A Review of the Exotic Species Inhabiting the Upper

San Marcos River, Texas, U.S.A

David E. Bowles & Beth Davis Bowles

May 28, 2001

Recommended citation: Bowles, D. E., and B. D. Bowles. 2001. A review of the exotic species inhabiting the upper San Marcos River, Texas, U.S.A. Texas Parks and Wildlife Department, Austin, TX. 30 pp.

A Review of the Exotic Species Inhabiting the Upper San Marcos River, Hays County Texas, U.S.A.

David E. Bowles

Texas Parks and Wildlife Department. 4200 Smith School Road, Austin, TX 78744, USA

Beth Davis Bowles

Molecular Cell and Developmental Biology, School of Biological Sciences, University of Texas, Austin, TX 78712, USA

Abstract.—The occurrence and current status of aquatic and semi-aquatic exotic species and their real or potential impacts on native species are assessed for the San Marcos River, Texas. Exotic species were found to be abundant in the river including 16 species of plants, four species of invertebrates, and 28 species of vertebrates. These species were introduced through a variety of means, but released aquaria specimens and stocking for the purpose of supplementing the sport fishery of the river are the primary sources. The geographic origin of the species reported here is diverse with most being native to tropical and subtropical areas of Asia, Central and South America, and other areas of the southern United States outside of central Texas. Solutions to address the problem of exotic species introductions are presented including some management and control options, regulatory mechanisms, and public education and outreach. Public education, and, when possible, management and removal of exotic species are proposed as the best means of alleviating threats to the native fauna and flora of the river.

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There has been a continual increase in the problematic because they are difficult, if rate of species invasions into freshwater not impossible, to control or manage once habitats in the United States (U.S.), and established (Courtenay and Robins 1975; the rate that mankind is intentionally Simberloff 1996). introducing species to new habitats also is The upper San Marcos River, from its increasing (Lachner et al. 1970; source at San Marcos Springs (impounded Courtenay and Hensley 1980; Schwartz as Spring Lake) in the City of San 1997). Introductions of non-native Marcos, Hays County, Texas to its species may seem harmless in some confluence with the Blanco River some 11 circumstances, or even desirable in the km downstream (Fig. 1), has been case of certain sport fishes. Indeed, impacted by exotic species for over 100 certain introduced species play major years. San Marcos Springs are the second roles in our culture and many have largest spring system in Texas producing socioeconomic benefits (e.g., sport fishes, some 4,500 liters per second average flow aquacultural enterprises). However, (Brune 1981). The San Marcos River is introductions of many non-native species an ecologically unique system that serves can have severe negative effects on as habitat to several threatened, ecosystem structure and functioning and endangered, and endemic species (United ultimately result in the loss of biological States Fish and Wildlife Service 1995). diversity (Lodge 1993). Exotic species The warm subtropical to Mediterranean compete with native species for food and climate of central Texas and the thermally space, serve as predators, introduce constant (~23oC) flows of the San Marcos disease and parasites, modify habitats, and Springs and River provide an excellent sometimes interbreed with native species. medium for establishment of non-native There also are aesthetic considerations species. No previous attempt has been associated with introduced species such as made to fully address the extent to which recreational and sport value degradation. exotic species have invaded the river. For instance, lakes and streams clogged In this paper, we present a list of the with Hydrilla are not popular for known exotic species that have been swimming and other aquatic sports reported from the San Marcos River because the abrasive texture of this ecosystem and address the current status invasive weed scratches the skin, and its of these species and their real and voluminous growth habits make potential impacts on the native flora and movement by swimmers and watercraft fauna. A survey of the exotic flora and difficult. Other activities such as hunting fauna of the San Marcos River is an and fishing also can be impacted. Exotic important step toward developing relevant species can cause serious economic losses management plans for protecting and when they detrimentally impact conserving rare, threatened and recreational, commercial and agricultural endangered species that naturally occur in enterprises, or pose risks to human health the river (U.S. Fish and Wildlife Service and welfare (Pimentel et al. 2000). To 1995). confound this issue further, invasive aquatic species are particularly 1 2

