Journal o f Shellfish Research, Vol. 11. N o. 2. 489-505. 1992

INTRODUCED MARINE AND ESTUARINE MOLLUSKS OF NORTH AMERICA: AN END-OF-THE-20TH-CENTURY PERSPECTIVE

JAMES T. CARLTONM aritime Studies Program W illiams College-M ystic Seaport 50 Greenmanville Avenue M ystic, Connecticut 06355

A B ST R A C T A review of the introduced marine and estuarine (brackish water) bivalves and prosobranch and pulmonate gastropods o f the Atlantic, Gulf and Pacific coasts o f North America reveals an established fauna of 36 non-indigenous species. Sixteen species are native to temperate or tropical coasts o f North America, and have been transported to regions o f the continent where they did not occur in historical time; the remaining 20 species are from Europe, the Mediterranean, South America, the Indo-Pacific, and the northwestern Pacific. The movement o f Pacific (Japanese) and Atlantic commercial oysters to the Pacific coast, and ship fouling, boring, and ballast water releases, have been the primary human-mediated dispersal mechanisms. Regional patterns are striking: 30 species are established on the Pacific coast, 8 on the Atlantic coast, and 1 on the G ulf coast (three species occur on both coasts); 19 (63%) of the Pacific species occur in San Francisco Bay alone. These patterns may be linked to a combination o f human-mediated dispersal mechanisms and regional geological-biological Pleistocene history: at least 27 species o f Japanese and Atlantic coast mollusks were introduced to the American Pacific coast by the oyster industry, in large part into geologically young regions with low native molluscan diversity. With the exception o f a few species, there is little experimental elucidation o f the ecological impact o f the introduced marine mollusks in North America. Negative effects by introduced gastropods on native gastropods have been demonstrated on both the Atlantic and Pacific coasts; for one species, the Atlantic pulmonate marsh snail Ovatella on the Pacific coast, experimental evidence suggests that its establishment did not arise at the expense o f native species. No introduced marine mollusk in North America has had a greater ecological impact than the periwinkle Littorina littorea, which colonized the Atlantic coast from Nova Scotia to New Jersey in the 30 year period between 1860 and 1890. and subsequently altered the diversity, abundance, and distribution, o f many animal and plant species on rocky as well as soft bottom shores. Future marine invasions, through ballast water release and perhaps through aquaculture activities, can be expected with confidence.

KEYW ORDS: mollusks, introductions, invasions, nonindigenous, exotics

IN TR O D U CTIO N

“ A good deal o f chess play has also been done with c l a m s "

-Charles S. Elton (1958)

A t the clo se o f the 2 0 th cen tury w e are w itnessing rapid ly g row ing in terest in the phenom enon o f b io log ical invasions o f coastal w aters. A s a resu lt o f an increasing num ber o f un in ten ­tional invasions o f m arine organ ism s due to the release o f ballast w ater th ro u g h in ternational sh ipping activ ities, and o f increasing pu rsu it o f the in ten tional use and release o f m arine o rgan ism s for m aricu ltu re p u rposes and fo r open sea fisheries enhancem en t, co n ­cern is grow ing relative to the potential ecological, genetic, eco ­nom ic, and social risks th a t m ay be associated w ith fu tu re inva­s io n s

I rev iew here the d iversity , d istribution , regional invasion pat­terns, and ecological im pacts o f the in troduced m arine and estu­arine (b rack ish w ater) b ivalves and p rosob ranch and pulm onate gastropods o f the A tlan tic , G ulf, and Pacific coasts o f N orth A m erica. In troduced species (exo tic , non -ind igenous, alien , or invader species) are those tax a transported by h um an activ ity to reg ions w here th ey d id no t ex ist in h istorical tim e (C arlton 1987). W hile there has been no p rev ious con tinen t-w ide rev iew o f the in troduced m o llusks, Q uay le (1964), H an n a (1966) and C arlton (1975 , 1979a, 1979b) have p rov ided reg ional lists and trea tm en ts fo r the P acific coast. A b b o tt (1974), B e rn ard (1983) and T urgeon (1988) list m any o f the species d iscussed here. I include all species w h ich have been recorded as free-liv ing ou tside o f m aricu ltu re operations. O ne species, the Japanese sea scallop P a tin o p ec te n

yesso en sis , is inc luded because o f its cu rren t m aricu ltu re use and

potential to becom e naturally established. I have excluded opistho- b ranch m ollusks (sacog lossans, nud ibranchs and pyram idellids), pend ing a g lobal and /o r continental rev iew o f the cand idate spe­cies. T here are no in troduced po lyp lacophorans (ch itons) o r sca- phopods (tu sk shells) in N o rth A m erica . I also exclude m ost records o f single specim ens o f liv ing m ollusks w hose anom alous p resence ou tside the ir recorded ranges appears to be due to dis­card ing th rough hobby (aquarium ) or fish ing activities.

M ech an ism s o f in troduc tion o f non -ind igenous m arine o rgan ­ism s to N o rth A m erican w aters have been rev iew ed by C arlton (1985 , 1987, 1989, 1992a). T he m o st im p o rtan t h u m an ac tiv ities have been o r are the follow ing: (1) the transporta tion o f o rgan ism s on the ou tside (fou ling species) o r on the inside (boring species) o f ships, (2) the transpo rta tion o f o rgan ism s inside vessels in solid ballast, such as rocks, sand, and detritus, (3 ) the m ov em en t o f oyste rs , and the co ncom itan t m ov em en t o f o rgan ism s on the oyste r shells o r in associated sed im ents and detritus, (4) the in tentional re lease o f species fo r fisheries purposes, and (5) the release o f larvae, ju v en iles , o r adu lts o f m arine o rgan ism s in the ballast w ater o f coastal, transocean ic , and in terocean ic vessels. I rev iew b elow the relative im portance o f each o f these m echan ism s to the estab lished in troduced m ollusks in N o rth A m erica.

M ETHODS

F ield , m useum , and lite ra tu re w o rk from 1962 to 1979 are sum m arized by C arlton (1979a). F ie ld w o rk du ring th a t period w as conducted from V ancouver Island to sou thern C alifo rn ia ; 18 m u ­seum s or p riva te co llections on the w es t and east coasts o f the U n ited S tates and C anada w ere studied . F ro m 1979 to 1992 field w o rk w as conducted from N ew fo u n d lan d to V irg in ia , as w ell as on

489

490 C a r l t o n

the Pacific coast, and m useum co llections w ere rev isited to ex am ­ine add itional species. T h roughout bo th periods I corresponded w ith m alaco log ists and o ther b io log ists and undertook continual litera tu re review s. The records and dates recorded here are thus based upon field w ork, m useum co llections, personal com m uni­ca tions, and the litera ture, and fo rm the basis o f a m o n ograph no w in preparation . I p resen t here an abstrac t o f th is w ork.

RESULTS

Regional Patterns o f Invasion

Table 1 is a com prehensive syn thesis o f the in troduced m arine and estuarine m ollusks repo rted since the early 19th cen tury in N o rth A m erica . T he in troduced m ollusks can be p laced in to 4 categories (T ab le 2): established (naturally reproducing popula­tions are know n), es tab lishm en t n o t certa in (no recen t records, but the species m ay still be presen t), no t estab lished (no t found in recen t su rveys or, i f presen t, natu rally reproducing popu la tions are n o t know n), and c ryp togen ic (C arlto n 1987; sta tus as in troduced or na tive is no t know n).

T hirty -six species o f non -ind igenous m arine and estuarine m ol­lusks are estab lished on the Pacific , A tlan tic , and G u lf coasts o f N o rth A m erica (T ab le 3). S ix teen species are native to tem perate o r trop ical coasts o f N o rth A m erica , and have been transported to reg ions o f the con tinen t w here they d id n o t occur in historical tim e. T hus, 14 species (T ab le 2 ) native to the A tlan tic coast have been transported to the Pacific coast (T ab le 3 ind icates 15 species on th is route; th is inc ludes the E uro p ean O vate lla , estab lished on the A m erican A tlan tic coast). A t least 3 species (R ang ia cunea ta , M y tilo p s is leu co p h a ea ta and T eredo bartsch i) have been tran s­ported from their apparen tly native sou thern ranges to m ore no rth ­ern localities (show n in T able 3 as 1 species from the G u lf o f M exico and 2 species from the northw est A tlan tic , respectively). The rem ain ing 20 species inc lude 4 fro m E urope, 1 questionab ly fro m E u ro p e (the sh ipw orm Teredo navalis), 1 from the M ed ite r­ranean (the m ussel M y tilu s g a llo p ro v in c ia lis ), 1 from S outh A m er­ica (the m ussel Perna perna). 1 questionab ly orig inating in the Indo-P acific (the sh ipw orm L y ro d u s p ed ice lla tu s) , and 12 fro m the no rthw estern Pacific.

F o u r species (T ab le 2 ) are questionab ly established; field w ork has n o t been focused on locating these species in recen t years , and they m ay still be present. S even species have no t becom e reg ion­ally established: the A tlan tic periw inkles L itto r in a litto rea and T ec ta ria s m urica tus, once found liv ing in C a lifo rn ia and the G u lf o f C a lifo rn ia respectively ; the E uropean snail T ru nca te lla su b c y ­lindrica , found in 1880 to be co m m o n a t N ew p o rt, R h ode Island; the A sian clam L a te rn u la lim ico la , found over a period o f several years in C oos B ay , O regon in the 1960s; th e E u ro p ean oyste r O strea edulis, w idely released on the A m erican Pacific coast, and the S outh A m erican m ytilid M y te lla ch a rru a n a w h ich appeared in num bers in Jacksonville , F lo rid a in 1986. O f these, L itto r in a lit­to rea and O strea ed u lis have becom e estab lished o n the A tlan tic coast, The Japanese sea scallop P a tin o p ec te n y e s so e n s is w hile p resen t in m aricu ltu re operations in B ritish C o lum bia has no t been reported in natural sets.

