Differences in tolerance to and recovery from zebra mussel (Dreissena polymorpha) fouling by Elliptio complanata and Lampsilis radiata

Zebra mussels (Dreissena polymorpha) in Lake Champlain have colonized the shells of many native unionids, causing declines in their abundance. Periodically cleaning zebra mussels from unionids may be an effective conservation technique, if unionids can recover from the stress induced by zebra mussels. Efforts will need to target species that are most vulnerable to fouling and subsequent energetic losses. We used glycogen as a biochemical indicator of energetic stores to assess species-specific differences in tolerance to zebra mussels. There was no evidence that glycogen levels decreased as dreissenid/unionid mass ratios increased in Elliptio complanata. However, dreissenid/unionid mass ratios as low as 0.25 in Lampsilis radiata were correlated with a significant decline in glycogen content. The ability of these species to recover glycogen after zebra mussel removal and replacement in situ was also evaluated. Mussels were cleaned of zebra mussels and replaced in situ. After 10 weeks, cleaned, heavily fouled, and never-fouled (control) mussels were collected. Glycogen levels in fouled mussels were lower than in the control mussels, while glycogen levels in cleaned mussels did not differ from the control mussels. Results suggest that heavily fouled E. complanata and L. radiata can recover glycogen levels if cleaned of zebra mussels and that cleaning may be a viable option for unionid conservation.