Methods the species reported here are diverse with most coming from Asia, Central and The terminology for exotic species used South America, and from other locations herein follows Shafland and Lewis (1984), within North America north of Mexico. and we thus define exotic species as those Under Texas law, possession, sale, and entering an ecosystem from beyond their distribution of several of the species historic range through non-natural means. discussed here are prohibited due to the The scope of this paper is restricted to real or potential risks they pose to native aquatic and semiaquatic species, but we species (Howells 1999). recognize that there are numerous terrestrial and riparian exotic species in the San Marcos River watershed that may have impacts on the ecology of the river. Aquatic Vegetation To the extent known, we also assess the current relative population status of these We found 16 species of aquatic and species and consider their potential semi-aquatic plants have been introduced impacts on native species and habitats. into the river and its headwaters at Spring Based on this information, we have Lake, and most of these have established assigned a relative ecological impact populations. Many of these species are (high, medium, low) to each species. considered noxious weeds in Texas and Known or suspected ecological impacts elsewhere in the world (Barrett 1989). are based on published information and Introduction of aquatic vegetation into our own observations. We also discuss large spring ecosystems in Texas presents the geographic origin of each species, several potentially significant problems. their probable means and dates of For example, invasive aquatic vegetation introduction, and summarize pertinent can impact human activity and safety, literature relating to their biology and interfere with navigation, increase risk and management in the river. severity of flooding, and disrupt ecosystem structure and functioning Results and Discussion (Gurnell and Midgley 1994; Madsen 1997). The many threats to aquatic The exotic species that presently occur ecosystems from invading hydrophytes or have been reported from the San were addressed by Cronk and Fuller Marcos River are presented in Table 1. (1995) and Barrett (1989). Common Forty-eight species including 16 plants, names for plants presented here follow four invertebrates, 18 fish, one reptile, Brako et al. (1995) and Correll and eight birds, and one mammal are listed. Correll (1975). Thirty-two of these species are established in the river and have breeding populations Arundo donax L., giant reed. —This while the remaining 14 species either have species apparently was introduced from localized populations or apparently did the Mediterranean and is now widely not become established following naturalized in the southern U.S. (Correll introduction. The geographic origins of and Correll 1975). Giant reed commonly 2 3

grows along the banks of the river and on along the upper river although the species elevated, partially dewatered areas and has been present there for nearly 100 sandbars within the stream channel. Once years. The species apparently was established, giant reed grows to several introduced sometime after 1907, and the meters in height and produces first herbarium record is dated 1929 considerable shading. In addition, the (Akridge and Fonteyn 1981). Elephant “islands” formed by giant reed can cause ear dominates the shoreline areas of accumulation of debris and sediments Spring Lake and the shallow, near bank ultimately forming larger islands that alter zone of the river to well downstream of its stream channel morphology. The date of confluence with the Blanco River. introduction of this species to the river is Elephant ear is considered highly unknown, but the most probable time was detrimental to the ecological functioning before 1900 given that it was widely of the river (Akridge and Fonteyn 1981; distributed in the southern U.S. in the U.S. Fish and Wildlife Service 1995). 1800s. Cryptocoryne beckettii Thw. ex R. Ceratopteris thalichtroides (L.) Brongn., Trim.—This hydrophyte is a native of floating fern.—Cook et al. (1974) stated southeast Asia (Cook et al. 1974). A this species is a native of Asia where it is population of Cryptocoryne becketti commonly cultivated for food in Japan. occurs in the river near the outfall of the The first report of this species from the San Marcos Wastewater Treatment river was by Morton (1967) from a Facility. The occurrence of this species in collection made in 1963, who further the river likely resulted from an reported the plant to be native to South unintentional release by an aquarist given America in addition to Asia. Hannen [sic. the popularity of this plant in the Hannan] (1969) followed Morton’s work aquarium industry. The year of documenting the establishment of C. introduction of C. becketti into the river is thalichtroides in the river, and he stated unknown, but biologists with the Texas that this species was intentionally Parks and Wildlife Department first introduced for purposes of commercial observed this species at its current production by the now defunct Texas location in 1993 (DEB, personal Aquatic Plants Company. This species is observation). common along the shoreline areas of Spring Lake and backwater areas of the Egeria densa Planch., leafy elodea.— river. Floating fern subsequently has been This native of South America (Cook et al. introduced into other large spring systems 1974) has been widely sold as an in Texas (Lemke 1994). aquarium plant suggesting its probable source of introduction into the river. Colocasia esculenta (L.) Schott, Egeria densa was not listed by Watkins elephant ear.—Elephant ear is native to (1930), but Devall (1940) reported it as southeast Asia and Indonesia (Cook et al. Elodea canadensis suggesting it was 1974). Akridge and Fonteyn (1981) first introduced into the river between 1930 reported C. esculenta to be naturalized and 1940. Leafy elodea is particularly 3 4

