of the woods was oakwoods, also ideal, once the trees were large enough to bear acorns, for white-footed mice and chipmunks. As the animals returned, so did the disease causing ticks and spirocetes.
Beginning in the 1960s the second growth woodland started to be subdivided into housing lots. Life under the trees had its charms.
In 1975 Lyme disease was recognized as a disease from a cluster of cases in Lyme, Connecticut, a center of upscale suburbia.
A few years later the spirochete was isolated from the gut of a tick. If the disease is recognized, it is easily treated with antibiotics. A bullseye rash is often diagnostic.
Not everyone gets the rash. Other symptoms of the disease include headache, fever, fatigue and depression. If the disease is not recognized early, it becomes, like syphilis, another disease caused by a spirochete, difficult to treat and can result in joint pain and arthritis (especially in the knees), heart trouble and neurological symptoms such as difficulty concentrating and short term memory loss.
What to do? Reducing the number of deer (to fewer than 8-20 per square mile) helps.
Letting in light and air helps. Dehydration is the enemy of insects. Ticks and small mammals like damp leafy woodland edges, unmortared stone walls, brushy areas. Letting forests mature and cutting brush along forest edges probably helps. A few old trees in a sunny mowed lawn is ideal. Such treatments will also make the landscape much less desirable for many birds, small mammals and butterflies.
Cardboard tubes filled with cotton impregnated with pyrethrum helps reduce the number of ticks on mice, if the mice use the cotton to build their nests.
Baited station where mice are treated with insecticide also work; such stations have also been used for deer. Squirrels also enjoy bait stations for mice. A laborious solution is to capture and vaccinate the mice against the spirochete, every year.
Bait stations probably spread chronic wasting disease in deer. Chronic wasting disease (CWD) is a disease related to mad cow disease that was once endemic but uncommon among elk in the Rockies but is rapidly spreading eastward, probably through the use of feeding stations for deer. At the feeding stations deer come in contact with each other’s saliva, thus spreading the disease.
Lyme disease is a problem of landscape design. The best defense against it is a more diverse ecosystem, in which ticks feed on more animals that are not reservoirs of the disease. Then the incidence of disease in the ticks will be lower. (The chance of getting Lyme disease from a tick bite is currently 1-15%.)
In California, habitats with good fence lizard habitat have fewer infected ticks (ticks feed on lizards and lizards are resistant to the disease).
In the Northeast, small areas of woodland (less than five acres, a huge area in the suburbs) have many more white footed mice, as well as many more ticks, and many many more infected ticks, per square meter. This is probably because most of the woodland is edge, with invasive shrub layers and thick invasive groundcovers, ideal habitat for mice, chipmunks, ticks and deer.
One needs a connected landscape so populations of foxes, coyotes, weasels, owls and hawks can catch mice, and populations of raccoons, opossums, skunks, amphibians, different small birds and foxes can be bitten by ticks. The more young ticks bite animals that don’t carry the spirochete, the less likely humans will get the disease.
The ideal suburban landscape has vegetated bridges over roads connecting small woodlands and amphibian friendly culverts under roads to accommodate migrating frogs and toads (also tick bait).
It has habitat for short tailed weasels and snakes. Mice flee an area at the smell of a snake. Cats that eat snakes are kept indoors.
It has coyotes to help control deer. Coyotes will also control feral or adventurous bird and snake eating cats.
And humans with bows hunting deer. A useful addition to the tool kit would be a curare tipped arrow. Then (as long as the poison enters its bloodstream) the slightest scratch will kill a deer. There are many ways to deliver the poison. Perhaps a groove along the point of a hard plastic disposable arrowhead contains curare, covered with wax (so the hunter doesn’t accidentally kill himself). Or a springloaded pellet propels itself upon impact into the animal’s flesh.
Curare kills by paralyzing the muscles. Respiration stops and the animal dies of asphyxiation. But the curare molecules are too large to pass through the gut wall (curare is harmless if taken orally) so the animal’s meat remains edible.
Since the point is population control as well as sport, does as well as bucks are hunted. Young does taste better anyway.
