Predicting Eurasian watermilfoil's (Myriophyllum spicatum) distribution and its likely response to biological control in aspring-fed river

摘要

Controlling invasive aquatic plants would benefit frorr development of predictive theories that can be used to sei priorities for when, where, and how to manage these species The invasion of Eurasian watermilfoil (Myriophyllum spicatun, L.) into a northern California river provides an opportunity to apply predictive relationships for it and its management To test a hypothesis (from the scientific literature) regarding habitat susceptibility to Eurasian watermilfoil invasior and evaluate prospects forits management, we collected water quality, temperature, and plant data from Fall River During 2009 and 2010 we determined Eurasian watermilfoil abundance and distribution at 71 locations within the rivei from an upstream to downstream direction. We alsc determined water temperature and total phosphorus (P) concentration. Eurasian watermilfoil frequency increased in the river downstream from the confluence of Spring Creek Based on measured total P concentrations and simulations from a physiologically based growth model, Eurasian watermilfoil should he able to grow upstream of this point as well. High water levels which prevent boats from passing under the bridge located at this point may limit the upstream spread of Eurasian watermilfoil. One proposalis to introduce the Eurasian watermilfoil weevil (Euhryciopsis lecontei Dietz) as a biological control agent. In other habitats the weevil has been most successful when 3 or more generations of weevils are produced each year. Degree-day calculations using Fall River water temperatures and 2 scenarios for weevil growth and development indicate that the weevil only achieves 3 or more generations per growing season at points downstream of the confluence of the Tule River. This represents the downstream one-third of the river. This information, in conjunction with simulations from a published model on the weevil/milfoil interaction, suggest that it is not likely that the milfoil weevil will reduce Eurasian watermilfoil biomass in Fall River.