Invasions of nonindigenous species continue to present a significant threat to marine environments worldwide. Invasions can adversely affect regional biodiversity, public health, energy and food supplies, and local economies. Although many aquatic microflora and microfauna have a cosmopolitan distribution, ballast water exchange practices can alter the abundances of harmful species and set up conditions where previously rare populations proliferate.

 The objective of this project was to characterize the bacteria, algae, and microzooplankton inhabiting ballast tanks of Department of Defense (DoD) vessels operating from harbors on both coasts of the United States.

Technical Approach

62 ballast tanks were sampled aboard 28 ships, including 16 ships at nine ports on the West Coast and 12 ships at four ports on the East Coast. Vessels included 11 fleet oilers, 15 roll-on/roll-off carriers, one container ship, and one lighter. Physical and chemical conditions were characterized in situ. Samples also were collected for nutrient and chlorophyll a analyses and for characterizing assemblages of bacteria, phytoplankton, and microzooplankton (maximum dimension less than 80 ìm). Phytoplankton and microzooplankton were quantified using published standard techniques and identified to the lowest possible taxonomic level. Bacteria were quantified using flow cytometry, and harmful taxa were identified using taxa-specific molecular probes. Taxa were evaluated for their geographic distribution based on historical records and categorized as cosmopolitan if distributed across coastal and oceanic waters. Bench-scale experiments also were conducted to examine the effectiveness of heat treatment on survival of selected species in ballast water samples.


A total of 100 phytoplankton species, all previously reported from U.S. coastal waters, were identified from the ballast tanks, including 19 potentially harmful taxa. Chain-forming diatoms and dinoflagellates were dominant. Microzooplankton assemblages were dominated by tintinnid ciliates with cosmopolitan distribution. Bacterial abundances were surprisingly consistent among ballast tanks. Results indicate that the abundances of these microbiota are influenced by a suite of factors, possibly including spatial and temporal variations in microbiota during ballasting, differential effects of ballast water management, and variation in sources of stress factors among ballast tanks and ships. In heat treatment experiments, all but one phytoplankton taxa tested were killed at 34º C or less, which most ships’ ballast tanks can attain using waste engine heat. The project also developed an atlas of phytoplankton species identified and constructed a database that allows included biological observations to be mapped in terms of voyage-specific ballasting history.


This project provided information on the potential for introduction of aquatic microbiota species by DoD vessels. Results suggest that development, evaluation, and adoption of treatment technologies or alternative management strategies will be necessary to meet proposed standards. To minimize the risk of introduction and improve compliance, DoD vessels should conduct ballast water exchange as far offshore as possible and maintain detailed records of ballasting activities. (Project Completed – 2005)