The Global 200 : a representation Approach to Conserving the Earth’s Distinctive Ecoregions

Indo-Malayan

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ekong River [144] – Cambodia, China, Laos, Myanmar, Thailand, Vietnam

Geographic Location: Southern Asia

Biodiversity Features: The Mekong, the longest river in Southeast Asia, is enormously rich. The Mekong system alone has a fish fauna totaling approximately 500 species, some of which may migrate hundreds of kilometers between the sea and upstream river reaches as water levels change with the seasons. the most diverse and distinctive large river fauna of tropical asia, with large-scale fish migrations

Selected Species: Among the numerous endemic fish species, one of the most imperiled and extraordinary is the giant Mekong catfish (Pangasianodon gigas), which can grow to over 300 kilograms and may have historically migrated up to 2000 kilometers. Other endemic fish that are under threat are Mae Khong herring (Tenualosa thibaudeaui), thicklip barb (Probarbus labeamajor), and a cave fish (Barbus speleops). The Mekong basin also provides habitat for the endangered Irrawaddy dolphin (Orcaella brevirostris). This ecoregion is a major wintering area for the endangered Siberian crane (Grus leucogeranus) and swan goose (Anser cygnoides), and is home to Sarus crane (Grus antigone).

General Threats: The Mekong River system suffers from a wide range of serious threats. Deforestation along rivers and in uplands has changed runoff patterns and increased sedimentation. The hydrologic regime is also heavily modified by flood control schemes, water diversions, and a vast array of hydropower projects, both big and small. Impoundments are of particular concern because they block the movements of the ecoregion’s numerous migratory fish species. Overfishing is a serious threat, particularly with the increased use of poisons. Urban, industrial, and agricultural pollution are largely untreated and growing problems.

Nearctic

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olorado River [145] – Mexico, United States

Geographic Location: Southwest North America

Biodiversity Features: The extreme conditions of the Colorado River—dropping two miles in elevation from its headwaters to the Gulf of Mexico, with associated high flows—in addition to the basin’s geographic isolation, have led to an exceptional freshwater fauna with morphological adaptations to fast-flowing water. Within this relatively species-poor ecoregion, 14 endemic fish species occur. Unusual warm, large river fauna adapted to high flow regimes

Selected Species: Imperiled endemic fish species include the largest North American minnow, the Colorado squawfish (Ptychocheilus lucius), and the oddly shaped razorback sucker (Xyrauchen texanus). Other fish species found in the turbid fast-flowing waters include flannelmouth sucker (Catostomus latipinnis), Sonora sucker (Catostomus insignis), and desert sucker (Catostomus clarki). Found in some of the smaller tributaries of the Colorado and in springs in this ecoregion, Little Colorado spinedace (Lepidomeda vittata), Kendall Warm Springs dace (Rhinichthys osculus), desert pupfish (Cyprinodon macularius), and springfish (Crenichthys baileyi) are species of special concern due to their restricted ranges. A number of fish are endemic to the Gila drainage, one of the larger tributaries to the Colorado. These include Gila trout (Oncorhynchus gilae), Gila topminnow (Poeciliopsis occidentalis), roundtail chub (Gila robusta), and spikedace (Meda fulgida). Springs in this ecoregion also support several species of endemic snails, including Overton assiminea (Assiminea sp.), Grand Wash springsnail (Fontelicella sp.), Pahranagat pebblesnail (Fluminicola merriami), Moapa pebblesnail (Fluminicola avernalis), and Hot Creek pebblesnail (Fluminicola sp.). Riparian forests provide critical habitat for the endangered willow flycatcher (Empidonax trailii).

General Threats: This unusual ecosystem has been severely damaged by development, dams, irrigation projects and water withdrawals, pollution, altered thermal regimes, and introduced species. Formerly extensive riparian areas associated with perennial and ephemeral streams in this ecoregion are much reduced. Today, only a tiny fraction of intact habitat remains and these remnants face continued threat from livestock grazing and development pressures.