abundant in the area immediately program associated with San Marcos upstream of Rio Vista Dam (Fig. 1). Springs recently was initiated by However, given its limited distribution in Southwest Texas State University and the river, ecological impacts caused by water hyacinth is now being actively this species probably are not significant. removed from the Spring Lake area. Water hyacinth is listed as a prohibited Eichhornia crassipes (Martinus) Solms., species in Texas (Howells 1999). water-hyacinth.—Barrett (1989) reported that water hyacinth is native to the tropical Hydrilla verticillata (L. f.) Royle, lowlands of South America, but it has now hydrilla.—This hydrophyte has become spread to more than 50 countries on five so widely introduced around the world continents. Around 1884, popular interest that its native distribution is uncertain. in water hyacinth began increasing, and For instance, Tiner (1993) reported that plants imported from Venezuela were hydrilla is native to Africa, but Langeland distributed as gifts by a Japanese (1996) stated it is native to the warmer delegation at a cotton exposition in New parts of Asia. Regardless, hydrilla is Orleans (Penfound and Earle 1948; considered among the most serious Williams 1980). The beautiful purple nuisance species of aquatic vegetation in flowers associated with this plant quickly the U.S. (Langeland 1996; Madsen 1997). led to its popularity and dispersal This species is well established in the throughout the southern U.S. The exact river where it now dominates the year of introduction into the San Marcos macrophyte community in some areas and River is unknown, but photographs of the eliminates habitat for native plants (Poole river taken in the early 1920s clearly show and Bowles 1999), fish, and invertebrates. water hyacinth in the background. The Hydrilla was first introduced into the U.S. first written record of this species from the in the late 1950s for use in aquariums river was by Devall (1940). Water (Williams 1980). Neither Hannan and hyacinth is considered to be to be among Dorris (1970) or Bruchmiller (1973) the 10 worst invasive weeds in the world reported hydrilla in their studies of the (Williams 1980; Barrett 1989), and it also river’s vegetation, but it was first reported is considered to be among the most from the river by Flook (1975). Lemke serious nuisance species in the southern (1989) noted that this species was among U.S. (Madsen 1997). However, water the most dominant macrophytes present. hyacinth primarily occurs along the Hydrilla verticillata is on the Texas margins of Spring Lake and backwater prohibited species list (Howells 1999). areas of the river, and its population densities in these locations are relatively Hygrophila polysperma (Roxb.) T. small. Penfound and Earle (1948) and Anderson, Indian hygrophila.—This Gopal (1987) gave detailed accounts of species is native to Malaysia and India. the biology of E. crassipes, and Barrett Angerstein and Lemke (1994) first (1989) discussed aspects of the biology of reported H. polysperma from the San E. crassipes that make this species such a Marcos River. However, based on noxious weed. A “wetland” restoration collection data from herbarium specimens, 4 5

it appears that H. polysperma has been success of this species as a weed. established in the river for well over 25 years (Angerstein and Lemke 1994). This Myriophyllum aquaticum (Vell.) Verdc., species is now naturalized in the upper parrot’s feather.—Nelson and Couch river where it constitutes a significant (1985) discussed the introduction and portion of the hydrophyte community, and distribution of this South American native it appears to have taken over much of the in North America. The first report of habitat formerly occupied by native parrot’s feather from the upper San species. Such impacts ultimately may be Marcos River was by Hannan and Dorris shown to have significant impacts on (1970), but Nelson and Couch (1985) endangered and endemic species living in reported that M. aquaticum was present in the river (U.S. Fish and Wildlife Service central Texas by the 1940s. This species 1995). Hygrophila polysperma has is restricted to Spring Lake and backwater several characteristics that make it a areas of the river, and it occurs at very low serious threat to the native flora and fauna densities. Sutton (1985) reviewed the of the river. These characteristics include biology and ecology of parrot’s feather, having a high growth potential, vigorous and he suggested that this species is not a vegetative reproduction, the ability to live major noxious weed. in shaded areas, and plasticity with respect to habitat choice (Botts et al. 1990; Myriophyllum spicatum L., Eurasian Kovach et al. 1992; Spencer and Bowes water-milfoil.—A native of North Africa 1985). Hygrophila is a popular aquarium and Eurasia, this species is considered to plant and likely was introduced into the be among the worst nuisance aquatic river by aquarists. The U.S. Department weeds in the U.S. (Madsen 1997). Couch of Agriculture (1983) placed this species and Nelson (1985) reported on the on the federal list of noxious weeds. introduction and distribution of M. spicatum in North America, and they Limnophila sessiliflora (Vahl) Blume, indicated that, based on herbarium limnophila.—This hydrophyte is native to records, this species was first introduced India and Southeast Asia (Lemke 1994). into Hays County, Texas during the The first record of limnophila in the river 1950s. However, the specific year of its was by Bruchmiller (1973). Lemke introduction into the San Marcos River is (1994) stated that he could find no unknown. Lemke (1989) reported M. evidence that this species is having any spicatum in his survey of aquatic deleterious effects on the growth of native vegetation of the river, but the species was hydrophytes in the river, but he warned not reported by Hannan and Dorris (1970) that the spread of this species should be suggesting that it may not have been closely monitored. However, Lemke introduced at the time of their study. (1999) later reported that he had not Lemke (1999) later reported that he had observed L. sessiliflora in the river since not observed Eurasian water-milfoil in the 1984. Spencer and Bowes (1985) river in recent years. The production reviewed the physiological characteristics biology and ecology of Eurasian water- of Limnophila that contribute to the milfoil were reviewed by Grace and 5 6

