PagelS4

CHAPTER 5. RESULTS

A! TAXONOMIC GROUPS OF INTRODUCED

In all,we documented 212species ofintroduced organisms inthe Estuary. Thenumbers of speciesper taxonomic group are presented in Figures 2 and3 at lowerand higher levels of aggregation.Invertebrates arethe most common major groupof introducedspecies, accounting for nearly 70'/o of the total, followed by vertebratesand plants with respectivelyabout 15 and 12 percent of thetotaL The mostabundant invertebrates were the arthropods 6'to of invertebrates! followed by molluscs0'10!, annelids 4'/o! andcnidarians 2'fo!. Nearly all thevertebrates were fish,and most of theplants were vascular plants, which were about evenly split between monocots and dicots. Thesenumbers are generally in accordwith our expectations prior to this study,based upon our knowledge of theEstuary's biota and consideration of other regionalreviews of introduced marine and aquatic species, with the exception ofthe numberof species ofvascular plants, which we had anticipated would be higher. Thisresult is in partdue to ourapplication of relatively more restrictive criteria for theinclusion of marsh-edge plants, as discussed inChapter 2. Pagel55 Results

For example,a studyof introduced speciesin theGreat Lakes using less restrictive criteriaproduced a listof 139introduced speciesof which59 species 2%!were vascular plants Mills et al., 1993!, and a similarstudy of the HudsonRiver produced a listof 154 introducedspecies with 97 3%! vascular plants Mills et al., 1995!. As suggested inthe "Methods"section, adding the plants in Appendix1 essentiaByterrestrial plants that havebeen reported in orat theedge of the tidaIwaters of theEstuary! to thelist of organismsin Table 1 producesa list of introducedspecies that can more reasonably be comparedto the Great Lakes and Hudson Riverlists, Thisexpanded list for the Estuary contains 240 introducedspecies of which49 0%!are vascular plants. These three and one otherstudy are compared in Appendix 5.

8! NATIVEREGIONS OF INTRODUCED SPECIES Thenumbers of speciesper native region are presented in Figure 4. Species weretreated as either marine or continental species, as shown in Table3, for assignmenttoappropriate regions. Nointroduced species were identified from the marineregions of the Eastern South Atlantic, the Western South Atlantic orthe EasternNorth Pacific, or from the continental region of Australia/New Zealand, so theseregions do not appear in Figure4. TheEstuary's marine introductions aredominated byspecies from the WesternNorth Atlantic accounting for 41% of allmarine introductions!, the WesternNorth Pacific3%! andthe Eastern North Atlantic 5%!. The Western NorthAtlantic provided mainly mollusks, arthropods andannelids, theWestern NorthPacific predominantly arthropods, followed by annelids,and the Eastern NorthAtlantic provided a few species from each of several groups. The Estuary's continentalintroductions aredominated byspecies from North America 4% of continentalintroductions; mainly fish! and Eurasia 9%, mainlyplants!. Resul ts Page 156

Table 3. Treatmentof IntroducedSpecies as Marine or Continental,for Analysis by NativeRegion

PLANTS Seaweeds marine Vascular Plants Spartirta spp. marine all othervascular plants continental

PROTOZOANS marine

INVERTEBRATES Annelida Ol i goch act a Braachiura sorverbyi continental Limrtodrilus mortothecus marine Parartais frici marine Patamothrix bavaricus continental Tubificaid es spp. marine Varichaetadrilus artgusti p crt ts continental Polychaeta Manayunkia speciasa continental all other polychaetes marine Cipattgopaludirta chinensis malleata con tmenta1 Melartoides tuberculata continental Carbicula flumirtea contin ental all other rnoUuscs marine Arthropoda: Crustacea crayfish continental all other crustaceans marine Arthropoda: Insecta Artisolabis maritima marine ¹ochetirta spp, continental Trigartatylus uhleri marine Entop roc ta Barerttsia bertedeni marine Urnatel la gracilis continental all other invertebrates marine

VE RTXBRATES Fish gobies marine Alosa sapidissima marine Mvrorte saxatilr's marine all other fish continental all other vertebrates con tin en tal Page757 ResutlS

c! TIMING OF INTRODUCTIONS

Analysesof thetiming of introductions,done with the intent to distinguish pulsesor patternsof invasions,are fraught with difficulties. In theSan Francisco Est ag'. as everywhere,larger and more conspicuous species such as certain , fi». »d rnollusks!tend to be noticed relatively soon after their arrival, while smallerand more cryptic organisms may be present but remain unnoticed for scores ofyears until thearrival of an appropriately specialized biologist. For example, the Resu1ts Page 158