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ower Mississippi River [146] – United States

Geographic Location: Southeastern United States

Biodiversity Features: The ecoregion lies within the lowland Gulf Coastal Plain—a trough between the Appalachians to the east and the Ozark and Ouachita Mountains to the west. This feature, combined with the Mississippi’s high turbidity, has served as a barrier to the dispersal of upland fish species between river systems on either side. Chosen for representation of large river biota in the Nearctic, this ecoregion contains numerous examples of fishes, amphibians, reptiles, and invertebrates that are adapted to the unique conditions found in large river systems. Many of these species persist as glacial relicts or are endemic to the river and its tributaries. OUTSTANDING EXAMPLE OF LARGE RIVER BIOTA IN THE NEARCTIC WITH EXTRAORDINARY SPECIES RICHNESS, INCLUDING MANY RELICTUAL SPECIES AND ENDEMICS

Selected Species: Among the endemic fishes found in tributaries to the mainstem Mississippi are two minnows (Notropis rafinesquei, N. roseipinnis), one catfish (Noturus hildebrandi), one cavefish (Forbesichthys agassizi), two killifish (Fundulus euryzonus, and F. notti), and five darters (Etheostoma chienense, E. pyrrhogaster, E. raneyi, E. rubrum, E. scotti). The ecoregion is better known for its assemblages of large river fish, which include five lamprey species (e.g, Atractosteus spatula and Lepisosteus spp.), Atlantic sturgeon (Acipenser oxyrhynchus), lake sturgeon (A. fulvescens), shovelnose sturgeon (Scaphirhynchus platorynchus), pallid sturgeon (S. albus), the only North American paddlefish (Polyodon spathula), and bowfin (Amia calva). Additionally, numerous marine species have been commonly recorded in the Mississippi’s lower reaches. This ecoregion also supports a large number of unionid mussel and crayfish species (63 and 57 species, respectively). Aquatic reptiles include American alligator (Alligator mississippiensis) plus two endemic turtles: ringed map turtle (Graptemys oculifera) and yellow-blotched map turtle (G. flavimaculata).

General Threats: Much of what was once forest, including bottomland floodplain forest, has now been converted for agriculture, constituting one of the most serious ecological disturbances in the ecoregion. Nonpoint source pollution from agriculture in the form of sedimentation and pesticide contamination, and wastewater discharges from urban areas, pose major threats to the water quality of these rivers. In addition, extensive hydrological modifications have destroyed instream habitat for native fishes and other taxa, such as highly vulnerable native mussels.
Neotropical

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mazon River and Flooded Forests [147] – Brazil, Colombia, Peru

Geographic Location: North-central South America

Biodiversity Features: The varzea and igapó freshwater ecosystems of the Amazon Basin represent some of the worlds most extensive seasonally inundated floodplain forests. Rising waters replenish nutrients in floodplain areas and regenerate floodplain lakes, floating meadows, and other seasonal habitats. Every year, fish, reptiles, and other aquatic animals migrate into these newly available habitats to feed and reproduce, then return to the main channels when the floodwaters recede. Terrestrial animals, such as a number of primate species, also rely on the floodplain forest habitats. Essential for the reproduction of many floodplain trees is the dispersal of their seeds by frugivorous animals, including several fish species. This cycle of flooding, and the annual regeneration that it produces, represent a globally outstanding ecological phenomenon. The entire Amazon basin contains the largest number of freshwater fish species in the world, with an estimated number of over 3000 species. Extraordinary migrations of fish species in and out of flooded forests, including a large degree of frugivory plus extremely diverse freshwater communities

Selected Species: Mammals include pink river dolphin or boto (Inia geoffrensis), grey river dolphin or tucuxi (Sotalia fluviatis), manatee (Trichecus inunguis), and the rare uakari (Cacajao calvus). The largest river turtle in South America, Podocnemis expansa, is also found here, as is the highly endangered black caiman (Melanosuchus niger). A few of the characteristic fishes of this ecoregion are the fruit-eating tambaqui (Colossoma macropomum), arawana (Osteoglossum bicirrhosum), pirarucu (Arapaima gigas), arapaima (Arapaima gigas), dourada catfish (Brachyplatystoma flavicans), one of the world’s few surviving lungfishes, Lepidosiren paradoxa; and tucunaré (Cichla acellaris).

General Threats: Varzea forests are among the most threatened of all forest types in South America due to logging and clearing. Upland areas face even greater logging threats, and there is potential that the entire hydrologic cycle, including annual rainfall, will be drastically altered. Open floodplains are being converted for cattle ranching, which can include introduced water buffalo (Bubalus bubalis). Overfishing, particularly of the largest species, is leading to observed species declines. Mercury pollution from gold mining in smaller streams may have long-term impacts. Population centers are increasing along the main rivers, and untreated sewage is a growing problem. Roads built through the region open up access to previously remote areas and lead to erosion and increased human pressures on resources. Some dams exist already in the basin, and others are planned; these have the potential to block species movements and alter hydrology.

