William W. Hargrove, Matt Fitzpatrick, Arthur Stewart, Don Catanzaro,
David Eskew, and Forrest M. Hoffman
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Aquatic invasive species are transported with normal ship traffic, often in ballast water. This study attempts to predict susceptibility by quantifying the degree of multivariate similarity of aquatic environments worldwide to selected locations within the Great Lakes, USA.
Our approach assumes that, sooner or later, transport of invasive aquatic organisms will occur to and from all points on the globe. Following such human-mediated transplantations, it is the degree of similarity of the new aquatic environment to the original environment that determines whether the invader will successfully establish a population in the new location.
Toward this end, we have produced multiple sets of aquatic ecoregions. Some sets included information on bathymetry, or water depth, while some did not. Calculation of the quantitative ecoregions is described in the parent pages referenced above.
We use these global quantitative aquatic ecoregions to calculate and map the degree of similarity between aquatic environments found within the Great Lakes and other aquatic environments throughout the rest of the world. In the third parent page listed above, we show degree of similarity between all global aquatic habitats and the most similar quantitative aquatic ecoregion present within the Great Lakes. In that work, we sequentially maped global similarity to the seven single largest quantitative ecoregions occurring within the Great Lakes, in order by their size. Here we map the degree of similarity between aquatic environments at the ten busiest ports within the Great Lakes and aquatic environments worldwide.
We assume that, beyond a certain minimum depth, the depth of the water is unimportant for comparison of aquatic environments between two locations. However, depth becomes important as a potentially limiting envrionmental characteristic in shallow-water, nearshore locations. For comparison of deep-water environments like the largest aaquatic ecoregions in the Great Lakes, we based our quantitative environmental similarities on global aquatic ecoregions calculated without bathymetry.
Here we calculate and map degree of global environmental similarity to aquatic environments at the busiest nine destination ports within the Great Lakes: Ashtabula OH, Cleveland OH, Conneaut OH, Detroit MI, Duluth-Superior, Marquette-Presque MI, Milwaukee WI, Oswego NY, and Toledo OH. For these shallower nearshore environments, we calculated environmental similarities on the basis of seven characteristics of surface water, including minimum, maximum, and mean temperature, chlorophyll content, turbidity, water leaving radiance, and bathymetry.
The similarity of aquatic environments at the nine busiest Great Lakes destination ports was calculated as the difference between the mean conditions of the aquatic ecoregion into which the destination port fell and mean conditions found in every other of the 5000 global aquatic ecoregions. The quantitative comparison was calculated as the Euclidean distance between the centroid of the global aquatic ecoregion nearest the destination port and the centroid of every other aquatic ecoregion in turn. Distance calculations were performed within the same orthogonal PCA space in which the aquatic ecoregion groups were originally formed. Within this data space, correlations between individual variables have been removed, so that Euclidean distance is an accurate representation of similarity.
We began with the terrestrial lat/long positions of the destination port cities. To find the appropriate global aquatic ecoregion, we used a GIS to locate the nearest grid cell containing water. Because of the resolution of the data, some riverine ports appear to be quite far from the nearest water. To prevent the incorrect identification of a representative aquatic ecoregion, we dropped ports that were farther from six grid cells from the nearest water from the analysis.
Two destination ports fell in the same global aquatic ecoregion: Marquette-Presque and Oswego. The remaining seven were all located within unique aquatic ecoregions.
Below, we will show maps of the degree of environmental similarity as gray shades, where dark gray or black indicates a high degree of multivariate similarity between aquatic environments, and white indicates very different aquatic habitats. Similarity with each of the busiest nine destination ports will be shown as maps at several extents. First, a map will be shown zoomed-in on the selected destination port within the context of the Great Lakes. Then, a global map showing degree of similarity with that destination port will be shown. Finally, a map zooming in on the Ponto-Caspian region will be presented. Clicking on any of the maps will open a higher resolution version in another window.
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Ashtabula, OH is shown as the black plus, and other ports of origin are shown as red plusses. Ashtabula has a high degree of similarity with other aquatic environments within Lake Erie, and a lower degree of match with the open waters of Lake Michigan. The "parent" aquatic ecoregion is shown in red.
Click on any of the maps to open a higher resolution version in another window.
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The Bearing Sea, southern Hudson Bay, the northern Gulf of Mexico, the North Sea, the Barents Sea, and the Yellow Sea all show similar aquatic environments to those found at Ashtabula, OH. In the southern hemisphere, locations off the eastern coast of Argentina and localized spots around Australia also show similarities. Red plusses show other ports actively trading with Great Lakes destinations.
