ENDOBENTHIC AND EPIBENTHIC DISTRIBUTION OF THE UNIONID MOLLUSK ELLIPTIO-COMPLANATA

18% of a population of Elliptio complanata was found living completely buried in the sediments of a Quebec lake during mid-summer. This population was found to descend into the sandy sediment as winter approached, and emerged in the spring. More than 60% of the population was endobenthic during late autumn. Endobenthic mussels were significantly smaller than epibenthic mussels (50-60% of average length) and most mussels that were endobenthic during mid-summer were juveniles. Shell morphology did not vary significantly between epi- and endobenthic mussels. Failure to count endobenthic E. complanata in population surveys could result in severe underestimates of actual population densities. A sampling program based strictly on epibenthic mussels would underestimate the contribution of young mussels to the biomass and production of this population.