Crayfish Predation on Juvenile Freshwater Mussels (Bivalvia: Unionidae)

North American native freshwater mussels are among the most endangered faunal groups in the world. Juvenile mussels are very small and potentially vulnerable to a wide variety of predators, including crayfish. This study examines predation by a native crayfish, Orconectes neglectus on juvenile mussels, Lampsilis siliquoidea. Crayfish preyed on mussels and preferred mussels to snails of similar size. Juvenile mussels buried in substrate were preyed upon and the presence or absence of substrate had little effect on predation. Large and small mussels were attacked at similar rates, but small mussels were consumed more frequently. Larger crayfish were able to consume larger mussels, and crayfish consumed larger individuals of a thin shelled species (Potamilus alatus) than of a heavier shelled species (Lampsilis siliquoidea). Based on these laboratory tests, it appears that mussels up to 50 mm in length of some native species may remain vulnerable to ringed crayfish predation. Many aquatic animals are capable of detecting water-borne chemical cues from predators and will decrease movement in order to avoid predation. Both horizontal and vertical movement of mussels decreased when exposed to water that contained or had previously contained crayfish. When crayfish cues were absent, mussels burrowed more readily in fine substrate and tended to move horizontally in coarse substrate. When crayfish were present, movement was reduced and similar in both substrates. Mussel responses to O. neglectus chemical signals appear to be innate.