61 



(1982)] and ttieir abserx^e may reflect chance 

 The planktontc larvae of sponges are short-lived 

 artti may survive onty short voyages 



1 1 True species diversity in these samples is under- 

 estimated because larval and postlarval forms of 

 many species are morphologically irxJistinguish- 

 able Also, animal, plant, and protist taxa smaller 

 than 80 \i.m {the size ol the plankton net mesh) 

 were not efliciently retained 



12- We estimate (assuming 20 to 30 taxa per vessel, 

 arxJ several thousand ships out o( a world fleet of 

 35.000 with ballast water at sea at any given time) 

 that, on any one day, several thousand sfiecies 

 may be m motion in ballast water conveyor belts" 

 arourxl the world Therefore, comparing known 

 invasions (Table 2) with any particular ballast 

 sample may rarely reveal the same taxa, under- 

 sconng the importance of recognizing this p>he- 

 nomerron a( a supraspecific level 



13, Densities of plankton were estimated by mixing 

 and splitting each replicate, counting the orga- 

 nisms, and multiplying by the volume o( water 

 sampled per replicate (9) 



14 R D Barnes, Invertebrate Zoology (Saunders, 

 Philadelphia, ed 5, 1987) 



15, A, Martel and F -S Chia. J Exp. Mar Biol Ecol 

 150, 131 (1991), R C Highsmith, Mar Ecol Prog 

 Ser 25, 169(1985) 



16 Organisms with a short larval phase can be 

 entrained in ballast water and then settle We 

 found metamorphosed ascidians (1 to 2 mm) 

 settled on floating wood chips, and, in five ships 

 that had completed voyages of 13 to 16 days, we 

 found unattached ascidian tadpoles but no 

 adults Although we found few fish in our samples, 

 rrwre than 20 ship s captains in the Great Lakes, 

 arxi on the U S Atlantic, Gulf, and Pacific coasts, 

 have reported to us live fish in ballast water tanks 



1 7 Freshwater ballast transferred to other trestiwater 

 endpoints (such as from Europe to the Laurenlian 

 Great Lakes, or vice versa) may transfer encysted 

 stages of many taxa (such as sponge gemmules 

 and bryozoan staloblasts) Such stages remain- 

 ing in ship s ballast sediments after open ocean 

 exchange may resist saltwater immersion 



18 The recent increase in invasions caused by bal- 

 last water may be due to a variety of factors, 

 including increases in the size, number, and 

 speed of ships (4, 5) 



19 We expect that several of the six species of Asian 

 copepods now recognized on the Pacific coast of 

 North America will also be found in eastern Aus- 

 tralia, a region that receives large volumes of 

 Ijallast water from the same sources in Japan and 

 China as does the North Amencan Pacific coast 



20 Over 50 examples are rrow known where intro- 

 duced species were mistakenly described as 

 "new" spjecies, some several times from different 

 places around the world (J T Carlton, in San 

 Francisco Bay The Urbanized Estuary. T J 

 Conomos, Ed (American Association lor the Ad- 

 vancement of Science, Washington, DC, 1979). 

 pp 427-444, J W Chapman and J T Carlton, J . 

 Crustacean Biol 11, 386 (1991), J, T Carlton, 

 unpublished results 



21 T J Conomos, Ed , San Francisco Bay The 

 Urbanized Estuary (American Association for the 

 Advartcerrwnt of Science, Washington, DC. 

 1979} 



22. P Moyte, in Ecology of Biological Invasions of 

 North America and Hawaii. H A Mooney and J 

 A Drake, Eds (Springer-Verlag, New York, 1986) 



23. J T Carlton. J K Thompson, L E Schemel, F H 

 Nichols, Mar Ecol Prog Ser 66, 81 (1990) 



24 R W Griffiths. D W Schloesser.J H Leach. W 

 P Kovalak, Can J Fish Aquat Sci. 48, 1381 

 (1991), P D N Hebert, C C Wilson. M H 

 Ivlurdoch. R Lazar. Can J Zool 69, 405 (1991) 



25 B May and E Marsden, Can J Fish Aquat Sci 

 49, 1501 (1992) 



26 M Ye Vinogradov ef al . Oceanology 29, 220 

 (1989), E A Shushkina ar»d E I Musayeva, 

 Oceanotogy 30, 225 (1990) 