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rinoco River and Flooded Forests [148] – Brazil, Colombia, Venezuela

Geographic Location: Northern South America

Biodiversity Features: The Orinoco’s varzea freshwater ecosystems form one of the world's most extensive areas of seasonally inundated forests. Migrations of fish and terrestrial animal populations into the flooded forests are timed to coincide with the rising waters that flood large areas of the forest floor. Truly a globally outstanding ecological phenomenon, these conditions support a number of endemic species that rely on these processes. More than 1000 fish species are estimated to occur in the entire Orinoco basin, the majority of which may be endemic. Local endemism is high, resulting from the diversity of aquatic habitats, including llanos, high-gradient mountain streams, white-sand flooded forests, and large river environments. GLOBALLY OUTSTANDING ECOLOGICAL PROCESSES AND RARE AND HIGHLY THREATENED HABITAT TYPE. TROPICAL RIVER EXTREMELY RICH IN FRESHWATER FISH SPECIES

Selected Species: Among the numerous fish found here are a number of well-known game and aquarium species: peacock bass or speckled pavon (Cichla temensis), blackspot pirahna (Pygocentrus cariba), cachama (Piaractus brachyponum) and red oscar (Astronotus ocellatus). These waters are also home to the critically endangered Orinoco crocodile (Crocodylus intermedius) and giant river otter (Pteronura brasiliensis), both of which suffer largely from hunting.

General Threats: Conversion of freshwater and wetland habitats for intensive agriculture and livestock grazing threatens the diverse aquatic fauna. Intensive logging and selective exploitation of certain tree species are accelerating deforestation. Large dams and water diversions are planned for several major tributaries, and these would destroy the hydrologic processes that support this ecoregion’s aquatic fauna. Pollution and siltation from mining and deforestation, as well as hunting of sensitive larger vertebrates, pose additional threats.
Palearctic

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angtze River and Lakes [149] – China

Geographic Location: Asia

Biodiversity Features: From an elevation of 4,900 meters (about 16,000 feet), the river—the third longest in the world—descends rapidly as it crosses gorges and runs past limestone hills. The river and the lakes it feeds undergo extreme seasonal changes in size and depth. During the summer rainy season, swollen waters of the Yangtze River flood into the surrounding lake basins; during winter and spring when river levels are low, the lakes drain back into the river. The flora and fauna are adapted to these cycles. Fish mix freely between lakes during flooding and terrestrial mammals swim to seek high ground. Poyang Lake, one of the largest lakes, serves as winter habitat for numerous waterfowl species. THE ECOREGION CONTAINS NUMEROUS FISH, MAMMAL, AND PLANT SPECIES ADAPTED TO THE DYNAMIC WATER REGIME OF THESE LAKES AND RIVERS; A LARGE NUMBER OF THE WATERBIRDS ARE DEPENDENT ON THE LAKES IN WINTER.

Selected Species: Two species of aquatic mammal, Chinese river dolphin (Lipotes vexillifer) and Yangtze finless porpoise (Neophocaena phocaenoides), are of special concern. The river dolphin, restricted to freshwater habitats of the Yangtze and its adjoining lakes, is considered the most endangered dolphin species in the world. The finless porpoise is also imperiled but is a more widespread marine species, visiting river mouths throughout the Indian Ocean and the Western Pacific. The dolphins are threatened by pollution and habitat destruction, and by their interaction with fishing operations. They are threatened by pollution and habitat destruction, and by their interaction with fishing and boating operations. Among the numerous threatened fish species are Yangtze sturgeon (Acipenser dabryanus), Chinese sturgeon (A. sinensis), and Chinese swordfish (Psephurus gladius). Other vertebrates include the largest salamander in the world, Audrias davidianus, red-crowned crane (Grus japonensis), and the highly endangered Yangtze alligator (Alligator sinensis).

General Threats: Fish farming, deforestation, cultivation of surrounding land for farming and grazing, pollution, oil drilling, industrialization, urbanization, and introduced diseases from domestic waterfowl pose widespread threats to this ecoregion. The most pressing and severe threat is construction of dams and dykes on the Yangtze and its tributaries, which alter the natural flow regime, block migratory routes, and sever the connection between the rivers and their floodplain habitats. The most notorious of these projects is the Three Gorges Dam, which when complete will be 185 meters high and will store 40x10⁹ m³ of water. Interbasin water transfers also threaten to upset water levels and create opportunities for the introduction of species.

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