What Is the Role of Habitat, Life History and Host Fish in Determining Distributions of Louisiana Mussels?

We worked with unionids from rivers north of New Orleans, sectioned shells to estimate life history traits, and studied the role of movement and shell morphology. Mussels were either cosmopolitan with opportunistic life histories (rapid growth, early maturation and short life cycles), moving quickly to track water levels, or big river species, with equilibrium life histories, and thick, ornamented shells protecting them from dislodgement. Host fish did not limit mussel distributions, as fish were cosmopolitan, but mussel diversity increased in larger rivers. We also studied the threatened, Inflated Heelsplitter (Potamilus inflatus) in the Amite River, determining its life history, as well as the relative abundance of its host fish. Inflated Heelsplitters were intermediate in abundance, matured after one year, lived for 8, and had rapid growth.  Such an opportunistic life history strategy (Haag 2012) is adapted to flashy rivers and low population densities.  It is however a long term brooder, linked to higher chances of extinction (Vaughn 2012). The Freshwater Drum host was the 17^th most abundant out of 44 fish sampled. Overall, mussel density was not clearly predicted by host fish relative abundance.  Spates and channel modification from gravel mining appear more important.