Wetzel (1978) and Smith and Barko naturalized in the U.S. (Abrams 1964). (1990), respectively. Myriophyllum This semi-aquatic plant is uncommon, but spicatum is on the Texas prohibited it is established in the Spring Lake area species list (Howells 1999). where it inhabits shallow and wetted areas around the lake margins. The date of Pistia stratiotes L., water lettuce.— This introduction is unknown, and this is the species may be native to the southern gulf first report of this species from the San coastal plain of the U.S., but apparently it Marcos River ecosystem. Correll and is not native to central Texas (Bailey Correll (1975) reported that this species 1949). However, Dray et al. (1993) has an acrid sap that can raise blisters on argued water lettuce is not native to the human skin. U.S. because there is a paucity of phytophagous specialists associated with Rorippa nasturtium-aquaticum (L.) it in this country compared to South Hayek, water cress.—A native of America. Lemke (1999) considers P. Europe, this species probably was stratiotes to be transplanted into the San introduced prior to 1900 by Europeans Marcos River from eastern or southern who settled in central Texas. However, Texas. The first known record of this the first report of water cress at San species from the river was by Watkins Marcos Springs was by Watkins (1930). (1930), indicating that it had been Some argue that water cress is native to introduced no later than the 1920s. Water North America (Whitley et al. 1990). lettuce is poorly represented in the river Water cress is uncommon in the river. where it is restricted to Spring Lake and backwater areas. Xanthosoma sagittifolium (L.) Schott., elephant ear.—This species of elephant Potamogeton crispus L., curled ear is native to tropical America from the pondweed.— This native of Europe was West Indies through South America first recorded from the San Marcos River (Bailey 1949). Presently, X. sagittifolium by Bruchmiller (1973). Potamogeton is restricted to small areas immediately crispus was well established in some areas downstream of the spillways of Spring of the river by 1984 (DEB, personal Lake Dam and Rio Vista Dam. Although observation). However, Lemke (1999) the date of introduction of X. sagittifolium reported that he had not observed curled to the river is unknown, Lemke and pondweed in the river since 1984, and Schneider (1988) first reported its Poole and Bowles (1999) likewise did not occurrence there. Xanthosoma report finding any examples of this sagittifolium is commonly used as an species in their study. The source of ornamental, and it has become introduction is likely from aquarists as this sporadically naturalized in the southern species is commonly used in aquariums. U.S. (Godfrey and Wooten 1979).

