EarthTrends: Featured Topic Title: Freshwater Biodiversity in Crisis Author(s: Carmen Revenga and Greg Mock Source Adapted from PAGE: Freshwater Systems 2000 and world Resources 1998-99 Date written: October 2000 In a world in which it seems that (Kristensen and Hansen 1994: 90) wetlands in 1999-about 9 percent nearly every natural ecosystem is Due to their limited area of the worlds total fish catch(not under stress. freshwater freshwater ecosystems only contain including aquaculture)(FAO 2000: 6) ecosvstems-the diverse about 2. 4 percent of all Earth's plant Rivers and lakes are also crucial as communities of species found in and animal species(Reaka-Kudla ansportation and shipping routes, as lakes, rivers, and wetlands-may be 1997: 90). On a hectare-for-hectare power sources, and, unfortunately, as the most endangered of all basis, however, they are richer in waste sinks. All of these human uses Freshwater ecosystems have lost a species than the more extensive take their toll on freshwate greater proportion of their species terrestrial and marine ecosystems. ecosystems. and habitat than ecosystems on land (See Figure 1. To date, scientists or in the oceans, and they face have discovered some 44,000 aquatic Why is Freshwater Biodiversity creasing threats from dam pecies in freshwater ecosystems, but Endangered? erextraction, pollution, and this probably only represents a overfishing portion of all freshwater spec Threats to species in freshwater ( Reaka-Kudla 1997: 90). In the last ecosystems are widespread. Habitat How Crucial Are Freshwater 18 years, scientists have described degradation, physical alteration from Ecosystems: about 309 new freshwater species dams and canals, water withdrawals, each year(Nelson 1976, 1984, 1994). overharvesting of fish and shellfish, Freshwater systems occupy only 0.8 In addition to being biologically rich, pollution, and the introduction of rcent of Earth's surface(McAllister freshwater ecosystems play a vital nonnative species have all increased et al. 1997 5), but they are rich in role in the lives of many people, in scale and impact in the last species and vital as habitat. An providing a source of drinking and century.(See Figure 2: Alteration of estimated 12 percent of all animal irrigation water, food, recreation, and Freshwater Systems Worldwide. )As a species live in fresh water employment. Indeed, the majority of consequence, the capacity of (Abramovitz 1996: 7). Many others, the world's population lives near and freshwater ecosystems to support including humans, depend on fresh depends on freshwater environments, biodiversity-the natural variety, water for their survival. In Europe with most inland cities located next abundance and distribution of for example, 25 percent of birds and to a waterway (Moyle and Leidy pecies across the aquatic 11 percent of mammals use 1992: 130). The world's fishe environment-is highly degraded at a freshwater wetlands as their main harvested some 8.2 million metric global level breeding and feeding areas tons of fish from lakes rivers and In a recent study of freshwater h, Harrison and Stiassny(1999) Teeming with Life found that while many factors can Figure 1: Species Richness by Ecosystem, 1997 simultaneously contribute to Percent of extinctions. habitat alteration and th introduction of nonnative spec Percent of Species* were the major causes driving the Relative extinction of fish species. Building Total Ecosystem Species Habitat Contains Richness** dams and water diversions channelizing riverbeds, and draining Freshwater wetlands are typical habitat 0.28 0.775 2.7 ns. The study reported that habitat alteration contributed to 71 percent of extinctions; nonnative Sum does not add to 100 percent because 5.3 percent of known pecies(which can compete with or ymbiotic species are excluded feed on native species)contributed to **Calculated as the ratio between the percent of known species and the 54 percent; overfishing contributed of ar by th t;and pollution to 26 Source: McAllister et al. 1997: 29 Stiassny1999298299) OEarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes
©EarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes. EarthTrends: Featured Topic Title: Freshwater Biodiversity in Crisis Author(s): Carmen Revenga and Greg Mock Source: Adapted from PAGE: Freshwater Systems 2000 and World Resources 1998-99 Date written: October 2000 In a world in which it seems that nearly every natural ecosystem is under stress, freshwater ecosystems—the diverse communities of species found in lakes, rivers, and wetlands—may be the most endangered of all. Freshwater ecosystems have lost a greater proportion of their species and habitat than ecosystems on land or in the oceans, and they face increasing threats from dams, overextraction, pollution, and overfishing. How Crucial Are Freshwater Ecosystems? Freshwater systems occupy only 0.8 percent of Earth’s surface (McAllister et al. 1997:5), but they are rich in species and vital as habitat. An estimated 12 percent of all animal species live in fresh water (Abramovitz 1996:7). Many others, including humans, depend on fresh water for their survival. In Europe, for example, 25 percent of birds and 11 percent of mammals use freshwater wetlands as their main breeding and feeding areas (Kristensen and Hansen 1994:90). Due to their limited area, freshwater ecosystems only contain about 2.4 percent of all Earth’s plant and animal species (Reaka-Kudla 1997:90). On a hectare-for-hectare basis, however, they are richer in species than the more extensive terrestrial and marine ecosystems. (See Figure 1.) To date, scientists have discovered some 44,000 aquatic species in freshwater ecosystems, but this probably only represents a portion of all freshwater species (Reaka-Kudla 1997:90). In the last 18 years, scientists have described about 309 new freshwater species each year (Nelson 1976, 1984, 1994). In addition to being biologically rich, freshwater ecosystems play a vital role in the lives of many people, providing a source of drinking and irrigation water, food, recreation, and employment. Indeed, the majority of the world’s population lives near and depends on freshwater environments, with most inland cities located next to a waterway (Moyle and Leidy 1992:130). The world’s fishers harvested some 8.2 million metric tons of fish from lakes, rivers, and wetlands in 1999—about 9 percent of the world’s total fish catch (not including aquaculture) (FAO 2000:6). Rivers and lakes are also crucial as transportation and shipping routes, as power sources, and, unfortunately, as waste sinks. All of these human uses take their toll on freshwater ecosystems. Why is Freshwater Biodiversity Endangered? Threats to species in freshwater ecosystems are widespread. Habitat degradation, physical alteration from dams and canals, water withdrawals, overharvesting of fish and shellfish, pollution, and the introduction of nonnative species have all increased in scale and impact in the last century. (See Figure 2: Alteration of Freshwater Systems Worldwide.) As a consequence, the capacity of freshwater ecosystems to support biodiversity—the natural variety, abundance, and distribution of species across the aquatic environment—is highly degraded at a global level. In a recent study of freshwater fish, Harrison and Stiassny (1999) found that while many factors can simultaneously contribute to extinctions, habitat alteration and the introduction of nonnative species were the major causes driving the extinction of fish species. Building dams and water diversions, channelizing riverbeds, and draining wetlands are typical habitat alterations. The study reported that habitat alteration contributed to 71 percent of extinctions; nonnative species (which can compete with or feed on native species) contributed to 54 percent; overfishing contributed to 29 percent; and pollution to 26 percent of extinctions (Harrison and Stiassny 1999:298–299). Teeming with Life Figure 1: Species Richness by Ecosystem, 1997 Ecosystem Percent of Earth’s Total Habitat Percent of Known Species* Each Ecosystem Contains Relative Species Richness** Freshwater 0.008 0.024 3 Terrestrial 0.284 0.775 2.7 Marine 0.708 0.147 0.2 *Sum does not add to 100 percent because 5.3 percent of known symbiotic species are excluded. **Calculated as the ratio between the percent of known species and the percent of area occupied by the ecosystem. Source: McAllister et al. 1997:29
consequent changes not only in the igure 2: Alteration of Freshwater Systems Worldwide temperature and chemistry of river water, but in the living functions of he riverine ecosystem. Water falls Alteration Pre-190019001950-6019851996-98 rapids, riparian vegetation, and , wetlands are some of the habitats Navigation 3,125km8,750km that disappear when dams impor riversDynesius and Nilsson 8,750km21,250km 63,125km 994:759). These habitats are Large Reservoirs* essential feeding and breeding area Number 2,836 for many aquatic and terrestrial Volume(km) ,68658796,385 pecies, and also help to remove 533 pollutants and maintain water quality Large Dams(>15m 5,749 41,413 How Threatened Are Fres water Installed Hydro Capacity <290,000542,000~660,000 Hydro Capacity Unde of freshwater biodiversity s the tion One measure of the actual condit Construction(MW) 126,000 extent to which species are 578 200~3,800 threatened with extinction. Globally Water Withdrawals km /year km/year km/year km/year scientists estimate that more than 20 nt of the worlds 10.00 Wetlands Drainage** ecorded freshwater fish species have become extinct. threatened *Large reservoirs are those with a total volume of 0. 