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Coastal Ecosystems


An ecosystem is a collection of organisms and non-living objects in a certain area. Coastal regions are those places where water and land meet. Coastal ecosystems are therefore the collection of organisms that are found on the boundaries of oceans, lakes, rivers, and other forms of liquid water. The intrusion of water into the land creates unique environmental conditions characterized by a large number of habitats. As a result, the species diversity found in most coastal ecosystems is usually quite large. Coastal ecosystems are extremely sensitive to environmental perturbations. Current changes in the climate put pressure on the stability of these ecosystems.

Historical Background and Scientific Foundations

Coastal ecosystems are found in places where reservoirs of water like oceans and lakes meet with land. Because reservoirs of water are found throughout the world, from high latitudes to low latitudes and from high altitudes to sea level, the climatic conditions are extremely variable in coastal ecosystems. In addition, the type of water that occurs in a coastal ecosystem can vary from marine to fresh or even brackish.

Although each coastal ecosystem has its own unique characteristics, coastal ecosystems as a whole do exhibit some shared characteristics. Because they are places with a lot of transition—from terrestrial habitat to aquatic habitat and in many cases from freshwater to marine water—coastal ecosystems are places where many different organisms can find suitable environmental conditions. They are places with some of the highest species diversity on the planet. The large number of species living in coastal regions makes the flow of energy through the feeding food webs in these places extremely complex.

As a result, the effects of perturbations to coastal ecosystems are often hard to predict. Some of these more common coastal ecosystems include estuaries, sandy beaches, rocky intertidal zones, and coral reef ecosystems.

Estuaries are found in places where rivers and streams flow into the ocean. In estuaries, water covers the land for at least part of the year and controls the development of the soil. There are many types of estuaries from small lagoons and inlets to larger bays and sounds. Some of the larger estuaries in the United States are found in the Florida everglades, in the Chesapeake Bay, along the Great Lakes, and on the coast of the Gulf of Mexico.

Estuaries are characterized by constant change. In estuaries that are affected by tides, organisms are repeatedly exposed to periods of flooding and drying. Fish that swim in estuaries must be able to tolerate osmotic fluctuations where freshwater and marine water mix. Plants must adapt to the constant movement of the unstable mud and sand in which their roots are secured.

Because of the inflow of freshwater carrying dissolved nutrients, estuaries are extremely productive places for plants to grow. This abundance of plant life creates many habitats that provide shelter for small animals and serves as an abundant food source. As a result many birds, as well as aquatic invertebrates and fish, use estuaries as places where they give birth to young or lay eggs. The juveniles of many species use estuaries as nursery grounds. The U.S. Fish and Wildlife Service estimates that 75% of the consumed fish and shellfish spend at least some part of their lives in estuaries.

Sandy beaches are places where sand has been deposited along coastlines. The energy from waves and other erosion processes break down rock into small particles called clay, gravel, and silt. Water then washes away the larger and smaller particles leaving only sand-sized pieces of quartz and calcium carbonate along the shore. Beaches are often found on the open water side of islands where wave activity is great. Like estuaries, beaches are places that are subject to constant fluctuations. Wave activity constantly washes away sand and replaces it with new sand. The balance between sand removal and sand deposition is a key factor in the maintenance of a beach habitat.

Beaches provide habitat for many types of organisms. Small microscopic plants called diatoms live between sand grains and provide food for small invertebrates that live along the beach. Burrowing organisms like worms, clams, shrimp, coral, starfish, and crabs make beaches their homes. Various species of birds like terns, gulls, pelicans, and sandpipers prey on the beach invertebrates and fish in shallow waters near beaches.

Rocky intertidal areas are found in places where wave action is great. In the United States, rocky inter-tidal ecosystems are common in the northeast coast between Massachusetts and Maine and along the entire western coast of the United States along the Pacific Ocean. Because rocks naturally form nooks and caves, they provide shelter for large numbers of animals and plants. However, the great power of wave action against the rocky substrate makes staying in place a challenge.