Bay'smud-dwelling worms received little attention until Olga Hartman began samplingin theBay in the1930s, and thus some of thepolychaetes derived from the Atlanticmight well have been introduced with Atlanticoysters! as early as the 1870s,The biasesintroduced by taxonomist-dependentrecords of arrival are not limitedto theearlier part of thiscentury. With enougheffort from appropriate taxonomicexperts, many species of tiny introducedorganisms such as protozoans, nematodes,flatworms and so forth couldcertainly be collectedtoday and identifiedfrom San FranciscoBay for the first time, althoughthey may have been in the Estuaryfor 100or moreyears. Given thesechallenges, we have,as notedin Chapter2, excludedfrom our tabulationsof the temporalpatterns of introductionsboth thosespecies whose only availabledates of first recordare the first written accounts,and thosespecies for which the date of first record seemsa clearartifact of the arrival or participationof an interested taxonomist e, g Olga Hartman in the 1930s polychaetes!,Eugene Kozloff in the 1940s symbiotic protozoans!, Willard Hartmanin the 1950s sponges!, and Ralph Brinkhurst in the 1960s oligochaetes!!,or an artifact of an especially focusedsampling effort e. g. the Albatrosssurvey of 1912-23,and our surveyof Bay fouling communitiesin 1993-95!,or simply the fortuitousdiscovery of a speciesin a restrictedhabitat or locality such as Transorchestiaenigrnatica, known only from the shore of Lake Merritt, and Lit torina saxatilis,known only from ten meters of cobblybeach in the EmeryvilleMarina!, and whoseinclusion would provide a misleadingview of the invasionhistory of the Estuary.These species are marked with an asterisk '! in Table 1. The datesof first recordwere tabulatedin five time periods four 30-year periods and one 26-year period! beginning in 1850.Tabulations of the datesof first record in the Estuary are shown in Figure 5, and of the datesof first record in the northwestern Pacific region in Figure 6. The results show a clear trend toward more first records in more recent periods. Over 40% of the first recordsof introductions in the Estuary date from 1970or later, and over 63%from 1940or later, Sincethe first recordsfor thenortheastern Pacific are inclusive of therecords for the Estuary,they necessarily averagesomewhat earlier; nevertheless,51% still date from 1940or later. Someof theseresults should be interpretedwith caution.The datesof arrival mustof courseprecede the dates of first record,by an unknownbut possibly significantaverage period. And althoughwe haveexcluded records that would causea specificand obvious temporal bias, there might exist a generalbias toward increasingnumbers of first records,which could be causedby suchchanges as an increasein samplingeffort, by the developmentof improvedtechniques for samplingand sorting, by a generalincrease in taxonomicknowledge, by anincreased availabilityand improvement of keysand other identification tools, or by other changes. On theother hand, several factors in theanalysis create a biastoward a lower numberof first recordsin the mostrecent period relative to earlierperiods. Thelength of themost recent period is a littleunder 26 years long, compared to 30years for theearlier periods. Extrapolating to 30years at thesame rate of productionof first recordsas has prevailed in theperiod so far wouldadd Page359 Resutts another9 species tothe recent period's tally for the Estuary, and 7 speciesto thetally for thenortheastern Pacific. ~ Whilea substantialnumber of firstrecords were excluded for the reasons discussedabove! from the third, fourth and fifth periods, virtually none were excludedfrom the first two periods. Someorganisms collected inthe most recent period but excluded from the list ofintroductions because of inadequate evidence to determinewhether they areestablished seeTable 8! will probably, with the passage oftime, be recogruzedas established.

