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Per capita invasion probabilities: A linear model to predict rates of invasion via ballast water - 10/10
Citation:
REUSSER, D., H. LEE, II, AND M. R. FRAZIER. Per capita invasion probabilities: A linear model to predict rates of invasion via ballast water - 10/10. Presented at PICES 2010 Annual Meeting, Portland, OR, October 22 - 31, 2010.
Impact/Purpose:
Ballast water discharges are a major source of species introductions into marine, estuarine, and freshwater ecosystems. For example, in the San Francisco Estuary, dubbed the “most invaded estuary in the world”, it is estimated to account for 38-76% of the aquatic invaders.
Description:
Ballast water discharges are a major source of species introductions into marine, estuarine, and freshwater ecosystems. For example, in the San Francisco Estuary, dubbed the “most invaded estuary in the world”, it is estimated to account for 38-76% of the aquatic invaders. To predict the potential rate of invasion from ballast water, we developed a linear invasion model based on historic invasion rates for the San Francisco Estuary and Great Lakes. The per capita invasion probability was calculated by dividing the number of ballast water invaders by the total number of organisms discharged via ballast water, which was estimated from total volume of ballast discharged times the mean ballast water concentration of organisms. The resulting per capita invasion probability represents the likelihood that a single discharged organism becomes established. In these calculations, we used a mean ballast water concentration of 4640/m3 for organisms >50 microns. Based on data from the National Ballast Information Clearinghouse, an average of 819,364 metric tons per year of ballast water from foreign ports was discharged into the San Francisco Estuary from 2004-2008. Between 1991- 1995 it is estimated that the invasion rate from ballast water in the San Francisco Estuary was 1.6-3.2 species per year. Assuming an underestimate of 100% due to unknown, unidentified and unclassified species, invasion rates were adjusted to 6.4 species per year. Assuming a linear dose-response relationship, the per capita invasion probability for San Francisco Estuary is 1.68 x 10-9. For the Great Lakes, the National Biological Invasion Shipping Study recorded that the total annual foreign ballast water discharged in 1991 was 1,395,461 metric tons. The invasion rate was estimated at 2 species per year, yielding a per capita invasion probability for the Great Lakes of 3.09 x 10-10. These two well studied systems provide a first approximation of per capita invasion probabilities that can be used to estimate the probability of invasion from either a single ship’s discharge, or the total volume of ballast discharged into a system. While these numbers will vary linearly along a continuum of ballast discharge values, organism concentrations, and invasions rates for individual places, we suggest that these per capita invasion probabilities for the San Francisco Estuary and the Great Lakes are viable surrogate values for other less studied estuarine and freshwater areas.