Endangered Species Handbook

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Aquatic Ecosystems

Benefits of Aquatic Ecosystems

    Water, the basis of life on Earth, is the most precious of all natural resources.  Freshwater and coastal wetlands cover only about 6 percent of the Earth's surface (Lean and Hinrichsen 1992), but produce three-fourths of the world's fish.  Coastal marshes and mangroves play a major role in supporting diversity in the oceans by serving as spawning grounds and nurseries for two-thirds of the saltwater fish and shellfish caught for commercial purposes worldwide (Lean and Hinrichsen 1992).  Wetlands perform a major role in preventing floods by retaining rainwater for slow release during the year and absorbing large amounts of rainfall, runoff and snowmelt. Wetlands also filter out contaminants.  Some communities in the United States now construct wetlands for the purpose of filtering treated sewage water. 
     In a new approach to nature conservation, "Earth's Worth" scientists have begun calculating the dollar values of services performed by nature.  Traditional economics value natural ecosystems only by practical use to human economies in short-term projects, such as real estate development or resource extraction.  For example, how much a wetland is worth is a reflection of tax assessments, which are based on development possibilities and resale values.  A boggy woodland might be appraised at a fairly low rate because it is difficult to develop for housing or other buildings.  For this reason, such habitats are often bought at low prices and destroyed by development.  By contrast, when one considers the ecological services rendered by that aquatic ecosystem, its values are far greater.  It absorbs rainwater, thus preventing floods, provides a nursery area for aquatic wildlife and preserves woodland, which produces oxygen.  The clean water supplied worldwide by natural filtration by marshes and mollusks that filter water was estimated by a group of ecologists to be valued at a minimum of $1.7 trillion (Stevens 1997).  Estuaries and coastal wetlands are nurseries for multi-billion-dollar fisheries and shell fisheries, while they are also valuable in preventing floods.  Yet such wetlands, which are often seen as ideal locations for ports and cities, are routinely filled for development.   Scientists at the University of California at Berkeley calculated that the remaining wetlands in that state, 91 percent of which have been destroyed, are worth $10 billion annually in ecosystem services (Williams 1996).  These ecosystems are usually considered virtually worthless by developers and industry. 
      The beautiful salt marshes of Georgia were under threat a few decades ago when it was discovered that large deposits of phosphate, which commercial interests wanted to mine for use as fertilizer, lay beneath them.  Dr. Eugene Odum, who founded the science of ecology (Odum 1971) and taught at the University of Georgia, was able to prove to the state legislature that the long-term gain from these marshes as nurseries for the valuable shrimp and fish industries far exceeded the short-term profits that would accrue from permanently destroying them by mining.  They received legal protection, an important precedent that recognized the economic value of wetlands. Since then, coastal marshes and other wetlands have attracted millions of tourists who come to see the wildlife and beautiful vistas that these habitats provide.  Such visitors provide more income to the localities involved than extraction of minerals or development, since ecotourism is permanent.
     The reason coastal wetlands and mangroves provide such important nurseries lies in the supply of nutrients they receive from ocean tides and freshwater runoff and rivers.  Delta wetlands are especially rich in these nutrients brought by inland rivers and the tides.  These floods bring nitrates, nitrites and minerals that nourish the vegetation of the wetlands.  This rich habitat was eloquently described in Rachel Carson's The Edge of the Sea (1955).  Among the grasses and reeds, microscopic life and invertebrates feed a great diversity of fish, shrimp, crabs, mammals, reptiles, amphibians and birds.  Bivalves filter the water of aquatic ecosystems, keeping it clear and free of silt and pollutants.  Freshwater marshes, lakes and ponds are breeding areas for crustaceans, mollusks and many vertebrates.  Millions of waterfowl breed in the seasonal sloughs and potholes of North America prairies.  Temporary wetlands, such as the vernal pools or wet season ponds, provide important habitat and breeding areas for frogs, toads, turtles, birds and a rich variety of invertebrates and plants.
     Ancient peatlands and sphagnum bogs can be found on every continent except Antarctica.  These wetlands absorb vast amounts of rainwater and store it year-round.  Their soils tend to be poor in nutrients, but a wide variety of plant life has adapted to these habitats, from mosses and carnivorous plants such as Venus Flytraps and sundews to sedges and exquisite orchids (Rezendes 1996).  
     Swamp forests, often lining rivers, were once extensive in many parts of the world, providing habitat for water birds, mammals, amphibians and other wildlife, while preventing floods. In the United States, such forests once covered the shorelines of the Mississippi River and millions of acres in southern states.  Deposits of soil from flooded rivers provide nutrients and anchoring for trees and plants.  Most of these swamp forests were cut and replaced with agriculture by settlers, and today the region is plagued by floods.