1 km or more. This is only a endangered in recent decades Moyle subset of the world's reservoirs nd Leidy 1992: 140). This number, **Includes available information for the drainage of natural bogs and low-lying however, may well be an grasslands as well as disposal of excess water from irrigated fields. There is no underestimate Brautigam 1999: 4) comprehensive data for wetland loss for the world According to the 1996 IUCN Red List of t Sources: Based on Naiman et al. 1995, as adapted from Lvovich and white 1990 of fish are classified as threatened. of Data on dams are from ICOLD 1998. Reservoir data are from Avakyan and which 84 percent are freshwater Iakovleva 1998. Hydro capacity data are from IJHD 1998 and L'vovich and White pecies(IUCN 1996:intro p 37; 1990. Water withdrawal data are from shiklomakov 1997 McAllister et al. 1997: 38). For some countries and regions more detailed Of the many ways in which under construction around the world, information is available. In South humans alter freshwater ecosystems, mostly in developing countries(HD Africa, 63 percent of freshwater fish dams are probably the most 1998:12-14 are threatened or e widespread and significant in their Dams provide unquestionable Europe, 42 percent; and in Iran, 22 impact. Today, the world's rivers are benefits-from water supply to percent Moyle and Leidy 1992: 138) dotted with more than 45,000 large power generation-but they disrupt Unfortunately, global data on the dams-dams higher than 15 meters ne hydrological cycle profoundly status of the range of different or impounding more than three suppressing natural flood cycles, freshwater species-plant and million cubic meters of water (WCD disconnecting rivers from their 2000:8, 11). Most of these dams were wetlands and floodplains, disrupting difficult to quantify the orca ery limal-is sparse, making it v built in the last 50 years (ICOLD fish migrations, and altering the ion of the worlds freshwater 1998:13) ion of sediments downstream Dam building has slowed in many For example, the World Commission biodiversity. Where we do have ommission however trends look bleak. In the countries, particularly in the n Dams found that more than 60 United States, which has developed world. In the United percent of the large dams it surveyed comparatively detailed data on States, for example, since 1998, more report significant problems with freshwater species, 37 percent of dams have been decommissioned disrupted fish migrations (WCD freshwater fish species, 67 percent of than built(WCD 2000: 10). However, 2000: 82) dam construction is still robust in Rivers with multiple dams can mussels, 51 percent of crayfish, and other countries. As of 1998. there 40 percent of amphibians are become little more than chains of hreatened or have become extinct were 349 dams over 60 meters high connected reservoirs, with (Master et al. 1998: 6). Indeed, studies OEarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes
©EarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes. 2 Of the many ways in which humans alter freshwater ecosystems, dams are probably the most widespread and significant in their impact. Today, the world’s rivers are dotted with more than 45,000 large dams—dams higher than 15 meters or impounding more than three million cubic meters of water (WCD 2000:8,11). Most of these dams were built in the last 50 years (ICOLD 1998:13). Dam building has slowed in many countries, particularly in the developed world. In the United States, for example, since 1998, more dams have been decommissioned than built (WCD 2000:10). However, dam construction is still robust in other countries. As of 1998, there were 349 dams over 60 meters high under construction around the world, mostly in developing countries (IJHD 1998:12-14). Dams provide unquestionable benefits—from water supply to power generation—but they disrupt the hydrological cycle profoundly, suppressing natural flood cycles, disconnecting rivers from their wetlands and floodplains, disrupting fish migrations, and altering the deposition of sediments downstream. For example, the World Commission on Dams found that more than 60 percent of the large dams it surveyed report significant problems with disrupted fish migrations (WCD 2000:82). Rivers