Wetlands have been called "biological supermarkets." Besides animals that live there permanently, many nonwetland animals, such as opossums, raccoons, and skunks, visit for food and water. Wetlands also provide shelter for mammals such as minks, moose, and muskrats. Wetland conditions make it necessary for the animals that live there permanently to adapt in special ways.
Microorganisms cannot be seen by the human eye. Those found in wetlands include protozoa and bacteria. Protozoa are single-celled animals that can use the Sun's energy to make their own food. Other protozoa are parasites that live on aquatic plants, on damp ground, or inside animals or plants. Bacteria are also single celled, but they cannot make their own food and must obtain it from the environment.
Some protozoa infect mosquitoes with malaria, a disease characterized by chills, fever, and sweating. The mosquitoes then spread the disease to humans. Malaria is found in temperate, subtropical, and tropical regions. Although its spread has been greatly reduced due to the use of pesticides to kill mosquitoes, it is still a problem in parts of Africa and in southeastern Asia.
Invertebrates are animals without a backbone. They range from simple sponges to complex animals such as insects, snails, and crabs.
More than twenty species of insects have adapted to life in the wetland. Some spend their entire lives in the water. Others live in the water while young but leave it when they become adults. Still other insects have gills, just like fish, which enable them to obtain oxygen from the water; and some breathe air. For example, the diving beetle traps air in the hairs on its body or under its wings, which helps it to float. Water spiders create bubbles of air under the water in which they feed and lay eggs. The water spider even hibernates underwater. When the weather gets cold, it constructs an air bubble in deep water and remains there until spring.
Some invertebrates, such as crabs, are able to survive in wetlands by creating watertight holes in the mud or sand and hide there during high tide. Other species, like the African mangrove snail, feed in the mud and sand when the tides are low. When the tides come in the snail climbs the mangrove trees to keep from drowning.
Food: Insects may feed underwater as well as on the surface. For instance the milkweed beetle feeds on insects that can be found on wetland plants, while the diving beetle adds tadpoles and small fish to its diet. The dragonfly larva eats tiny floating organisms and water fleas. The larva of a certain species of caddisfly weaves a silk net under the water in which to catch floating algae.
Some snails are plant feeders, and others eat the eggs and larvae of other invertebrates, or even decaying matter. Crabs are often omnivorous, meaning they eat both plants and animals.
Reproduction: Most invertebrates have a four-part life cycle that increases their ability to survive in wetlands. The first stage is the egg. The second stage is the larva, which may actually be divided into several steps where the insect increases in size, between which there is a shedding of the outer casing or skin. The third stage is the pupal stage, during which the insect lives in yet another protective casing. Finally, the adult emerges. Some wetland dragonflies lay their eggs in the tissues of submerged plants. The insects remain in the water as larvae. As they mature, they move to dry land.
Common invertebrates: Perhaps the most well-known and unpopular wetland invertebrate is the mosquito. Mosquitoes breed in shallow wetland waters. In their larval form, they have tubes in their abdomens that stick out of the water, allowing them to breathe. Even though the larvae are often eaten by frogs, fish, and aquatic insects, many mosquitoes survive. Those that do face being eaten by bats, sprayed with pesticides, and swatted by humans. In spite of these hazardous conditions, mosquitoes in large numbers are responsible for diseases in both humans and animals.
More than 190 species of amphibians can be found in wetlands. Amphibians are vertebrates, which means they have a backbone. There are two kinds of amphibians, those with tails, like salamanders and newts, and those without tails, like toads and frogs.
Amphibians live at least part of their lives in water and are found in primarily freshwater environments. Most are found in warm, moist regions and in a few temperate zones. Because amphibians breathe through their skin, they must usually be close to water so they can stay moist. Only moist skin can absorb oxygen. If they are dry for too long they will die. Their lower layer of skin, called the dermis, also helps them to stay moist by producing mucous, a thick fluid that moistens and protects the body.
Amphibians are cold-blooded animals, which means their body temperatures are about the same temperature as their environment. They need warmth and energy from the Sun in order to be active. As temperatures grow cooler, they slow down and seek shelter so they can be comfortable. In cold or temperate regions, some amphibians hibernate (become inactive) during the winter, hiding in mud or trees. When the weather gets too hot, they go through another period of inactivity called estivation.
