Coastal Ecosystems

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Coastal Ecosystems

Introduction

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

WORDS TO KNOW

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.

IN CONTEXT: ELECTRONICS WASTE

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.

BIBLIOGRAPHY

Books

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. http://www.enviroliteracy.org/subcategory.php/9.html (accessed February 1, 2008).

National Oceanic and Atmospheric Administration. “Coastal Ecosystems.” June 20, 2005. http://www.ncddc.noaa.gov/ecosystems (accessed February 1, 2008).

U.S. Fish and Wildlife Service. “Coastal Program.” September 27, 2006. http://ecos.fws.gov/coastal/viewContent.do?viewPage=home (accessed February 1, 2008).

Juli Berwald

Environmental Science: In Context