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 s hells of many native unionids, causing declines in their abundance. Periodi cally cleaning zebra mussels from unionids may be an effective conservation technique, if unionids can recover from the stress induced by zebra mussel s. Efforts will need to target species that are most vulnerable to fouling and subsequent energetic losses. We used glycogen as a biochemical indicato r of energetic stores to assess species-specific differences in tolerance t o zebra mussels. There was no evidence that glycogen levels decreased as dr eissenid/unionid mass ratios increased in Elliptio complanata. However, dre issenid/unionid mass ratios as low as 0.25 in Lampsilis radiata were correl ated with a significant decline in glycogen content. The ability of these s pecies to recover glycogen after zebra mussel removal and replacement in si tu was also evaluated. Mussels were cleaned of zebra mussels and replaced i n 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 di ffer from the control mussels. Results suggest that heavily fouled E. compl anata and L. radiata can recover glycogen levels if cleaned of zebra mussel s and that cleaning may be a viable option for unionid conservation.