Into the Deep
Scientists Navigate Ship Ballast Tanks to Study Exotics

Entering a ship's ballast tank is similar to exploring a cave, says University of Michigan researcher Dr. Thomas Johengen. Steel beams and partitions contribute to the dark, close quarters in which Johengen's research team must work.

This environment is important because fish and other organisms from foreign ports - exotic species - can be carried in the ballast tanks of transoceanic ships and later discharged into the Great Lakes. Johengen, director of the Cooperative Institute for Limnology and Ecosystems Research (CILER), serves as co-program manager for a multidisciplinary ballast water project geared toward preventing further introductions of exotic species. The project focuses on those ships declared NOBOBs, or having No Ballast On Board. During the 1990s, more than 80 percent of ships entering the Great Lakes were loaded with cargo and classified as NOBOBs.

"Even though they don't carry water, they often have residual amounts of water and mud in their ballast tanks," says Johengen. These residuals can support living organisms as well as various forms of resting stages or eggs. "When you take into account the size of the ships, this could be a significant source of exotic species."

While operating in the Great Lakes, NOBOB vessels offload their cargo, taking on water as ballast to maintain their trim and stability. This water mixes with the residual water and mud in the ballast tanks. Organisms in these tanks can later be discharged with the ballast water as the vessel takes on cargo for the outbound voyage.

One goal of the multidisciplinary research program is to collect samples and analyze the biological life contained in NOBOBs. In 2001, researchers and assistants boarded 22 vessels, collecting samples from 43 ballast tanks. The researchers conduct sampling as ships travel within the Great Lakes to examine the extent that organisms may be discharged under actual operating conditions.

Preliminary results suggest that following good ballast management practices can reduce the amount of residual ballast accumulation and lower the risk of introduction. However, to date, researchers have found that all tanks sampled contained live invertebrates and phytoplankton, and/or viable resting stages of zooplankton and phytoplankton.

Researchers are also analyzing the microbial community within the ballast residuals including a variety of potentially pathogenic microbes.