Passive transport of a benthic bivalve (Corbicula fluminea) in large lakes: implications for deepwater establishment of invasive species

Once introduced into a new ecosystem, the benthic bivalve Corbicula fluminea (Asian clam) will spread rapidly through both active and passive transport. In Lake Tahoe, CA-NV, where C. fluminea was introduced in 2002, populations have been found to thrive at shallow depths, where individuals are reproductive, but also at deeper depths where the only possible mechanism of population growth is downslope recruitment. This study used a variety of field and laboratory measurements to parameterize a hydrodynamic drag force model to predict passive clam transport under varying flow conditions. Laboratory results for clam shells ranging from 5 to 20 mm in length under flow conditions from 10 to 25 cm s⁻¹ were used to solve for drag and lift coefficients. Field results are presented during weak stratification (September 2010–March 2011) when cooler water temperatures acted as a potential stressor for buried individuals to rise to the surface and be subjected to flows from which they would otherwise be isolated. During episodic wind events throughout this time period, peak horizontal water velocities of 25 cm s⁻¹ and peak vertical (downwards) water velocities of 4 cm s⁻¹ were measured in which all size classes of adult C. fluminea were potentially transported. Using a fundamental hydrodynamic drag force model approach to predict passive transport, the results of this study can be extended to other bivalve species for a wide array of flow conditions.