Lyme disease is caused by a spirochete bacterium of the genus Borrelia that lives in some small mammals ((white-footed mice, chipmunks, meadow voles) and some birds (robins, grackles, house wrens) without causing them distress. Such animals are reservoir species for the disease. White tailed deer are not a reservoir species.
However the tick of the genus Ixodes that spreads the spirochete has deer for one of its hosts. So the ticks are called deer ticks.
Eggs laid by mature female ticks hatch into larvae (tiny ticks) in early spring. The larvae feed on a small animal, preferably a white footed mouse, but a chipmunk, a bird, a frog or a human will do. The larvae need a blood meal to mature into the next insect stage, a nymph. Feeding lasts a few days. After its meal, the larvae drops off its host, winters over in the leaf litter and the next spring sheds its cuticle to become a nymph.
Nymphs also need a blood meal to mature and also feed preferentially on white footed mice, but again will feed on any animal with blood. Nymphs, as a result of their first blood meal, are more likely to be infected with the spirochete that causes Lyme disease than larvae. Many climb high enough in the vegetation to bite people. Their activity in southern New England and New York State peaks in early summer.
By fall the nymph sheds its skin to become an adult. Adults are able to climb still higher in the vegetation, from where they attach themselves to any animal that brushes against them. Their preferred (or most common) host is deer. The blood meal from the deer or a human lets them develop sexually and survive until spring, when the female lays her eggs and dies.
Lyme disease was here when the Native Americans inhabited the continent (some Puritans seem to have contracted it) but was uncommon. It also exists (with similar ticks carrying it) in Eurasia. Peter Kalm, a Swedish botanist, remarked on the abundance of ticks in the eighteenth century New Jersey forest. Of course Peter Kalm didn’t wear shorts in the woods.
Deer ticks in the Northeast today prefer young forest and forest edges. They probably became much less common around human habitations as the landscape was cleared and settled. The virtual elimination of white tailed deer in the Northeast by 1900 may also have helped break the transmission of the disease to humans.
As northeastern farms were abandoned in favor of better farmland in California or Ohio and as northeastern industries used up their natural resources or failed during the first half of the twentieth century, the land emptied of people and grew back to young woodland, ideal habitat for ticks and deer. Much of the woods was oakwoods, also ideal, once the trees were large enough to bear acorns, for white-footed mice and chipmunks. As the animals returned, so did the disease causing ticks and spirocetes.
Beginning in the 1960s the second growth woodland started to be subdivided into housing lots. Life under the trees had its charms.
In 1975 Lyme disease was recognized as a disease from a cluster of cases in Lyme, Connecticut, a center of upscale suburbia.
A few years later the spirochete was isolated from the gut of a tick. If the disease is recognized, it is easily treated with antibiotics. A bullseye rash is often diagnostic.
Not everyone gets the rash. Other symptoms of the disease include headache, fever, fatigue and depression. If the disease is not recognized early, it becomes, like syphilis, another disease caused by a spirochete, difficult to treat and can result in joint pain and arthritis (especially in the knees), heart trouble and neurological symptoms such as difficulty concentrating and short term memory loss.
What to do? Reducing the number of deer (to fewer than 8-20 per square mile) helps.
Letting in light and air helps. Dehydration is the enemy of insects. Ticks and small mammals like damp leafy woodland edges, unmortared stone walls, brushy areas. Letting forests mature and cutting brush along forest edges probably helps. A few old trees in a sunny mowed lawn is ideal. Such treatments will also make the landscape much less desirable for many birds, small mammals and butterflies.
Cardboard tubes filled with cotton impregnated with pyrethrum helps reduce the number of ticks on mice, if the mice use the cotton to build their nests.
Baited station where mice are treated with insecticide also work; such stations have also been used for deer. Squirrels also enjoy bait stations for mice. A laborious solution is to capture and vaccinate the mice against the spirochete, every year.