In order to withstand the great energy of water crashing against their habitat, many of the animals and plants that live in rocky intertidal ecosystems have developed adaptations to minimize lift and maximize the ability to hold on to a surface. For example, most of the


ECOSYSTEM: The community of individuals and the physical components of the environment in a certain area.

HABITAT: The natural location of an organism or a population.

SPECIES DIVERSITY: The number of different species living in a particular place.

photosynthetic organisms in rocky intertidal areas are kelp. Many of these species have rootlike structures called holdfasts that cement the kelp to rocks. In addition, kelp are extremely flexible and can bend and move in the wave motion without breaking. Small snails called limpets have developed a low, almost aerodynamic profile that prevents them from being dislodged from surfaces. In addition, limpets create a strong suction on their underside that holds them in place.

Coral reefs occur in tropical waters throughout the world. The reefs are created out of the skeletons of the coral animals. Coral live in symbiosis with a type of algae called zooxanthellae that requires adequate light intensities in order to photosynthesize. So coral growth is restricted to shallow waters where light can penetrate.


Modern computer and communications technology can indirectly contribute to the many forms of pollution—including what some call “e-waste.” In July 2007, researchers from China and Great Britain published data in the journal Environmental Science & Technology that indicated that regions in China where workers recycle electronic parts were found to have high blood levels of flame-retardant chemicals used in the production of computer and other plastic and/or electronic components. The identified chemicals included more than 200 forms of polybrominated diphenyl ethers (PBDEs) such as deca-BDE. PBDEs are classified according to numbers of the bromine atoms they contain.

Prior laboratory studies showed a link between exposure to PBDEs with five to eight bromine atoms and neural damage in developing rat and mice embryos. The new evidence strengthens claims that deca-BDE (containing 10 bromine atoms) causes similar damage. Researchers have not ruled out that breakdown products of deca-BDE are responsible.

Although China is not the only country battling such pollution, in the published study, Chinese workers involved with electronic component recycling or disposal had deca-BDE concentrations in excess of 200 times what was found in European workers doing similar work. Finding of elevated levels in villages remote from the recycling plants indicates that the deca-BDE molecules may have attached to airborne dust particles and that exposures were continuous and renewing.

The largest coral reef in the world is the Great Barrier Reef that stretches along the northeastern coast of Australia.

Like the rocky intertidal ecosystems, coral reefs naturally form nooks and caves that serve as shelter for plants and animals. Coral reefs are among the most species diverse ecosystems in the world. Typical animals that live in coral reef ecosystems include fish, crabs, shrimp, sponges, urchins, sea cucumbers, worms, and numerous types of kelp and seagrasses.

Impacts and Issues

Coastal ecosystems are extremely sensitive to environmental perturbations. Nearly 50% of the human population lives in coastal areas, and human activity exerts significant pressure on coastal ecosystems. One of the major problems that occurs in an impacted coastal ecosystem is that the composition of species living in the ecosystem changes. This often results from a decrease in species diversity when coastal habitat is destroyed for human development. In some cases, changes to the species composition allows for the invasion of non-native or intrusive species that compete with the local populations for limited resources. Changes to the species composition also have the potential to alter the food supply and the balance of competition between species in an ecosystem.

Naturally occurring extreme weather and extreme weather resulting from warming of the global climate contribute to the destruction of many coastal areas. Powerful storms not only damage the physical environment, but they also displace animals and disrupt the natural food web. Storms associated with El Nino are blamed for decreases in fish populations in some coastal regions of the Pacific Ocean. Coral bleaching is also attributed to storm action on some reefs.

Agricultural lands are covered with nitrogenous fertilizers to allow farmers to grow crops more quickly. When rainwater carries these fertilizers into the oceans, they can stimulate algal blooms, also known as red tides. In some places, like the Chesapeake Bay and Long Island Sound, these blooms can be toxic to fish, shellfish, and humans. In other places, like the Gulf of Mexico, the algal blooms can produce a secondary growth of bacteria that deplete the water of oxygen, killing many animals.

