EFFECTS OF SUSPENDED CLAY ON ZEBRA MUSSEL (DREISSENA-POLYMORPHA) FECES AND PSEUDOFAECES PRODUCTION

Zebra mussels occur in a wide variety of freshwater environments, incl uding those that may occasionally predispose individuals to high level s of suspended clay and silt. In this study, we employ time-lapse vide ography to explore mechanisms by which zebra mussels respond to elevat ed concentrations of illite-smectite clay (< 2 mu m). The frequency of mussel valve closures was slightly elevated in all clay treatments (2 5-250 mg . 1(-1)) relative to suspensions lacking clay, though the per centage of time spent with open valves was not affected by clay presen ce. Mussels increased the production of faeces and especially pseudofa eces at all clay concentrations tested. The ratio of pseudofaeces to f aeces expelled increased with increasing clay concentration. Thus, the primary, short-term response of Dreissena exposed to suspended sedime nts may be increased production of waste products rather than avoidanc e of sediments by cessation of filtering activity. Toleration of high suspended sediment concentrations is essential for Dreissena establish ment in turbid habitats in the southern United States of America.