Managing Multiple Vectors for Marine Invasions in an Increasingly Connected World

Invasive species remain a major environmental problem in the world's oceans. Managing the vectors of introduction is the most effective means of mitigating this problem, but current risk assessments and management strategies are largely focused on species, not on vectors and certainly not on multiple simultaneous vectors. To highlight the issue that multiple vectors contribute to invasions, we analyzed the historical and contemporary contributions of eight maritime vectors to the establishment of nonindigenous species in California, where most species were associated with two to six vectors. Vessel biofouling looms larger than ballast water as a major vector and a management opportunity, but aquaculture risk appears reduced from historic levels. Standardized data on species abundances in each vector are lacking for a robust cross-vector assessment, which could be obtained in a proof-of-concept “vector blitz.” Management must shift away from one or two target vectors to coordination across multiple vectors.