Sensitivity of glochidial stages of freshwater 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 marsupia of gravid Villosa iris (I. Lea, 1829) exhibited no observable effect following a 30-d copper exposure at levels up to 19.1 mu g Cu/L. Similarly, transformation of encapsulated glochidia of Actinonaias pectorosa (Conrad, 1834), Pyganodon grandis (Say, 1829), and V. iris to the juvenile stage was unaffected by 12- to 20-d copper exposures of largemouth 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 concentrations (24-h) for Lampsilis fasciola (Rafinesque, 1820) ranged from 26 to 48 mu g Gun, from 36 to 80 mu g Cu/L for V. iris, from 37 to 81 mu g Cu/L for Medionidus conradicus (I. Lea, 1834), from 42 to 132 mu 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 sensitivity of released glochidia to copper was comparable to previously reported values for juvenile mussels, the juveniles may be at greater risk given their residency in benthic sediments where toxicants such as metals may be sequestered at high levels. An evaluation of this risk is an urgent priority for further research.