Vector Pathways and the Spread of Exotic Species in the Sea

Prepared at the 25th meeting of the ICES Working Group on Introductions and Transfers of Marine Organisms (WGITMO), Vancouver, Canada, March 2003.

This document is intended to review the current state of knowledge concerning vectors of species introduc-tions, provide a brief overview of the potential risks associated with each broad category of vectors, and identify significant knowledge gaps. It has evolved from discussions of the ICES WGITMO and SGBOSV. 

Although our understanding of the vectors is reasonably good, assigning vector strengths can be difficult and largely dependent on local or regional trading activities, and political and socio-economic circum-stances. Not all vectors continue to operate, and some become more powerful at specific times (e.g., Campbell and Hewitt, 1999). In this account, we attempt to outline the principal vectors that are likely to result in further non-indigenous species spread, including both introductions and transfers. Some vectors may transport fundamentally different sets of organisms (e.g. mussels attached to a ship’s hull, juvenile creatures within the mussel clumps, species encrusting on the mussels, species burrowing into the mussel shells, and pathogens or microalgae inside the mussels). Conversely, some species may be spread by several different vectors (e.g., larval mussels may be transported in the plankton in ballast water; adult mussels may be transported as hull foulers, as intentional aquaculture species, or as associated species accidentally intro-duced with stock for culture).