Many studies exist which examine hydrodynamic drag acting on the shells of marine snails, whereas studies examining effects of the same force on freshwater snails are lacking. A clearer understanding of how freshwater snails are affected by hydrodynamic drag is timely, however, given their ecological importance in freshwater ecosystems and their declining conservation status. We have been developing a technique to measure drag on freshwater snails that relies on the concept of terminal velocity. Terminal velocity studies have been used to examine drag characteristics of such organisms as fishes, tadpoles and large bivalve molluscs, but applying this approach to measuring drag in small benthic snails has proven challenging.

Results/Conclusions

We have measured a significant relationship between drag and shell length for one Ozark stream-dwelling species (Elimia potosiensis), showing a strong curvilinear relationship across a wide range of shell lengths. Finding such a relationship for the larger, syntopic Pleurocera acuta has proven more difficult due to a trade-off between functional buoyancy and relevant Reynolds numbers. We report on continued improvements to this technique that will yield accurate measurements across a wider range of shell sizes, allowing for determination of the importance of drag in diverse lotic snail communities.