with multiple dams can become little more than chains of connected reservoirs, with consequent changes not only in the temperature and chemistry of river water, but in the living functions of the riverine ecosystem. Waterfalls, rapids, riparian vegetation, and wetlands are some of the habitats that disappear when dams impound rivers (Dynesius and Nilsson 1994:759). These habitats are essential feeding and breeding areas for many aquatic and terrestrial species, and also help to remove pollutants and maintain water quality. How Threatened Are Freshwater Species? One measure of the actual condition of freshwater biodiversity is the extent to which species are threatened with extinction. Globally, scientists estimate that more than 20 percent of the world's 10,000 recorded freshwater fish species have become extinct, threatened, or endangered in recent decades (Moyle and Leidy 1992:140). This number, however, may well be an underestimate (Bräutigam 1999:4). According to the 1996 IUCN Red List of Threatened Animals, 734 species of fish are classified as threatened, of which 84 percent are freshwater species (IUCN 1996:intro p. 37; McAllister et al. 1997:38). For some countries and regions more detailed information is available. In South Africa, 63 percent of freshwater fish are threatened or endangered; in Europe, 42 percent; and in Iran, 22 percent (Moyle and Leidy 1992:138). Unfortunately, global data on the status of the range of different freshwater species—plant and animal—is sparse, making it very difficult to quantify the overall condition of the world’s freshwater biodiversity. Where we do have data, however, trends look bleak. In the United States, which has comparatively detailed data on freshwater species, 37 percent of freshwater fish species, 67 percent of mussels, 51 percent of crayfish, and 40 percent of amphibians are threatened or have become extinct (Master et al.1998:6). Indeed, studies Endangering Freshwater Biodiversity Figure 2: Alteration of Freshwater Systems Worldwide Pre-1900 1900 1950-60 1985 1996-98 3,125 km 8,750 km - >500,000 km - Canals 8,750 km 21,250 km - 63,125 km - Large Reservoirs* Number 41 581 1,105 2,768 2,836 Volume (km3 ) 14 533 1,686 5,879 6,385 - - 5,749 - 41,413 - - 15m high)
indicate that freshwater species are being lost at an"ever-accelerating Figure 3: Species Richness and Endemism by River Basin, 1998 rate"(Moyle and Leidy 1992: 16) Based on recent extinction rates. an estimated 3.7 percent of freshwater animal species will be lost in North America each decade, a rate nearly five times that of terrestrial animal (Ricciardi and Rasmussen 1999: 1221) Responses to Freshwater Threats Concern for freshwater systems and their biodiversity parts of the world, particularly among scientists. There is also recognition of the need to maintain functioning ecosystems that continue to provide High number of fish species the goods and services humans High number of endemic fish depend on and value, like clean water, fish, and recreation. In some cases, this has resulted in a change in practices for the better. For example, Source: Revenga et al. 1998 when Argentina recently sought World Bank funding to address approved a $7.8 billion project in mean the difference between survival flooding along the Parana River near southern Florida to help restore nd death for the large range of one of its richest agricultural regions, some of the natural water flow in the species that depend on the river's it agreed to adopt a"living river Everglades, an immense system of riparian zone(WCD 2000: 81) approach to the USS400 million freshwater wetlands disrupted in the Unfortunately, these signs of flood control project. This means 1950s with an extensive system of greater awareness of freshwater the river's floodplain and wetlands canals and levees for flood control ecosystems are still the exception will be left intact as much as possible There have also been some rather than the rule(duda 2001) to preserve their functions positive changes in dam operations With rising demand for water and Consequently, traditional flood to try to minimize ecological damage. food, as well as the increasing control structures like levees and For example, at least 29 countries number of w ater development concrete channels will be have adopted policies aimed at projects worldwide, experts stress minimized--a significant departure insuring that dams release enough that the need to manage freshwater from past practices(Castro 2001) ecosystems as the critical resource More positive still is a nascent that supports the aquatic organisms they are-not an afterthought or a downstream. During the dry season luxury damaged freshwater ecosystems. In or in drought times, these the United States, Congress has environmental flow releases" can REFERENCES Abramovitz, J. N. 1996. Imperiled waters, Imporerisbed Future: The Decline of Freshwater Eco y stems. Worldwatch Paper 128 Washington, DC: Worldwatch Institute. Brautigam, A. 1999."The Freshwater Crisis. "WOrld Conserration, 30 (2):4-5. Castro, Gonzalo. 