The Effect of Flow on Burrowing in Juvenile Freshwater Mussels (Bivalvia, Unionidae)

Burrowing is a significant factor in the survival of freshwater mussels; it helps to prevent dislodgement from the sediment, and it reduces the risk of predation. In this study the burial time and orientation of juvenile mussels were tested in response to flow and substrate in a recirculating flow tank. Two species were compared: a habitat specialist, Lampsilis reeveiana, and a habitat generalist, Lampsilis siliquoidea. Three flow rates were tested: no flow (zero cm per second), low flow (4.6 cm per second) and high flow (33 cm per second). Juvenile mussels were placed on two substrates: 2-4 mm (gravel) and 1-2 mm (sand). Twenty mussels of each species were placed onto each substrate and observations were made every 5 minutes for 1 hour. Each flow rate was tested three times. Mussels were classified as recumbent, upright, partially embedded and completely embedded, and orientation was observed relative to the direction of flow of water. Mussels burrowed more rapidly in high flow treatments than in either no flow or low flow treatments. Lampsilis reeveiana burrowed more rapidly and more deeply in one hour than did L. siliquoidea. Substrate type had no significant effect on burrowing behavior. Both species were found to position themselves parallel to flow and with the posterior end downstream significantly more often than any other position tested.