Ranunculus sceleratus L., cursed Invertebrates buttercup.— Cursed buttercup is native to Europe, but it has become widely Four species of exotic invertebrates have 6 7 been recorded from the San Marcos River. Dundee 1969; McMahon 1982). Britton All four species are mollusks that are (1982) briefly reviewed several ecological considered highly detrimental to the and biological studies pertaining to the ecological functioning of the river. Asian clam in Texas. Ecological studies for Texas populations of this species were Corbicula fluminea (Müller), Asian conducted by Horne and McIntosh (1979) clam.—This species was introduced into and Bushek and Cameron (1992). The the U.S. from southeast Asia prior to the Asian clam is no longer listed as a early 1920s (Britton 1982; McMahon prohibited species in Texas primarily 1982; Counts 1986). Asian clam is well because it already occurs statewide established in the upper San Marcos (Howells 1999). River. In some areas of the river, accumulations of shells from dead Marisa cornuarietis (L.), giant rams- specimens constitute a large portion of the horn snail.—This large snail is a native of surface substrate. The exact year of tropical America from Panama southward introduction of C. fluminea into the river into South America (Neck 1984). Rams- is unknown. However, this species was horn snail was first reported from the San well established throughout much of Marcos River in 1983 (Neck 1984) where Texas by the early 1970s (Metcalf 1966; it is now established. Release by aquarists Murray 1971b, Metcalf and Smartt 1972; is the presumed source of introduction. Murray 1972; Britton and Murphy 1977; The voracious appetite of this herbivorous Britton 1982; McMahon 1982), and it was species suggests it has significant common in the river by 1982 (DEB potential for disrupting the ecological personal observation). How C. fluminea functioning of the river by feeding on was introduced into the river is unknown, native aquatic vegetation (Seaman and but probable sources include discarded Porterfield 1964; Horne et al. 1992; fishing bait (Britton 1982; McMahon Howard 1998). Among this vegetation is 1982), released aquarium specimens, and the federally-endangered Texas wild-rice accidental transport. However, as noted (Zizania texana Hitchcock). Robins by McMahon (1982), C. fluminea has (1971) reported that grackles (Quiscalis remarkable inherent dispersal abilities and sp.) in Florida preyed heavily on M. may well be responsible for its own rapid cornuarietis occupying shallow waters spread throughout Texas and elsewhere. suggesting that similar predation may A considerable body of literature has been occur along areas of the San Marcos River amassed on Asian clam largely due to its that are frequented by these birds. Marisa invasive nature and the negative cornuarietis is listed as a prohibited ecological impacts it creates in aquatic species in Texas (Howells 1999). ecosystems (e.g., Sinclair 1971; McMahon 1982, 1983; Britton and Melanoides tuberculatus (Müller), red- Prezant 1986; McMahon and Williams rimmed melania.—This thiarid snail is a 1986; Strayer 1999). The introduction native of southern Asia and it has been and spread of C. fluminea in the U.S. has commonly sold in the aquarium industry been thoroughly documented (e.g., (Murray 1971a). The date of introduction 7 8 to the San Marcos River is unknown, but Comal counties suggesting a this species was reported (as Thiara corresponding timeframe for introduction tuberculata) from neighboring counties in into the river. Lindholm (1979) first the 1960s (Murray 1964). Lindholm reported this species from the river in his (1979) first reported its occurrence in the study of the gastropods of that system. river. Murray (1971a) indicated that M. However, the actual date of introduction is tuberculatus has high reproductive rates unknown. Murray (1971a) noted that, and can displace native snails. However, much like M. tuberculatus, quilted we have observed that this species, melania has high reproductive rates and although established, occurs in fairly low can displace native snails. Indeed, densities in the river. Pointier et al. wherever this species is introduced, its (1994) found that this species along with populations become quickly established Tarebia granifera (see below) effectively and grow to enormous densities (Abbott excluded the native snail Biomphalaria 1950; Murray 1971a). Recent collections glabrata (Say) from the streams to which from the San Marcos River show this they were introduced. The impacts of species constitutes to up to 60% of the thiard snails on the native snail benthic invertebrate density in some areas Biomphalaria obstructus Morelet in the (DEB, personal observation), and shells river are unknown. The red-rimmed from dead individuals litter the stream melania apparently serves as an bottom. Tarebia