2001. Senior Biodiversity Specialist, Environment Department, World Bank, Washington, DC (personal communication). Contacted April 2001 Duda, Alfred. 2001 or Advisor, Water Resources, Global Environment Facility, Washington, DC (personal ommunication). Contacted April 2001 OEarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes
©EarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes. 3 indicate that freshwater species are being lost at an “ever-accelerating rate” (Moyle and Leidy 1992:163). Based on recent extinction rates, an estimated 3.7 percent of freshwater animal species will be lost in North America each decade, a rate nearly five times that of terrestrial animals (Ricciardi and Rasmussen 1999:1221). Responses to Freshwater Threats Concern for freshwater systems and their biodiversity is growing in many parts of the world, particularly among scientists. There is also recognition of the need to maintain functioning ecosystems that continue to provide the goods and services humans depend on and value, like clean water, fish, and recreation. In some cases, this has resulted in a change in practices for the better. For example, when Argentina recently sought World Bank funding to address flooding along the Parana River near one of its richest agricultural regions, it agreed to adopt a “living river” approach to the US$400 million flood control project. This means the river’s floodplain and wetlands will be left intact as much as possible to preserve their functions. Consequently, traditional flood control structures like levees and concrete channels will be minimized—a significant departure from past practices (Castro 2001). More positive still is a nascent trend toward restoring some damaged freshwater ecosystems. In the United States, Congress has approved a $7.8 billion project in southern Florida to help restore some of the natural water flow in the Everglades, an immense system of freshwater wetlands disrupted in the 1950s with an extensive system of canals and levees for flood control. There have also been some positive changes in dam operations to try to minimize ecological damage. For example, at least 29 countries have adopted policies aimed at insuring that dams release enough water to maintain a minimum flow that supports the aquatic organisms downstream. During the dry season or in drought times, these “environmental flow releases” can mean the difference between survival and death for the large range of species that depend on the river’s riparian zone (WCD 2000:81). Unfortunately, these signs of greater awareness of freshwater ecosystems are still the exception rather than the rule (Duda 2001). With rising demand for water and food, as well as the increasing number of water development projects worldwide, experts stress that the need to manage freshwater ecosystems as the critical resource they are—not an afterthought or a luxury—is urgent. REFERENCES Abramovitz, J. N. 1996. Imperiled Waters, Impoverished Future: The Decline of Freshwater Ecosystems. Worldwatch Paper 128. Washington, DC: Worldwatch Institute. Bräutigam, A. 1999. “The Freshwater Crisis.” World Conservation, 30 (2): 4-5. Castro, Gonzalo. 2001. Senior Biodiversity Specialist, Environment Department, World Bank, Washington, DC (personal communication). Contacted April 2001. Duda, Alfred. 2001. Senior Advisor, Water Resources, Global Environment Facility, Washington, DC (personal communication). Contacted April 2001. Fish by River Basin Figure 3: Species Richness and Endemism by River Basin, 1998 Source: Revenga et al., 1998 High number of fish species High number of endemic fish High number of fish species and endemics Basins with neither high numbers of total fish nor endemics No data