Overfishing is another negative environmental impact on coastal ecosystems. When fish populations decline because too many are removed by commercial and recreational fishermen, coastal ecosystems can become unstable. Just as when the species composition is changed because of habitat degradation, overfishing can change the structure of the food web and the balance of competition between species. In addition, it may open up habitat for invasive species.

In order to try to protect coastal ecosystems, several laws and regulations have been enacted in the United States and around the world. For example, the Clean Water Act, the Coastal Zone Conservation Act, the Marine Mammal Protection Act, and the Endangered Species Act have all been used to protect threatened coastal ecosystems.

See Also Algal Blooms; Aquatic Ecosystems; Bays and Estuaries; Benthic Ecosystems; Clean Water Act; Coastal Zones; Coral Reefs and Corals; Ecosystems; El Niño and La Niña; Environmental Protection Agency (EPA); Flood Control and Floodplains; Floods; Freshwater and Freshwater Ecosystems; Global Warming; Greenhouse Effect; Habitat Alteration; Habitat Loss; Hydrologic Cycle; Invasive Species; Island Ecosystems; Lakes; Maps and Atlases; Marine Ecosystems; National Oceanic and Atmospheric Administration (NOAA); Nonpoint-Source Pollution; Ocean Tides; Oceans and Coastlines; Recreational Use and Environmental Destruction; Red Tide; Reef Ecosystems; Runoff; Sea Level Rise; Tsunami Impacts; Water Conservation; Water Pollution; Water Resources; Weather and Climate; Wetlands



Garrison, Tom. Oceanography: An Invitation to Marine Science, 5th ed. Stamford, CT: Thompson/Brooks Cole, 2004.

Web Sites

Environmental Literacy Council. “Coastal Ecosystems.” August 3, 2007. (accessed February 1, 2008).

National Oceanic and Atmospheric Administration. “Coastal Ecosystems.” June 20, 2005. (accessed February 1, 2008).

U.S. Fish and Wildlife Service. “Coastal Program.” September 27, 2006. (accessed February 1, 2008).

Juli Berwald

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Coastal Waters Management

Americans love the seashore and the water. Nearly half of all the construction in the United States since the 1970s has been on the seacoast. By the year 2000, 80 percent of Americans lived an hour's drive or less from the seashore. The National Oceanic and Atmospheric Administration, the primary federal agency responsible for managing the oceans, has projected that by 2010 half of all Americans will be living in coastal counties. Globally almost two-thirds of the world's largest cities are coastal. Sixty percent of people on Earth live within 97 kilometers (60 miles) of the sea.

The reasons why so many humans are coastal dwellers are that coastal areas and oceans have provided a large part of the food that people eat, and have served as the major transportation highways long before there were adequate roads, railroads, or airplanes. The coasts are desirable places to live, offering recreational opportunities such as swimming, boating, fishing, snorkeling, and diving. Coastal areas also are home to marine mammals and other sea life, and can be rich in minerals and other energy sources.

The Need for Coastal Management

This massive habitation at and growing migration to the ocean's edge has brought with it serious side effects. More people have increased the need for infrastructure such as roads, sewers, sewage treatment facilities, bridges, fresh-water sources, and solid waste (garbage) disposal. The increased human activity has strained the ability of nature to replenish and clean itself. Therefore, Americans have gradually established regulations to guide how the seashore is developed and how coastal waters are managed. The three major water resources to examine are (1) the ocean itself, (2) brackish waters, and (3) fresh waters.


The ocean itself is often considered the planet's most vital ecosystem for making life possible. Oceans comprise 97 percent by volume of all the Earth's living space for plants, animals, and humans. The oceans contain vast living and nonliving resources. Reefs, beaches, and other areas are among the ocean environments directly affected by the quality and temperature of the water. Moreover, coastal areas have served as the entry and exit point for what has always been and still is the major mode of commercial transportation: marine shipping.

Ocean temperatures and the flow of currents are vitally important in regulating climate. Many scientists have shown that the rising temperature of the oceans could be contributing to global warming . In addition, warming temperatures may cause polar ice to melt, which would raise the level of the oceans and cause vast flooding in the heavily populated seaside areas.