granifera appears to be intermediate host in the life cycle of a rapidly displacing native snails such as fluke (Trematoda) that parasitizes the gills Elimia comalensis Pilsbry in the river. of certain percid fishes including the Abbott (1950) discussed aspects of the federally-endangered fountain darter biology of the quilted melania, and it has (Etheostoma fonticola Jordan and Gilbert) been shown to be an intermediate host of (Mitchell et al. 2000). Murray and Haines various flukes (Trematoda), including the (1969) similarly reported the red-rimmed human lung fluke (P. westermani) (Abbott melania to be the intermediate host of a 1952; Murray and Stewart 1968; Murray trematode in Texas with adult flukes being and Haines 1969). parasites of waterfowl, and Murray (1971a) noted that it is an intermediate Fish host of the human lung fluke (Paragonimus westermani). We report here 18 species of fish that have been introduced into the San Marcos Tarebia granifera (Lamarck), quilted River. Some of the species presented here melania.—The means by which this are known only from single occurrences Asian species was introduced to the San and are not thought to have breeding Marcos River is unknown although it has populations in the river. Nevertheless, we been commonly sold in the aquarium list these records because of their potential industry (Murray 1971a) and may have for possible reintroduction and originated from released aquarium stocks. establishment into the river. Other Murray (1964) reported this species (as species, primarily gamefishes, that Thiara granifera) from nearby Bexar and perhaps could be considered introduced 8 9 species are not listed here, including the tetra.—Mexican tetras are native to the Florida subspecies of the largemouth bass Rio Grande and possibly Nueces River (Micropterus salmoides Lacépède) which drainages in Texas. However, this species has been widely introduced for was widely introduced into the Guadalupe recreational sport fishing in Texas. This River Basin between 1908 and 1930 strain now occurs in the river although its (Brown 1953; Hubbs et al. 1978). The impacts, exclusive of genetic dilution of first record of Mexican tetra from the San native largemouth bass (Morizot et al. Marcos River is 1938 (Brown 1953). This 1991), are probably negligible. Hubbs species is established and common in the (1982) gave an excellent account of the river where it is particularly abundant in various exotic fishes introduced to Texas heavily vegetated areas (Jurgens 1951). at that time. In addition, Howells and Ecological impacts associated with Garrett (1992) reported that a wide variety Mexican tetra introductions are unknown. of non-native species of fish have been Carrasius auratus (L.), goldfish.—This imported and stocked in Texas waters species is native to Asia. Goldfish over the past century, but most of these occasionally can be observed in the San introductions failed to establish. The Marcos River (Kelsey 1997) where they former two papers illustrate that there is a likely originated from released aquarium significant potential for additional stock. The species does not appear to be introductions of exotic fishes into Texas established in the river. However, waters including the San Marcos River goldfish have been reported as established drainage. Although there are many in other areas of Texas (Courtenay et al. potential environmental impacts of 1984, 1986). Ecological impacts introduced fishes on aquatic ecosystems, associated with goldfish in the San they are rarely documented (Courtenay Marcos River probably are negligible. and Taylor 1982; Courtenay and Stauffer 1984). Cichlasoma cyanoguttatum (Baird and Girard), Rio Grande cichlid.—This Amblopities rupestris (Rafinesque), rock cichlid is native to the Rio Grande and bass.—Rock bass were transplanted to Pecos River drainages in Texas and Texas from Missouri as a food and sport Mexico, and it has been widely introduced fish (Hubbs et al. 1991), and they are now into other river drainages in Texas for the established in many areas of the state. purpose of sport fishing (Brown 1953). The date of first introduction of this Rio Grande cichlids were first brought to species into the river is thought to be 1897 the San Marcos area in 1928, and (Brown 1953). Rock bass are now subsequent releases were made into the common in the river where they have been Guadalupe River Basin, including the San found in several locations (Kelsey 1997). Marcos River (Brown 1953). This species The ecological impacts associated with is now established and common in the this species are unknown. Rock bass are a river. Rio Grande cichlid is a predatory popular sport fish among fishermen. species and likely competes with or preys on other species, including the endangered Astyanax mexicanus (Fillippi), Mexican fountain darter (E. fonticola), threatened 9 10