C ryp togen ic species include (T ab le 1) the pu lm onate lim pet S ip h o n a ria p e c tin a ta and th e sh ip w o n n T ered o nava lis. N in e ­teen th cen tury o r earlier sh ipp ing has been im plicated in creating the m odem distribu tions o f bo th species, bu t details o f th e ir h is­

torical b iogeography in the no rth A tlan tic O cean rem ain u n inves­tigated.

R egional patterns (T ab le 3) are striking: 30 species are estab­lished on th e Pacific coast, 8 on the A tlan tic coast, and 1 on the G u lf coas t (3 species, the snail O vatella , the c lam C orbicu la , and the sh ipw orm T ered o b a rtsch i occu r on bo th the A tlan tic and Pacific coasts). M o st (27 species) o f the in troduced m ollusks on the Pacific coast o rig inate either from A sia o r the A tlan tic coast o f N o rth A m erica. O f the Pacific species, 5 are recorded from on ly 1 locality: the A tlan tic w helk B u sy c o ty p u s and the A sia n clam P o ­ta m o co rb u la occur only in San F rancisco B ay , the A tlan tic c lam M e rc e n a ria occurs only in C olorado L agoon , A lam itos B ay , the A tlan tic oyster C ra sso strea v irg in ica n o w survives on ly in the Serpen tine and N ico m ek l R ivers o f th e B oundary B ay region, B ritish C olum bia , and the sh ipw orm L y ro d u s ta ka n o sh im en sis has been reported only from L adysm ith H arbor, B ritish C olum bia. I do no t include here the c lam M a c o m a “b a lth ic a ” w h o se San F rancisco B ay population appears to arise from an A tlan tic coast stock, as th is geno type m ay in fac t be w idespread in central C a l­ifo rn ia em baym ents.

F our species are restricted to the Pacific N o rth w est (W ash ing ­to n and B ritish C olum bia): the Japanese snails C ecin a m a n ch u rica and N a ssa r iu s fra te rc u lu s , the Japanese clam T rap eziu m lira tum and the Pacific oyste r (C rassostrea g ig a s (w hich rare ly reproduces south o f W illapa B ay , W A ). Tw o additional species reported only from B ritish C o lum bia are the questionab ly estab lished C la n cu lu s a ter and S u b ia con ica . F o u r A tlan tic species are w ell established in a few restricted localities: the slipper lim pet C rep id u la convexa occurs only in San F rancisco and B oundary B ays (new ly recog­nized in B ritish C o lum bia by R obert Fo rsy th ); the m udsnail I ly ­a n a ss a o b so le ta o c c u rs on ly in S an F ra n c isc o , W illap a . and B oundary B ays; th e angelw ing c lam P etr ico la p h o la d ifo rm is oc- curs only in S an F rancisco . N ew p o rt, and B oundary B ay s, and the gem clam G em m a g em m a is restricted to 5 bays in central C ali­fo rn ia (B odega H arbor (no t B o d eg a B ay ), T óm ales B ay. B o linas L agoon , San F rancisco B ay , and E lk h o m Slough). Seven oyster- associated in troduc tions occu r in B ritish C olum bia/W ash ing ton and in C a lifo rn ia , b u t fo r reasons th a t rem ain u nclear do no t occur “ natu rally” in O regon bays and estuaries: these are the Japanese snail B a tilla r ia a ttra m en ta ria and the A tlan tic gastropods I ly a ­n a ssa obso le ta , C rep id u la convexa . C. fo rn ic a ta , C. p la n a , and U rosa lp inx cinerea; the fifth species, the Japanese c lam V enerup is

p h ilip p in a ru m , occurs in N etarts B ay , O regon on ly by v irtue o f an in tensive p lan ting p rog ram (the only bay in O regon w here the Japanese oyster drill C e ra to sto m a in o rn a tu m is also established).

The A sia n clam T h eora lu b rica and the A tlan tic m ussel G eu ­ken sia dem issa occur d isjunctly in San F rancisco B ay and again in sou thern C a lifo rn ia bays. T he abundan t and w idesp read freshw ater clam C o rb icu la f lu m in e a appears occasionally in estuarine situa­tions in O regon and C alifornia . T he trop ical A tlan tic sh ipw orm T ered o b a rtsch i has been in troduced to at least 2 sites in w estern M ex ico , and is probab ly m ore w idespread th an these records in ­dicate.

O f the 30 in troduced species on th e P acific coast, then, only 12 are relatively w idespread. T hese are the gastropods C rep id u la fo r - nicua ta , C rep id u la p la n a , B a tilla r ia a ttram en taria , U ro sa lp in x ci- nereu . C e ra to sto m a inorna tum , and O vate lla m yoso tis, and the bivalves M y tilu s g a lloprovincia lis , M u sc u lis ta senhousia , V eneru ­

p i s p h ilip p in a ru m , M y ra urenaria , T eredo nava lis, and L y ro d u s p ed ice llu tu s.

I n t r o d u c e d M a r i n e M o l l u s k s o f N o r t h A m e r i c a 491

TABLE 1.

Introduced marine and estuarine mollusks o f North America (exclusive o f opisthobranch gastropods). Com m on nam es after Turgeon 1988; (*) species listed without common name in Turgeon 1988; (+) species not Usted in Turgeon 1988.

N A TIV E TO/Introduced To(date of collection) /MECHANISM (M)

Species (see keys, below) References and Remarks

G A S T R O P O D A : Prosobranchia TrochidaeClanculus ater Pilsbry. 1911 (+ topsnail)

PomatiopsidaeCecina manchurica A. Adams, 1861

(+ Manchurian cecina)

LittorinidaeLirrorina littorea (Linnaeus, 1758) (common

periwinkle)

Tectarius muricatus (Linnaeus, 1758) (beaded periwinkle)

TruncatellidaeTruncatella subcylindrica (Linnaeus, 1767)

(+)

PotamididaeBarillaria attramentaria (Sowerby, 1855)

(= Batillaria zonalis auctt.) (Japanese false cerith)

HipponicidaeSabia conica (Schumacher, 1817) (*hoofsnail)

CalyptraeidaeCrepidula convexa Say, 1822 (convex

slippersnail)

NW PACIFIC/NE Pacific: BC: Queen Charlotte Sound (1964). M: BW?

NW PACIFIC/NE Pacific: BC (date?); WA: W hatcom Co. (1961); W illapa Bay (1963) M: COI

NE ATLANTIC/NW Atlantic: (< 1840) Canada to VA/NWATLANTIC/NE Pacific: see remarks. M: Atlantic: SB or IR; Pacific: DA

N W A TLA N TIC /M exico: G u lfo fC alifom ia (1986, 1988). M: ?

N E A TLA N TIC /N W A tlantic: RI: N ew port (1880). M: SB?

NW PACIFIC/NE Pacific: BC (1959) to WA (1920s), but not Grays Harbor or Willapa Bay: CA: Tómales Bay (1941); Monterey Bay Elkhom Slough (1951). M: COI

NW PACIFIC/NE Pacific: BC: Queen Charlotte Sound: Table Island (1940); Vancouver Island (1963). M: BW?

NW ATLANTIC/NE Pacific: BC: Boundary Bay (R. Forsyth, personal communication, 1991); CA: San Francisco Bay (1898); M: COI

Clarke. 1972. N o t reported since 1964; status not known.

M orrison, 1963a, D uggan, 1963, Carlton, 1979a. K ozloff and Price, 1987:210. High intertidal, com m on, co-occurring with O vatella myosotis, found by digging down inside piles o f old oyster shells in damp, rich organic debris (W illapa Bay, 1977. JTC), a m icrohabita t sim ilar to the one in its native Japan (Davis, 1979: 117). Also at base o f salt m arsh plant Salicornia.

C arlton, 1982, C arlton e t al. 1982, Vermeij. 1982a.b. Lubchenco, 1978, 1983, 1986. Brenchley, 1982, Brenchley and Carlton,1983, Kemp and Bertness, 1984. Bertness.1984, Blackstone, 1986, Yamada and M ansour. 1987, Petraitis, 1989: Becam e extinct in N orth A m erica in precontact tim es: reestablished through either intentional release (for food) or accidentally w ith ballast rocks. C ollected in San Francisco Bay in 1968-1970 and again in 1977 (Carlton, 1969. 1979a). but not found since despite sporadic searchesthroughout the bay (JTC, personal observations). N ow one o f the m ost predom inant m ollusks o f the A tlantic rocky shore, and in som e regions the m arshes and m udflats, from Newfoundland to New Jersey.

Bishop. 1992, Chaney, 1992. N o records since 1988.

Burch ( 1962) is the m ost recent to repeat this early record o f V errili (1880). who found th is species to be com m on; it has not been collected since.

Hanna, 1966, M acDonald, 1969a, 1969b. W hitlatch, 1974, Carlton, 1979a. W hitlatch andO brebsk i, 1980, Y am ada, 1982. A bundant locally on m udflats.