27 Recent changes in policy have reflected a recog- 

 nition of the damage caused by introductions 

 mediated through ballast water Federal regula- 



82 



(ions to control the discharge of ballast water into 

 the Great Lakes. Australia, arxl New Zealand are 

 in effect and national studies are under way in 

 Australia. Canada, and the United States on con- 

 trol mechanisms to reduce the number ol living 

 specimens arriving in port -ot- origin ballast water 

 and sediments The United Nations International 

 Maritime Organization has ratified international 

 protocols for ballast control 



28 R J Larson and A C Arneson. Bull South Calif 

 Acad Sci 89. 130 (1990) 



29 C Erseus et al . Proc Biol Sac Wash 103. 839 

 (1990) 



30 C Lardicci and A Castelli, Oebalia 13. 195 

 (1986) D Panagopoulos and A Nicolaidou. ibid 

 16, 35 (1990) 



31 K Essink and H L Kleef. Zool Bi/dr No 38 

 (1988) 



32 N D Yan. W I Dunlop. T W Pawson, L E 

 MacKay, Can J Fish Aquat Sci 49. 422 (1992) 



33 S A Grabe. Proc Biol Soc Wash 102. 726 

 (1989) 



34 M M Jones, Bull Bureau Rural Resources. Dept. 

 Primary IndusI Energy. Australia. Canberra No. 

 48(1991) 



35 M S Hoffmeyer. Crusteceana 58, 186(1990). 



36 J R Cordell, C A Morgan. C A Simenstad. J. 

 Crustacean Biol 12. 260 (1992) 



37 J J OrsiandT C Walter, Bull Plankton Soc Jpn 

 (special volume, 553 (1991)] 



38 J J OrsiT E Bowman, D C Marelli. A Hutchin- 

 son, J Plankton Res 5. 357 (1983) 



39 F D FerranandJ Orsi. J Crustacean Biol 4. 106 

 (1984) 



40 K Hirakawa. Bull Mar Sci 42, 337 (1988) 

 41 Cnjstaceana 51 . 296 (1986) 



42 D C McAden. G N Greene, W B Baker. Tex J 

 Sci 39, 290 (1987) 



43 J J McDermott, Biol Bull (Woods Hole) 181. 195 

 (1991) 



44 N H Campos and M Turkay, Senckenb Marit 

 20. 119(1989) 



45 D Cadien, Newsl So Calif Assoc Mar Invert 

 Tax 5, 1 (1986) 



46 M K Wicksten. Proc Biol Soc Wash 102, 644 

 (1989) 



47 S D Salman arxJ J M Bishop. Crvstaceana 59. 

 281 (1990) 



48 J Carlton, J Shellfish Res 11,489(1992) 



49 R C Willan. Bull Mar Sci 41, 475 (1987) 



50 T W deBoer, Boll Ma/aco/og^co 20. 258 (1984) 



51 J Berman, L Harris, W Lambert, M Buttnck, M 

 Dufresnen, Conserv Biol 6, 435 (1992) 



52 D M Pratt, W H Blust, J H Setgeby, Can J 

 Fish Aquat Sci 49, 1616 (1992) 



53 D Jude, R H Reider. G R Smith, Can J. Fish. 

 Aquat Sci 49, 416 (1992) 



54 P J Miller et al . J Nat Hist 23. 311 (1989) 



55 L A J Al-Hassan and P J Miller, Jpn J Ichthyol. 

 33. 405 (1987) 



56. J. E Randall, personal communication 



57. P A Hutchings, J T van der Velde, S J Keable, 

 Occ Repts Australian Mus 3, 1 (1987) 



58. V G, Springer. Pac Sci 45. 72 (1992) 



59. We are very grateful to D Carlton for l^xjratory 

 and field assistance throughout every stage of 

 this work We thank J Chapman and S Cohen for 

 cntical comments on the manuscript, T Johnson 

 for phytoplankton identification, and T Stevens, 

 K KieferO Williams, and C Hewitt for laboratory 

 and field support Laboratory support was provid- 

 ed by the Oregon Institute of Manne Biology 

 Supported by National Oceanic and Atmospheric 

 Administration Sea Grant (Oregon) R/EM-21 



16 February 1993: accepted 5 May 1993 



SCIENCE • VOL.261 • 2 JULY 1993 



