58 



nism that has no analog in terrestrial 

 ecosystems. We report here a survey of 

 plankton in ballast water. 



Ships have used water as ballast regularly 

 since the 1880s, drawing ambient water into 



ballast tanks and floodable holds for balance 

 and stability (6). This water is discharged 

 while under way and at subsequent ports-of- 

 call as cargo is loaded (7). Water taken 

 aboard may contain any platJctonic orga- 



nisms in the water column (8). Thus, rich 

 plankton assemblages may be entrained by 

 vessels and then released within days or 

 weeks on a continent or island thousands of 

 kilometers away. 



Table 1 . Frequency of occurrence and abundance of organisms in ballast 

 water from ships arriving from Japan to tfie Port of Coos Bay, Oregon, after 



a transoceanic trip of 11 to 21 days (average 15 1 (SD 19) days) 

 Specificity of identification depended on the phylum or dnflslon considered 



