Zebra Mussel Invasion Risk: Identifying Lakes Critical to the Spread and Establishment of Zebra Mussels and Modeling the Western Spread of the Species

One of today’s greatest conservation challenges is the proliferation of invasive species. A particularly ecologically and economically damaging invasive species is the zebra mussel (Dreissena polymorpha). First arriving in North America in the Great Lakes region, zebra mussels have expanded across most of the eastern half of the US and pose an ongoing concern for potential introduction and establishment in the western United States. Zebra mussels are already present within parts of Texas and if current trends persist, there are concerns that this invasion front may reach New Mexico. Our study applies network analysis and habitat suitability indices to identify the lakes most critical to the spread and establishment of zebra mussels in Texas and New Mexico’s waterbodies. Our water quality-based habitat suitability indices identified many lakes in east Texas with no or low suitability for zebra mussel infestation. Nearly all lakes in other regions of the study area were classified as having moderate to high suitability. We created a network consisting of lake nodes and connecting roadway edges, using a maximum edge length of 363 km based on Texas boater movement surveys. Using graph analysis, we identified lakes critical to the spread of zebra mussels by acting as hubs (lakes connected to a high number of nearby lakes), steeping stones (lakes that facilitate a disproportionate amount of dispersal within the network), or cutpoints (lakes when removed from the network, increase the network fragmentation). Hubs were concentrated in eastern and central Texas, with connectivity rapidly declining further west as lakes became more isolated. However, due to high connectivity throughout the overall network, no cut points were identified. Stepping stones were distributed throughout the study area, with no obvious pattern. We then compiled a list of lakes that were found at least twice among the top 20% of most suitable habitats, hubs, and stepping stones. These 16 lakes represe