The secret life of a pond
In the hidden wonderland of an ordinary pond a population so vast it can barely be comprehended lights ferociously for food and a brief moment in the sun
To most people a pond is merely a mosquitoridden patch of stagnant water that smells of rotting weeds, can't be used for swimming or drinking, and gets in the way of road builders and real-estate developers. But to a naturalist it is a battleground for a host of weird creatures: the scene of a silent, relentless, invisible struggle for life by billions of fighting organisms.
BY FRANKLIN RUSSELL
-L o most people a pond is merely a mosquitoridden patch of stagnant water that smells of rotting weeds, can't be used for swimming or drinking, and gets in the way of road builders and real-estate developers. But to a naturalist it is a battleground for a host of weird creatures: the scene of a silent, relentless, invisible struggle for life by billions of fighting organisms.
In every type of pond—in swampy forest pools, in western sloughs and potholes, in farm ponds created with bulldozers, even in puddles—the struggle goes on endlessly. Perhaps nowhere in Canada has this everlasting aquatic fight for survival been studied by scientists as closely as in an oversized pond two miles from the downtown section of Hamilton, Ont. Although this pond is crossed by a bridge that carries a heavy stream of traffic, it has no name, few visitors and fewer admirers.
Behind its serene and disregarded beauty lies a gripping story of birth and death, of the hunter and the hunted, of charm and hor-
ror. that is typical of ponds everywhere in the world. It is almost a lake, its elongated shallow basin covering about six acres. It is surrounded by steep slopes covered with trees and is flanked by a rock garden maintained by the Royal Botanical Gardens of Hamilton. The gardens maintain the Dundas Marsh (also called Cootes Paradise) south of the pond.
The location of the pond close to Dundas Marsh's six hundred acres of aquatic plants, insects, fishes and wild fowl, is important. The area is one of Canada's largest field laboratories for scientists. It is particularly convenient for scientists at McMaster University and the dramas of life in marsh and pond are exhaustively chronicled in their notebooks.
But the pond remains mysterious. All its secrets aren't known. It may contain the answer to how life began on earth.
While we are still only at the surface of the deep mystery of life in the pond, we do know that at the beginning of any year there arc billions of ruthless enemies in the pond
lying asleep side by side waiting for their chance to stalk, chase, ambush, and kill one another. We know that this one pond's inhabitants outnumber the earth's human beings many billions of times.
We know that as the motorists slither and skid on the bridge in mid-winter January, the creatures of the pond below are sinking toward their lowest ebb of life. Beneath the thick ice there is a repelling silence of seeming death. The ice above looks like an imperfectly translucent roof. The winter sun comes through in a pale and sickly glow. The w reckage of last summer's water plants straggles down from the clutch of the ice. The only signs of underwater life are some slow-moving sunfish, carp, pike, bass, perch, suckers, and perhaps some oversize goldfish which have been washed into the pond from the nearby rock garden.
An occasional muskrat swims underwater toward its ice-bound home in the shallows, and there are vague, mysterious flickerings of life in the shadowcontinued on page 44
I'AINTINC.S BY BRI CK JOHNSON
THE UNDERWATER STRUGGLE TO SURVIVE
No pond is safe from sudden death. In this cycle: a small mouth bass, a green frog, a great diving beetle, a dragonfly nymph, and a tadpole. For the tadpole's prey see the painting at right.