Bait stations probably spread chronic wasting disease in deer. Chronic wasting disease (CWD) is a disease related to mad cow disease that was once endemic but uncommon among elk in the Rockies but is rapidly spreading eastward, probably through the use of feeding stations for deer. At the feeding stations deer come in contact with each other’s saliva, thus spreading the disease.
Lyme disease is a problem of landscape design. The best defense against it is a more diverse ecosystem, in which ticks feed on more animals that are not reservoirs of the disease. Then the incidence of disease in the ticks will be lower. (The chance of getting Lyme disease from a tick bite is currently 1-15%.)
In California, habitats with good fence lizard habitat have fewer infected ticks (ticks feed on lizards and lizards are resistant to the disease).
In the Northeast, small areas of woodland (less than five acres, a huge area in the suburbs) have many more white footed mice, as well as many more ticks, and many many more infected ticks, per square meter. This is probably because most of the woodland is edge, with invasive shrub layers and thick invasive groundcovers, ideal habitat for mice, chipmunks, ticks and deer.
One needs a connected landscape so populations of foxes, coyotes, weasels, owls and hawks can catch mice, and populations of raccoons, opossums, skunks, amphibians, different small birds and foxes can be bitten by ticks. The more young ticks bite animals that don’t carry the spirochete, the less likely humans will get the disease.
The ideal suburban landscape has vegetated bridges over roads connecting small woodlands and amphibian friendly culverts under roads to accommodate migrating frogs and toads (also tick bait).
It has habitat for short tailed weasels and snakes. Mice flee an area at the smell of a snake. Cats that eat snakes are kept indoors.
It has coyotes to help control deer. Coyotes will also control feral or adventurous bird and snake eating cats.
And humans with bows hunting deer. A useful addition to the tool kit would be a curare tipped arrow. Then (as long as the poison enters its bloodstream) the slightest scratch will kill a deer. There are many ways to deliver the poison. Perhaps a groove along the point of a hard plastic disposable arrowhead contains curare, covered with wax (so the hunter doesn’t accidentally kill himself). Or a springloaded pellet propels itself upon impact into the animal’s flesh.
Curare kills by paralyzing the muscles. Respiration stops and the animal dies of asphyxiation. But the curare molecules are too large to pass through the gut wall (curare is harmless if taken orally) so the animal’s meat remains edible.
Since the point is population control as well as sport, does as well as bucks are hunted. Young does taste better anyway.
Sunday, May 2, 2010
Tales of the North Pacific
No one wants to illustrate Biology Comics!
Imagine the drawings…
Tales of the North Pacific
The other name for orcas is ‘killer whale.’ Orcas are the most fearsome predator in the sea.
When attacked by orcas, a pod of great whales formed a daisy pattern, head toward the center, tails out. Great whales are several times the size of orcas. The idea was probably to whack the attacking killer whales with their tails; or to limit their access to whale bodies.
Orcas are intelligent, powerful and not easily discouraged. Their dentition resembles that of Tyrannosaurus rex. Wounded great whales would be nudged back into formation by their companions, trailing their intestines or missing great flaps of skin. The whole pod might be killed.
Dead whales sink to the bottom of the ocean, where they become the base of a novel ecosystem including polychaete worms that live on the fat in whalebone. Before industrial whaling, 850,000 whale carcasses may have littered the seafloor at any one time. Besides supporting their own ecosystem, the carcasses contributed nutrients to the deep sea.
Orcas are opportunistic hunters and also eat seals, sea lions and fish, including herring and salmon. They have a high metabolic demand and need a lot of food. Stellar sea lions, which weigh up to a ton, provide a good meal.
During World War II, fishing in the ocean almost stopped. After the war, life returned to normal. The whale hunt in the North Pacific resumed. About 500,000 great whales were killed there.
During the 20 years of the hunt, orcas learned to respond to the sound of exploding harpoons and whale distress calls. Like gulls, they followed cruising ships. Many harpooned whales escape. These were fat years for the killer whales.
When the hunt ended, whales were few. The biomass of fin and sperm whales in the North Pacific had been reduced by 90% or more.
