Comparison of the structure and composition of bacterioplankton communities in the ballast water of commercial ships and the Duluth-Superior Harbor

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Comparison of the structure and composition of bacterioplankton communities in the ballast water of commercial ships and the Duluth-Superior Harbor

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Ship ballast water is a potential vector for the introduction and spread of aquatic nonindigenous species (NIS). Although most studies focus on invasive plants and animals, there is an increased interest in the potential for invasive microbes. The Duluth- Superior Harbor (DSH), located in a freshwater estuary at the confluence of Lake Superior and the St. Louis River, receives more ballast water discharge than any other Great Lakes port yet little is known about the bacterioplankton communities in the harbor or the ballast water released into the harbor. The two most important factors affecting the successful establishment of an aquatic NIS through ballast water discharge are propagule pressure, and the abiotic and biotic characteristics of the new environment. Water was collected at six sites in Lake Superior, the Duluth-Superior Harbor, and the lower St. Louis River to characterize bacterioplankton communities. Other water samples were collected from the ballast tanks of ten commercial ships visiting the Duluth-Superior Harbor and the Western Lake Superior Sanitary District (WLSSD) because these sources may influence the genetic structure and composition of natural bacterioplankton communities in the harbor. Three distinct bacterioplankton communities representative of Lake Superior, the Duluth-Superior Harbor, and the St. Louis River habitats were detected in water samples collected on one day in early September 2009 (ANOSIM, p < 0.05) using a DNA fingerprint analysis (T-RFLP). These results were consistent with findings of other investigations that found distinct bacterioplankton communities in estuarine mixing zones. Water temperature, dissolved organic carbon (DOC), ammonium (NH4 +), and nitrate (NO3 −) were more highly correlated with differences in the genetic structure of bacterioplankton communities along a transect from the river through the harbor than other environmental variables. DNA fingerprint analyses also indicated that bacterioplankton communities discharged into the DSH with ballast water and treated wastewater effluent were different from bacterioplankton communities found within the harbor. The most common bacterial phyla found in freshwater habitats (i.e., Alphaproteobacteria, Betaproteobacteria, Actinobacteria, Bacteroidetes) were also seen in 16S rRNA gene clone libraries of freshwater ballast and the Duluth-Superior Harbor. The genetic structure and species composition of the seawater ballast bacterioplankton community from an ocean-going ship was fundamentally different than the bacterioplankton communities in freshwater ballast, and was uncharacteristically dominated by bacteria from the Epsilonproteobacteria. Interestingly, three environmental DNA sequences from the seawater ballast of this ship were similar to Tennacibaculum soleae, a marine fish pathogen (phylum Bacteroidetes, Class Flavobacteria). DNA from this pathogenic marine bacterium, if not its intake cells, survived in the ballast tank of a transoceanic ship for at least two weeks before the ballast water arrived at the Duluth-Superior Harbor. This example illustrates the potential for transporting potentially harmful bacteria over long distances in the ballast water of commercial ships to harbors in the Laurentian Great Lakes.


University of Minnesota M.S. thesis. August 2012. Major: Water Resources science. Advisor:n Randall E. Hicks. 1 computer file (PDF); x, 149 pages, appendix p. 138-149.

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Welch, Jacqueline B.. (2012). Comparison of the structure and composition of bacterioplankton communities in the ballast water of commercial ships and the Duluth-Superior Harbor. Retrieved from the University Digital Conservancy,

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