The secret life of a pond continued from page 21
Invisible from the shore, a swarm of life in a dozen brilliant colors spreads through the pond
filled recesses in the basin of the pond. In the clear cold water, plains and hills and valleys can be seen on the pond bed. The piles of a long disused canal jut from the bottom, relics of the days when the pond was a river draining the Dundas Marsh before it was sealed off by two railroad embankments. Above, heavy snow blankets the ice and the gloom of the pond grows. The oxygen is diminishing fast and the lives of many creatures depend on an early thaw. Some of the fish begin to die of starvation and suffocation. It is only when the équinoxial gales begin to blow in March, melting the snow and sending warmer water tumbling beneath the ice into the pond, that the organisms there begin to feel the first stimulus of spring. Tiny primitive plants wake and reproduce. These are the algae and they are the pond’s food. They are among the smallest organisms in the world, each one a single tiny cell of living matter. Forty million of them would fill one cubic inch. Individually they are insignificant. Collectively, they are one of the most important organisms of the pond and of the world. The algae stock rivers, lakes, oceans, in countless billions. Though plants, many of them can swim, lashing the water with tiny hairy propellers. They color lake waters green, and, in some instances, blue. They make the Red Sea red. They are the green slime on stones, the soft green clouds in still water. They can reproduce at fantastic speed and at short notice and are eaten by many animals and plants. The increase of the algae as the water warms seems to be a catalyst to other forms of microscopic life. The peculiar rhizopods, which include amoebae, and
are the lowest animals on the scale of life, protrude long threadlike arms from their protoplasmic bodies to seize passing algae in millions. The arms swiftly withdraw and the algae disappear into the jelly mass where they are visible as they are being digested. As the days lengthen through spring, an underwater observer with microscopic eyes would see life begin to teem. The single-celled animals—called the protozoans—are dividing and redividing constantly. The algae grow children within their bodies, then burst to release them. If protozoans and algae were left unchecked all over the world for one year, they would grow to a mass as large as the earth itself. The observer’s eyes would be caught by a profusion of rich color spreading in every quarter of the pond. There would be greens, crimsons, indigo blues, purples, oranges, and glistening silver filaments branching through the water. In one species of tiny animal or plant there might be a dozen different colors in a hundred different physical forms. These brilliant underwater colors, this swarming of life, are invisible to an observer on the shore. But each spring John Lamoureux, the gardens' conservationist, notices the surface of the pond slowly turning red at this time of the year. The sluggish carp, roused from their winter sloth, are busy at a silty inflow to the pond at the western end, digging for food, fanning the silt so that it rises in fine red clouds and spreads throughout the pond. The shapes of the microscopic animals would be astounding to Lamoureux's eyes, if he could see them, as they spread through the reddening water. Some would look like ducks floating on a lake, some
Some minute underwater animals resemble ducks, some harps, bears, swans, sea serpents, whales
like a rising atomic cloud, some like the barrel of a gun exploding; others would look like miniature whales, like harps, like bears, like swans with long graceful necks. Some would look like sea serpents, others like the design work on an Indian rug. Just as surprisingly, the animals and plants, visible and invisible, would have legs, wings, arms, paddles, oars, wheels, snorkel tubes and even jet propulsion.
There would be strange sounds echoing through the water world. The underwater observer might be surprised to hear the sound of propellers approaching. He would sec a tiny transparent animal, called a rotifer, bearing down on him with two small rapidly rotating wheels mounted along the front border of its body. Situated between the wheels would be a primitive mouth scooping in algae and other single-celled organisms. The “wheels" are actually two discs bearing marginal wreaths of tiny hairs which vibrate so rapidly that they look as though they are revolving.
The rotifer passes on but in a second is seized and eaten by what seems in comparison to be a gigantic ten-legged flea. While one hundred times the size of the rotifer, this creature is one of the smallest visible to the naked eye. It’s one of the crustacean family and is a fully developed cousin of the lobster although it’s less than one twelfth of an inch long.
Its simple coiled gut is visible and its heart, a very thin transparent disc near the stomach, pumps discernibly at one hundred and fifty beats a minute. Even the blood cells are visible as they course round the body.
As early summer blooms the water is warm and the life in it is increasing a million times a day, or a minute, or even a second for. all the scientists know. Lamoureux, making a casual inspection tour, notices the water becoming darker with masses of newly created creatures —insects, animals, plants. A thousand frogs have crawled from their winter hiding places under logs, under mats of leaves, from under the slime and mud at the bottom of the pond. The brightly colored salamanders — lizard-like amphibians—have slid out of their hibernating holes under logs among the trees and have gone down to the pond to breed. The water beetle larvae have pupated into winged creatures, dug themselves out of shallow winter cells in the earth and, paradoxically, have gone flying down into the pond to lead a life that will be spent largely underwater.
Even the plants have become part of the desperate fight for life which is now beginning. They fight for oxygen, sunlight and breathing space. All through the shallows of the pond countless plants are jostling and struggling to reach the surface. Under the bridge the water lilies spread their broad flat leaves as widely as possible; if they shade a competing plant they will kill it.
The duckweeds come hastening after them and surround the lily pads in a thick scummy mass and smother competing seedlings. Bulrushes are springing up around the pond. Sago pondweeds and smartweeds float on or under the surface; the whorled leaves of coontail crowd together underwater. The carnivorous bladderworts, branching out underwater, extend tiny hinged traps which, on one plant, may catch half a million tiny animals an hour.
For the scientists this is a fascinating time. Dr. Norman W. Radforth, McMaster's professor of biology and one of the world’s great authorities on muskeg, studies in the marsh the ecology of water plants—how billions of tiny plants can eventually fill in a pond. John Uamoureux checks the new species of plants he has established in the marsh as part of a project financed by the Toronto Anglers’ and Hunters' Association to find the best conditions to attract waterfowl. McMaster students use the marsh and the pond to win master’s degrees and PhDs by studying the complicated biology of the plants, animals and insects there.