Food: In their larval form, amphibians are usually herbivorous (plant eating). Adult amphibians are usually carnivorous (meat eating), feeding on insects, slugs, and worms. Salamanders that live in the water suck their prey into their mouths. Those that live on land have long, sticky tongues that capture food. One of the favorite foods of the frog is the mosquito.
Reproduction: Most frogs, newts, and toads lay lots of tiny eggs. Some are held together in a jelly-like substance. As the female lays her eggs in the water, the male releases sperm, which is carried to the eggs by the water. The female newt, for example, lays from 200 to 400 eggs on the submerged leaves of aquatic plants to await fertilization from the male's sperm.
The most common wetland amphibians are salamanders, frogs, and toads. Frogs and toads can be found all over the world, at all altitudes, and in both fresh and salt water.
Frogs: The frog spends half its life in the water and half out of it. Frogs can lay up to as many as 3,000 eggs, which float beneath the water's surface. Frog eggs hatch into tadpoles (larvae), which swim and breathe through gills, like those on a fish. The larvae feed on small plants and animals in the water. As they mature, they develop legs and lungs, which they will need on land.
Adult frogs feed mainly on insects, especially mosquitoes, but bullfrogs have been known to eat birds and snakes. In the food web, they in turn become meals for herons, raccoons, and other wetland animals.
Frogs are considered "bio-indicators." This means that when many frogs are sick their entire environment may be in trouble. If they disappear from a habitat or if they do not sing, the area maybe polluted and its resources may be dwindling. Frogs are totally absent from some wetlands in the United States, indicating their environment was no longer a healthy place for them to live.
Reptiles are also cold-blooded vertebrates that depend on the environment for warmth. Thousands of species of reptiles live in the temperate and tropical wetlands of the world. They include snakes, lizards, turtles, and crocodiles. Reptiles are more active when the weather and water temperature become warmer. Unlike amphibians, though, reptiles have skin that are waterproof, and therefore they do not dry out. This allows them more freedom to move away from the wet areas.
Because they are so sensitive to their environment, reptiles often go through a period of hibernation in cold weather. Turtles bury themselves in the wetland mud. They barely breathe, and their energy comes from stored body fat. When the weather warms in spring, they come out of hibernation and become active. At the other extreme when the weather becomes very hot and dry, some reptiles go through estivation, another inactive period.
Food: Some wetland reptiles, such as the dice snake are carnivores, eating frogs, small fish, and crayfish. The pond turtle, which inhabits tropical swamps, is an omnivore. When it is young it feeds on insects, crustaceans, mollusks, and tadpoles. As an adult, it eats primarily wetland plants.
Reproduction: The eggs of lizards, alligators, and turtles are either hard or rubbery and do not dry out easily Most are buried in the warm ground, which helps them hatch. In a few species of lizards and snakes the young develop inside the female's body until birth.
The dice snake lays it eggs on land, close to the water. Crocodiles and alligators keep eggs in warm nests, which can be simple holes in the ground or constructions above the ground made from leaves and branches.
Two well-known and dangerous wetland reptiles are the crocodile and the cottonmouth snake.
Crocodile: Crocodiles are found in warmer parts of North and South America, Africa, Australia, and Southeast Asia. They have inhabited the Earth more than 170,000,000 years. Perhaps their long survival has been due in part to the fact that they will eat almost anything or anyone. Crocodiles are responsible for killing at least 10 humans every day in Africa, and a large crocodile will attack even a 4,000-pound (1,816-kilogram) adult rhinoceros given the chance. A crocodile's teeth are rounded and made for holding, not cutting, and it first tries to swallow its prey whole. If the prey is too large, the crocodile pulls it underwater and stashes it where it can decay. When the meat is soft, the crocodile rips off a piece at a time.
The largest crocodile officially recorded was almost 20 feet (6 meters) long, more than 4 feet (1.2 meters) tall when upright, and probably weighed well over a ton (.9 metric ton). A crocodile continues to grow throughout its life, and a very large one may be as much as 200 years old. Their speed out of the water over short distances may be more than 35 miles (56 kilometers) per hour. By contrast, a very fast human may run 25 miles (40 kilometers) per hour over the same distance.
