Research ProjectSpecies dispersal through shipping networks

Characterizing commercial shipping networks and creating models for invasive species dispersal

  • A diagram of port-to-port connectivity of ship traffic passing through the Panama Canal.

    A diagram of port-to-port connectivity of ship traffic passing through the Panama Canal. Courtesy of Jim Muirhead

  • A view of Miraflores Locks in the Panama Canal, looking toward Gatun Lake.

    A view of Miraflores Locks in the Panama Canal, looking toward Gatum Lake. Photo Courtesy of Kristen Larson

  • A Panamax ship entering Miraflores Lock, Panama.

    A Panamax ship entering Miraflores Lock, Panama. Photo Courtesy of Kristen Larson

Project Goal

The objectives of this study are to characterize commercial shipping networks and develop epidemiology-based models for invasive species spread, with an emphasis on the Panama Canal and Caribbean basin.


How connected are the world’s ports, and how do these connections influence the risk of spreading introduced marine species? To address these questions we are examining the network structure of commercial shipping traffic, through connections between ports and ships at various spatial scales, including localities, countries, and oceans. We describe network structure by examining the number of trips between ports in a given time frame (strength of connectivity), as well as measures of port or country importance/centrality. For example, some ports, described as “hubs”, have a high number of inbound or outbound connections to other ports and may increase the spread of invasive species relative to ports with few inbound or outbound connections. Similarly, if we consider the shortest paths connecting all ports, ports that lie on a large number of these shortest paths are more central and may influence the spread rate of invasive species across the network. With this information on network structure and port connectivity, we are able to characterize the risk of spreading invasive species.

The second component our work involves the development of an epidemiology-based model to simulate the spread of hull-fouling invasive species with different reproductive strategies and coming from different native ranges. We are developing a population-based model to simulate the transmission of hull-fouling organisms between ships and ports. This is similar to models used to predict the spread of infectious diseases such as the transmission of malaria between mosquitoes and humans. This model lends itself towards examining how species-specific characteristics influence the overall pattern and rates of spread. Some of these characteristics include the number of offspring adults produce in a given time period, the chances that different lifestages will survive and transition to the next lifestage, and the probability that a particular lifestage will establish in a port or on a ship's hull. In addition, the model can be run under different scenarios to examine how aspects of commercial traffic also influence patterns of spread. For example, we plan to simulate the effects of freshwater exposure to hull fouling organisms as ships pass through the Panama Canal. For many marine organisms, freshwater exposure during canal transits likely reduces species survival and subsequent spread.

Feature Stories

Don’t Let the Opening of Arctic Passages Spread Invasive Species – Put Preventive Measures in Place Now. By Monaca Noble  June 2014

Could Expanding the Panama Canal Increase the Risk of Invasion? By Monaca Noble and Jim Muirhead. October 2014


Holzer, Kimberly K., Jim R. Muirhead, Mark S. Minton, Katharine J. Carney, A. Whitman Miller, Gregory M. Ruiz. 2016. Potential effects of LNG trade shift on transfer of ballast water and biota by ships. Science of The Total Environment. Online December 2016, 

Muirhead, Jim R., Minton, Mark S., Miller, A. Whitman and Ruiz, Gregory M. 2015. Projected effects of the Panama Canal expansion on shipping traffic and biological invasions. Diversity and Distributions, 21(1): 75-87. doi:10.1111/ddi.12260

Ruiz, Gregory M, Julio Lorda, Ashley Arnwine, and Kelly Lion. 2006. Shipping Patterns Associated with the Panama Canal: Effects on Biotic Exchange? In Gollasch, S, BS Galil and AN Cohen (eds) Bridging divides: maritime canals as invasion corridors. Series: Monographiae Biologicae, Vol. 83. Springer. Pgs 113-126


Jim Muirhead