Cowan, 1974, Carlton, 1979a, Kay, 1979. Current status not known.

H anna, 1966, C arlton and Roth, 1975. Carlton, 1979a. V ery com m on on snail shells on m udflats along shores o f San Francisco Bay.

con tinued on nex t page

492

Species

Crepidula fornicata (Linnaeus, 1758) (common Atlantic slippersnail)

Crepidula plana Say. 1822 (eastern white slippersnail)

MuricidaeCeratostoma inornatum (Recluz. 1851)

(= Ocenebra japonica (Dunker. I860)) (+ Japanese oyster drill)

Urosalpinx cinerea (Say. 1822) (Atlantic oysterdrill)

MelongenidaeBusycotypus canaliculatus (Linnaeus, 1758)

(channeled whelk) Nassariidae

NassatiidaeIlyanassa obsoleta (Say. 1822) (= Nassarius

obsoletus) (eastern mudsnail)

Nassarius fraterculus (Dunker. 1860) (Japanese nassa)

Pulm onataMelampodidaeO vatella m ysotis (D rapam aud. 1801)

(= P hytio se tifer) Cooper. 1872)) (*European ovatella)

SiphonariidaeSiphonaria pectinata (Linnnaeus, 1758) (striped

falselimpet)

BIV A LV IAMytilidaeMytilus galloprovincialis Lamarck. 1819

(=M . edulis ernsM). (+ M editerranean mussel)

C a r l t o n

TA BL E 1.

continued

NATIVE TO/Introduced To (date of collection) /MECHANISM (M)

(see keys, below)

NW ATLANTIC/NE Pacific: WA: Puget Sound (1905?); Grays Harbor (1970s); W illapaB ay (1937): CA: H um boldt Bay (S. Lam ed, collector, 1989); Tóm ales Bay?; S an F ran c isco B ay (1 8 9 8 ).M : COI

NW ATLANTIC/NE Pacific: WA?: Puget Sound?; Willapa Bay (1937); CA: San Francisco Bay (1901). M: COI

NW PACIFIC/NE PACIFIC: BC (1931); WA: south to Puget Sound (1924); Willapa Bay (present populations since 1960s?); OR: N etarts Bay ( 1930-34); C A: Tóm ales Bay (1941); Morro Bay?; M: COI.

NW ATLANTIC/NE Pacific (1890 and later years): BC: B oundary Bay; W A: Puget Sound and W illapa Bay; CA: Hum boldt,San Francisco, Tóm ales, andN ew port Bays. M: COI

NW ATLANTIC/NE Pacific: CA: San Francisco Bay ( 1938). M: COI?

NW ATLANTIC/NE Pacific: BC: Boundary Bay ( 1952); W A: W illapa Bay ( 1945); CA: San Francisco Bay (1907). M: COI

NW PACIFIC/NE Pacific: BC: Boundary Bay (1959); WA: Puget Sound region (1960). M: COI

N E A T LA N TIC /N W Atlantic: N ova Scotiato W est Indies: Bermuda; NW ATLANTIC/NE Pacific: BC: Boundary Bay (1965) to Mexico: Scammons Lagoon (1972). M: A tlantic: SB; Pacific: COI

MEDITERRANEAN?/NW Atlantic (19th century o r earlier): FL to M exico, Caribbean Cuba, and northern South A m erica. M: S

MEDITERRANEAN/NE Pacific: Northern C A (date?) to southern CA (1880s?), Mexico M: S

References and Remarks

H anna, 1966, Carlton, 1979a

C arlton, 1979a, W icksten, 1978 (as Crepidulaperforans)

Chew, 1960, Hanna, 1966, Squire. 1973. R a d w in a n d D ’A ttilio, 1976, Carlton, 1979a. Locally com m on on oyster beds in

the Pacific Northwest.

C arlton, 1979a; populations last reported in H um boldt Bay in 1950 are still present (S. Lam ed, collector, 1989). Locally com m on on oysters and rocks.

Stohler, 1962, Carlton, 1979a (who reviews evidence fo r retention o f 193 8 date).

Hanna. 1966, Carlton, 1979a. Race, 1982 A stronom ically abundant in San F rancisco Bay.

H anna, 1966, Carlton, 1979a, Cernohorsky. 1984:184-185

Stim pson, 1851, M orrison. 1963a, Abbott. 1974, Carlton, 1979a, Berman and Carlton,1991. Earliest Pacific coast record is 1871 (San Francisco Bay): earliest record on A tlantic co astis 1841 (M assachusetts). Very com m on in high salt m arsh and drift habitats.

M orrison, 1963b, 1972. M orrison believed this species to be introduced from the M editerranean on ships R. T. A bbott (personal communication, 1990) concurs.G. Verm eij (personal com m unication, 1990) questions th is conclusion based on habitat and broad W estern A tlantic distribution. C ryptogenic(seetext).

M cD onald and K oehn, 1988, Koehn. 1991. Seed. 1992. Late tw entieth century distribution probably enhanced by ballast w ater transport as well as ship fouling. A n abundant fouling mussel.

con tinued on nex t page

I n t r o d u c e d M a r in e M o l l u s k s o f N o r t h A m e r i c a 493

T A B L E 1.

continued

Species

Musculista senhousio (Benson, 1842)

Geukensia demissa (Dillwyn, 1817) (ribbed mussel)

P erna p erna (Linnaeus. 1758) (+edible brow n mussel)

M ytella charruana (d ’Orbigny. 1846) (+, charm mussel)

PectinidaePatinopecten yessoensis (Jay. 1856)

(+ Japanese seascallop)

AnomiidaeAnomia chinensis Philippi. 1849 (= Anomia

lischkei Dautzenberg and Fischer, 1907) (+ Chinese jingle)

OstreidaeCrassostrea gigas (Thunberg. 1793) (Pacific

oyster)

Crassostrea virginica (Gmelin, 1791) (eastern oyster)

NATIVE TO/Introduced To (date of collection) /MECHANISM (M)

(see keys, below)

NW PACIFIC/NE Pacific: BC: Boundary Bay (R. Forsyth, personal com m unication.1991); Puget Sound (1959); northern CA: Bodega Harbor (1971) to Elkhom Slough ( 1965), earliest record fo r Pacific coast is 1941 (San Francisco Bay); southern CA: Newport Bay (1977) to San Diego Bay (1976); M exico: Papilote Bay. south o f Ensenada (1970). M: Pacific NW, northern CA: COI; southern CA-Mexico: BW?

NW ATLANTIC/NE Pacific: CA: San Francisco Bay (1894), southern CA: Alamitos (1957), Anaheim (1972) and Newport (1940) Bays, Bolsa Chica Lagoon, O range Co. (M. W icksten, personal communication, 1979). M: San Francisco Bay: COI: southern California: S7/COI?

EASTERN SOUTH AMERICA/Gulf of Mexico: TX: Port Aransas (1990) to Port Mansfield (1991). M: BW/S

EASTERN SOUTH AMERICA/NW Atlantic: FL: Jacksonville (1986). M: BW ?/S?

N W PA C IFIC /N E Pacific: BC (1984-85). see rem arks. M: IR

N W PA C IFIC /N E Pacific: W A: Sam ishB ay (1924). W illapa B ay (1952): OR: T illam ook B ay (<1970s). M: COI

N W PA CIFIC /N E Pacific: Cultured from A K to M exico: well established in BC, W A, sporadically reproducing south to CA: T o m alesB ay .N W Atlantic: Sporadic plantings along A tlantic and G u lf coasts since 1930s. No established populations reported as o f 1992, despite reported unauthorized private plantings o f 1000s o f bushels in Chesapeake Bay about 1988-90. M: IR.

NW ATLANTIC/NE Pacific: BC: Boundary B ay only (since 1917-1918). Population in W illapa Bay W A is now extinct (K. Sayce, personal communication, 1990)

References and Remarks

H anna, 1966, M orton, 1974, Carlton, 1979a. A bundant locally in dense m ats over soft bottoms.

H anna, 1966, Carlton, 1979a, S a rv e re ta l..1992. Juvenile Geukensia occur in fouling on ships, suggesting a m echanism for intracoastal transport from S an F ranci seo Bay to southern California. A bundant in m arshes, m udflats, and at bases o f retaining w alls in San Francisco Bay.

H icks and Tunnell, 1993. A lso recorded from N am ib ia to M ozam bique (K ennelly, 1969).

Lee, 1986. A ppeared briefly in large num bers in seaw ater intake o f pow er plant in 1986. but disappeared by 1987 (H. Lee. personal com m unication, 1992). Perhaps released in ballast w ater o f oil tankers from V enezuela.

R aised in open sea aquaculture operations in BC (T. Carey, personal com m unication,1990). but naturally reproducing populations not reported as o f 1992.

Carlton, 1979a. Current status not known. May be established (Hanna, 1966, Abbott. 1974), although Bernard (1983) believed otherwise.

Pacific: G alstoff, 1932, Barrett, 1963, Hanna, 1966, Quayle, 1969, Carlton, 1979a, Bourne, 1979, Chew , 1979, K etchen e t al. 1983, Foster. 1991:41. A tlantic: Galtsoff, 1932, Nelson, 1946; Turner, 1949, 1950, M ann, 1979, M ann e t al. 1991. Experim ental introductions in 1875 in W A (Barrett, 1963:48-49) were follow ed by regular attempts throughout the Pacific N orthw est starting in 1902; CA plantings began in 1928.

