Long-term monitoring of growth in the Eastern Elliptio, Elliptio complanata (Bivalvia: Unionidae), in Rhode Island: A transplant experiment

The lengths of marked specimens of the freshwater mussel, Eastern Elliptio (Elliptio complanata [Lightfoot 1786]), were monitored annually in 3 lakes in Rhode Island, USA, from 1991 to 2005. Mussels growing in Worden Pond showed a change in mean shell length of only 4.3 mm over 14 y, whereas mussel growth in 2 nearby lakes was 3 to 8x greater than growth in Worden Pond over the same time period. L???, the length at which shell growth stops, was significantly different (p < 0.001) among lakes and ranged from 60.5 to 87.4 mm. Transplant experiments revealed that mussels moved to Worden Pond stopped growing, whereas mussels moved from Worden Pond to the 2 other lakes grew at rates similar to the rates observed for resident mussels in the 2 lakes. Standard water-quality measures did not explain the observed growth cessation and lower condition indices of mussels in Worden Pond. Our growth data are consistent with food limitation. The consistent slow growth of E. complanata in Worden Pond, without high mortality, and its ability to increase growth when placed in environments more favorable than Worden Pond, suggests both growth plasticity and longevity in these animals. ?? 2007 by The North American Benthological Society.