As the hunt wound down in the 1970s, harbor seals began to decline, followed by Stellar sea lions and fur seals. The declines were rapid and surprising. Stellar sea lions are now considered endangered.
Fur seals had been hunted almost to extinction by American and Russian sealers toward the opening of the twentieth century. Their populations had recovered under a treaty that let the Aleut natives of the Pribolov Islands, their breeding grounds, manage them.
The reason for the decline of these marine mammals was unknown. It was first blamed on overfishing, specifically for pollock, which had begun to replace herring (a more oily fish) in the warming Bering Sea. The white flesh of the pollock is used by chains like McDonald’s in its fish sandwiches.
The decline was also thought to be related to the replacement of the (oily) herring by the (less oily) pollock. Oily fish provide more calories, which sea mammals living in cold water need to maintain their layer of insulating fat; and maintain their metabolisms.
Declaring the Stellar’s sea lion endangered brought boatloads of federal funding. When scientists investigated the pollock fishery, it seemed, for the time being, sustainable. There were enough fish for everybody.
Animals known to have been taken by orcas include blue whales (the largest whale), dogs, great white sharks, sea turtles, moose and sea otters. Orcas capture seal pups resting at the edge of the beach, sliding in on a wave to grab them. Great white sharks flee at the sound of orcas.
In the 1990s sea otters started to disappear. By 1998, 90% of the sea otters were gone from a 1000 kilometer stretch of the central Aleutians. Several tens of thousands of otters were gone.
Sea otters are another predatory animal whose munching on herbivores is thought to keep the world green. They live, or once lived, in the kelp forest of the Pacific coast from northern Japan to Baja California.
Sea otters eat animals that live in the kelp. They are fond of abalone and will hunt them until only those hiding in clefts in the rock are left. They pound the abalone off the bottom with stones. This behavior irritates human fishers (sea otters do the same with beds of mussels) but makes room in the ocean for other invertebrates.
Another favorite food is sea urchins. Sea urchins are covered with spines. Sea otters bite into the soft bottom of the large ones and lick out the insides. The fold up the spines of small ones and pop them in their mouths. The favorite food of sea urchins is kelp.
Sea otters have no layer of fat to keep them warm. Their thick coats do that. To maintain their body temperatures in the cold water in which they live they must eat a quarter to a third of their body weight of 30-100 pounds daily. A lot of sea urchins.
When the shipwrecked German naturalist Stellar wintered on Bering Island in 1741 sea otters were abundant and tame. Like the arctic foxes, whose constant scavenging drove the men crazy, they could be killed with clubs.
Since the otters lack blubber, their insulating fur is the densest of any animal and extremely valuable. The men with Stellar sailed away with 1000 skins, abandoning some of his laboriously prepared specimens on the island. The small boat they cobbled together had only so much room.
Undeterred by the remoteness of the Pacific Northwest, Russian hunters were soon slaughtering sea otters for their skins. They enslaved the native Aleuts to help them. In no time, the Russians were joined by the Americans, who hunted further south.
By 1900 otters were gone from most of their former haunts. The Alaskan otters were hunted out by 1800, but recovered by the 1860s, when they were hunted down again. Sea otters were finally protected by the same treaty that protected the fur seals.
Some otters survived and in the 1970s their influence on the health of kelp forests began to be recognized. Alaska is the center of the sea otter population. Where there were sea otters in the Aleutians in the 1970s, there were dense kelp forests and small sea urchins, where there were no otters, the kelp was grazed down to the bottom by herds of enormous urchins.
In the waving strands of kelp live many fish and invertebrates. Following the abundant fish come harbor seals, sea birds and bald eagles, in numbers greater than where the kelp is missing.
Some sea otter reintroduction programs were successful in reestablishing colonies along the Pacific coast south of Alaska. A colony in Big Sur that had escaped the hunters expanded.
Otters didn’t do as well as formerly. Their habitat was degraded by fishing and runoff. They are susceptible to a disease carried by house cats, whose agents are washed with cat feces down storm drains into the sea.