The ground under oceans, especially near coastal areas, contains enormous oil and gas resources. As easy and ample supplies of these hydrocarbons so necessary for an energy-intensive economy and society such as the United States become scarce, pressure increases to commercialize these suboceanic sources of energy.

Drilling for, pumping, and transporting ocean-based oil and gas resources to onshore refineries without creating serious damage to the water and marine life is a delicate process. Both federal and state laws regulating offshore drilling are constantly being reexamined. The interests of oil companies, electric power-generating plants, consumers who enjoy affordable energy, and environmentalists can sometimes collide.

Brackish Waters.

Rivers and their coastal estuaries supply coastal areas with brackish water. Estuaries are extremely important habitats for a wide variety of animal and plant life. Turtles, fish, crabs, clams, mussels, and other sea life (including coastal mammals) all benefit from healthy estuaries and other coastal wetlands that often are the nurseries for young animals.

Coastal wetlands and marshes also act as sponges and filters, retaining water and slowing or preventing it from rushing uncontrollably downstream, which would produce erosion. These wetlands also slowly filter out sediments and chemical contaminants that otherwise would reach the ocean.

Development as well as contamination from pesticides and herbicides, industrial pollutants, sewage spills, and other sources of pollution are degrading the quality of coastal ecosystems. For example, in the 1990s a huge area deemed the "Dead Zone" was discovered in the Gulf of Mexico at the mouth of the Mississippi River. This area, covering 12,800 square kilometers (5,000 square miles), is almost devoid of any life as a result of runoff containing nitrates (a component of some fertilizers), pesticides, herbicides, and other chemicals from farms and industries upriver. The Dead Zone threatens fish, shrimp, and other commercial seafood, as well as recreational fishing, and is a potential risk to tourism.

Fresh Waters.

Construction and intensive development are threatening fresh groundwater that is especially vulnerable at sea level. Streams, springs, and aquifers easily can be contaminated by runoff from streets and parking lots. Fresh-water issues also include proper management of the Great Lakes, which are considered part of the coastal zones of the United States because of their vast sizes.

One of the most serious fresh-water problems is infiltration by sea (salt) water, often known as salt-water intrusion. Fresh water is in short supply in most areas of the United States, but it is especially precious in coastal zones because of the demand for fresh water for drinking, cooking, bathing, irrigation of crops and lawns, and industrial uses. In April 2001, for example, the state of Florida asked for a waiver of federal law, which would allow the state to pump untreated rainwater into underground aquifers that were being depleted at rates much faster than natural seepage could replace them.

Coastal Zone Management Act

In order to protect the salt-water and fresh-water resources of the American coastal areas described above, numerous federal laws have been enacted. The most important is the Coastal Zone Management Act (CZMA) of 1972. This law resulted from several studies that showed extensive pollution of the nation's estuaries and that recommended action to clean these up. The legislation also was the result of a growing awareness of environmental problems in the United States, and active pressure from environmental groups such as the Sierra Club, the Audubon Society, and groups such as the Friends of the Earth and the Natural Resources Defense Council.

The CZMA provides for a wide range of programs and regulations of which the following are the most significant:

  • Protection of the estuaries and coastal wetlands;
  • Protection of beaches, dunes, bluffs, and rocky shores;
  • Regulation of seaport development; and
  • Redevelopment of urban ports.

Today over 97 percent of the U.S. shoreline is under the CZMA program.

Over the years, the CZMA has been strengthened and expanded. Moreover, additional specialized laws and regulations have been enacted that extend the management of water and coastal resources. The objective of these laws directed at the waters and lands along the seacoast is to lay out a strategic land-use policy that will protect coastal water resources and beaches. The objective of land-use policy is to achieve sustainable development of these coastal resources; that is, using them so that they do not deteriorate but instead have a chance to replenish themselves for future generations.