~ Withthe passage oftime, the taxonomic problems thatbar the listing ofsome specieswill beresolved. There appear to be a substantialnumber of species thatwere only recently recorded from the Estuary that fall intothis category. Takingthese factors into account, it appears that the data signal a substantial pulseof invasions detected m the Estuary since 1970. The overall rate of introductionsto the Estuary12 speciesbetween ] 85pand ],995!averages one new speciesestablished every36 weeks. Inthe period since 1970, the dates offirst record indicatea rateof onenew species every 24 weeks even after excluding one-third of the212 documented introductions from the analysis, for reasonsdiscussed above!, Results Page160

D! MECHANISMS OF INTRODUCTION

Carlton 994! presenteda tabularoverview of globaldispersal mechanisms by humanagencies in fivebroad categories: ! Vessels;! Aquaculture,Fisheries, and Aquarium Industries;! Other Commercial,Goverrunent, and Private Activities; ! Scientific Research;and ! Canals.These have been reviewed in detail by Carlton979a, 1979b, 1985, 1987, 1992a! and by Carltonet al. 995!. Ourdata indicate that all of these mechanismsexcept for canalshave served to transport non- native speciesto the SanFrancisco Bay area.Within thesecategories, twelve mechanisms Table 1! and their approximate time of initiation relative to human- mediated invasions of the San FranciscoEstuary are summarize here a thirteenth mechanism, "gradual spread," accountsfor the arrival of a number of species, including muskrats,purple loosestrife,and watercress,all in the 20th century,that spreadeither naturally, by human activities,or both, from easternto westernNorth America!. We focus here primarily on those mechanismsthat serve to transport new speciesto the northeastern Pacific, rather than on intraregional vectors. The latter may include, for example, the intentional movement of fish between watersheds by members of the public with the intent of establishing new populations for sport fisheries or pest control such as the mosquitofish Garrtbusia!;the accidental movement of invertebrates in river gravels dredged for use as aggregatefor concrete such as the Asian clam Corbicula!,and the spreading of organismsby dredging activity such as the cordgrass Spartinaalterniflora!. No studies are available on the scaleor role of these within-system vectors. We note later that such work would be of great value in terms of both understanding dispersal potential and dispersal histories and in establishing management policies.

1. VESSELS

a nsi w d s The transport of marine organisms to San FranciscoBay by ships has been theoretically possible since the 16th century, when ships either traveling along the coast and passing by the entranceto the Bay, or making landfall on the shores of the gulf outside the Bay, could have releasedorganisms that made their way into the Bay. Thus, for example, Carlton & Hodder 995! have shown that vesselspassing the California coast in the 1570scould have releasedlarvae-laden hydroid palyps that could have drifted into the Bay. The first ship known to actually enter the Bay was the SanCarlos, on August5, 1775 Galvin, 1971!.By the turn of the 18thcentury a number of ships from the Atlantic and Pacific oceanshad entered the Bay Kemble, 1957!.After 1849,international shipping to the Baypicked up dramaticallydue to a combination of the California Gold Rush, the increasedexport of lumber, grain, minerals,furs, hides,and other productsfrom the rapidly developingindustries of central California, and increasedcolonization and industrialization in general. Kemble957! reviewsthe generalmaritime history of the Bay area- Page161 Resatfs

Little is knownof the modernrole of ship foulingin transportingmarine animalsand plants into San Francisco Bay, although there is evidence that this mechanismcould assume an increasinglyhigher profile due to thedecreasing use forenvironmental reasons! globally ofeffective antifouling paints such as those includingtributyltins TBTs!! A. Taylor, BHP Inc., Australia, pers. comm., 1995!. Theearliest clear records of shipfouling-mediated introductions though not recognizedassuch at the time! are the collections ofseveral North Atlantic fouling organismsinSan Francisco Bay between 1853 and 1860: the Balances irnprovisus853!, the hydroid Tubularia crocea 859! and the hydroid Sarsia tubulosa860! Table1!. Approximately 26percent of Bay invasions 5 species! havearrived by shipfouling and boring Figure7!.

In soli allast rock and t . carriedin a i 's ld Nohistory ofthe release ofships' solid ballast into the Bay Area is available. It presumablyparallels the general history ofshipping into the Bay, but source regionsfor rock and sand ballast, amounts released, and so forth remain tobe investigated. Thatrock and sand ballast may have played an early role is suggested bythe appearanceof the South African shore plant brass buttons Cotula coronopifolia! andthe Atlanticmarsh snail Ovatellamyosotis in the Bayin the 1870s Table 1!. Anotherexample of suchactivity was the release of ballastderived fram Chilean portregions such asIquique and Valparaiso! into the Oakland Estuary up until aboutthe 1920s, a transportvector that may have ]ed to the introduction ofthe southernhemisphere beach hopper Transorchesfia intonearby Lake Merritt. About 3 percentof Bay invasions species! are linked to this mechanism Figure 7!. It is Res uBs Page 162 probablethat this is an underestimate,and that with further studiesmore species especial]yamong non-crustacean arthropods, such as coastalinsects and spiders! will be found to have been ballast-transported, similar to the studies of Lindroth 957! on North Atlantic beetles.

