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BOX 1-1Life beyond Ballast
The modern ship transports living organisms on the hull, in sea chests, and elsewhere on and in the vessel, such as in seawater piping systems, on the rudder, entangled in the anchor or in the anchor chain, in chain lockers or caught up in fish nets. Ballast water has a clearly identified role in directly and consistently releasing large numbers of organisms in every major port of the world every day. This report focuses on ballast water as the major vector for the dispersal of nonindigenous aquatic organisms.
Of particular concern are organisms carried on the ship's hull and in sea chests (also known as sea boxes or suction bays). Despite numerous modern studies on the diversity of organisms transported in ballast water, relatively little is known about the diversity of marine life transported on hulls or in sea chests. In a number of cases there is obvious taxonomic overlap. For example, barnacles occur commonly both as adults on ships' hulls and as larvae in ships' ballast water. Should a new barnacle invasion occur, it would be difficult to determine which of these two vectors was responsible.
In the case of sea chests, the extent of potential overlap is much less clear. Thus, although starfish (seastars) are not likely to survive long sea voyages on the exposed hull of a vessel and seastar larvae occur in ballast water, sea chests may also conceivably support seastar populations. Sea chests, because of their protected nature, may harbor relatively larger accumulations of organisms—including mobile species such as snails that would normally be washed away from the ship's hull—than the outside of the ship. Carlton et al. (1995) suggested that the modern sea chest may be an analogue of the deep and protected shipworm galleries off wooden sailing ships. However, the committee is not aware of any modern scientific studies of sea chest fouling.
The general perception is that, because of anti-fouling paints, modern vessels typically do not develop the massive fouling communities that were the bane of mariners a century and more ago. However, the role of ships' fouling in transporting nonindigenous species remains unclear. Increased modern vessel speeds, decreased port time, and increased vessel performance (to offset vessel operating costs) suggest that the number of marine organisms transported in fouling communities may have decreased over time. Conversely, the role of ship fouling may have increased for some species and for some trade routes for a number of reasons, including the evolution of strains of certain seaweeds resistant to anti-fouling paint; the greater sea-going speeds of modern vessels, which lead to decrease in