San Marcos salamanders (Eurycea nana introduced and widely propagated in Bishop), and benthic invertebrates. Hubbs Texas between 1879 and 1900. According (1968) reported that the transplantation of to Kuehne (1955), they probably were this species into areas of Texas to which it stocked into the Guadalupe River Basin is not native has resulted in rigorous, several times during this period. albeit unsuccessful, attempts to remove it. However, the date of the first occurrence of this species in the San Marcos River is Cichlasoma nigrofasciatum Günther, unknown. State supported stocking of this convict cichlid.—This native of Central species ended in 1885 when the Texas America was first collected from the San legislature abolished the Texas Fish Marcos River in 1989 with additional Commission (Cox 1999). Whiteside and collections being made in 1991 Berkhouse (1992) reported on a collection (Whiteside and Berkhouse 1992). Convict of Koi carp, a variety of C. carpio, taken cichlid may be established in the river at the intake screen for the A.E. Wood though this has not yet been confirmed. Fish Hatchery in 1990. They speculated The impacts of this species on the these fish had probably escaped from the ecological functioning of the river are hatchery because at that time Koi carp unknown. However, Courtenay and were used as prey for sport fish being Hensley (1980) suggested this species reared at the hatchery. However, release competes with native sunfishes for by aquarists cannot be entirely ruled-out spawning sites in areas where it is as a source for these fish. Large (/30 cm) introduced. Convict cichlids likely were Koi carp can occasionally be seen in the introduced by aquarists. upper river. The ecological impacts of carp on aquatic ecosystems are substantial Colosomma sp., pacu.—Howells et al. and well documented (Taylor et al. 1984; (1991) reported a 1990 collection of pacu Lever 1996). from the San Marcos River. In addition, Texas Parks and Wildlife Department staff Hypostomus sp., suckermouth catfish, biologists have observed two large Armadillo del Río (Hubbs et al. unidentified pacu (ca. 30-40 cm in length) 1991).—These fish are native to Central swimming about Spring Lake on several America and the Amazon Basin in South occasions during 1997-1999 (DEB, America. Barron (1964) found that personal observation). These specimens suckermouth catfish could overwinter in likely were released into Spring Lake by central Texas. Whiteside and Berkhouse aquarists. Several species of pacu are (1992) first reported this species from the commonly sold in the aquarium trade, and upper San Marcos River. Suckermouth some of these have been reported escaped catfish are now established and in other Texas aquatic systems (Howells reproducing in the river (DEB, personal et al. 1991). Pacus are generally observation), but ecological impacts distributed in South America. associated with this species probably are negligible. According to Burgess (1989), Cyprinus carpio L., common carp.— Hypostomus species feed mainly on algae Carp are native to Eurasia and were and other vegetable matter, but they also 10 11 will occasionally eat small invertebrates. the river in 1967, and Kelsey (1997) also collected representatives of the species Lepomis auritus (L.), redbreast showing its continued presence there. sunfish.—This species was introduced Edwards (1979) reported the ability of this from the Atlantic slope of the U.S. as a species to hybridize with native food and sport fish. However, the date of Guadalupe bass (Micropterus treculi). first introduction into the San Marcos Faraquhar (1995) reported hybrids of River is unknown. Jurgens (1951) did not these two species from the Blanco River report redbreast sunfish in his study, but near its confluence with the San Marcos Kuehne (1955) found them to be River, and he also presented data to show widespread in the Guadalupe River Basin that smallmouth bass compete with native thus indicating the species was introduced black basses for available habitat. well before 1955. Presently, it is established and abundant in the river Oncorhynchus mykiss (Walbum), rain- where it is a popular sport fish. Wallace bow trout.—Rainbow trout are native to (1984) studied the food habits of this the Pacific Northwest slope of North species in the river. America from California to Alaska, but they have been widely introduced Menidia beryllina (Cope), inland throughout Texas for the purpose of sport silversides.—This species is native to fishing. In the spring of 1983, a fisherman estuaries along the Atlantic and Gulf caught a rainbow trout (approximately 15 coasts of the U.S. and was transplanted cm total length) while fishing downstream into the river through an unknown source. of the San Marcos Fish Hatchery outfall In 1993, U.S. Fish and Wildlife Service (DEB, personal observation). This fish biologists collected several examples of certainly had escaped from the hatchery this species from the river near the A.E. where this species was being reared at the Wood State Fish Hatchery outfall. The time for eventual stocking elsewhere in current status of this species in the river is Texas. We are unaware of any additional unknown, but it probably is not records of rainbow trout from the river, established. However, Tilton and White but we suspect that other specimens (1969) documented the spread of this escaped from the hatchery before it was species in the nearby Colorado River renovated during the late 1980s. Basin of Texas, suggesting it potentially could become established in the San Oreochromis aureus (Steinachner), blue Marcos River. tilapia.—This cichlid is a native of the Middle East and the Mediterranean coast Micropterus dolomieu Lacépède, small- of Africa. Blue tilapia are established and mouth bass.