b lla w t Ballastwater may havebeen released into SanFrancisco Bay as early as the 1880s-1890s,but, as with solid ballast,the early history of ballastwater in the Estuary remainsto be studied. Of particularinterest would be data on the timing of increasedpulses of ballastwater release into theEstuary. Modern ballast patterns for selectedports within San FranciscoBay have been investigated by Carlton et al. 995!. In the Ports of Oakland and San Franciscoalone there were more than 2,000 arrivals of bulk cargo vesselsand petroleum product tankers in 1991. "Acknowledged"ballast water releasedfrom thosevessels in thesetwo ports exceeded130,000 metric tons approximately 34,000,000gallons! of water. "Unacknowledged"ballast water water that is on board but not recorded becausethe vesselis classifiedas being "in cargo"rather than "in ballast"! arriving in thesetwo ports is estimated at approximately an additional 130,000metric tons 4,000,000 gallons! Carltonet al., 1995!.Thus, more than 68 million gallonsof ballastwater per year are releasedby bulkersand tankersalone in the CentralBay area.Additional ports in the Bay system receiving large volumes of water include Sacramentoand Stockton, In 1991the Portsof Oaklandand SanFrancisco primarily receivedshipping fromother North Pacific ports. Shipping from Asiaaccounted for 26percent of ship arrivals in San Francisco and 48 percent in Oakland. Ships and thus water! also arrived from Central Pacific and South Pacific ports and, to a smaller extent, from the Atlantic and Indian Carlton et al., 1995!. While somespecies may havebeen brought to the Estuaryin the first half of the20th century by ballastwater Table1!, thefirst reasonablyunambiguous signal of therole of ballastwater was the arrival of two Asianspecies, the shrimp Palaernonrnacrodactylus first collectedin 1957!and the Japanesegoby Triderttiger trigonocephatus first collected in 1962!,The arrival of both may have been associatedwith increasedtranspacific shipping related to theKorean War. Twenty- threepercent 8 species!of the Estuary'snonindigenous species are now linked to ballastwater transport, with a greatlyincreasing number of theseapparently having arrived sincethe 1960s Figure 5!. Thepulse of recentballast invaders into the Fstuaryis particularly evidentin the discovery,since the 1970s,of 15species of small Asian crustaceans copepods, one cumacean,one isopod, 3 mysids, and 2 amphipods!, and, since the 1980s,of two Asian clams Potamocorbufaand Theora!, oneJapanese fish Trr'dentigerbifasciatus!, and a New Zealandcarnivorous sea slug Phitine!.The appearanceof the Chinesemitten Eriocheirsinenst's in the Bay may also be linked to ballast water but see mechanism 11, below!. Results Page163