Elsey, 1933, Barrett, 1963, Hanna. 1966, Carlton, 1979a, Bourne, 1979. Plantings began in 1869-1870 in San Francisco Bay with completion of Transcontinental Railroad, and continued along entire Pacific coast in subsequent years.

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494 C a r l t o n

T A B L E 1.

continued

NATIVE TO/Introduced To (date of collection) /MECHANISM (M)

Species (see keys, below) References and Remarks

Ostrea edulis Linnaeus, 1758 (edible oyster)

MactriadeR angia cuneata (Sow erby, 1831 ) (A tlantic

rangia)

TellinidaeMacoma “balthica” (Linnaeus, 1758) (Baltic

macoma)

SemelidaeTheora lubrica Gould. 1861 (Asian semele)

DreissenidaeDreissena polymorpha (Pallas. 1771) (+ zebra

mussel)

Mytilopsis leucophaeata (Conrad. 1831) (dark falsemussel)

NE ATLANTIC/NW Atlantic: ME (1949) and RI (1991). N E Pacific: See rem arks. M: M aine: IR; Rhode Island: ?

G U LF OF M EX IC O /N W A tlantic: FL east coast to Chesapeake Bay (1955); NY: H udson River ( 1988, C. Letts, collector). M: to Chesapeake Bay: CO I7/BW ?, to Hudson River: BW

NW ATLANTIC/NE Pacific: San Francisco Bay. M: COI

N W PA C IFIC /N E Pacific: CA: Los A ngeles Harbor. A naheim Bay. N ew port Bay (earliest southern C A record, 1968): San Francisco Bay (1982). M: BW

NE ATLANTIC/NW Atlantic: estuarine populations in NY: Hudson River (summer 1992, up to 5/00, W . W alton, personal communication, 1992). M: from Europe to the G reat Lakes (1988), B W : w ithin N orth A m erica: see C arlton, 1992b

NW ATLANTIC-GULF OF MEXICO/NW Atlantic: NY: H udsonR iver(1937); MA: no locality (Marelli and Gray, 1985: 118), perhaps Boston: Charles River? M: S/BW

Loosanoff, 1962, W elch, 1966, H idu and Lavoie, 1991. M ay be established in bays and harbors o f Rhode Island (J. D.K arlsson, collector, 1991). R aised in aquaculture facilities on the Pacific coast, but not know n to be naturally established (rare natural settlem ent has occurred in Tóm ales Bay CA (D avis and Calabrese,1969)). R aised along N W A tlantic coast with small natural sets north to H alifax County. N ova Scotia (M . H elm , personal communication, 1990).

H opkins and Andrew s. 1970. N ew ly established in low er H udson R iver perhaps due to release as larvae in ballast w ater from A tlantic o rG u lf coasts

M eehan et al. 1989. The genetic sim ilarity o f San Francisco Bay populations to N W A tlantic populations (as opposed to specimens from Europe or further north on the Pacific coast) suggest that the San F ra n c isco M “ba lth ica” were probably introduced in the 19th century. V ery common.

Seapy, 1974, C arlton et al. 1990. It is o f in terest to note the increase o f th is species in 1978-79 in polluted environm ents in the Inland Sea o f Japan (Sanukida et al. 1981 ). the source o f m uch ballast w ater carried to the N W Pacific, and its appearance in the early 1980s in San Francisco Bay. Intracoastal m ovem entto S anFrancisco Bay from southern C A is also possible.

G riffiths e t al. 1991, S trayer, 1991, H ebert et al. 1991. Carlton. 1992b. N alep aa n d Schloesser, 1992. B allast w ater in coastal vessels and ballast, bilge, or incidental w ater in sm all sailing vessels could transport zebra m ussels betw een estuaries along the A tlantic coast. U sually in low densities in brackish w ater (W. W alton, personal communication, 1992).

Rehder, 1937, Jacobson. 1953. Specim ens are believed to have been collected from the low er C harles R iver, near Boston (R. T. A bbott, personal com m unication, 1990; R. Turner, personal communication.1992). Native (?) from Chesapeake Bay south.

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TABLE 1.

continued

NATIVE TO/Introduced To(date of collection) /MECHANISM (M)

Species (see keys, below) References and Remarks

TrapeziidaeTrapezium liratum (Reeve, 1843) (+ Japanese

trapezium)

CorbiculidaeCorbicula fluminea (Muller, 1774) (= C.

m anilensis auctt. ) (A sian clam )

VeneridaeVenerupis philippinarum (A. Adams and

Reeve, 1850) (= Tapes semidecussata Reeve, 1864; = T. ja p o n ica D eshayes, 1853: also placed in subgenus Ruditapes). (Japanese littleneck)

Gemma gemma (Totten, 1834) (amethyst gemclam)

Mercenaria mercenaria (Linnaeus, 1758) (northern quahog)

PetricolidaePetricola pholadiformis (Lamarck, 1818 (false

angelwing)

MyidaeMya arenaria Linnaeus, 1758 (softshell)

NW PACIFIC/NE Pacific: BC: Ladysmith H arbor (1949?); W A: W illapa Bay? (1947?). M: COI

NW PACIFIC/NE Pacific: estuarine populations in OR: S iuslaw River; CA:Smith River, San Francisco Bay; NORTH AMERICA/NW Atlantic: estuarine populations in Chesapeake Bay: James River. Freshwater populations throughout the U nited States, northern M exico. M: from A sia to N. A m erica ( 1920s- 1930s),IR; w ithin N orth A m erica: see C ounts, 1986

N W PA CIFIC /N E Pacific: BC (1936) to CA: Monterey Bay: Elkhom Slough (1949). OR: N etarts Bay (see rem arks). M: CO I except for OR: IR

N W A TLA N TIC /N E Pacific: CA: Bodega Harbor (1974) to Elkhom Slough (1965); earliest record 1893, San Francisco Bay. M: COI

N W A TLA N TIC /N E Pacific: CA: A lam itos Bay (1967). M: IR

N W A TLA N TIC /N E Pacific: W A: W illapa Bay (1943); CA: San Francisco Bay (1927), N ew port Bay (1972). M: COI

N W A TLA N TIC /N E Pacific : A K ( 1946) to M onterey Bay: E lkhom Slough (<1911).M: COI

Carlton, 1979a. Populations are present in BC (R. Forsyth, personal com m unication,1991 ). Status in W A not known. N ever established in CA; report in A bbott (1974) o f appearance "prior to 1935" based upon interceptions in Pacific oyster shipm ents. N estling infou ling com m unities.

Counts, 1986, 1991; estuarine populations: Diaz, 1974, Carlton. 1979a, N icho ls e t al. 1990, Counts, 1991:105. A bundant locally, but in low er densities in brackish water.

F isher-Piette and M etivier, 1971 (specific taxonom y and synonym y), Bourne, 1982, A nderson et al. 1982, Bernard. 1983. K e tch en e ta l. 1983. G eneric placem ent follow s E. Coan and P. Scott (personal com m unication, 1992). Intentional plantings in OR: N etarts B ay sporadically from 1960s-1980s resulted in a naturally

reproducing population (Gaumer and Farthing, 1990); also planted in other O R bays, w here specim ens should be expected. Com m on to abundant in coarser sediments.

Carlton, 1979a. Records from north o f Bodega or south o f M onterey B ay are based upon m isidentifications. A bundan tin so ft sediments.

Crane et al. 1975, M urphy, 1985a, 1985b.The only established population on the Pacific coast o f th is com m on A tlantic species is in th is sm all C A bay. H ertz and Hertz ( 1992) report a single live specim en from M ission Bay, San Diego, probably from discarded bait or food.

H anna, 1966, C arlton, 1979a. In higher shore hard shale, clay, m ud substrates.

C arlton, 1979a. Bernard, 1979. Became extinct on Pacific coast from southern A K south in late Tertiary ; reestablished (earliest record 1874, San Francisco Bay) through accidental introduction w ith A tlantic oysters. N ow one o f the m ost com m on upper bay clam s from W A to San Francisco Bay.

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496 C a r l t o n

TABLE 1.

continued

Species

NATIVE TO/Introduced To (date of collection) /MECHANISM (M)

(see keys, below) References and Remarks

CorbulidaePommocorbula amurensis (Schrenck, 1861)

(+ A m ur river corbula)N W PA C IFIC /N E Pacific: CA: SanFrancisco

Bay (1986). M: BWC arlton e t al. 1990, N icho ls e t al. 1990. In

densities o f tens o f thousands per square m eter in estuarine reaches o f San Francisco; to be expected in o ther CA bays through intracoastal transport o f larvae in ballast water.

TeredinidaeLyrodus pedicellatus (de Quatrefages. 1849)

(= Teredo diegensis Bartsch. 1927) (blacktip shipworm)

Lyrodus takanoshim ensis Roth. 1929 (+)

Teredo barrschi W. Clapp. 1923 (Bartsch shipworm)

Teredo novalis Linnaeus. 1758 (naval shipworm)

Teredo furcifera von Martens in Semon, 1894

(+)

LaternulidaeLaternula lim ico la(R se\/e , 1863) (=L.

ja p o n ica auctt.) (+)

INDO-PACIFIC7/NE Pacific: C A: San Francisco Bay (1920); Monterey Bay (1935): Santa Barbara to San Diego Bay (earliest southern C A record 1871). M: S

NW PACIFIC/NE Pacific: BC: Ladysmith H arbor(1981). M: COI (in w ooden oyster boxes)

NW ATLANTIC/NW Atlantic: NJ: Bamegat Bay (1974), CT: Long Island Sound: W aterford (1975): N E Pacific: G u lf o f California: L a Paz (<1971): M exico: Sinalao (1978-79). M: S

NE ATLANTIC7/NE Pacific: BC: Pendrell Sound (1963): WA: Willapa Bay (1957); OR: C oosB ay(1988): CA: S anFrancisco Bay (1913): southern CA? NW ATLANTIC: see rem arks. M: S

NW ATLANTIC (Caribbean north to FL)/NW Atlantic: N J Bam egat Bay (1974). M: S

N W PA C IFIC /N E Pacific: OR: Coos Bay (1963). M: BW

K ofoid and M iller, 1927, Turner, 1966, E cklebarger and Reish. 1972, Carlton. 1979a

Popham 1983.