Clearly, coastal water management is a vitally important process for the future prosperity, continued enjoyment, and effective economic use of oceans, beaches, seashores, and coastal waters.

see also Artificial Recharge; Balancing Diverse Interests; Coastal Ocean; Estuaries; Land-Use Planning; Mineral Resources from the Ocean; National Oceanic and Atmospheric Administration; Ocean Health, Assessing; Petroleum from the Ocean; Pollution of Groundwater; Pollution of Lakes and Streams; Pollution of the Ocean by Plastic and Trash; Ports and Harbors; Transportation.

Steffen W. Schmidt


Barker, Rodney. And the Waters Turned to Blood: The Ultimate Biological Threat. New York: Simon & Schuster, 1997.

Cicin-Sain, Biliana, and Robert W. Knecht The Future of U.S. Ocean Policy: Choices for the New Century. Washington, D.C.: Island Press, 2000.

Dean, Cornelia. Against the Tide. New York: Columbia University Press, 1999.

Internet Resources

Celebrating 30 Years of the Coastal Zone Management Act. Office of Ocean and Coastal Resource Management, National Ocean Service, National Oceanic and Atmospheric Administration. <>.

EPA Action Plan for Beaches and Recreational Waters. U.S. Environmental Protection Agency. <>.

Gulf of Mexico Hypoxia Assessment. National Ocean Service. <>.

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Coastal Ecosystems

An ecosystem is an interacting community of organisms and their non-living physical environment occupying a certain place and time. Coastal ecosystems occupy the margins of the land and the sea. There are many different types: salt marshes, mangrove swamps, sand dunes, seagrass meadows, coral reefs, kelp forests, tidal flats, rocky intertidal , maritime forests, and coastal heathlands. All are heavily influenced by some combination of saltwater, ocean waves, currents, and ocean breezes, though not necessarily all of these.

Components of Coastal Ecosystems

The major interactions of organisms and their environment in coastal ecosystems include energy transfer and cycling of materials. These involve several functional groups of organisms. Plants and algae are the major primary producers, that is, organisms that produce their own food through the process of photosynthesis. They use the energy from the sun and the nutrients washed down to the coast from the surrounding land or brought to the coast by the ocean.

The plants living in constant or periodic contact with ocean water are called halophytes ("salt plants"). They must have special adaptations to be able to thrive because saltwater is toxic to most plants.

Plants and algae are the bases of the coastal food chain. They may be consumed by herbivores , such as insects or geese that feed on salt marsh grasses, snails that consume seaweeds on rocky shores, or fish that graze on tropical seagrass beds. Except for the intertidal marshes and mangrove swamps, the place of insects in coastal ecosystems is minor, their ecological role being replaced by crustaceans (such as crabs, shrimp, lobsters, and beach fleas) and mollusks (snails, clams, mussels, etc.) All these, in turn, may become food for carnivores, such as birds (shorebirds, waterfowl, hawks, etc.) or fish. Many animals living in coastal ecosystems do not feed directly on plants or other animals but feed on detritus , nonliving plant material that may contain a large amount of bacteria and fungi. The bacteria and fungi that colonize particles of detritus act to break down this material to simple chemical compounds that can be recycled.

Coastal versus Terrestrial Ecosystems

Coastal ecosystems differ from terrestrial ones in several significant ways. The ocean contributes to the exchange of materials, bringing nutrients and removing waste products. In terrestrial ecosystems, the exchange of materials between organisms and their environment does not involve this major mediating agent.

The dominant types of producer organisms in terrestrial ecosystems are plants. In coastal ecosystems they include plants, macroalgae (seaweeds), and phytoplankton (unicellular algae). Seaweeds reach their greatest level of diversity and productivity in coastal ecosystems.


An estuary is a semienclosed body of water where freshwater meets the sea. Typically located at the mouth of rivers, estuaries have characteristics of both fresh and marine habitats and serve as a vital ecological link between the two realms. One of the major factors that determines the place where different organisms can live within an estuary is the gradient of salt concentration, that is, the salinity. The upper reaches of the estuary are most influenced by the river and therefore may be almost completely freshwater. As one moves downstream the influence of the sea becomes increasingly dominant. The salinity of the water gradually increases until at the mouth of the estuary, it is similar to that of the surrounding coastal ocean.