2. FISHERIESIMARSH RESTORATION AND BIOCONTROI. AcrlvITIKS a h'met fla ' te d a' a

The first Atlantic oysterswere plantedin SanFrancisco Bay in 1869,the year of the completionof the TranscontinentalRailroad. Early shipmentswere largely from New York and New Jerseyand occasionallyfrom ChesapeakeBay. The industrygrew and flourished in the 1890s,tapering off sharplyafter 1900 for reasons variouslycited as increases in pollutionand changes in the Bay'shydrology and flushingdynamics; see Carlton, 1979a!. The last oyster seed shipments occurred about1910, and adult oysterscontinued to be receivedfor holding in the Bay until the 1930s.Barrett 963! and Carlton 979a! review the history of Atlantic oystering in the Bay in detail. Thefirst Japaneseoysters were plantedout in the Ba.yin 1932,with plantings continuinguntil 1939.Occasional plantings for "experimental"purposes were started in the 1950s.Carlton 979a! reviews this brief and little-known history. The "signal"of Atlantic oysteringin terms of invasionsoccurred early, with the appearanceof the commonAtlantic soft-shelled clam Mya arenariain theBay by 1874 it was,oddly enough, not recognizedas such, and described as a newspecies!!. The Atlantic marshsnail Qvatellamay have also arrived with oysters,if not with ship'sballast, at this time.Coincident, however, with thegreatly increased pulse of plantingsin the 1890sof Atlantic oysterswas the appearancein the Bay of a variety of we/1-knownEast Coast clams and snails, including the oyster drill Urosalpinx 890!, the tiny gem clam Gemma893!, the marsh musselArcuatula =Ischadium! demissa894', two species of slipper Iimpets Crepidula convexaand plana 898, 1901!and the mudsnail Jlyanassa907!. Similarly, the Atlantic shell-boring sponge Cliona 891! and the common Atlantic pileworm Nereis succinea896! had been recordedby this time. Thirty speciesrepresenting about 15% of the introduced biota are now recogruzedas originating from Atlantic oystering activity. In concert with the much lower level of Japaneseoystering in the Bay, only a few speciesin the Bay are recognized as having arrived with this industry. After the pulse of 1.930plantings, the Japanesemussel Musculista 946! and the Japanese clam Venerupis philippinarum = Tapesjaponica! 946! were collected in the Bay. The immediate role of Japaneseoystering in transporting other speciesis not as clear, as many candidate taxa may also have entered the Bay by ship fouling or other means Table 1!. The Japanesebrown seaweedSargassum muticum, while apparently introduced to the Pacific coastby Japaneseoystering, may have entered the Bay as drift seaweedfrom elsewhere on the coast or, even more likely, as fouling on coastalship traffic. The Japaneseparasitic copepod Mytilicola may similarly have been transported into the Bay in mussels in ship fouling from more northern stations.About 4 percent of the Bay's invasions are linked to Japaneseoystering Figure 5!.

Fish or shellfish stocked b th overnrnent to establish or su fi he We review the early attempts to move Eastern fish West, facilitated by the completionof the TranscontinentalRailroad, in Chapter3. Americanshad, white Results Page164 catfish,several species of bullhead,and striped bass were all successfullytransported, released, and establishedin the Bay commencing in the 1870s.Intentional fish stockingby governmentagencies of freshwaterand estuarine fish into California and the Bay region has continuedto varying degreesthroughout the 20thcentury seediscussions in Chapter3!. Nineteenspecies 9 percent!of the exoticbiota owe their origins to this mechanism.

a a r t Plantingseither for marshrestoration or possiblyfor erosioncontrol were involved in the introduction of four speciesof the cordgrass Spartirtain the Bay in the 1960sand 1970s.One was plantedin Washingtonstate, and then transplanted from there to San Francisco Bay; another was likely introduced to Washington in solid ballast, and later independently introduced to the Bay from the Atlantic coast for marsh restoration; the third was introduced to Humboldt Bay in solid ballast, then transplanted to San FranciscoBay; the fourth, first reported in the Bay in 1968, presumablyarrived with an undocumentedrestoration or erosioncontrol project Chapter 3!. As we based our analysis on the mechanismsthat brought to the northeastern Pacific the stocks of organisms introduced to the Estuary, we counted three of these cordgrassesas introducedvia marshrestoration or erosioncontrol .4/0 of the exotic biota!, and one via solid ballast.

idental ea W ra i Accidental releasesof plants, fish, and invertebratesthrough stocking and planting programs began to be detected in the 1950sin the Bay region, although these may have occurred much earlier. Thus the rainwater killifish Lucartiaparva appeared in 1958on the Bay's margins, apparently having been releasedaccidentally with shipments of other fish in more eastern localities. The green sunfish and bigscalelogperch, as well as the curly-leaf pondweed, are additional accidental releases.Less than 3 percent of the Estuary's invaders comeunder this category.

