Identifying lakes critical to the westward spread and establishment of zebra mussels
Damaging aquatic invasive species, such as the zebra mussel ( Dreissena polymorpha), pose an ongoing concern for potential introduction and establishment in the western United States. Our study applied habitat suitability indices and network analysis to identify lakes critical to the continued westward spread and establishment of zebra mussels from a key invasion front in Texas. We created multiple networks consisting of lake nodes and connecting roadway edges. Each network represented the potential connectivity of lakes for recreational users depending on the distance boaters were likely to travel. We evaluated three networks with different maximum edge lengths based on boater movement surveys: 363-km, 125-km, and 51-km. Via graph analysis, we identified lakes critical to mussel spread by acting as hubs, stepping stones, or cutpoints in each network. Water quality-based habitat suitability indices classified most lakes in the study area as moderate to high suitability. In all networks, hubs were concentrated in northeastern Texas. At the lowest maximum edge lengths, stepping stones were also concentrated in the northeast, but could be found in the western portions of the study area as maximum travel distance increased. No cutpoints were found in the 363-km maximum edge length network, indicating a highly connected network with the potential for further western spread facilitated by stepping stones in western Texas and New Mexico. Identifying critical lakes using network analysis and habitat suitability indices provides a predictive tool for resource managers to guide the allocation of limited time and resources for management actions.