N W Atlantic: H oagland and Turner, 1980. H oagland, 1981,1986, R ichards e ta l.1984. G u lf o f California: R. T u rn erin Keen, 1971:282, H endrickx, 1980. Reported by A bbott (1974) as introduced to CA , a record based upon specim ens from San D iego B ay in the 1920s (K ofoid-and Miller. 1927). M ay no longer be present in B am egat Bay in therm al effluents, bu t still established in Long Island Sound heated pow er plant effluents a t M illstone.

Turner, 1966. Carlton, 1979a. C oos Bay record: JTC. field records. Cryptogenic in N W A tlantic: early A m erican records include reports both from visting vessels (Russell, 1839, M A ) and from established populations (D eK ay. 1843, N Y ). Grave (1928) enigm atically noted. “ The date o f its first appearance in [W oods Hole] is not known,” noting records as early as 1871. If introduced, it m ay have arrived centuries ago w ith visits o f earliest E uropean vessels.

H oagland and Turner, 1980, R ichards e t al., 1984. Probably only tem porarily established in Barnegat Bay in therm al effluents o f pow er plant (K. E. H oagland, personal com m unication, 1992) and m ay no longer be p resen tthere. T urner(1966) records an earlier nonestablished population inN C .

K een, 1969. N ot recorded in Coos B ay since 1965, and not re-discovered there despite intensive searching from 1986-1989 (JTC and students, field records).

Mechanisms o f introduction S = Ships (fouling and boring)SB = Ships (solid ballast: rocks, sand)BW = Ships (ballast w ater)COI = Fisheries: A ccidental release w ith com m ercial oyster industryIR =Fisheries: Intentional releaseDA = Fisheries: A ccidental release w ith discarded algae (seaw eed) in shellfish packing

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TABLE 1.

continued

NATIVE TO/Introduced To(date of collection) /MECHANISM (M)

Species (see keys, below) References and Remarks

R egions (as used here: )Northwest (NW) Pacific = A sia: China. Japan, K orea Northeast (NE) Pacific = Pacific coast o f N orth A m erica: A laska to M exico N orthw est (N W ) A tlantic = A tlantic coast o f N orth A m erica: C anada to F lorida Northeast (NE) Atlantic = Europe: northern and w estern

AK Alaska NJ New JerseyBC British Columbia NW NorthwestCA California NY New YorkCT Connecticut OR OregonFL Florida RI Rhode IslandMA Massachusetts TX TexasME Maine VA VirginiaNC North Carolina WA WashingtonNE Northeast

I t is o f in terest to note th a t 19 (63% ) o f th e 30 species occu r in San F rancisco B ay. O n ly the em baym en ts o f the Pacific N o rth w est approach th is n um ber o f established species, w ith W illapa B ay hav ing 12 species, P u g e t S ound 11 species, and B ou n d ary B ay 13 species. T hese num bers w ill increase w ith fu rther exp loration (for exam ple, T rapezium lira tum , C rep id u la co n vexa and C rep id u la

p la n a should be expected m ore w idely th an no w reported in W ash ­ing ton and B ritish C o lum bia) and w ith n ew in troductions.

F our o f the in troduced m ollusks on the A tlan tic coast are from E u rope and 3 (as no ted above) are sou thern species n o w estab ­lished in northern localities. O nly 2 species are w idespread , the E uro p ean periw ink le L itto r in a littorea , and the G u lf o f M exico clam R a n g ia cunea ta . T he E u ro p ean oyste r O strea edulis, long restric ted to M aine, n o w occurs in R h ode Island as w ell, a lthough the m eans o f in troduc tion o f th is p opu la tion (w hether by transpo rt from M aine as a sh ip -fou ling organ ism s, o r by intentional release, o r by escape fro m aquacu ltu re facilities) is no t y e t know n. The sh ipw orm T ered o b a rtsch i occurs w ith in the therm al p lum e o f a n uclear p ow er p lan t in L on g Island Sound; the status o f the p o p ­u la tion o f th is species, and o f ano ther sou thern te red in id , in N e w Jersey is no t clear. E stuarine populations o f 2 typ ica lly freshw ater b ivalves, the A sian clam C o rb icu la f lu m in e a and th e E u ro p ean zeb ra m ussel D re isse n a p o lym o rp h a , are know n from lim ited lo ­cations.

The sole clearly in troduced m arine m ollusk in the G u lf o f M ex­ico, P e rn a p ern a , is from S outh A m erica. W ere it n o t fo r th is recen t repo rt, there w ou ld be no certain records o f in troduced m ollusks in the G u lf fauna.

Regional Patterns o f Mechanisms o f Introduction

The hum an-m ed ia ted d ispersal m echan ism s th a t have led to the in troduc tion o f non-ind igenous m ollusks to N o rth A m erican coasts have p layed strikingly d ifferen t regional roles (T ab le 4). F ar ex­ceed ing all o ther m echan ism s in term s o f num ber o f species suc­cessfu lly transported and in troduced is the no w largely historical m ovem en t o f the A tlan tic oyste r C ra sso strea v irg in ica and the Pacific (Japanese) oyste r C ra sso strea g ig a s to the bays and estu ­aries o f the P acific coast o f N o rth A m erica from the 1870s to the 1930s. and fro m the 1900s to the 1970s, respec tive ly (T ab le 1).

A tlan tic oyster im porta tion ceased due to lack o f breed ing success and because o f com petition w ith the increasing im porta tion and culture o f the Pacific oyster. Pacific oyste r im portations stopped after su ffic ien t natural sets and reg ional aquacu ltu re operations w ere ab le to supply adequate am oun ts o f seed.

These industries led to th e in troduc tion o f a t least 22 m ollusks to th e Pacific coast (T ab le 4: the 20 species show n for C O I p lus the 2 species o f oysters); 9 are fro m Japan and 13 are from the A t­lantic. In ten tional fishery releases added ano ther 2 species (the A sian clam C o rb icu la f lu m in e a and th e A tlan tic quahog M e rce­n a r ia m ercenaria , w h ich curiously d id no t becom e established th ro u g h the oyste r industry ) to the Pacific coast fauna.

P rio r to these industries and releases, only a few species o f m ollusks had been transported to o r w ith in N o rth A m erica . The earliest in troduc tion m ay have been the cryp togen ic sh ipw orm T ered o n a v a lis to th e N e w E ng land coast. T he E u ro p ean snail L itto r in a littorea , p reh isto rically p resen t in the northw estern A t­lan tic , w as retu rned to N o rth A m erica before 1840 e ither in ten ­tionally (released by E uropean settlers in eastern C anada to estab­lish a periw inkle fishery) o r accidentally (w ith ballast stones). A late 18th cen tu ry -early 19th cen tury in troduc tion to the A tlan tic coast w ith ballas t stones m ay have been the E uro p ean m arsh snail O va te lla m yo so tis (subsequen tly th en transpo rted w ith oyste rs to the Pacific coast). O n the Pacific coast, m id -19 th to early 20 th c e n tu ry sh ip -m e d ia te d in tro d u c tio n s in c lu d e d th e sh ip w o rm s T ered o n a v a lis and L y ro d u s p ed ice lla tu s , as w ell as the M ed ite r­ranean m ussel M y tilu s g a lloprovincia lis , w hose in troduced status w as long overlooked in C alifo rn ia due to its prev ious iden tifica tion as the “ native” M y tilu s edulis.

B allas t w ate r has p layed a sm all ro le in te rm s o f the num bers o f in troduced species, a lthough a t least 2 o f the species in troduced by th is m eans are ecologically and /or econom ically significant inva­sions. F o r a num ber o f species, the ro le o f ballast w ater as a m echan ism is subm erged am ong a nu m b er o f o th er m echan ism s th a t are n o t easily d istingu ished from each other. T hus, ballast w a te r o r sh ip fou ling m ay have led to th e 20 th cen tury m ovem en t o f the N o rth A m erican native dreissen id M y tilo p s is leu co p h a ea ta to the H u d so n R iver. E ith er m echan ism m ay also have p layed a ro le in the appearances o f the S outh A m erican b ivalves M yte lla

498 C a r l t o n

TABLE 2.

Introduced marine and estuarine mollusks o f North America: Established and other species arranged by donor region.Regions: See Table 1, footnote.