As the vegetation spreads like some wild green fire across the surface, the reddish water itself is being tinged green with the growth of billions of algae. But they aren’t the most numerous organisms. In every drop of the warming water of the pond there are several million bacteria, ever present and all-powerful, so tiny that powerful microscopes can barely reveal the details of their bodies.
As we watch, some of them are attacking the proteins in the water and are pro-
ducing ammonia. Others are attacking the ammonia—which feeds plants—and are changing it to simpler compounds like nitrites. Others are transforming these nitrites into nitrates—which feed the algae. The pond’s store of nitrogen, normally locked up in the living bodies of plants and animals, is thus released for further use. One science student, E. A. Botan, earned his PhD in the marsh with years of study of how bacteria decompose nitrogenous organic matter. When, in 1957, five hundred fish were found dead in the pond after the thaw, he theorized that the decomposing bodies of billions of algae had exhausted the oxygen and had actually suffocated the fish. A mortally injured robin, shot by a youngster’s air rifle, splashes into the water and drowns. In their efforts to eat the dead bird the bacteria begin its putrefaction, a process which maintains the undiminished growth of life in the pond and in the world. Now it is mid-summer. The pond life, as well as fighting desperately for survival. is reaching its breeding peak. The frogs and salamanders are laying strings of gelatinous eggs in the shallows. Dragonflies bomb the surface with eggs. Midges settle on the water in millions
and let clusters of eggs into the water attached to floating rafts. A black wasp, using a homemade tow-rope, buzzes over the pond dragging a paralyzed spider which will be a meal for her young. Young birds fall from their nests overhanging the water and are eaten by pike and bass. The creatures of the pond are laying eggs, giving birth to live young, pupating into adults, dividing their cells, eating one another with a fantastic urgency which foreshadows the approach of fall even though summer is still at its highest peak.
In the swarming surface waters the hideous hydra, a creature straight from science fiction, is breeding by an unearthly process of budding. Its body is a narrow quarter-inch-long cylindrical bag with tentacles and stingers at one end; its other end is fastened to the surface skin of the water, or to a plant. The young hydras are growing like the buds of a plant on their parents’ bodies and they will fight their parents for food, even though they do not yet have stomachs of their own and depend on their parents to do their digesting for them.
Two hundred years ago a Dutch scientist, Tremblcy, wrote with some surprise, “If one of them (the hydra) be cut in two, the fore part which contains the head, mouth and arms, lengthens itself, creeps, and eats on the same day.” Frequently a hydra scores a near miss in its clutch for passing worms or larvae. Its prey slips through its tentacles but its body is riven by the deadly stings. Slowly the shaft-impaled body falls to the bottom. It has fallen from one way of life —the swarming life of the July-warmed surface—to another way of life which
is quite different. Near the body is a bear. It stands stiffly erect and its short legs have sharp claws at the ends. It is a water bear, a rare microscopic animal, and it will soon be dead. A turbellarian worm—one twentieth of an inch of ferocity—glides into view and gulps down the water bear in a puff of mud dust. Nearby, a microscopic worm —Aeolosona—is snuffling like a raccoon along the bottom, grazing on decaying fragments of plants and fine debris which have fallen from the surface. It moves among a small group of tubes which look like chimneys. From these sprout the waving, questing bodies of tubifex worms which duck into the chimneys when danger threatens. Nearby, a mayfly nymph is thrusting its bladelike forefeet into a patch of sand, scooping out a shallow hole into which it digs two large tusks and rapidly disappears from view. A foot away, a horsefly larva collects blood at the rear of its spindleshaped body, then drives one pointed end into the mud. It pumps the blood forward, enlarging the hole. It drives down again, repeats the process and disappears from view. Just above the disturbance it has made in the mud a great diving beetle, nearly two inches long, is swooping down on a dragonfly nymph which has incautiously ducked up from its sandy hiding place. The beetle grabs the nymph with two large hollow mandibles. A tiny pump in the beetle’s body sucks the carcass dry. The beetle returns to the surface to pick up another supply of air under its wing covers. Winner eat all The dragonfly nymphs, some of them nearly two inches long, dull colored, slow and clumsy in their movements, are easily overlooked by their prey. One of the nymphs makes iis home among the duckweed meadows in the shallows where tadpoles and other creatures are plentiful. A young fat-bodied tadpole, about three inches long, comes angling down from the surface, moving steadily closer to the motionless nymph. Suddenly, the nymph pumps a jet of water from its rear end and as it shoots unexpectedly forward, rapidly ejects a hooked apparatus from