The variability in habitat conditions in large lake basins may provide areas favourable for unionid recruitment and growth. Here we test whether the distribution, body size, and growth rate of Elliptio complanata differ between upwind and downwind sites in a 5.8 km long lake basin. We measured density and morphological characteristics of E. complanata at nine upwind and nine downwind sites. We also measured growth rates and stable isotope (δ13C, δ15N) signatures at three upwind and three downwind sites. We found no difference in density or body size of E. complanata between upwind and downwind sites, despite clear differences in water temperature and food availability. Contrary to our expectations, the growth rate of E. complanata was higher (by 62%) at upwind sites. The reason for this difference is uncertain, but higher shell erosion and a negative relationship between δ13C and C/N ratio suggest that E. complanata may be more stressed at downwind sites. The δ15N of E. complanata did not differ systematically between upwind and downwind sites, but increased with increasing body size. It would therefore be prudent to standardize the size of E. complanata used to measure the baseline of lake food webs.
Opposing diel migration of fish and zooplankton in the littoral zone of a large lake