     Migratory aquatic animals need several types of habitats during the year.  Salmon live in the open ocean but spawn and die in freshwater streams and rivers where the next generation hatches.  Cranes and other water birds feed and breed in both salt and freshwater marshes, while using other types of wetlands during migration.  Wetlands and surrounding ecosystems, such as woodlands, interact to provide habitat for many types of wildlife.  When trees bordering wetlands are cut, this can adversely affect the water flow and wildlife living in wetlands.  Some kinds of toads, for example, need both wetlands, such as ponds or lakes where they lay their eggs, and woodlands, where they seek out damp areas to spend most of the year.  Thus, when considering the protection of wetlands, the neighboring environments must also be preserved.
     Salt marshes in the tropics produce great quantities of plant matter.  A reed marsh can produce many times more vegetation than the most fertile grasslands, and some can out-produce an average American wheat field by eightfold (Lean and Hinrichsen 1992). 
     Mangroves line almost 75 percent of the world's tropical shores (Mydans 1996).  They are important in creating conditions for sea grass and coral reefs that are extremely productive ecosystems.  Some 50 species of mangroves and related salt-tolerant trees and shrubs grow in silt-laden coastal waters in tropical latitudes (Ripple 1995).  Mangroves are pioneer species ‒ they create new land. By setting down shoots into the sand or mud, they gradually trap sediment and create soil.  These trees' ability to survive in saltwater allows them to colonize coastal areas where no other type of land tree can live.  Anchored by roots in mud, they absorb oxygen through breathing roots that grow in the open air above the mud, enabling them to survive in soils devoid of oxygen. 
As they grow, they produce new rootlets at successively higher levels above the high tide level (Collins 1990).  Old mangrove trees have huge, above-water roots that form a network of hanging branches, and their trunks grow from the new land created.  Their fallen leaves decay and provide food for fish and shrimp.  The hanging roots become overgrown with an array of algae, sponges, barnacles and mussels, providing shelter for crabs, fish and shrimp, while the upper branches are used by water birds for perching and nesting.  Alligators, crocodiles, manatees, young sea turtles and dolphins find refuge here.  Sediments are held in place by mangroves, preventing clouding and silting of waters farther offshore so that dense mats of sea grass can flourish, providing shelter for fish, crabs and other marine life.  These, in turn, further stabilize the sediment and allow formation of coral beds in clear water further offshore (Luoma 1993).  These three ecosystems--mangroves, sea grass and coral reefs ‒ often exist together, each helping create an environment for the other.  Mangrove forests also buffer coasts from wave action, preventing inland floods.  Bangladesh and other countries that have cut their mangroves have been inundated by disastrous floods, causing great loss of human life and property.
     Oceans are vital in recycling important elements that represent the basic building blocks of living organisms:  carbon, nitrogen, oxygen, phosphorus and sulphur (Daily 1997).  Phytoplankton living in marine environments produces between 33 and 50 percent of the world's oxygen supply while absorbing vast amounts of carbon dioxide (Brown 1994).  Oceans are the most important factor affecting the world's weather patterns.  In turn, they are affected by changes in world temperatures, such as global warming, which create extreme weather from droughts to torrential rainfalls on land.  This vast realm is of vital importance to human survival, yet we are only beginning to learn about its role in preserving life on Earth and its ecology, life forms and ecosystems.  We have found an increasing use for many of its species for medicine and industry, and each year, new, useful compounds are isolated from marine animals and plants.  Although the biological diversity of the ocean is known to be great, research is poorly funded and lags far behind the research on possible life forms on Mars, for example.  The latter project consumes billions of dollars while oceanic creatures are fading into extinction prior even to being named.
     Corals are among the oldest ecosystems, with a residence on Earth of at least 450 million years (Wells and Hanna 1992).  Many reefs have been growing in the same place for millions of years.  Glovers Reef off the Belize coast in the Caribbean rises 6,000 feet from the sea floor and began developing about 20 million years ago (Carter 1997).  Coral reefs occur in a band approximately 30 degrees north and 30 degrees south of the Equator.  Reefs buffer shorelines from ocean waves and in turn prevent erosion, as well as provide quiet waters for sea grasses to grow closer to shore.  These grasses, in turn, are fed on by endangered manatees, sea turtles, fish and shellfish. Species diversity, a key to ecological stability on Earth, is very rich in coral reefs, rivaling that of tropical rainforests (Wells and Hanna 1992).  The diversity, beauty and productivity of coral reefs make them vital ecosystems to conserve, yet they are in extreme danger of disappearing within the next century.  They are the most endangered aquatic ecosystem on Earth.
