Nghiên cứu điển hình: Độ nhạy của vẹm Glochidia và các sinh vật thử nghiệm quy định Mercury và các độc tố một tham khảo Quần thể loài trai nước ngọt đã giảm đáng kể ở Bắc Mỹ, và hơn hai phần ba các loài được xác định (Unionidae) được phân loại như đã tuyệt chủng, có nguy cơ tuyệt chủng, bị đe dọa, hoặc đặc biệt quan tâm (Williams et al 1993; Naimo 1995; Jacobson và các cộng sự năm 1997.) | 14 Case Study Sensitivity of Mussel Glochidia and Regulatory Test Organisms to Mercury and a Reference Toxicant Theodore W. Valenti Donald S. Cherry Richard J. Neves Brandon A. Locke and John J. Schmerfeld INTRODUCTION Freshwater mussel populations have declined substantially in North America and more than two-thirds of the identified species Unionidae are classified as extinct endangered threatened or of special concern Williams et al. 1993 Naimo 1995 Jacobson et al. 1997 . Although exploitation from commercial over-harvest and the introduction of nonnative species have had substantial impacts Williams et al. 1993 Yeager Neves and Cherry 1999 many declines are attributed to anthropogenic stresses that have eliminated or degraded the natural habitat of mussels Keller and Zam 1991 Williams et al. 1993 Naimo 1995 Milam and Farris 1998 Henley and Neves 1999 Diamond Bressler and Serveiss 2002 Weinstein 2002 . Scientists have addressed these potential risks by improving agricultural practices waste management and pollution monitoring in the United States and consequently water quality has substantially improved. Furthermore the implementation of regulatory policies that are focused on preserving wildlife and the environment such as the Endangered Species Act of 1973 and Clean Water Act of 1977 promotes the protection of not only native unionids but also their habitat. However despite clear progress there is still concern about the future conservation of native mussels as survey efforts have shown little recruitment Neves and Widlak 1987 Breunderman and Neves 1993 Henley and Neves 1999 . Researchers have observed that of the remaining diverse mussel assemblages many are comprised primarily of older adult mussels and few have an abundance of young mussels present Henley and Neves 1999 Weinstein 2001 . These trends indicate that populations are unstable and declining. Conservationists are especially concerned because it may take years for young mussels currently residing .
