Animal life in swamps and marshes

Swamps and marshes differ from ponds and lakes in two primary ways: they are shallower, with seasonally fluctuating water levels, and they have little or no open water, being dominated by emergent vegetation. The predominant vegetation in marshes comprises grasses, sedges, and rushes. Marshes tend to have shallower water than swamps and are more apt to dry out completely during the drier part of the year. The predominant vegetation in swamps comprises trees and shrubs. Not only is the water generally deeper in swamps, but it is often more permanent, although water levels still tend to fluctuate seasonally.

Although swamps and marshes are usually thought of as freshwater wetlands, saline swamps, and marshes also exist, either in desert-like environments where evaporation rates are high or in coastal areas. Coastal swamps and marshes tend to fluctuate in depth and salinity as the tides change. Coastal swamps are often referred to as mangrove swamps or mangals. Coastal marshes are often called estuaries. Most of the following information will focus on freshwater swamps and marshes.

Insects and Other Invertebrates

The smallest invertebrates are primary consumers at the base of the consumer food chain in wetlands. When algae is abundant in the water, primary consumers also proliferate. One of the most common is the water flea (Daphnia), which is barely visible to the naked eye. When viewed under the microscope, the reason for its name becomes apparent, as it looks remarkably like a flea. Many species of water fleas exist, varying greatly in size, head shape, swimming appendages, and other traits. Water fleas and other small invertebrates are preyed upon by larger invertebrates, tadpoles, and small fish.

The bulk of the invertebrates are insects in either their adult or juvenile forms. Many flying insects, such as mosquitoes and dragonflies, spend their early life in the water. Dragonfly nymphs are especially vicious predators, preying upon almost anything small enough for them to grab in their strong jaws, including small fish. Adult dragonflies and their cousins, the damselflies, are commonly seen flying around marshes and swamps. Other insects, such as water striders, backswimmers, water boatmen, and diving beetles, are also abundant in the still waters, making their entire lives in or on the water. Even a few spiders (which are arachnids, not insects) have adapted to the aquatic way of life, able to stay underwater for extended periods by trapping bubbles of air next to their bodies.

Another common invertebrate group is the shellfish. Freshwater clams live buried in the sediment and filter food out of the water, while mussels can form dense assemblages on rocks and other debris in the water. A few clams and mussels from tropical and semitropical parts of the world have inadvertently been introduced to some temperate wetlands with devastating effects. Snails can also be found in many marshes and swamps, where they feed on algae growing on rocks and on the submerged stems and leaves of plants.

Fish, Reptiles, and Amphibians

The occurrence of fish is most often associated with water depth. In shallow, seasonal marshes or swamps, fish are often absent. In deeper marshes and swamps, they can be abundant and provide food for other animals, especially birds. These fish can range from the unique, bottom-dwelling catfish to more active fish, such as perch and bass. Many smaller, less noticeable species also occur, some of which are near extinction due to the loss of unique habitat. In the swampy area of the Florida Everglades, panthers, snail species, American alligators, and several types of birds face the loss of swamp habitat, affecting their ecosystems' delicate balance. Over thirty-five species that inhabit the Florida Everglades are candidates or are listed as endangered under the Endangered Species Act of 1973.

The most common reptile in marshes and swamps is the turtle. Most turtles are predators, although some feed primarily on plant material. The snapping turtle has a reputation for eating almost anything, plant or animal. Although turtles can be observed swimming in the water, they are most often seen sunning themselves on warm rocks just in reach of the water, where they can quickly escape from potential predators. Among the more dangerous reptiles of swamps and marshes are the alligators, crocodiles, and caimans. These are exclusively predatory, and although generally not very aggressive toward humans, they do attack on occasion. Snakes are also predators. Garter snakes grab their prey using their mouth and gradually swallow it. The cottonmouth is a poisonous viper that injects venom into its prey to incapacitate it before swallowing. Although snakes are more often thought of as terrestrial, they are expert swimmers.