     Coral reefs cover 360,000 square miles, an area equal to only 0.3 percent of the world's oceans and smaller than British Columbia, yet an estimated 25 percent of the world's marine fish species live here (Chadwick 1999, Zuckoff 2000b). The greatest diversity of coral grows in the Pacific and Indian Oceans, in the Indonesian-Australian region where at least 450 species are found (Doubilet 1999).  Corals have evolved into many forms.  Among the many forms of coral, brain coral is nearly round, while elkhorn grows great branches, and delicate black coral forms thin strands in deep water.   Surrounding most mainland and island masses in these regions, corals also populate shallow areas far offshore, as in the Red Sea.   The world's largest coral reef, Australia's Great Barrier Reef, runs for 1,400 miles along the northeastern coast of that continent.  Up to 3,000 species of plants and animals inhabit a typical Asian coral reef, and more than 1,000 live in Caribbean reefs (Wells and Hanna 1992). They are an oasis of life in warm waters which, in contrast to cold waters, are often poor in nutrients (Doubilet 1999).   
     Some coral has been found to be 800 to 1,000 years old, based on annual growth rings (Wells and Hanna 1992).  Growing very slowly, often less than 1 inch a year, the coral communities are made up of thousands of individual animals.  Hard coral secretes calcium carbonate, a substance that becomes as hard as concrete (Doubilet 1999).  When corals die, another generation grows on their skeletons, creating gigantic underwater structures that can grow for millions of years. 
     About 2,000 species of fish inhabit Southeast Asian reefs, and worldwide, between 4,000 and 5,000 fish species have been found in coral reefs so far (Wells and Hanna 1992), including starfish, sea urchins, sea cucumbers, crustaceans and mollusks in an incredible array of forms and colors, some resembling feathery anemones, others boldly striped to warn of poison. Many squeeze into crevices in the corals, creating a tapestry of textures and hues.  On the Great Barrier Reef alone, some 4,000 species of mollusks are found, including sea slugs, clams, snails and hundreds of species of cones, trumpet shells, cowries and scallops (Wells and Hanna 1992). 
     Coral reefs provide habitat for many endangered species.  Sea turtles find food and shelter here.  The now endangered Hawksbill Turtle (Eretmochelys imbricata) was once commonly seen in coral reefs around the world, feeding on sponges and invertebrates (Wells and Hanna 1992).  Large numbers of sea birds live on the fish produced in coral reefs, and many sea birds nest on islands around the world that are surrounded by coral reefs.  In recent years, coral reef ecotourism has increased.  Tourists now gaze at the reef wonders through glass-bottomed boats and scuba masks, generating a new source of income for many countries.  Tourism accounts for 55 percent of the Gross National Product of the Bahamas and is playing an increasingly important role in other tropical countries.  Tourism is a major incentive for countries to enact strict legislation protecting their marine environments.
     Ocean creatures have proven valuable to medical research, supplying compounds that treat inflammations, asthma, heart disease, tumors, infections, viruses and pain (Chadwick 1999).  Sea animals, such as cone shells, sea snakes and stonefish, contain some of the most toxic poisons in nature. Such compounds are offering non-addictive solutions to the treatment of pain and other medical problems.  Some chemicals in sponges and sea slugs may be useful as insecticides, and coral itself is being investigated for possible use in bone grafts (Chadwick 1999).  Glucosamine, a compound found in the shells of crabs and related animals, has proven to be extremely effective in treating osteoarthritis, controlling both pain and the progression of the disease which destroys cartilage.  It seems to be a building block for cartilage and has been used safely in Europe for generations.  This nutritional supplement has been tested by the Arthritis Foundation in clinical trials, after which it endorsed the use of Glucosamine for osteoarthritis.  Finding new treatments for disease, and substances that can be used as glues obtained from barnacles, are among other ocean-based useful products.  Future discoveries will depend on a healthy ocean that maintains its diversity.
     Likewise, other types of sea and coastal ecosystem tourism have prospered in recent years.  Whale watching has become a $1 billion industry worldwide, according to a 2000 study by the International Fund for Animal Welfare (BG 2000).  At least 87 countries sponsor whale watching trips in 500 communities, allowing 9 million people to view these great mammals in 1998 (BG 2000).  Cruises to Alaska, sport fishing, bird watching, hiking and other activities in non-tropical and freshwater destinations have also become far more important sources of income than resource extraction in many areas.  The effects of the latter industries, including oil pollution, sedimentation from logging and pollution from mining, have decreased their income potential while destroying these precious ecosystems.

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