Food and Agriculture Organization of the United Nations(FAO). 2000. Fisheries Global Information System(FIGIS factfileonLineat:www.fao.org/fi/statist/snapshot/99vs.98.asp Harrison, I.J. and M. J Stiassny. 1999. "The Quiet Crisis: A Preliminary Listing of the Freshwater Fishes of the World that Are Extinct or "Missing in Action,pp. 271-331 in Extinctions in Near Time, MacPhee, ed. New York, New York Kluwer Academic/Plenum Publishers ICOLD (International Commission on Large Dams). 1998. World Register of Dams 1998. Paris, France: ICOLD HD (International Journal of Hydropower and Dams). 1998. 1998 World Atlas and Industry Guide. Surrey, U. K: Aqua- Media International IUCN (The World Conservation Union). 1996. 1996 IUCN Red List of Threatened Amimals. Gland, Switzerland: IUCN The World Conservation union Kristensen, P and H.O. Hansen, eds. 1994. European Rivers and Lakes: Assessment of Their Enironmental State. EEA Environmental Monographs 1. Copenhagen, Denmark: European Environment Agency (EEa) Master, L L., S.R. Flack, and B. A Stein, eds. 1998. Rirers of l ife: Critical Watersheds for Protecting Freshwater Biodirersin Arlington, Virginia, U.S.A.: The Nature Conservancy. McAllister, D.E., A. L. Hamilton, and B. Harvey. 1997. " Global Freshwater Biodiversity: Striving for the Integrity ol Freshwater Ecosystems. " Sea llind-Bulletin of Ocean Voice Internationa/11(): 1-140 Moyle, P B and R.A. Leidy. 1992. " Loss of Biodiversity in Aquatic Ecosystems: Evidence from Fish Faunas, Pp. 127 169 in Consernation Biology: Tbe Theory and Practice of Nature Conserration, Preservation and Management. P L. Fiedler and S.K. Jain, eds. New York, New York: Chapman and hall. Nelson, J.S. 1976. Fisbes of the World. New York, New York: Wiley. Nelson,J. S. 1984(2d ed. ) Fishes of tbe World. New York, New York: Wiley Nelson,]. S. 1994(3d ed. ) Fishes of tbe World. New York, New York: Wiley Reaka-Kudla, M. L.1997. " The Global Biodiversity of Coral Reefs: A Comparison with Rain Forests, " Pp. 83-108 in Biodiversity II: Understanding and Protecting Our Biological Resources, M. L. Reaka-Kudla, D. E. Wilson, and E O. Wilson, eds Washington, DC: Joseph Henry Press Ricciardi, A and J. B. Rasmussen. 1999. "Extinction Rates of North American Freshwater Fauna. " Conserration Biology 13 WCD(World Commission on Dams). 2000. Dams and Derelopment: A New framework for Decision-Making. London: Earthscan. OEarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes
©EarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes. 4 Dynesius, M. and C. Nilsson. 1994. “Fragmentation and Flow Regulation of River Systems in the Northern Third of the World.” Science 266: 753–762. Food and Agriculture Organization of the United Nations (FAO).2000.Fisheries Global Information System (FIGIS) fact file. Online at: www.fao.org/fi/statist/snapshot/99vs.98.asp. Harrison, I. J. and M. J. Stiassny. 1999. “The Quiet Crisis: A Preliminary Listing of the Freshwater Fishes of the World that Are Extinct or ‘Missing in Action’,” pp. 271–331 in Extinctions in Near Time, MacPhee, ed. New York, New York: Kluwer Academic/Plenum Publishers. ICOLD (International Commission on Large Dams). 1998. World Register of Dams 1998. Paris, France: ICOLD. IJHD (International Journal of Hydropower and Dams). 1998. 1998 World Atlas and Industry Guide. Surrey, U. K.: AquaMedia International. IUCN (The World Conservation Union). 1996. 1996 IUCN Red List of Threatened Animals. Gland, Switzerland: IUCNThe World Conservation Union. Kristensen, P. and H.O. Hansen, eds. 1994. European Rivers and Lakes: Assessment of Their Environmental State. EEA Environmental Monographs 1. Copenhagen, Denmark: European Environment Agency (EEA). Master, L. L., S. R. Flack, and B. A. Stein, eds. 1998. Rivers of Life: Critical Watersheds for Protecting Freshwater Biodiversity. Arlington, Virginia, U.S.A.: The Nature Conservancy. McAllister, D. E., A. L. Hamilton, and B. Harvey. 1997. “Global Freshwater Biodiversity: Striving for the Integrity of Freshwater Ecosystems.” Sea Wind—Bulletin of Ocean Voice International 11(3): 1–140. Moyle, P.B. and R.A. Leidy. 1992. “Loss of Biodiversity in Aquatic Ecosystems: Evidence from Fish Faunas,” pp. 127– 169 in Conservation Biology: The Theory and Practice of Nature Conservation, Preservation and Management. P.L. Fiedler and S.K. Jain, eds. New York, New York: Chapman and Hall. Nelson, J. S. 1976. Fishes of the World. New York, New York: Wiley. Nelson, J. S. 1984 (2d ed.). Fishes of the World. New York, New York: Wiley. Nelson, J. S. 1994 (3d ed.). Fishes of the World. New York, New York: Wiley. Reaka-Kudla, M. L.1997. “The Global Biodiversity of Coral Reefs: A Comparison with Rain Forests,” pp. 83–108 in Biodiversity II: Understanding and Protecting Our Biological Resources, M. L. Reaka-Kudla, D. E. Wilson, and E. O. Wilson, eds. Washington, DC: Joseph Henry Press. Ricciardi, A. and J. B. Rasmussen. 1999. “Extinction Rates of North American Freshwater Fauna.” Conservation Biology 13 (5): 1220–1222. WCD (World Commission on Dams). 2000. Dams and Development: A New Framework for Decision-Making. London: Earthscan
