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Predicting Invasive Species in the Great Lakes

Zebra Mussels

Photo courtesy of NOAA Great Lakes Environmental Research Laboratory

EPA releases new report predicting invasive species in Great Lakes

The Great Lakes have suffered ecological as well as substantial economic harm from some of the aquatic nonindigenous species (non-native species) that have invaded their waters. The first non-native species that was detected in the Great Lakes was the sea lamprey (Petromyzon marinus), which came via the Erie and Welland canals, in the 1830s. Since then, over 180 additional non-native species have been detected in the Great Lakes.

Non-native species are plant, animals, or other organisms that have been transferred to areas outside their native range. If these species become established in their new environment by reproducing and spreading, they have the potential to become "invasive." Invasive species are those non-native species that cause ecological damage, economic harm, or affect human health.

To help prevent the further spread of invasive species in the Great Lakes, the U.S. Environmental Protection Agency (EPA) recently released the report Predicting Future Introductions of Nonindigenous Species to the Great Lakes.

Using ecological models, scientists predicted the potential spread of non-native species into the Great Lakes. This glimpse into the future will help resource managers focus monitoring activities on particular species at the most vulnerable U.S. Great Lakes ports.

"Once non-native species become established, they are almost impossible to remove and very difficult to control. So prevention and early monitoring are critical" explains Mike Slimak, Associate Director for Ecology in the National Center for Environmental Assessment. The model used in the report employs science-based information about species, coupled with information about ballast-water discharges, to predict the most likely geographic areas where non-native species might become established.

Stow Aways at Sea
Since the St. Lawrence Seaway opened in 1959, ballast water released from transoceanic vessels during commercial shipping operations has been identified as the predominant pathway for non-native species to enter the Great Lakes. Vessels traveling the open sea without a heavy cargo need to pull water (ballast) into big tanks to make the ship heavier, more stable, and hence safer. The ballast water pulled in will likely contain living creatures. When ships load cargo at a port, they discharge the no longer needed ballast water and organisms associated with it are released into open water.

Even vessels that enter the Great Lakes without ballast water may have residual material harboring non-native species in the bottom of their tanks. Once these vessels unload their cargo, they may take on ballast water from the Great Lakes, and the ballast water mixes with the residual material. Before leaving the Great Lakes, this ballast water can be discharged with the possible release of non-native species.

U.S. Coast Guard and St. Lawrence Seaway ballast water regulations require vessels with ballast water to exchange ballast water at sea and vessels without ballast water to flush their tanks before entering the Seaway. These regulations make it less likely that non-native species will enter the Great Lakes. Yet, a few may still get in from ballast water discharges or from other pathways such as aquaculture, imported bait, and the construction of new canals.

Quagga Mussel Map

GARP-predicted habitat suitability of quagga mussel (Dreissena bugensis) in the Great Lakes. Inset map shows the locations where the species has been reported.

Gathering Data and Making Predictions
EPA's report includes and analyzes information about the sources of ballast-water and discharge practices to help predict which species could potentially invade the Great Lakes.

EPA analyzed ballast water releases into U.S. Great Lake Ports using 2006–2007 data obtained from the National Ballast Information Clearinghouse, and 2006 data from the National Vessel Movement Center.

The ports that received the most ballast water discharges are Duluth, MN; Toledo, Ashtabula, and Sandusky, OH; Superior, Green Bay, and Milwaukee, WI; and Gary, IN. The most frequent original sources of ballast water from transoceanic vessels came from Antwerpen, Belgium; Puerto Cabello, Venezuela; Haraholmen, Sweden; and Bremen, Germany.

Based on a review that considered a species' potential to spread to the Great Lakes and the potential to cause ecological impacts, the report identifies 156 species that could become invasive to the Great Lakes. However, it is difficult to determine with any certainty if and when any of the non-native species of concern will become invasive. In fact, some of the 156 non-native species have already been detected in the Great Lakes, but for most of them the number of organisms and the area they cover has not been extensive enough to cause significant problems.

To predict future invasions in the Great Lakes, it is necessary to consider two important factors: 1) the suitability of habitat for a non-native species to survive; and 2) the release of sufficient numbers of individuals for the species to reproduce and spread. A species-distribution model known as the Genetic Algorithm for Rule-Set Production (GARP) was used to identify areas of the Great Lakes that could provide suitable habitat for non-native species of concern. Commercial shipping and ballast water discharge data were also analyzed to predict which ports are most vulnerable to invasion.

GARP predicts the potential distribution of non-native species by comparing the environmental conditions of the organism's current habitat with conditions in the Great Lakes. The model used variables related to water temperature, water clarity, and biological productivity to help determine if a non-native species would find suitable habitat in areas of the Great Lakes. Ample data were available to create models for 14 of the species of concern.

Range maps were produced for each of the 14 modeled species, predicting the locations of suitable habitat within the Great Lakes for each species.

In general, it appears that all of Lake Erie and the shallower portions of the other Great Lakes are the most vulnerable to invasion by the 14 modeled species. Water depth appears to be a limiting factor for many the 14 modeled species which, historically, are only found in shallower depths. However, this is not necessarily the end of the analysis. Some species may adapt and evolve. For example, the quagga mussel has already been reported in all five Lakes (see illustration) and is surviving at greater depths in the Great Lakes than found in its native habitat. (The quagga mussel's natural geographic range is the Dneiper River drainage of Ukraine.)

The findings explained in the report support the need for detection and monitoring efforts at those ports believed to be at greatest risk. The study demonstrates the importance of understanding the most important factors determining when an organism may become invasive. Further, it is an illustration of how remote sensing data can be used in conjunction with GARP to predict the spread of aquatic invasive species.

Predicting Future Introductions of Nonindigenous Species to the Great Lakes is intended to help scientists and water resource managers focus their monitoring activities and resources by identifying new invasive species, the potential for the new species to spread, and which ports in the U.S. Great Lakes are most vulnerable to invasion.

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