When in the 1990s, the otters along the Aleutians began to disappear, orcas were not one of the usual suspects. Lacking blubber, otters are not a desirable food for orcas. Three or four hungry orcas could have eaten the tens of thousands of vanished otters over 10 years but more likely several pods of orcas were indulging in otters as a side dish to fur seals, Stellar sea lions, fish and the occasional great whale.
The sea otter tale is one of a predator controlling a grazer, even in the simplified invertebrate fauna of the modern kelp forest (simplified by human fishers).
The orcas demonstrate what happens when a main prey animal is removed: the predatory cascade goes awry. The remaining animals in the ocean can’t satisfy the great hunters’ appetites. They will eat everything available and then starve.
Predatory control of grazers is not always perfect. Sea otters reduce populations of some shellfish to where they are not commercially exploitable (but far from extinct). Wolves will reduce failing populations of moose to zero. Insect populations escape from the control of their bird and rodent predators and eat themselves out of house and home, until controlled by the collapse of the vegetation or by microbes (the ultimate predators). The fear of mountain lions keeps remnant populations of bighorn sheep on their Sierra cliffs during the winter (where they fall on icy rocks) rather than face the hungry lions in the lowlands.
But in most of these cases, the ecosystem has been originally messed up by us.
Imagine the drawings…
Tales of the North Pacific
The other name for orcas is ‘killer whale.’ Orcas are the most fearsome predator in the sea.
When attacked by orcas, a pod of great whales formed a daisy pattern, head toward the center, tails out. Great whales are several times the size of orcas. The idea was probably to whack the attacking killer whales with their tails; or to limit their access to whale bodies.
Orcas are intelligent, powerful and not easily discouraged. Their dentition resembles that of Tyrannosaurus rex. Wounded great whales would be nudged back into formation by their companions, trailing their intestines or missing great flaps of skin. The whole pod might be killed.
Dead whales sink to the bottom of the ocean, where they become the base of a novel ecosystem including polychaete worms that live on the fat in whalebone. Before industrial whaling, 850,000 whale carcasses may have littered the seafloor at any one time. Besides supporting their own ecosystem, the carcasses contributed nutrients to the deep sea.
Orcas are opportunistic hunters and also eat seals, sea lions and fish, including herring and salmon. They have a high metabolic demand and need a lot of food. Stellar sea lions, which weigh up to a ton, provide a good meal.
During World War II, fishing in the ocean almost stopped. After the war, life returned to normal. The whale hunt in the North Pacific resumed. About 500,000 great whales were killed there.
During the 20 years of the hunt, orcas learned to respond to the sound of exploding harpoons and whale distress calls. Like gulls, they followed cruising ships. Many harpooned whales escape. These were fat years for the killer whales.
When the hunt ended, whales were few. The biomass of fin and sperm whales in the North Pacific had been reduced by 90% or more.
As the hunt wound down in the 1970s, harbor seals began to decline, followed by Stellar sea lions and fur seals. The declines were rapid and surprising. Stellar sea lions are now considered endangered.
Fur seals had been hunted almost to extinction by American and Russian sealers toward the opening of the twentieth century. Their populations had recovered under a treaty that let the Aleut natives of the Pribolov Islands, their breeding grounds, manage them.
The reason for the decline of these marine mammals was unknown. It was first blamed on overfishing, specifically for pollock, which had begun to replace herring (a more oily fish) in the warming Bering Sea. The white flesh of the pollock is used by chains like McDonald’s in its fish sandwiches.
The decline was also thought to be related to the replacement of the (oily) herring by the (less oily) pollock. Oily fish provide more calories, which sea mammals living in cold water need to maintain their layer of insulating fat; and maintain their metabolisms.
Declaring the Stellar’s sea lion endangered brought boatloads of federal funding. When scientists investigated the pollock fishery, it seemed, for the time being, sustainable. There were enough fish for everybody.
Animals known to have been taken by orcas include blue whales (the largest whale), dogs, great white sharks, sea turtles, moose and sea otters. Orcas capture seal pups resting at the edge of the beach, sliding in on a wave to grab them. Great white sharks flee at the sound of orcas.