under its chin. This reaches even farther forward and seizes the wriggling tadpole. The tadpole is too big for the nymph to handle comfortably and both creatures tumble among the weeds, flailing and lashing. Clouds of disturbed mud rise from the scene of battle. In the extremity of their concentration both creatures have ignored the fundamental rules of pond safety—caution, stealth and cunning. The fight ends abruptly when a bulky body shoots into the mud cloud and emerges impartially clutching both creatures in its enormous mouth. It is an eight-inch-long bullfrog. It is a law of the pond, and of all nature, that every creature has an enemy. Later in the summer, the bullfrog dies, caught by a youngster with a net, watched by a gardener working in the rock garden. Its legs may end up on a restaurant table in Toronto. By following the trapped bullfrog to the surface, it is surprising to look again at the pond above the water. The motorists are still grinding back and forth across the bridge in a pattern of life that changes little. But the pond has changed radically. The overhanging trees have the full rich look of late summer. The weeds have half-covered the surface of the water. The rose-pink flowers of marsh smartweed have wilted into seed heads. Submerged plants are gently cast-
ing their seeds on the bottom. A thousand young spiders, airborne on threads of silk, fall to their deaths in the water. The placid surface is continually broken by strange ripplings and splashings. Insects dart and weave across the water.
As the lazy summer days pass easily, the great exodus from the pond gets under way. The same creatures that shrugged off the sleepiness of hibernation and plunged down to the water now must leave their summer home. A dragonfly nymph crawls laboriously up the stem of a bulrush. It bursts from its larval case, reveals a shrunken body with stubby wings. It gulps air, pumps blood into its wing stubs and then flashes away across the pond and disappears.
A great diving beetle humps out of the water onto a tiny beach and begins hollowing a small cell in the damp earth. It will either quickly pupate and a fledged beetle will fly back to the pond, or it will winter in its cell. Millions of mayflies, which hung under their egg rafts, are bursting from the water, their massed nuptial dances a feast for birds, dragonflies and fishes. A hundred types of fly are creeping, crawling, swimming and jumping from their larval existences n the water to their brief airborne lives. The leopard frogs are ranging far through the trees in search of food. The tree frogs are singing in the elms.
For nighthawks, flycatchers, swallows, chickadees, titmice, warblers, sparrows, raccoons, skunks and snakes, the pond during the summer is such an overflowing storehouse of food that they are attracted and held in its vicinity. They, in their turn, play their part in keeping the pond’s population under control.
As larvae emerge from the water, they face sudden death. The skunks dig up the pupating grubs and the raccoons scoop up molluscs and snails in the shallows. The birds help in this balancing process by eating scores of millions of beetles, larvae, pupae, worms, slugs, snails and flies.
Meanwhile, as summer wanes, a brief but fantastic upsurge of life begins under the water again. The microscopic creatures — rhizopods, crustaceans, algae — must build up their numbers to ensure some chance of survival through the bitter winter. They must do this against the combined efforts of the larger creatures to eat them. The urge of life in the pond is to gain strength for the winter, to hunt fattening protein food, to acquire as much resistance as possible to the oncoming crises of cold, lack of oxygen and starvation.
Then, suddenly, the proliferation of life in the pond wanes. The summer is dying too and the water is slowly clearing, losing its rich reddish-green color as the life in it disappears and the silt settles. The exodus from the pond slows, the mists of early summer mornings are replaced by the threatening chill of fall and the trees frame the pond with a border of changing color.
This is the sad time. The gay dragonflies go. leaving their empty larval husks studding the wilting water plants. Insect arid beetle transform to semi-dormant
grubs, waiting patiently under the water or earth for spring. The algae are dying in billions, literally blanketing the bed of the pond with their invisible bodies.
Through the fall, to the accompaniment of impatient honks morning and night from the bridge, the browning vegetation dies. rots, retreats from the water. The creatures, large and small, decrease their metabolism and their appetites so there may be enough food to last the winter. The birds stream overhead for the warmth of the south and the leaves rain down on the passive water.
Toward the end of the year, with the curtain of life nearly drawn, the raccoon and skunks are sleeping soundly in the surrounding woods. The muskrats have built their submerged homes of stalks and leaves and will spend the winter eating them. The frogs are buried in the mud, hidden under logs with the salamanders, sleeping among the leaves.
The ice forms slowly and the familiar silence of seeming death begins again. The long winter months stretch ahead to the pulsing touch of spring and the miracle of the pond.