Canals, invasion corridors and introductions

Abstract

Aquatic species spread via canals as a result of unaided, gradual and often unperceived movements through a canal system, with human activities or as combinations of these. It may be tempting to presume that unaided movements of species through a canal system are attributable to natural spread. However, without the presence of a canal, their spread would not have been possible. For this reason, we even consider these unaided movements to result from human activities and they do not represent a natural spread. Indeed, many species may become distributed with passing traffic as well as by their own abilities to disperse. Canals act in similar fashion to other recognised vectors of aquatic biological invasions: they eliminate biogeographic barriers and create links at different scales between lakes, watersheds and oceans. This in turn provides opportunities for populations of species that have evolved in isolation over long periods of geological time to expand and interact with other populations. The three grand engineering projects discussed in this book, the Kiel, Panama and Suez canals, each demonstrably acts as a corridor of invasions. These canals created significant economic, social and political stress during development, yet the economic benefits, and safer shipping conditions they provided were considered to justify the costs. When these canals were built however, no thought was given to the impacts arising from species invasions.