aw ed a 'v bai W Miller 969! first described this mechanism focusing on lobster packing! as an active vector for transporting northwestern Atlantic marine organisms to San FranciscoBay. As discussedin Chapter 3 under the periwinkle Litforina saxatilis!, this mechanismcontinues vigorously today. Largequantities of Atlantic bait worms, and with them as packingmaterial Atlantic rocky shoreseaweeds mainly Ascophyllumnodosum!, are air-shippedweekly to sport-fishingsupply storesin the Bay Area. Investigations in progress Lau, 1995;Cohen, Lau & Carlton, in prep.! reveal that these seaweedssupport large numbers of living Atlantic coast invertebrates, including mollusks, worms, crustaceans,and insects, which are routinely releasedinto the Bayby anglers The apparentlyrecent appearance of the Atlantic red alga Callithamrtiottin the Bay, the establislunentof a populationof the Atlantic periwinkle saxatilis,and perhapseven the appearanceof the Atlantic green crab Carcinus maenasmay be linked to this active and unregulated Page165 Results flowof New England rocky shore organisms to the Bay. To date, less than one percentofthe Estuary's invaders areclearly linked to this mechanism, butthe occasionalappearance of other species not yet known to bewstablished such as the Atlanticperiwinkle Liftorirta tittorea; Table 8! and the continual release of living seaweedsin the Bay which could themselves become established for example, Ascophyllumnodosum hasnow gained a foothold mthe Hood Canal, I'uget Sound; L.Goff, pers. comm., 1992!, predictably herald the imminent establishment ofyet additionalAtlantic species.

'oc ntr 1 rel B Invertebratesand hsh released for biocontrol in theBay region have been few, althoughtherelease ofmuskellunge andsea lions in San Francisco's LakeMerced to controlintroduced carp is a noteworthyincident in the history of human attemptsatbiocontrol Chapter 2!.Two South American weevils Neochetirta spp.! werereleased in the 1980s for water hyacinth control; these became established but appeartohave had little impact on these weeds Chapter 3!.An early introduction 922!to the state was the mosquitofish Gambusia affinis which arrived on Bay shoresatleast by the1960s if not much earlier. The inland silversides Menidia berytlina,brought tothe state for gnat and midge control in 1967, soon entered 971! Baywaters. These four species represent about two percent ofthe Estuary's exotic biota.

3. OTHER COMMERCIAL AND I RIVATK ACIVv'ITIES a Releases b an indiv'dual whether inte ' nal ar accidental RI Underthis mechanismwe includenon-government releases to establishfood resources the snail Cipangopaludina, theclam Corbicuta, the crayfish Procambarus ctarkii,carp, bullfrog, and perhaps the Chinese mitten crab Eriocheir sinensis and thepond slider turtle!; releases or escapesfrom residential ponds and aquariums plants and oligochaete worms with them!, possibly the snail Metanoides, goldfish, carp,and the turtle!; escapes from commercial breeding or rearingponds crayfish, carp,bullfrog! and discards of marketgoods the snailCipangopatttdina again!. Fifteenspecies representing 7 percent of the introducedbiota have been linked to this mechanismaccording to our data.With the possibleexception of carp,water hyacinthand Cipangopaludina,these have all been20th century activities.

4. SCIENTIFIC RESEARCH a Releases as a result of researchactivities whether inte tional o accidental R Scientificresearch efforts have resultedin relatively few introductionsto the Estuary.The bullfrog and- the virile crayfishboth owetheir establishment,at least in part,to releasesfrozn educational and research institutions in thelast half of this century.The green crab Carcinus maenas, as noted below, may be a furtherand more recentexample of this vectorI.ess than one percent of theEstuaries nonindigenous biota has arrived via this rnechanisrn. Results Pagel66

Thecomplexities andchallenges inanalyzing andproperly weighting these manytransport vectors, in termsof both developing anhistorical perspective and establishingeffective management options, isiHustrated bythe many species in Table1for which multiple transport vectors can be assigned. Therecent appearance ofthe Atlantic green crab Carcinus maenas inSan Francisco Bayis a superb illustrationofthe analytical andmanagerial hurdles involved. The green crab could havearrived by at least four different mechanisms Cohen et al., 1995!, whose relativelikelihood isdifficult toestimate. Asdiscussed inChapter 3,it may have arrivedin ballast water from any of several different source regions Atlantic America,Australia, Europe orSouth Africa, with the first two perhaps more likely basedon shipping patterns!; viaseaweed released from the bait worm industry; via activerelease from a schoolorresearch aquarium; orvia a ship'ssea chest or seawaterpipe system. Clearly, the control offuture invasions hinges on a clearer andmore detailed resolution of whichmechanism served to introduceCarcinus to theBay. Recent collections in the Estuary ofthe Atlantic amphipod Gammarus daiberi{1983!, the Atlantic worm Marenzelleria viridis 991! and the Atlantic snail Littorinasaxatilis 993! may point to the Atlantic as the source region for Carcinus {1989/1990!,andmay further suggest themodern resurgence ofan active Northwest Atlanticto SanFrancisco Bay transport corridor.