Ballast water appears to be the most important vector for marine species transfer throughout the world. Organisms transported through ballast water have resulted in the unintentional introduction of tens to hundreds of freshwater and marine species to the U.S. and elsewhere (Carlton and Geller 1993, NRC 1995, Carlton and Cohen, 1998)

Ballast water is carried by ships to provide stability and adjust a vessel's trim for optimal steering and propulsion. The use of ballast water varies among vessel type and with cargo and sea conditions. Ballast water often originates from ports and other coastal regions, which play host to a rich planktonic assemblage. As part of normal ship operations, ballast water can be discharged in port, along coastlines and at sea, resulting in a diverse mix of organisms that is transported and released around the world.

MIRL has developed a research program which investigates several different facets of ballast-mediated invasions including:

• The ecology of ballast water tanks and
• The effectiveness of management tools utilized to slow the rate of invasion due to ballast water discharge and exchange.

Although the effects of many introductions remains undetermined, it is clear that some invaders do have significant economic, ecological and human-health consequences. Ballast water introductions such as zebra mussels in the U.S Great Lakes and toxic dinoflagellates in Australia have had tremendous ecological and economic impacts.