Amphibians include salamanders and frogs, both of which spend their early life entirely in the water, where their eggs are laid. Frog eggs develop into tadpoles with tails and no legs; as they develop, the tail disappears, and the legs start to grow. Salamander larvae have legs from the beginning, and they never lose their tail. When young, frogs and salamanders feed mostly on algae and small invertebrates in the water. As adults, frogs typically eat insects, and salamanders eat a variety of invertebrates, including worms and grubs.

Birds and Mammals

Near the top of the food chain, a large variety of birds either live in swamps and marshes or come there to hunt. Common residents include ducks, geese, herons, and egrets. In these shallower waters, “puddling” ducks predominate, characterized by feeding behavior where they reach for vegetation on the bottom with only their rumps protruding from the surface. Herons and egrets frequently wade slowly and deliberately, searching for frogs or fish to quickly grab and eat. Many songbirds take advantage of the habitat; some, such as the marsh wren, even make their nests in the bullrushes near the margin of the water. Predatory birds, such as hawks, eagles, falcons, owls, and osprey, come to prey on other birds, snakes, fish, or smaller mammals.

Various mammals also take advantage of the aquatic bounty. Mink and otters freely swim in search of fish. Others, like raccoons, tend to hunt for food on the margins. Rodents of various kinds eat greens and seeds, abundant because of the water supply, and foxes and coyotes hunt the rodents. Other mammals, such as deer, come for the water and sometimes eat the tender vegetation as well. Beaver may even be responsible for developing a new swamp or marsh by building a dam across a creek.

Human Destruction of Swamps and Marshes

Despite the great richness of life present in swamps and marshes, human society, in general, views these ecosystems as unsightly and useless. Consequently, many wetlands have been drained to make way for farmland, roads, or other developments. Because so much has been lost, environmental laws in the United States now prohibit further wetland destruction unless new wetlands are formed to replace those that are lost. These laws recognize the ecological importance of swamps and marshes.

The primary productivity of swamps and marshes is only surpassed by tropical rainforests, algal beds, and reefs. Shallow water and ample light allow rich plant and algae growth, which supports the wide variety of organisms that take refuge in wetlands, including fish, animals, insects, and plants. Swamps and marshes are especially important to migrating waterfowl, who need them for their abundant food supplies. As wetlands are lost, waterfowl populations decrease. Their high productivity also makes them important in absorbing excess carbon dioxide from the atmosphere and in filtering pollution and sediment from runoff, which keeps other bodies of water healthy, like beaches and rivers. They also protect nearby areas from flooding and shorelines from eroding. However, as humans continue to urbanize wetlands and cause pollution, their ability to protect the Earth and prevent climate change decreases.

Principal Terms

Consumer Food Chain: a simplified description of the grazing and predator/prey relationships within an ecosystem

Emergent Vegetation: aquatic vegetation that grows tall enough to be visible above the water

Invertebrate: a simple animal lacking a backbone

Primary Consumer: an organism that gets its nourishment from eating primary producers, which are mostly green plants and algae

Primary Productivity: production of biomass mainly by green plants

Bibliography

Bransilver, Connie, et al. Florida’s Unsung Wilderness: The Swamps. Englewood, Westcliffe, 2000.

Rutledge, Kim, et al. "Swamp." National Geographic Society, 19 Oct. 2023, education.nationalgeographic.org/resource/swamp. Accessed 10 Sept. 2024.

Scheffer, M. Ecology of Shallow Lakes. Boca Raton, Chapman and Hall, 1998.

Streever, Bill. Bringing Back the Wetlands. Darlinghurst, Sainty & Associates, 1999.

“Threatened + Endangered Species – South Florida Aquatic Environments.” Florida Museum, 3 Oct. 2018, www.floridamuseum.ufl.edu/southflorida/habitats/freshwater-marshes/endangered-species. Accessed 6 July 2023.

Tiner, Ralph W. In Search of Swampland: A Wetland Sourcebook and Field Guide. 2nd ed. New Brunswick, Rutgers University Press, 2005.

Vileisis, Ann. Discovering the Unknown Landscape: A History of America’s Wetlands. Washington, D.C., Island Press, 1999.

Wetzel, Robert G. Wetzel’s Limnology Lake and River Ecosystems. 4th ed., San Diego, Academic Press, 2024.