ESTABLISHEDCecina manchurica Batillaria attramentaria Ceratostoma inornatum Nassarius fraterculus Musculista senhousia Crassostrea gigas Theora lubrica Trapezium liratum Corbicula fluminea

Venerupis philippinarum Potamocorbula amurensis Lyrodus takanoshimensis Lyrodus pedicellatus Littorina litrorea Ovatella myosotis Ostrea edulis Dreissena polymorpha Mytilus galloprovincialis Teredo navalis Crepidula convexa Crepidula fornicata Crepidula plana Urosalpinx cinerea Busycotypus canaliculatus Ilyanassa obsoleta Ovatella myosotis Geukensia demissa Crassostrea virginica Macoma “ balthica ”Gemma gemma Mercenaria mercenaria Petricola pholadiformis Mya arenaria Perna perna Rangia cuneata Teredo bartschi

Mytilopsis leucophaeata ESTA BLISH M EN T N O T CERTAINClanculus ater Sabia conica Anomia chinensis Teredo furcifera N O T ESTABLISHED Littorina littorea Ostrea edulis Tectarius muricatus Truncatella subcylindrica Mytella charruana Patinopecten yessoensis Laternula limicola CRY PTO G EN IC Siphonaria pectinata Teredo navalis

ch a rru a n a in F lorida and P e rn a p e r n a in Texas. B a llas t w a te r or the m ov em en t o f com m ercial oyste rs m ay have transported the clam R a n g ia cu n ea ta from the G u lf o f M exico to C hesapeake B ay, from w here it m ay have spread do w n the coast to F lo rida , and

Donor Region Receiver Region

NW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificN America NW AtlanticNW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificIndo-Pacific? NE PacificNE Atlantic NW AtlanticNE Atlantic NW AtlanticNE Atlantic NW AtlanticNE Atlantic NW AtlanticMediterranean NE PacificNE Atlantic? NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE Pacific’NW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificNW Atlantic NE PacificSouth America G ulf o f M exicoG ulf o f M exico NW AtlanticNW Atlantic CT : Long Island SoundNW Atlantic NE PacificNW Atlantic NY: Hudson River

NW Pacific NE PacificNW Pacific NE PacificNW Pacific NE PacificNW Atlantic NJ: Bamegat Bay

NW Atlantic NE PacificNE Atlantic NE PacificNW Atlantic NE PacificNE Atlantic NW AtlanticSouth America NW AtlanticNW Pacific NE PacificNW Pacific NE Pacific

Mediterranean? N W A tlantic?NE Atlantic? N W A tlantic?

from w here it m ay have been carried in ballast w a te r to th e H udson River.

O n the C a lifo rn ia coast, a com plex m ix tu re o f ballast w ater, ship fou ling , o r the m ovem ents o f shellfish m ay have led to the

I n t r o d u c e d Ma r in e M o l l u s k s o f N o r t h A m e r ic a 499

TABLE 3.

Summary of introduced marine and estuarine mollusks (excluding opisthobranchs) o f North America.

EstablishedEstablishm ent N o t Certain

NotEstablished Cryptogenic

To Pacific coast (Northeast Pacific) from:Northwest Pacific 12 3 2Indo-Pacific? 1Northwest Atlantic 15 2Northeast Atlantic? 1Northeast Atlantic 1Mediterranean 1

Subtotal 30 3 5To Atlantic coast (Northwest Atlantic) from:Northeast Atlantic 4 1 1?Gulf o f Mexico 1Northwest Atlantic 2 1South America 1North America 1

Subtotal 8 1 2 1To G ulf o f Mexico from:Mediterranean 1?South America 1

Subtotal 1 1

Total 39(*) 4 7 2

(*) Total of 36 species; Ovatella, Corbicula, and Teredo bartschi are each scored twice (see Table 2). because they originate from different donor regions depending upon the recipient regions.

transporta tion o f the A tlan tic m ussel G eu ken sia dem issa from cen ­tral C a lifo rn ia to sou thern C a lifo rn ia and o f the Japanese m ussel M u sc u lis ta senhousia from the no rth ern P acific coast to sou thern C alifornia . Superim posed upo n these po tential intracoastal m ech ­an ism s and rou tes is the probab ility th a t A s ia n m ollusks have been in troduced m ore th an once to the Pacific coast; early in troduc tions o f the m ussel M u sc u lis ta are linked to the com m ercial Pacific o yste r industry , w h ile its appearance in th e 1970s in sou thern C alifo rn ia m ay be due to ballast w ater release d irectly from A sian ports. S im ilarly , the A sian clam T h eora lu b rica m ay have been in troduced in separa te inciden ts from A s ia to bo th cen tral and sou thern C alifornia; nearly 15 years separa te its initial d iscovery in sou thern C alifo rn ia bays (to w here it w as probab ly in troduced in the ballas t w a te r o f sh ips retu rn ing from Ind o n esia and sou theast A s ia during the V ie tnam W ar) from its la ter d iscovery in San F rancisco B ay. The la tter invasion m ay be linked (T ab le 1, re­m arks) to an increase in T h eora ’s p opu la tion in reg ions w h ich no w supply large am oun ts o f ballast w a te r to the Bay.

In con trast to these com plex d ispersal h istories, 2 b ivalves have appeared in N o rth A m erica w hose in troduction is clearly linked to b allast w ater release. T hese are the A sia n corbu lid clam P o ta ­m o co rb u la a m u ren sis and the E uras ian zeb ra m ussel D re issen a p o lym o rp h a . P o ta m o c o rb u la established large populations in San F rancisco B ay in the 1980s (C arlton e t al. 1990, N ich o ls e t al. 1990). a t th e sam e tim e D re issen a w as establish ing large popula­

tions in the G rea t L ak es (G riffith s et al. 1991). D re issen a is in­cluded here by virtue o f its spread into b rack ish (o ligohaline) w aters (T ab le 1). A second species o f D re issen a (M ay and M ars- den 1992), w hose specific nam e rem ains unclear, also in troduced by ballast w a te r in to the G rea t L akes, has no t appeared (as o f N o v em b er 1992) in estuarine env ironm en ts in N o rth A m erica .

DISCUSSION

Regional Patterns and Mechanisms o f Introduction

The strik ing d ifferences b etw een the n um ber o f m o lluscan in ­vasions on the A tlan tic , P acific , and G u lf coasts o f N o rth A m erica (T ab le 3) m ay be due to a com bination o f hum an-m edia ted d is­persal events and regional geological and bio logical P leistocene history. The tw o are d ifficu lt to separate.

A global m echan ism for the po tential in troduc tion o f non- ind igenous m ollusks to all shores is sh ipping. W ith the ebb and flow o f h um an co lon iza tion and com m erce , sh ipp ing has had a d ifferential im pact upon d ifferen t regions a t d ifferen t tim es. Soci­etal changes (the co lon iza tion o f new lands, the open ing and c los­ing o f ports due to political changes, the b irth o f n ew or the dem ise o f o ld c o m m o d itie s , reg io n a l an d w o rld w a rs ) an d sh ip p in g changes (the rep lacem en t o f w o o d w ith iron ships, increased ves­sel speed, the developm en t o f m ore effective an tifou ling pain ts, the adven t o f ba llas t w a te r in the 1880s) have led to n ew invasions in largely unpred ictab le m anners. C o lon iza tion and com m ercial sh ipp ing have occurred o n a regu lar basis be tw een E urope and A tlan tic A m erica since the early 17th cen tury (o r fo r about four centuries). W hile con tac t be tw een E urope and P acific A m erica is

ju s t as o ld , regu lar sh ipping d id no t com m ence until the early 19th cen tury , o r abo u t tw o cen turies la ter (C arlton 1987). D esp ite th is tw o cen tury d icho tom y, sh ipping does n o t con tribu te significantly to the regional d ifferences in invasions betw een the A tlan tic and P acific coasts (T ab le 4).

A m ajo r m echan istic d istinction occurs, how ever, in the history o f com m ercial oyste r m ovem ents to the tw o coastlines. M assive inocu la tion o f the Pacific coast o f N o rth A m erica fo r 60 years be tw een 1870 and th e 1930s w ith m illions o f tons o f liv ing oysters

500 C a r l t o n

TABLE 4.

Introduced marine and estuarine mollusks: Mechanisms o f introduction o f established species (M) in parentheses indicates one o f two possible transport mechanisms; see key, Table 1 footnote.

To:

A tlantic Pacific G ulfC oast C oast C oast

MECHANISMShipping:Fouling/Boring Mytilopsis (BW)

TeredoMytilusGeukensia (COI) Lyrodus pedicellatus Teredo (2 spp.)

Perna (BW)

Shipping:Solid Ballast Littorina (IR)

OvatellaShipping:Water Ballast Rangia (**)

Mytilopsis (S) Dreissena (*)

TheoraPotamocorbula Musculista (COI)

Perna (S)

Commercial Oyster Rangia (**) CecinaIndustry Batillaria

Crepidula (3 spp.)CeratostomaUrosalpinxBusycotypusIlyanassaNassariusOvatellaGeukensia (S)Musculista (BW)MacomaTrapeziumVenerupisGemmaPetricolaMyaLyrodus takanoshimensis

Intentional Littorina (SB) Crassostrea (2 spp.)Release Ostrea Venerupis (Oregon)

Corbicula (**) MercenariaCorbicula (***)

* Dreissena was transported to North America in ballast water from Europe (Carlton, 1992b). but its occurrence in the oligohaline zone of the lower H udson R iver is probably due to natural transport as larvae o r as juven iles on floating m aterials from the upper R iver basin.

