**1. Introduction**

136 Biodiversity Loss in a Changing Planet

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The loss of biodiversity worldwide has been well documented for decades, and while much of the attention of the media and scientific community has been focused on terrestrial ecosystems, other biomes such as freshwater lakes and streams have received less consideration (Myers et al., 2000). Despite the current decade (2005-2015) being declared an International Decade for Action – 'Water for Life' by the United Nations General Assembly, freshwater ecosystems worldwide are as threatened as ever by the activities of a rapidly growing human population. Surface freshwater ecosystems only constitute 0.8% of the Earth's surface, yet they contain almost 9.5% of the Earth's known species, including as many as one-third all known vertebrate species (Balian et al., 2008; Dudgeon et al., 2006). The impact of human disturbances on this disproportionate amount of biodiversity has made the extinction rate in freshwater ecosystems equal to that of tropical rainforests (Ricciardi and Rasmussen, 1999).

#### **1.1 Freshwater ecosystem services**

Because we depend on water both as a biological necessity and for the myriad of resources and services it provides us, over half of the world's population lives within 20 km of a permanent river or lake (Small and Cohen, 1999). Direct benefits and ecosystem functions of freshwater lakes, streams, and wetlands include providing sources of water for municipal and industrial use, irrigation, hydroelectric power generation, transportation corridors, recreation, and producing fish and other resources used for food and medicine. Freshwater ecosystems also provide many indirect ecosystem services such as water filtration, buffering against storms and flooding, cycling of nutrients and organic matter through the environment, and supporting ecosystem resilience against environmental change (Aylward et al., 2005; Jackson et al., 2001). These indirect ecosystem services have very real economic values. One study valued the ecosystem services of freshwater aquatic ecosystems worldwide at \$6.5 trillion USD, or 20% of all the world's ecosystem services (Costanza et al., 1997).

As human populations continue to develop aquatic resources to maximize a few of these anthropogenically beneficial services such as water storage, generation of electricity, and fish production, other environmental services that are less directly important to humans are being reduced or lost (Bennett et al. 2009). The reduction of these ecosystem functions can significantly alter an ecosystem's natural character. After more than a century of

Biodiversity Loss in Freshwater Mussels: Importance, Threats, and Solutions 139

(Abell, 2001; IUCN, 2007; Strayer and Dudgeon, 2010). While almost all taxonomic groups of freshwater organisms are facing unprecedented declines, some groups are especially

Fig. 1. Conservation status of selected groups of terrestrial and freshwater organisms using

Of all groups of threatened aquatic animals, freshwater mussels (also known as unionid or pearly mussels) are the most imperiled, with 67% of North American species considered threatened (Williams et al., 1993). 35 North American freshwater mussel species have gone extinct since 1900 (Williams et al., 1993), and some scientists have estimated a 1.2% per decade extinction rate for this group, with others predicting that unless effective conservation action is taken 127 more species will become extinct over the next 100 years

Freshwater mussels (order Unioniformes) belong to the subclass Paleoheterodonta, class Bivalvia, and phylum Mollusca. A total of 18 bivalve families have at least one species found in freshwater, although only about 9 have radiated to any degree there (Bogan, 1993). The order Unioniformes contains the largest number and diversity of groups with 180 out of 206 genera and 797 out of 1026 species. Within the Unioniformes, the family Unionidae is the largest, comprising nearly 80% of both the genera and species within the order (Bogan and Roe, 2008). Other important families include Hyriidae (17 genera, 83 species), Mycetopodidae (12 genera, 39 species), Sphaeriidae (8 genera, 196 species) (Bogan and Roe, 2008). As the order Unionidae is the most diverse, and has had the most research dedicated to it, we shall from here on out refer to freshwater mussels simply as Unionids, or unionid

NatureServe conservation status designations (after Master et al., 2000).

(Ricciardi and Rasmussen, 1999).

mussels.

**2.1 Classification of freshwater mussels** 

**2. Freshwater mussels: North America's most threatened animals** 

affected.

unprecedented human population growth and global economic development, we have created widespread and long-term ecological disturbances to freshwater ecosystems in almost all parts of the inhabited world (Strayer and Dudgeon, 2010).


Table 1. Ecosystem services provided by freshwater lakes, rivers, and wetlands (after Postel and Carpenter, 1997).