There are daily changes in the movement of water and the salinity profile within an estuary. At high tide the estuary is flooded with higher salinity seawater, and at low tide the river water may dominate and the flow is in a downstream direction. Seasonal changes in response to times when greater rainfall and snowmelt wash down the rivers also strongly influence the estuary.

Another characteristic of estuaries is the salt wedge. Since saltwater is more dense than freshwater, the saltwater tends to underlie the river water where the two meet. Thus the surface water of the estuary is usually much fresher than that at the bottom.

These changes in salt concentration within the estuary present a real challenge to plants and animals. They not only have to be salt tolerant, but they also have to be able to tolerate changes in salinity, thus estuaries have their own unique species that differ from those of wholly freshwater or marine habitats. Those few plants that have been able to adapt to life in the estuaries, such as seagrasses, salt marsh plants, and different types of algae, are often extremely productive because having adapted to tolerate the stresses of changing salinities, growing conditions are ideal. Intertidal plants, such as salt marsh grasses and mangrove trees, submerged sea grasses, and algae, are constantly moist with a steady supply of nutrients coming from the sea or the river. As a result, estuaries are among the most productive ecosystems on Earth in terms of the amount of organic matter produced by plants and algae. Estuaries are home to abundant fish, bird, and invertebrate populations, which take advantage of this tremendous plant and algal productivity. Many species of ocean fishes, including a number that are commercially important, spend their juvenile stages in the relative safety of estuaries where the abundance of life sustains their growth to adulthood.

Located at the end points of watersheds, estuaries are often sites where pollutants accumulate and thus the estuaries are very sensitive to human activities. Pollutants generated in the watershed and transported downstream by rivers tend to settle out once they reach estuaries. Thus estuaries serve as barometers of the health of entire watersheds.

Coastal Dunes

Coastal dunes are an unstable, shifting habitat whose very structure is a product of ocean currents, winds, and storms. Currents and waves along the shore deposit sand on the beach, then winds shape the sand into series of small hills that often gradually migrate inland to be constantly replaced at the beachfront by new dunes. Winter storms may completely reshape the landscape, blowing holes in the dunes closest to the ocean and starting the process over.

Sand is unstable, which is why dunes can achieve a maximum stature of only several hundred feet. Dune plants have to be able to tolerate life in shifting sands where water rapidly percolates through the soil and out of the reach of plant roots. Plants that grow on sand dunes must be able to tolerate harsh, desert-like conditions where, as any beachgoer who has walked barefoot on hot sand will attest, there is no shade and daytime temperatures can be extremely hot. Dune plants have a lot in common with desert plants, in which fresh water loss and overheating are real problems. Thus many are succulent or have thick cuticles on their leaves and deeply sunken stomata to prevent water loss. These same kind of adaptations are found in cacti and other desert plants.

The roots of some dune plants play a role in stabilizing sand dunes, helping to shape the nature of this ecosystem. Beach grass is particularly notable in this regard and is often planted deliberately by people to keep dunes in place. The rapidly growing network of roots produced by beach grass penetrates deep into the dune, lending structural support that can keep the dune in place except under the most severe coastal storms. Beach naupaka, a shrub, is valued the same way on Hawaii and other Pacific islands. A dune initially covered by these stabilizing plants is ripe for colonization by other plants, thus the original plant colonizers set the stage for a successional cycle.

see also Aquatic Ecosystems; Halophytes.

Robert Buchsbaum


Bertness, Mark. The Ecology of Atlantic Shorelines. Sunderland, MA: Sinauer Associates, 1999.

Carson, Rachel. The Edge of the Sea. Boston: Houghton-Mifflin, 1979.

Teal, John, and Mildred Teal. Life and Death of the Salt Marsh. Boston: Little Brown, 1969.

Valiela, Ivan. Marine Ecological Processes, 2nd ed. New York: Springer-Verlag, 1995.