** R angia m ay owe its reappearance on the A tlantic coast in H olocene tim es either to the transportation o f oysters from the G u lf o f M exico to C hesapeake B ay or to its transportation as larvae in ballast w ater from the Gulf. B allast w ater is the probable m echanism o f its recen t introduction to the oligohaline portions o f the H udson River. G enetic analyses w ould be o f interest to establish w hether the H udson R iver population originates from the A tlantic coast (such as C hesapeake Bay) or the G u lf coast, i f indeed these potential parental populations are genetically distinct.*** Corbicula was probably transported and released intentionally in Western North America no later than the 1920s-1930s (perhaps in more than one incident): subsequent dispersal from western to eastern America has been both through anthropogenic means (the use of the clam as bait, for example), and by natural dispersal along w ater corridors.

from Japan and fro m th e A tlan tic coast led to the sim ultaneous un in ten tional in ocu la tion o f scores i f no t hundreds o f species o f associated pro tists, invertebrates , algae, seaprasses, and perhaps fish. N o such in troduc tions o f exo tic oysters o n th is scale occurred on the A tlan tic coast o f N o rth A m erica.

A s a result, 27 species o f A sia n and A tlan tic m ollusks have becom e estab lished on Pacific shores. The bays and estuaries o f the Pacific coast w here these species are established are geolopi- cally y o ung (recen tly flooded , < 10,000 years o ld) and do no t have a d iverse native bio ta , suggesting th a t these system s w ere re la­t iv e ly su sc e p tib le to in v a s io n (C a r lto n 197 5 , C a rlto n 1979b. N ich o ls and T hom pson 1985). O n ly one in troduced species, the

M ed ite rran ean m ussel M y tilu s ga lloprovincia lis , occurs in open coast, h igh energy env ironm ents on the Pacific coast; all rem ain ­ing species are restricted to bays and estuaries. W hile the ex traor­d inarily d iverse m olluscan fauna o f these open coast rocky shores m ay thus, in tu rn , resis t invasion , few hum an-m ed ia ted m echa­n ism s serve to transport rocky shores species, and it m ay be that fe w i f an y n o n - in d ig e n o u s sp e c ie s f ro m c o m p a ra b le h a b ita ts a round th e w orld been released in to these com m unities. T hus, on the Pacific coast, there w as an apparen tly coincidental com bina­tio n o f b io tically depauperate reg ions subjected to invasions by a transport m echan ism th a t served to b ring species appropria te to those hab ita ts from o th er reg ions o f the w orld .

I n t r o d u c e d Ma r in e M o l l u s k s o f N o r t h A m e r ic a 501

It is o f in terest to note th a t in a parallel sense the m ost signif­ican t m ollu scan invasion o f the A tlan tic shore also occurred in a geologically young (recently deglaciated , < 10,000 years o ld), bi- o tically depauperate environm ent. T he E uro p ean periw ink le L it­to rina litto rea invaded hard and som e soft bo ttom intertidal com ­m unities o f the A tlan tic coast in the presence o f relatively few native herb ivorous o r om nivorous gastropods. W h y , how ever, o ther w este rn E uro p ean rocky shore gastropods failed to co lonize A m erican A tlan tic shores during cen turies o f in tensive sh ipping is no t clear. I t m ay be th a t E uro p ean p o pu la tions o f the com m on periw inkle L itto r in a sa x a rilis have been m ixed in w ith aborig inal popu la tions and th u s gone undetected . H ow ever, it is c lear th a t a variety o f o ther sm all to m edium size E uro p ean snails (su ch as troch ids and patellid lim pets) e ither w ere n o t in troduced or w ere no t successfu l. H ere aga in tran sp o rt m echan ism s m ay have been rare , w ith little solid (rock) ballast o rig inating from these habitats (w h ich m ay suggest th a t ballast rocks m ay n o t have been the m eans o f in troduc tion o f L itto r in a litto rea to A m erica).

The near absence o f recorded in troduced m ollusks in the G u lf o f M ex ico m ay be linked, as w ith the A tlan tic coast, to the absence o f large scale im portations o f com m ercial oysters o r o ther shellfish from o ther regions. P re -ballast w a te r sh ipp ing con tribu ted few or no clear in troductions, although a detailed b iogeograph ic analysis o f th e sh ipw orm s o f the G u lf o f M ex ico w ou ld be o f interest. The recen t appearances o f the S ou th A m erican fou ling b ivalves M y ­tella and P e rn a in F lo rida and T exas m ay suggest th a t the global increase in ballas t w ater-m ed ia ted invasions (C arlton 1985, 1987) m ay be an active m echan ism th a t w ill add to the non-ind igenous m ollusks o f the G ulf. T he m o v em en t o f the zeb ra m ussel D re is ­se n a p o ly m o rp h a dow n the M ississipp i R iv er and its arrival (perhaps by 1993) in the o ligohaline w aters o f th a t de lta w ill add a second species to the list o f G u lf m arine and estuarine in ­vasions.

Ecological Im pacts

W ith the excep tion o f a few species, there is little experim ental elucidation o f the ecological im pact o f the in troduced m arine m ol­lusks in N o rth A m erica . C arlton (1979b) rev iew s general eco log ­ical considerations, including a rem arkable , albeit anecdotal, early accoun t o f the in terac tions betw een the in troduced A tlan tic m arsh m ussel G eu ken sia d em issa and the C a lifo rn ia c lapper rail. N icho ls and T hom pson (1985) docu m en t th e p ersis tence o f an “ in troduced m udfla t co m m unity” in San F rancisco Bay. w here all o f the m ol­lusks are in troduced (M acom a “b a lth ic a ” ind icated as native in th e ir paper, w as la ter show n to be a probab le in troduc tion to the B ay (M eeh an e t al. 1989)).

R em ain ing largely un investigated is the a lteration o f benth ic com m unity dynam ics by the abundan t in troduced b ivalves on the P acific coast, such as M y tilu s g a lloprovincia lis , G eu ken sia d e ­m issa , M u sc u lis ta senhousia , M y a arenaria , C ra sso strea v irg in ­ica, V en eru p is p h ilip p in a ru m , and G em m a gem m a. A ll o f these species can occur in g reat densities. C ertain com m unity -level in ­terac tions fo r som e o f these species (such as G eukensia , M ya , and G em m a) are k n ow n in the ir d onor reg ions, b u t are app lied w ith d ifficulty to the Pacific coast w here d ifferen t su ites o f potentially in teracting species occur. O nly the m ost recen t b ivalve in troduc­tion , the A sian clam P o ta m o co rb u la am urensis, has been th e sub ­je c t o f in tensive observational studies relative to its rapid p redom ­inance in certain parts o f San F rancisco B ay , reach ing densities o f > 10 ,0 0 0 per square m eter a t sites w here the fo rm er b io ta has becom e rare o r absen t (N icho ls e t al. 1990). P o ta m o c o rb u la th u s jo in s M ya , M u scu lis ta , and G em m a as species potentially critically

im portan t in regu lating phy top lank ton dynam ics in the B ay (C arl­to n e t al. 1990).

O n the Pacific coast and A tlan tic coasts, in teractions betw een several pairs o f native and in troduced gastropods have b een ex­am ined. In terac tions b etw een the in troduced E uro p ean periw ink le L ir to r in a litto rea and native gastropods on the A tlan tic coast have been studied by a num ber o f w orkers. In experim ental studies. P e tra itis (1989) found th a t L itto r in a litto rea negatively affected the g row th o f the native lim pet T ectura testud ina lis . Y am ad a and M an so u r (1987) also experim en ta lly d em onstra ted th a t L itto r in a litto rea can dep ress the g row th rate o f the native rocky shore snail L itto r in a saxa tilis . B ren ch ley (1982) d o cum en ted th a t L itto r in a litto rea w as th e m o st abu n d an t con su m er o f eggs o f the native m udsnail I ly a n a ssa ob so le ta in m id-in tertidal habitats on the A t­lan tic coast. B rench ley and C arlton (1983) fu rther dem onstra ted th a t the re has been a h isto rical change in th e d istribu tion o f I ly a ­n a ssa due to com petitive exclusion by L itto r in a littorea , w ith m i­crohab ita t d isp lacem en t in the m id in tertidal zone o f 70% o f I ly a ­nassa , calculated from littorin id rem oval experim ents. L itto r in a also lim its bo th the upper and low er d istribu tion o f I lyanassa .

O n th e o th er hand , R ace (1982) found th a t the A tlan tic I ly a ­n a ssa obso le ta , in troduced to S an F rancisco B ay , in tu rn lim its the d istribu tion o f the native m udsnail C erith id ea ca lifo rn ica , by m e a n s o f c o m p e titiv e in te ra c tio n s an d b y p re d a tio n o n C e r­ith id ea ’s egg capsules. W hitla tch and O brebsk i (1980) found that w hile the in troduced Japanese snail B a tilla r ia and the native P a ­cific coast snail C erith id ea can be sym patric in T óm ales B ay , C A , sim ilar-sized ind iv iduals exclude each o ther w h en feed ing on the sam e size diatom s.

B erm an and C arlton (1991) exam ined the poten tial in terac tions b etw een the in troduced A tlan tic m arsh snail O va te lla m yo so tis and the native Pacific coast m arsh snails A ssim in e a ca lifo rn ica and L itto r in a su b ro tu n d a ta . N o observational o r experim ental ev i­dence o f com petitive superiority by O va te lla cou ld be found , and they concluded th a t the es tab lishm en t o f the in troduced species in h igh shore, sem iterrestrial env ironm ents d id no t arise a t the ex­pense o f the native species.

