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Number of Species of Vascular Plants, Which We Had Anticipated Would Be Higher PagelS4 CHAPTER 5. RESULTS A! TAXONOMIC GROUPS OF INTRODUCED SPECIES 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 Mollusca 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 crabs, 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
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