Aquatic Nuisance Species
More than 160 nonindigenous species have entered the Great Lakes. Of these, some 10 percent are considered nuisance species, profoundly altering native ecosystems and processes. Many nonindigenous species arrived from foreign ports, harbored in the ballast water of ocean-going freighters. Innovative Sea Grant research employs marine engineering, DNA technology and economics to shed light on ways to prevent and control future invasions. Using research-based information, outreach has focused on reducing the impact of aquatic nuisance species and educating Michigan citizens.

The spiny water flea (Bythotrephes longimanus) is an exotic species that preys upon native zooplankton in the Great Lakes.

Building a Better Ship
Rather than eliminating nonindigenous species carried in ballast water, a University of Michigan project takes a different approach—eliminating the ballast tanks that harbor foreign species. Led by marine engineer Michael G. Parsons, the project examined the cost and technical feasibility of building a ship that eliminates ballast tanks, replacing them with a series of slow flow ballast tubes, or trunks.

The ballast-free ship concept utilizes a varying flow of water through the tubes to change a ship’s buoyancy and maintain optimum stability. When no cargo is on board, the structural tubes are opened to the sea, and the flooding lowers the ship to its required ballast drafts. The pressure difference between the entrance to the tubes near the bow of the ship and the exit openings near the stern produces a slow flow of water. The flow ensures that the ballast trunks are always filled with “local” sea water—eliminating the transfer of foreign ballast water and nonindigenous species.

Results of Computational Fluid Dynamics studies and model tests have shown that the trunk operation will result in a modest increase in required ship power. The need to lower the ballast tubes below the ballast draft for flooding to occur raises the cargo hold and requires that the hull become deeper to accommodate the same cargo volume. However, according to researchers, the new hull configuration can be accomplished by adding a few hundred tonnes of hull weight. The extra costs would be offset by the elimination of a ballast water treatment system and the ballast piping within a ship’s cargo region. For more information contact Michael Parsons at parsons@engin.umich.edu or (734) 763-3081.