Cottonmouth Snake: The cottonmouth snake inhabits marshes and swamps in the south and southeastern United States. A thick-bodied snake, it spends most of its life in or near water. It is active at night, when it preys on amphibians, fish, snakes, and birds. Its venom is extremely poisonous. Because the venom has the ability to coagulate (solidify or partially solidify) blood, it is extracted and used medically in treating bleeding disorders.
Like amphibians and reptiles, fish are cold-blooded vertebrates. They use fins for swimming and gills for breathing. Two-thirds of all fish used for human food depend on wetlands during some part of their lives. Most commercial game fish breed and raise their young in marshes and estuaries. When the wetlands are not healthy, the fish die, and the commercial and recreational fishing industries suffer.
Food: Some fish eat plants while others depend upon insects, worms, crustaceans, or smaller fish. Some fish may simply grab an insect from the surface of the water or use a more elaborate scheme.
The archerfish, for example, has grooves in the top of its mouth that lets it spit water at its prey. The force of the spit knocks the insect off its perch and into the water, where it is quickly eaten. Archerfish are found in the swamps of southeast Asia.
Reproduction: Fish that breed in wetlands include the flounder, sea trout, striped bass, and carp. Some European carp live in rivers and move to the floodplains during spawning (breeding) season. Others live in the ocean and spawn in mudflats, marshes, or mangrove swamps.
Fish that commonly rely on coastal wetlands are striped bass, sea trout, African lungfish, mudskippers, and flounder. Brackish marshes, which contain both salt and fresh water, support sole, sardines, and common mackerel.
African Lungfish: The African lungfish, which lives in pools surrounded by swampland, has adapted to the wet/dry cycle of wetlands. When there is plenty of water, the fish breathes through its gills. In the dry season, when the water disappears, the fish burrows into the mud and seals itself into a moist cocoon, breathing through special pouches on its underside. It can remain inactive in its cocoon for months or even years.
Mudskipper: Also well adapted to life in the wetland is the mudskipper, found in coastal areas of Bangladesh. This fish usually lives out the water on exposed mud at low tides. Mudskippers breathe air trough membranes at the back of their throats. Enlarged gill chambers hold a lot of water, which helps them remain on land for long periods. They also keep water in their mouths, which they swish over their eyes and skin to help them stay wet. They feed on crabs that are easily caught during low tide.
Many different species of birds live in or near wetlands. These include many varieties of wading birds, waterfowl, shore birds, and perching birds. One of the special adaptations of birds to wetlands is their bill. Some bills, like those of the egret, are shaped like daggers for stabbing prey such as frogs and fish. Other bins, like those of the spoonbill, are designed to root through mud in search of food.
Wetlands provide a variety of hiding places in which birds can build nests and protect their young. Dense underbrush or hollows in the ground are good hiding places, especially when nests are made from reeds, flowers, and grasses, which help them blend. Wood ducks build their nests in hollow cavities in the trees that line the wetland shores.
Food: Plants and small animals in wetlands provide a ready food source for birds. Some birds feed on vegetation, while others are predatory. The pike and marsh harrier, for example, feed on mussels, small fish, or insects and their larvae. Herons and egrets feed on fish, frogs, and snakes.
Reproduction: All birds reproduce by laying eggs. Male birds are brightly colored and sing, both of which attract the attention of females. After mating, female birds lay their eggs in nests made out of many different materials. These nests may be found in a variety of places throughout the wetland area. Different species of birds lay varying numbers of eggs. The tufted duck, for example, lays from six to fourteen eggs, which hatch in a little less than a month. The baby ducks begin to swim within days.
Birds found in wetland environments can be grouped as wading birds, shorebirds, waterfowl, and perching birds.
Wading Birds: Wading birds, such as herons and egrets, have long legs for wading through the shallow water. They have wide feet, long necks, and long bills that are used for nabbing fish, snakes, and other food. Herons and egrets are the most common in freshwater marshes of North America. The great blue heron stands 4 feet (1.2 meters) tall. This is the tallest recorded wading bird in North America.
Shorebirds: Shorebirds feed or nest along the banks of wetlands and prefer shallow water. Their feet are adapted for moving in water, and some have long, widely spread toes to prevent them from sinking in the mud.