In the 1990s sea otters started to disappear. By 1998, 90% of the sea otters were gone from a 1000 kilometer stretch of the central Aleutians. Several tens of thousands of otters were gone.
Sea otters are another predatory animal whose munching on herbivores is thought to keep the world green. They live, or once lived, in the kelp forest of the Pacific coast from northern Japan to Baja California.
Sea otters eat animals that live in the kelp. They are fond of abalone and will hunt them until only those hiding in clefts in the rock are left. They pound the abalone off the bottom with stones. This behavior irritates human fishers (sea otters do the same with beds of mussels) but makes room in the ocean for other invertebrates.
Another favorite food is sea urchins. Sea urchins are covered with spines. Sea otters bite into the soft bottom of the large ones and lick out the insides. The fold up the spines of small ones and pop them in their mouths. The favorite food of sea urchins is kelp.
Sea otters have no layer of fat to keep them warm. Their thick coats do that. To maintain their body temperatures in the cold water in which they live they must eat a quarter to a third of their body weight of 30-100 pounds daily. A lot of sea urchins.
When the shipwrecked German naturalist Stellar wintered on Bering Island in 1741 sea otters were abundant and tame. Like the arctic foxes, whose constant scavenging drove the men crazy, they could be killed with clubs.
Since the otters lack blubber, their insulating fur is the densest of any animal and extremely valuable. The men with Stellar sailed away with 1000 skins, abandoning some of his laboriously prepared specimens on the island. The small boat they cobbled together had only so much room.
Undeterred by the remoteness of the Pacific Northwest, Russian hunters were soon slaughtering sea otters for their skins. They enslaved the native Aleuts to help them. In no time, the Russians were joined by the Americans, who hunted further south.
By 1900 otters were gone from most of their former haunts. The Alaskan otters were hunted out by 1800, but recovered by the 1860s, when they were hunted down again. Sea otters were finally protected by the same treaty that protected the fur seals.
Some otters survived and in the 1970s their influence on the health of kelp forests began to be recognized. Alaska is the center of the sea otter population. Where there were sea otters in the Aleutians in the 1970s, there were dense kelp forests and small sea urchins, where there were no otters, the kelp was grazed down to the bottom by herds of enormous urchins.
In the waving strands of kelp live many fish and invertebrates. Following the abundant fish come harbor seals, sea birds and bald eagles, in numbers greater than where the kelp is missing.
Some sea otter reintroduction programs were successful in reestablishing colonies along the Pacific coast south of Alaska. A colony in Big Sur that had escaped the hunters expanded.
Otters didn’t do as well as formerly. Their habitat was degraded by fishing and runoff. They are susceptible to a disease carried by house cats, whose agents are washed with cat feces down storm drains into the sea.
When in the 1990s, the otters along the Aleutians began to disappear, orcas were not one of the usual suspects. Lacking blubber, otters are not a desirable food for orcas. Three or four hungry orcas could have eaten the tens of thousands of vanished otters over 10 years but more likely several pods of orcas were indulging in otters as a side dish to fur seals, Stellar sea lions, fish and the occasional great whale.
The sea otter tale is one of a predator controlling a grazer, even in the simplified invertebrate fauna of the modern kelp forest (simplified by human fishers).
The orcas demonstrate what happens when a main prey animal is removed: the predatory cascade goes awry. The remaining animals in the ocean can’t satisfy the great hunters’ appetites. They will eat everything available and then starve.
Predatory control of grazers is not always perfect. Sea otters reduce populations of some shellfish to where they are not commercially exploitable (but far from extinct). Wolves will reduce failing populations of moose to zero. Insect populations escape from the control of their bird and rodent predators and eat themselves out of house and home, until controlled by the collapse of the vegetation or by microbes (the ultimate predators). The fear of mountain lions keeps remnant populations of bighorn sheep on their Sierra cliffs during the winter (where they fall on icy rocks) rather than face the hungry lions in the lowlands.
But in most of these cases, the ecosystem has been originally messed up by us.
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