W hile the in troduced freshw ater b ivalves C o rb icu la flu m in e a and D re isse n a p o ly m o rp h a have had and are hav ing profound im pacts on the com m unities in w h ich they have invaded (refer­ences in Table 1), eco logical in teractions o f these species in b rack­ish w ate r rem ain largely uninvestigated .

P erhaps no in troduced m arine m ollu sk in N o rth A m erica has had a grea ter im pact th an the periw ink le L itto r in a littorea , w h ich co lon ized m ost o f the A tlan tic coast from N o v a Scotia to N e w Jersey in only 30 years , b e tw een 1860 and 1890 (references in Table 1). P erhaps because little o r no econom ic im pact has been associated w ith th is invasion , it has attracted relatively little notice g lobally as a classic exam ple o f an invasion , aquatic o r terrestrial. L itto r in a has fundam en ta lly altered the d istribu tion and abundance o f algae on rocky shores (references in Table 1), altered hard- bo ttom , soft-bo ttom , and salt m arsh hab ita t dynam ics (B ertness 1984) negative ly in teracted w ith native gastropods (rev iew ed above), dram atically altered the herm it crab shell resource (p ro ­v id ing an abundan t larger shell) and m odified shell u tilization and prefe rence patterns o f the native herm it c rab P a g u ru s lo n g i­ca rp u s (B lackstone 1986), and as g razing h erb ivo res and v acu u m ­ing om nivores, m ay have im portan t im pacts on a w ide variety o f sm all invertebrates, such as barnacles, w hose new ly settled larvae a re c o n su m e d in la rg e n u m b e rs (see “ L ife H a b it” re v ie w in B ren ch ley and C arlto n 1983).

In sum m ary , all bu t the snail O va te lla o f the abundan t species

502 C a r l t o n

o f in troduced m ollusks th a t have been studied have been show n to have dram atic im pacts on the p re-ex isting structure o f the co m ­m unities in w h ich they have invaded. T hese resu lts w ou ld suggest th a t the ex tensive populations o f those species n o t y e t studied m ay also have had. o r are hav ing , substantial im pacts on population dynam ics and in teractions am ong co-occu rring species, bo th na­tive and in troduced. N u m ero u s fru itfu l investiga tions rem ain to be undertaken .

F uture Invasions

P red ic tions o f w h a t species w ill invade, and w here and w h en invasions w ill occur, rem ain one o f the m ore elusive aspects o f b io logical invasion science (M ooney and D rake 1986; D rake et al. 1989). T housands o f species o f m arine and estuarine m ollusks th a t

occur in E urope. A frica. S outh A m erica , A sia , and A ustra lia over­lap in basic env ironm enta l requ irem ents w ith hab ita ts th a t occu r in N o rth A m erica . S electing probab le invasion candidates from th is vast fauna, and pred icting com petitive, p redato ry , o r o ther in ter­actions w ith previously established m olluscan species o r eco log i­cal equ ivalen ts as poten tial m ediato rs o f successfu l estab lishm ent, is a frustrating task. I t is doubtful, fo r exam ple, i f an exam ination o f the A sia n b io ta w ou ld have identified the clam P o ta m o co rb u la am urensis, am ong a background o f scores o f o ther estuarine taxa, as a h igh profile po tential invader.

N evertheless certain lim ited pro jections m ay be m ade. The N e w Z ealand fresh and brack ish w ater snail P o ta m o p y g u s a n ti­p o d i u m , es tab lished in w estern E urope, and occurring in densi­ties o f up to 800,000 snails p er square m eter, is a p robab le fu tu re invader o f eastern N o rth A m erican fresh and o ligohaline habitats (JT C . C. L. Secor, and E. L . M ills , in p reparation). A bu n d an t fou ling b ivalves in Ind ia and A sia , such as the m ussels M o d io lu s str ia tu lu s and L im n o p e rn a fo r tu n e i (M o rto n 1977). m ay y e t reach N o rth A m erica. I f large scale inocu lations o f the Pacific oyster C ra sso strea g ig a s on the A tlan tic coast com m ence in the 1990s (as opposed to the m any sm aller prev ious releases), successfu l estab­lishm en t m ay take place (p resum ably the species w ill be raised on the A tlan tic coast from larvae o r c lean seed, and the in troduction o f associated organ ism s w ith large stocks o f adu lt oysters w ill not take place).

A lso pred ictab le are the eventual de tec tion o f natural sets o f the Japanese sea scallop P a tin o p ec te n ye s so e n s is in B ritish C olum bia, the spreading o f the E uropean edib le oyste r O strea ed u lis from R h ode Island sou th and w es t in to L on g Island S ound, the estab ­lishm en t o f the periw ink le L itto r in a litto rea in San F rancisco B ay i f n o t e lsew here on the Pacific coast, th e es tab lishm en t o f the N e w Z ealand green lipped m ussel P e rn a ca n a licu lu s (C arlto n 1992a: 16) in C a lifo rn ia (to w here it is n o w im ported daily in large num ­

bers fo r d irec t h u m an consum ption ) and the spread ing o f the A sia n c lam P o ta m o c o rb u la a m u ren sis from San F rancisco B ay to o ther bays o n the Pacific coast.

B road ly , the recen t appearances o f R a n g ia cu n ea ta in th e H u d ­son R iver, o f P e rn a p e rn a in T exas, o f tw o species o f the zeb ra m ussel D re issen a in the G rea t L ak es and th u s m u ch o f the rest o f

N o rth A m erica , and o f P o ta m o c o rb u la a m u ren sis in S an F rancisco B ay , argue strongly th a t fu tu re, ba llast-w ater m ediated invasions w ill con tinue to be a regu lar p h enom enon in N o rth A m erica . O n any day, perhaps any hour, it is likely th a t the larvae o f dozens o f species o f m ollusks are released in to coastal w aters o f N orth A m erica by ballast w ater. S im ilarly , steadily increasing local, na­t io n a l, an d g lo b a l p re ssu re s to ex p a n d m a ric u ltu re in d u s tr ie s th rough the im porta tion o f n ew candidate species w ill a lm ost cer­ta in ly m ean the accidental (o r intentional) re lease o f novel species.

T hese pred ictions arise from the p ro jec tion th a t the basic m ech ­an ism s o f hum an-m ed ia ted transpo rt o f non -native species ou t­lined at the beg inn ing o f th is paper w ill rem ain in place fo r m any years to com e. This fo recast is desp ite the ex istence o f a num ber o f in ternational gu idelines (includ ing those o f the In ternational C ouncil fo r th e E x p lo ra tion o f th e Sea, C arlton , 1989) th a t ex is t to p reven t the release o f detrim enta l species th ro u g h fisheries and m aricu ltu re activ ities, and desp ite g row ing in ternational aw areness o f the ro le o f ballast w a te r in transporting exotic species trans- oceanically and interoceanically . W hile our inability to alw ays d istingu ish betw een certain m echan ism s o f in troduc tion o f exotic species m ay m ake full contro l d ifficult, identify ing and quantify­ing the ro le o f such m echanism s, fo llow ed by cooperative m an ­agem en t effo rts, are the necessary p recursors to even tually m o d ­ifying the rate o f “ chess p lay” o f new invasions.

A CK N O W LED G M EN TS

F o r g e n e ro u s ly su p p ly in g re c o rd s an d a d v ic e , I th a n k R. T ucker A b b o tt, the late F ra n k B ernard , T im othy C arey , John C h a p m a n . K e n n e th C h e w . E u g e n e C o a n , M ic h a e l H e lm , K . E la ine H oag land , R obert F o rsy th , John K arlsson , the late M y ra K een. S co tt L am ed , H arry L ee , C h ristopher L etts , R o g er M ann , Jam es M cL ean , A rleen N av arre t, K a th leen Sayce, P aul Scott, R u ­d o lf S tohler, R u th T urner, G eera t V erm eij, W illiam W alton , and M ary W icksten . M y graduate students a t the U n iversity o f O regon Institu te o f M arine B io logy (O IM B ), includ ing P atrick B aker, Jody B erm an , C had H ew itt, and Jo h n M eg ah an , m y postdoctoral associa tes a t O IM B , inc lud ing R icha rd E vere tt, Jona than G eller, and G regory R uiz , and m y constan t field com panion , D ebby C arl­ton , w ere m y cow orkers in th e field in C oos B ay. This w o rk began as a rev ision o f G (no p e r io d fo llow s his firs t nam e, G ) D allas H a n n a ’s 1966 Pacific coast m onograph , an u ndertak ing I beg an in 1969 under th e aeg is o f th e late A lly n G. Sm ith , the late L eo G. H ertle in , the late D oc H anna, C harles R. S tasek , and V icto r Z u llo , all th en a t the C a lifo rn ia A cadem y o f S ciences in San Francisco . This w o rk w as supported in part by a N ational S cience F oundation (N SF) N ational N eeds Postdoctoral F ellow ship a t the W oo d s H ole O ceanograph ic In stitu tion , by N S F G ran t N o . D A R -8 0 0 8 4 5 0 and by the N O A A /O reg o n S ea G ran t C ollege P rogram , p ro jec t R /E M - 19. S tim ulus to prepare th is b r ie f overv iew w as prov ided by the o rgan ization o f a special sym posium , “ M olluscan In troductions and T ransfers: R isk C onsidera tions and Im plica tions,” held a t the 82nd A nnual M eeting o f the N ational Shellfisheries A ssocia tion on A p ril 4 -5 , 1990, in W illiam sburg , V irginia.

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