The bills of shorebirds are adapted to help them find food. The ruddy turnstone, for example, has a short, flattened, upturned bill, which helps it sift through mud or overturn pebbles and shells. A favorite food of the oystercatcher is the mussel. Each young oystercatcher learns from its parents a technique for opening the mussel shells to get at the meat. Some birds hammer a hole in the shell with their bills, and others prop the shells at an angle so they can pry them open. It may take the birds several years of practice to get the technique just right.
The more than 200 species of shorebirds inhabiting wetlands include sandpipers, which are found in marshes, wet woodlands, and on inland ponds, lakes, and rivers.
Waterfowl: Waterfowl are birds that spend most of the time on water, especially swimming birds such as ducks, geese, and swans. Their legs are closer to the rear of their bodies than those of most birds, which is good for swimming, but awkward for walking. Their bills are designed for grabbing wetland vegetation, such as sedges and grasses, on which they feed.
Perching Birds: Perching birds can also be found living along wetland areas where food and shelter are readily available. They are land birds, with feet designed for perching. Their feet usually have three long toes in the front and one in the back. The barred owl can be commonly found in swamps, while red-winged blackbirds live in cattail marshes, and bogs are home to golden plovers, skylarks, and meadow pipits.
Mammals are warm-blooded vertebrates that are covered with at least some hair and that bear live young. Aquatic mammals, such as muskrats, have waterproof fur that helps them blend into their surroundings and webbed toes for better swimming. Some of these mammals live permanently in wetlands and others, such as raccoons, visit for food, water, and shelter during some part of their lives.
Food: Some aquatic mammals, like the otter, are carnivores, eating rabbits, birds, and fish. Muskrats, however, are omnivores, eating both animals, such as mussels, and plants, such as cattails. Beavers are herbivorous and eat trees, weeds, and other plants.
Reproduction: Mammals give birth to live young that have developed inside the female's body. Some mammals are helpless at birth while others are able to walk and even run immediately. Some are born with fur and with their eyes and ears open. Others, like the muskrat, are born hairless and blind. After about three weeks, however, young muskrats are able to see and swim.
The American beaver is well adapted to the wetland environment. It has webbed feet for powerful swimming and warm, waterproof fur. Other mammals that can be found in wetlands include the mink, the water shrew, and the Australian platypus. The sitatunga, a type of antelope, lives near swamps in central and east Africa. It feeds on emergent wetland plants.
Red Deer: Although peatlands generally do not support many species of animals, the red deer at 4 feet (1.2 meters) tall — the largest animal found in Ireland-lives in the bogs. It can be seen rolling in the peat in order to get rid of parasites and insects.
Muskrat: The muskrat, which resembles a beaver, is a heavy-bodied rodent about 12 inches (30 centimeters) long, not including the long tail. It is a native of North America and common to marshes all over the country. Its hind feet are webbed for swimming and it can often be seen floating on the water's surface. Marsh plants such as sedges, reeds, and the roots of water plants provide most of its diet.
Muskrats build dome-shaped houses in water. They pile up mud, cattails, and other plants until the mound rises above the water's surface. Tunnels lead into the mound in which one or more rooms are hollowed out above the water's surface. Muskrats have been hunted for their fur, which is brown and consists of soft underfur and a dense coat. They are also sold as food, often labeled as "marsh rabbit."
Over half of the endangered or threatened fish and other wildlife in the United States — about 240 species altogether — rely partly on wetlands for food, water, shelter, or a place to reproduce. Over one-third of these live only in wetlands.
In North America, endangered species include the whooping crane and the manatee. The whooping crane lives in coastal swamps and feeds on roots and small reptiles. It has been threatened by hunting, pollution, and dredging (dragging a net along the bottom of a body of water to gather shellfish or plant specimens).
The manatee is a slow-moving, seal-like animal. Manatees live in shallow coastal wetlands in the Caribbean, the Amazon, and Africa. They have become endangered because of overhunting, being caught and strangled in fishing nets, or being killed by boat propellers. Pollution has also affected their habitats and food sources.
In Ireland, the Greenland white-fronted goose, which relies on bogs for feeding and breeding, is endangered because many bogs have been lost.
Source: "Wetland." U·X·L Encyclopedia of Biomes, Vol. 3. U·X·L, Detroit: 2000.