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),
+), 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.
Welch, Jacqueline B..
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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