Freshwater Mussels of Florida

Chapter 7. Mussel Conservation

Chapter 7 Mussel Conservation The continental United States has the highest diversity of freshwater mussels in the world, with approximately 300 species in two families, Margaritiferidae and Unionidae. The southeastern United States is a mussel biodiversity hot spot harboring 94 percent of the 300 species, including 98 percent of the taxa listed as federally endangered or threatened (Williams et al. 2008). About 30 southeastern species are now considered extinct (Haag 2009). Decline of mussels over the past century and their level of imperilment have been greater than that of any other wide-ranging faunal group in North America (Strayer et al. 2004; Strayer and Dudgeon 2010). The loss of mussel diversity reflects a global pattern of freshwater mollusk imperilment (Abell et al. 2000). Freshwater mollusks currently have the highest global extinction rate of any group of organisms , far exceeding that of terrestrial faunas (Ricciardi and Rasmussen 1999; Régnier et al. 2009). Mussels have extinction rates three times higher than estimations for other species over geological time (Nott et al. 1995). The level of mussel imperilment continues to increase due to habitat alteration and population fragmentation (Haag 2009; Williams et al. in review). The complex life history of mussels has served them well for millions of years but recently has become a handicap for many species, limiting successful reproduction and recruitment. Many mussels are host specific and have narrow windows of opportunity for successful reproduction (Barnhart et al. 2008; Haag 2012). Strayer (2008) surmised that mussel size, number of host fishes, and their dispersal capability are significant predictors of conservation status. Increased sensitivity to anthropogenic stressors, particularly at early life stages, represents a major limitation to recruitment (Cope et al. 2008). The limited ability of mussels to seek refuge from threats and their susceptibility to habitat alterations at all life stages also play key roles in their imperilment (Galbraith and Vaughn 2011). The multitude of complex stressors in aquatic environments may combine to compromise reproduction and recruitment, reduce population viability, and drive populations to extirpation and ultimately species to extinction (Ormerod et al. 2010). Concern for mussel populations due to anthropogenic impacts began over 150 years ago (Higgins 1858). Habitat alteration from disposal of municipal and industrial wastes was a major contributing factor to early mussel declines (Simpson 1899; Ortmann 1909a, 1924b, 1925). Harvest of pearls and shell for pearl buttons was also cited as a causal factor for the decline of mussels (Coker 1919; Williams et al. 2008). In the early 1900s, biologists at the U.S. Bureau of Fisheries became alarmed at the depletion of mussel resources (Ellis 1931a, 1931b). A search for management options to reverse the decline of mussel populations prompted years of research on life history and culture at the U.S. Bureau of Fisheries laboratory in Fairport, Iowa. Initial goals of the Fairport lab were to replenish depleted mussel stocks and propagate fishes (Coker 1914). Seminal works of Lefevre and Curtis (1912) and Coker et al. (1921) contributed to the foundation of modern mussel conservation biology. Research by many scientists continued until the lab closed in 1933 (Pritchard 2001). Over a century of mussel decline occurred before the issue of imperiled mollusks received significant attention. In 1968 the American Malacological Union hosted a Mussel Conservation 95 symposium on rare and endangered aquatic mollusks, which resulted in a series of papers published in the scientific journal Malacologia, including the first list of extinct and imperiled mussels (Table 7.1). The following year USFWS convened a meeting to discuss management and protection options for imperiled species (Stansbery 1971). The renewed interest in conservation during the late 1960s and early 1970s resulted in national legislation culminating, in part, with the Endangered Species Act of 1973. This act directed the USFWS to identify, list, and recover endangered and threatened terrestrial and freshwater species. As of 2012 a total of 87 species of mussels (29 percent of the fauna) have been added to the federal list, of which 15 (25 percent) occur in Florida. In 1993 the American Fisheries Society Endangered Species Committee reviewed the conservation status of mussels in the United States and Canada (Williams et al. 1993). The review determined that the imperilment rate for the Florida fauna exceeded 50 percent. The committee recently reconvened and generated a draft list updating the status assessment (Williams et al. in review). Of the 42 Florida taxa recognized in both assessments (after taxonomic and nomenclatural changes were considered), the status of 9 (21 percent) declined over the nearly two-decade...