The biota of the sediment in ballasted cargo holds of arriving ships are not well known. Williams et al. (1988) reported that vessels arriving in Australia contained diverse and abundant invertebrates that could be released if and when the sediment is discharged. Hallegraeff and Bolch (1992) further reported that ballast sediment may contain numerous dinoflagellate cysts. The biota of the sediment in ballast tanks are also not well known. The committee directly observed benthic communities established on the bottom of a dedicated ballast tank on a coastal trade vessel that, when deballasted, held unpumpable ballast to a depth of 15 to 30 cm (see Appendix B). A permanently submerged assemblage of polychaete worms, amphipods, shrimp, hydroids, nematodes, and other species had become established. These organisms could release planktonic larvae into the overlying ballast water, which could subsequently be discharged, and the resident adult community would remain on the bottom of the tank.
The release of nonindigenous species into a novel environment constitutes their inoculation but not necessarily their successful introduction. Inoculation is followed by differential survival; a long-standing observation is that most individuals disappear after release and do not form established populations (Carlton et al., 1995). It is not known how long most inoculated individuals simply survive. Older, isolated individuals of nonindigenous species that do not form reproducing populations are occasionally found, which indicates that a certain number grow to adulthood (Carlton, 1995).
As is true of all transport vectors (natural and synanthropic) and of all quarantine concerns, the greater the difference in the physical and chemical states of the donor (source) and receiver (target) regions, the lesser the probability of survival. Thus many organisms from tropical ports will not survive or reproduce in cooler, temperate or boreal ports, and vice-versa.4 However, some species of marine invertebrates and algae occur from subpolar to tropical waters. Thus, the transport of organisms from a warm-water port to a cold-water port, or vice versa, cannot be classified as a "zero risk" scenario. Further, it is impossible to make a complete list of all potential unwanted introductions from a foreign source because many species do not manifest nuisance characteristics within their native ranges. Biological science cannot predict whether a species that is harmful at its source will present a risk when introduced to a new location. Thus, it is not possible to identify areas of zero risk where ballast controls are unnecessary.
Regardless of the match or mismatch in any one physical or chemical variable between a source environment and a release site for a species, numerous