#### **1.2 Human disturbances to freshwater systems**

Humans now capture more than 50% of the world's precipitation runoff behind dams for electricity generation and water storage, and through diversion canals for irrigation. 16% of all runoff is consumed, or not returned to the rivers after use, while the remainder of the captured runoff is returned but with altered timing, amount, and quality (Jackson et al., 2001). Water pollution, including siltation, is endemic to almost all inhabited parts of the world and is consistently ranked as one of the major threats to freshwater ecosystems (Richter et al., 1997). Pollution in aquatic ecosystems not only consists of chemical toxicants like heavy metals, industrial waste, and pesticides, but also includes excessive nutrient enrichment and pharmaceuticals and personal care products (PPCPs) (Jobling and Tyler, 2003; Smith et al., 1999). Habitat loss and habitat degradation are also major reasons for worldwide biodiversity loss in aquatic ecosystems, and are caused by a multitude of anthropogenic disturbances (Allan and Flecker, 1993; Richter 1997 et al. 1997). Many freshwater species are also being overharvested for human consumption or the pet trade. This affects mostly vertebrate species, especially fishes, but can impact invertebrate species like mussels and crustaceans as well (Dudgeon et al., 2006). The threat of global climate change is pervasive across all of the Earth's ecosystems, and is also often cited as a major threat to freshwater biodiversity (Sala et al., 2000; Strayer and Dudgeon, 2010).

All of these environmental disturbances alter the "natural" chemical, physical, and biological patterns of a system, and when those conditions are changed, both the absolute and functional biodiversity of that system can be threatened. This loss of biodiversity can in turn create a feedback loop that further alters ecosystem functioning. The theory that ecosystem services depend on the biological diversity of the system is well supported for terrestrial ecosystems (Kinzig et al., 2002; Loreau et al., 2001), and recent studies have shown that maintaining biodiversity in aquatic ecosystems is crucial to the continued functioning of ecosystems and the delivery of ecosystem services as well (Covich et al., 2004).

It is widely accepted that freshwater ecosystems worldwide are suffering from a "biodiversity crisis", with estimates of 10,000-20,000 species currently extinct or threatened

unprecedented human population growth and global economic development, we have created widespread and long-term ecological disturbances to freshwater ecosystems in

Table 1. Ecosystem services provided by freshwater lakes, rivers, and wetlands (after Postel

Humans now capture more than 50% of the world's precipitation runoff behind dams for electricity generation and water storage, and through diversion canals for irrigation. 16% of all runoff is consumed, or not returned to the rivers after use, while the remainder of the captured runoff is returned but with altered timing, amount, and quality (Jackson et al., 2001). Water pollution, including siltation, is endemic to almost all inhabited parts of the world and is consistently ranked as one of the major threats to freshwater ecosystems (Richter et al., 1997). Pollution in aquatic ecosystems not only consists of chemical toxicants like heavy metals, industrial waste, and pesticides, but also includes excessive nutrient enrichment and pharmaceuticals and personal care products (PPCPs) (Jobling and Tyler, 2003; Smith et al., 1999). Habitat loss and habitat degradation are also major reasons for worldwide biodiversity loss in aquatic ecosystems, and are caused by a multitude of anthropogenic disturbances (Allan and Flecker, 1993; Richter 1997 et al. 1997). Many freshwater species are also being overharvested for human consumption or the pet trade. This affects mostly vertebrate species, especially fishes, but can impact invertebrate species like mussels and crustaceans as well (Dudgeon et al., 2006). The threat of global climate change is pervasive across all of the Earth's ecosystems, and is also often cited as a major

threat to freshwater biodiversity (Sala et al., 2000; Strayer and Dudgeon, 2010).

ecosystems and the delivery of ecosystem services as well (Covich et al., 2004).

All of these environmental disturbances alter the "natural" chemical, physical, and biological patterns of a system, and when those conditions are changed, both the absolute and functional biodiversity of that system can be threatened. This loss of biodiversity can in turn create a feedback loop that further alters ecosystem functioning. The theory that ecosystem services depend on the biological diversity of the system is well supported for terrestrial ecosystems (Kinzig et al., 2002; Loreau et al., 2001), and recent studies have shown that maintaining biodiversity in aquatic ecosystems is crucial to the continued functioning of

It is widely accepted that freshwater ecosystems worldwide are suffering from a "biodiversity crisis", with estimates of 10,000-20,000 species currently extinct or threatened

almost all parts of the inhabited world (Strayer and Dudgeon, 2010).

and Carpenter, 1997).

**1.2 Human disturbances to freshwater systems** 

(Abell, 2001; IUCN, 2007; Strayer and Dudgeon, 2010). While almost all taxonomic groups of freshwater organisms are facing unprecedented declines, some groups are especially affected.

Fig. 1. Conservation status of selected groups of terrestrial and freshwater organisms using NatureServe conservation status designations (after Master et al., 2000).
