The North American Great Lakes are one of the most highly invaded ecosystems in the world. Historically, invaders have arrived through vectors such as the trades in live aquatic organisms, through canals, and in the ballast tanks and on the hulls of ships. Over the last 50 years by far the greatest number of new nonindigenous species have been introduced as contaminants of shipping. These species include many harmful invaders, many number of which have spread beyond the Great Lakes and across the continent. Reducing total invasive species impacts in the Great Lakes, and across North America, therefore depends largely on the degree to which the introduction of new species to the Great Lakes through shipping can be prevented. We have used a database of international shipping traffic to determine the ports that ships most commonly visit on their voyage to the Great Lakes. This has been combined with an analysis of the environmental similarity of all global ports to determine which regions are most likely to donate species to the Great Lakes in the future.
Results/Conclusions
Shipping traffic connects the Great Lakes and most coastal, and many inland, ecosystems of the globe. Analyzing a global database of shipping movements has shown that regions with the greatest volume of shipping traffic (frequency of ship traffic weighted by ship size) traveling directly to the Great Lakes are the Eastern seaboard of North America, Western Europe, the Baltic, the Ponto-Caspian Basin, and Eastern and South-East Asia. Next, we gathered data on temperature and salinity in all global ports, and used principle components analysis to determine similarity of each to the Great Lakes. High similarity ports are most abundant in Western Europe, the Balkans and the Ponto-Caspian basin, but are also common in Australia, New Zealand, and East Asia. We have combined shipping and environmental similarity results to predict the most likely ports to contain species that could survive in the Great Lakes, and that are likely to be transported there. This has enabled a port-by-port analysis of invasion risk from shipping vectors, and the identification of a suite of species that are likely to be introduced in the future.