Aquatic plants out of water: Implications of desiccation tolerance for predicting invasiveness

The introduction of nonindigenous aquatic plants can dramatically alter native benthic communities.  “Hitchhiking” on recreational boats is an important dispersal mode between waterbodies for many invasive plant species.  However, movement through this pathway comes with a fitness cost: plant fragments desiccate during transport, resulting in reduced establishment success as a function of time or distance traveled.  Here, we compare the desiccation rates of a suite of invasive plants found throughout North America:  Myriophyllum spicatum, M. aquaticum, Cabomba caroliniana, and Egeria densa. We air-dried plant fragments from each species for varying time lengths (0-24hr), then returned fragments to water to monitor survival and growth.  We compared species’ desiccation rates using a repeated measures linear model.  Among M. spicatum fragments, approximately 70% water loss occurred within one hour, and 90% water loss occurred within 3 hours.  The desiccation rates differed between plant species.  Additionally, we evaluated the desiccation of coiled fragments, similar to plants wrapped around the propeller of a boat, and found a substantial decrease in desiccation rate.  Specifically, we found Eurasian watermilfoil benefitted from one hour desiccation, establishing roots more readily than control fragments when returned to water.  Desiccation tolerance may be an indicator of invasiveness of aquatic plants.