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. Currently, the movement of ballast water is regarded as the most important mechanism for transfer of aquatic nonindigenous species, including zooplankton.
The objective of this project was to characterize variation in the zooplankton communities inhabiting the ballast tanks of Department of Defense (DoD) vessels operating from harbors on both coasts of the United States.
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. Sampling methods (plankton tows, pump samples, light traps) retained zooplankton greater than 80 ìm in size. All zooplankton present were counted and identified to the lowest possible taxonomic level. Taxa then were categorized as cosmopolitan, coastal, or oceanic based on historical records. Zooplankton also were identified in 49 samples collected from amphibious vessels.
Results suggest that the ballast water of DoD vessels contain up to four orders of magnitude lower concentrations of zooplankton than commercial vessels. Depending on sampling method, 23-24% of ships and 34-36% of ballast tanks contained no large zooplankton. Of the 157 zooplankton taxa identified, all the organisms identified to the species level were known to already occur in coastal waters off the continental United States. The majority of taxa (62%) were found to be widespread across oceanic and coastal waters, while 26% were restricted to coastal and 10% to oceanic environments. Copepods were generally the most abundant taxa in the ballast tanks. Results indicate that the abundance of zooplankton cannot be accounted for solely by ballast age. Rather, abundance is influenced by a suite of factors, possibly including spatial and temporal variation in zooplankton concentration and community structure during ballasting, differential effects of ballast water management, and variation in sources of physiological stress among ballast tanks and vessels. Results also suggest that multiple sampling methods may be necessary to assess zooplankton species present in ballast water.
This project provided information on the potential for introduction of aquatic nonindigenous species by DoD vessels. Ballast water discharge standards currently under consideration set concentration limits on zooplankton that are unlikely to be attained by ballast water exchange. To improve performance and compliance, DoD vessels should conduct ballast water exchange as far offshore as possible and maintain detailed records of their ballasting activities. Development, evaluation, and adoption of treatment technologies or alternative management strategies that meet these standards and are appropriate for use on DoD vessels also is necessary to ensure safe and environmentally sound operations. (Project Completed – 2006)