SENSITIVITY OF GLOCHIDIAL STAGES OF FRESH-WATER MUSSELS (BIVALVIA, UNIONIDAE) TO COPPER

The sensitivity of glochidial stages of unionid mussels was evaluated in a series of exposures to aqueous copper. Glochidia held within mars upia of gravid Villosa iris (I. Lea, 1829) exhibited no observable eff ect following a 30-d copper exposure at levels up to 19.1 mu g Cu/L. S imilarly, transformation of encapsulated glochidia of Actinonaias pect orosa (Conrad, 1834), Pyganodon grandis (Say, 1829), and V. iris to th e juvenile stage was unaffected by 12- to 20-d copper exposures of lar gemouth bass, Micropterus salmoides (Lacepede), at levels up to 200 mu g Cu/L. in contrast, released glochidia of all species were sensitive to copper at comparatively low concentrations. The median lethal conc entrations (24-h) for Lampsilis fasciola (Rafinesque, 1820) ranged fro m 26 to 48 mu g Gun, from 36 to 80 mu g Cu/L for V. iris, from 37 to 8 1 mu g Cu/L for Medionidus conradicus (I. Lea, 1834), from 42 to 132 m u g Cu/L for A. pectorosa, and from 46 to 347 mu g Cu/L for P. grandis . Copper sensitivity varied with changes in test conditions, including length of exposure, water temperature, and water hardness. Although s ensitivity of released glochidia to copper was comparable to previousl y reported values for juvenile mussels, the juveniles may be at greate r risk given their residency in benthic sediments where toxicants such as metals may be sequestered at high levels. An evaluation of this ri sk is an urgent priority for further research.