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.
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, http://dx.doi.org/10.1016/j.scitotenv.2016.12.125
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