Urbanization and a threatened freshwater mussel: evidence from landscape scale studies

The inflated heelsplitter, Potamilus inflatus, a federally listed freshwater bivalve, has been eradicated from northern portions of its range in the Amite River in Louisiana, USA. We hypothesized that the remaining populations of Potamilus inflatus in the southern part of the Amite River are being affected by increased urbanization of the watershed caused by growth of the surrounding Baton Rouge metropolitan area. Comparison of catch per unit effort in 2007 with a study conducted in 1994 indicated a significant drop in CPUE from 1.76 heelsplitters per site to 0.87. The size distribution of heelsplitters also had decreased in mean shell length from 116 to 97 mm, owing either to dislodgement of larger individuals in spates, or die-offs of larger males. Logistic regression suggested that site variables like substrate type and current velocity were not as important as landscape scale variables in predicting heelsplitter presence at a site. Heelsplitter presence was positively related to the amount of wetland riparian forest, and negatively related to the amount of residential development at the reach (1 km upstream) scale. Our results are significant because we show (1) that statistical models of GIS-based land use can predict the distribution of threatened mussel species, and that (2) conservation of endangered freshwater mussels will require more emphasis on the integrity of the riparian corridor.