Variation in growth rates of the zebra mussel, Dreissena polymorpha, within Lake Wawasee

1. Field experiments conducted in Lake Wawasee in 1995 and 1996 measured th e response of shell growth of Dreissena polymorpha to environmental gradien ts. 2. Shell growth decreased with initial shell length in four mussel size cla sses ranging between 8 and 22 mm, and decreased with depth, with mussels in shallow water ( <4 m) having growth rates nearly twice those of mussels in deeper water (4-7 m). 3. Growth occurred early in the spring-summer period (May-Tune) with relati vely little shell added later in the summer (July-September), and varied si gnificantly among sites within Lake Wawasee, but not between the 2 years of this study. 4. Rank order of sites was consistent for both years implying that environm ental conditions responsible for variation in shell growth were stable with in Lake Wawasee. 5. Cage design did not have a significant effect on mussel shell growth nor did the distance of growth cages above the bottom (0.5-0.75 m above the bo ttom versus directly on the bottom). 6. This study demonstrates the sensitivity of adult mussel growth to subtle variation in environmental conditions occurring within and among lakes, wi th potential consequences for mussel population dynamics and community stru cture and function.