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Ashtabula shows a low degree of similarity with much of the Black Sea, but a higher degree of environmental match with the periphery of the Caspian and Black seas. Parts of the coast of the Mediterranean and the Persian Gulf also show similarities.
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Cleveland, OH is shown as the black plus, and other ports of origin are shown as red plusses. The aquatic environment in Cleveland is unlike most others found in the Great Lakes region. The extent of even the "parent" aquatic ecoregion containing this destination port is small.
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There are also few global locations showing high degrees of similarity to the unique aquatic environment found at Cleveland. Red plusses show other ports actively trading with Great Lakes destinations.
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Cleveland shows little similarity with aquatic environments within the Ponto-Caspian region.
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Conneaut, OH is shown as the black plus, and other ports of origin are shown as red plusses. The "parent" aquatic ecoregion is visible as a thin red sliver near the southern border of Lake Erie. The overall pattern of similarities is similar to that shown by Ashtabula, but not identical.
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The Bearing Sea, the North Sea, the northern Caspian, and the Yellow and East China Sea show similarities to the aquatic conditions at Conneaut, OH. Red plusses show other ports actively trading with Great Lakes destinations. No similarities are seen in the southern hemisphere.
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Conneaut shows similarity with the periphery of the Caspian, the northwest nearshore of the Black Sea, and reduced similarity to the periphery of the Persian Gulf.
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Detroit, MI is shown as the black plus, and other ports of origin are shown as red plusses. The "parent" aquatic ecoregion is visible as a red blob in south central Lake Erie. The overall pattern of similarities is similar to that shown by Ashtabula and Conneaut, but not identical to either.
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The Bearing Sea, the North Sea, the northern Caspian, and the Yellow and East China Sea show similarities to the aquatic conditions at Detroit, MI. Red plusses show other ports actively trading with Great Lakes destinations. A few localized spots show limited similarities in the southern hemisphere.
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Detroit shows similarity with the periphery of the Caspian, the northwest nearshore of the Black Sea, and reduced similarity to the periphery of the Persian Gulf.
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Duluth-Superior, WI is shown as the black plus, and other ports of origin are shown as red plusses. The "parent" aquatic ecoregion is so small that it is not visible. The aquatic environment at Duluth-Superior is unique, with no other similarities within the Great Lakes region.
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There are no areas with high similarity to the unique aquatic environment present at Duluth-Superior.
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There are no areas with high similarity to the unique aquatic environment present at Duluth-Superior within the Ponto-Caspian region.
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Marquette-Presque, MI is shown as the black plus, and other ports of origin are shown as red plusses. Similarities are identical for the destination port of Oswego, NY, which shares the same quantitative aquatic ecoregion as Marquette-Presque. The "parent" aquatic ecoregion for both of these destination ports is visible as a series of small nearshore areas in Lake Superior and Ontario. The majority of Lake Superior and Lake Ontario, as well as parts of Lakes Michigan and Huron show high degrees of similarity with the aquatic environment at Marquette-Presque and Oswego.
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Extensive areas of similarity with the aquatic environment at Marquette-Presque and Oswego are shown within a latitude band centered on the Great Lakes. A less-extensive band of reduced similarity is also present in the southern hemisphere at homologous latitudes. The aquatic environment present at Marquette-Presque and Oswego is common to many other locations. Thus, considerable invasive risk potential exists for these two destination ports.
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Within the Ponto-Caspian region, much of the Caspian Sea and the Persian Gulf are highly similar to these two destination ports. In addition, much of the Mediterranean shows reduced levels of similarity, as does the Red Sea.
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Milwaukee, WI is shown as the black plus, and other ports of origin are shown as red plusses. The "parent" aquatic ecoregion is shown as a few small red areas near the western shore of Lake Michigan. Similar regions, shown in black, also follow the western shores of Lakes michigan and Huron.
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The aquatic environment at Milwaukee, WI shows little similarity with other aquatic environments of the world.
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The Garaboghazgol Gulf within the Caspian Sea shows the best (albeit moderate) match with the aquatic environment at Milwaukee.
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Toledo, OH is shown as the black plus, and other ports of origin are shown as red plusses. The "parent" aquatic ecoregion is so small as to be invisible everywhere but the western tip of Lake Huron. Small black areas of moderate similarity are barely visible as nearshore spots in Lakes Erie and Huron.
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The aquatic environment at Toledo, OH shows little similarity with other aquatic environments of the world, outside the Great Lakes.
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Limited areas along the northwestern shoreline of the Caspian Sea and the Black Sea, especially the Sea of Azov, show aquatic environments similar to Toledo.