—Smallmouth bass have have a breeding population in the San been widely transplanted from other areas Marcos River. The source of introduction of the U.S. into the Guadalupe River of blue tilapia in the river is unknown, but Basin, including the San Marcos River. most introductions of this species stem Hubbs and Peden (1968) reported a single from escaped aquaculture specimens, specimen of M. dolomieu collected from efforts aimed at controlling aquatic 11 12 vegetation, or escaped baitfish. Lever at the Lula B. Sams State Fish Hatchery in (1996) stated that large populations of Olmito, Texas (Hubbs 1964). Drewry et blue tilapia cause increases of turbidity al. (1958) first reported the Amazon molly due to their rolling behavior, and they may from the river, where it is now displace and compete with other species. established. Amazon mollies are Nonetheless, there is no conclusive aggressive fish and will harass and chase evidence to this end, and most ecological other fishes that enter their territory. The impacts associated with this species are ecology of this species is discussed in largely anecdotal and contradictory (Lever Meffe and Snelson (1989). 1996). Muoneke (1988) reviewed the occurrence and ecology of tilapia in Texas Poecilia latipinna (Lesueur), sailfin waters. All species of tilapia are on the molly.—Sailfin mollies are native to the Texas prohibited species list (Howells Atlantic and Gulf coasts of the U.S. and 1999). Mexico. The source of introduction of the sailfin mollies in the river is unknown, but Oreochromis mossambicus (Peters), released aquarium specimens is the most Mossambique tilapia.—This cichlid is a probable source. Sailfin mollies native to Africa. Brown (1961) first apparently were introduced into the river reported this species from the San Marcos in 1944 (Brown 1953) and are now River, and Hubbs (1982) and Courtenay et abundant in shallow and backwater areas. al. (1984) reported its continued Sailfin mollies also harass other fishes occurrence there. Lever (1996) reported that enter their territory. that in 1958 the Texas Game and Fish Commission (now Texas Parks and Pseudotropheus sp., rift-lake cichlid.—A Wildlife Department) introduced single specimen of this species was Mossambique tilapia into Spring Lake, captured by a fisherman in 1991 and additional specimens escaped into the downstream of the Spring Lake Dam river from the outflow drain of the A. E. (Whiteside and Berkhouse 1992). The Wood State Fish Hatchery. Hubbs (1968) source of introduction probably was an warned of the possible ecological aquarist who released the fish. The consequences assoc-iated with the species apparently is not established in the introduction of this species. Muoneke river. Rift-lake cichlids are native to (1988) reviewed the occurrence and Africa. ecology of tilapia in Texas waters. All species of tilapia are listed on the Texas Pterygoplichthys disjunctivus (Weber), prohibited species list (Howells 1999). vermiculated sailfin catfish.— Examples of this were captured from the San Marcos Poecilia formosa (Girard), Amazon River during 1996 (Edwards 2001). molly.—Amazon mollies are native to the Burgess (1989) reported that this genus is Rio Grande drainage and southward into distributed in South America with Mexico. They were accidentally released examples being known from Brazil, from the San Marcos State Fish Hatchery Paraguay and Peru. Sailfin catfish are into the river in 1955 from stocks obtained closely related to Hypostomus and they 12 13 have similar ecological characteristics. during periods of migration. The The source of introduction likely is from waterfowl we report here do not leave the released aquarium specimens. upper river and are considered permanent residents, but the respective population Reptiles sizes for each of these species are small and do not exceed one dozen animals. Pseudemys nelsoni Carr, Florida red- The impacts these species have on the bellied turtle.—The only known exotic native species and their habitats in the reptile occurring in the upper San Marcos upper river are unknown, but they feed on River (Spring Lake) is the Florida red- and among aquatic vegetation causing bellied turtle. The first occurrence of this physical damage to plants. Tupa and species in the river was reported by Rose Davis (1976) reported various waterfowl et al. (1998) who reported that it probably to feed on aquatic moss and the alga is established there based on the Lyngbya sp. and they may have localized occurrence of large fecund females and impacts on such vegetation. Long (1981) hatchlings in Spring Lake. However, this provides an exhaustive review of exotic species is localized and potentially could birds, including the species presented be eliminated from Spring Lake through here, and notes on the types of damage standard capture methods. Although the they are known to cause. source of introduction for P. nelsoni is not known, the population likely was founded Alopochen aegyptiacus (L.), Egyptian by escaped or released pets. The Florida goose.—This species is native to the red-bellied turtle is a native of Florida and southern two-thirds of Africa (Long southeastern Georgia (Ernst et al. 1994). 1981), and it has been widely distributed Impacts caused by this species on native throughout the world for domestic species or their habitats are not known. purposes. We observed a pair of these However, potential impacts may include birds at Spring Lake during June 2000. hybridization with native turtles, and They likely escaped from a domestic competition for food resources. source.

Birds Anas platyrhynchos (L.), mallard duck.—Included here is the domestic Eight species of exotic waterfowl have white duck which is a variant of the been introduced to the San Marcos River. mallard. The range of the mallard has Some of these, such as the domestic increased in North America due in part mallard duck, Anas platyrhynchos (L.), due to captive-reared birds reverting to the and Canada goose, Branta canadensis wild (Long 1981). This species occurs (L.), could be considered marginal naturally in the U.S. and migratory forms exotics. However, we consider the non- overwinter along the river, but migratory, domesticated forms of these domesticated individuals can be found species as exotic because naturally throughout the year, particularly around occurring representatives of these species Spring Lake. normally occur in the watershed only 13 14

Anser anser (L.), domestic goose.— This native of Eurasia has been widely Several domestic geese frequent the upper introduced in the U.S. including the upper San Marcos River and occasionally Spring San Marcos River where they are semi- Lake. These geese apparently are domesticated. However, the original date domesticated varieties of the Greylag of introduction is unknown. Mute swans goose, a species common to Europe and are established and actively nest and northern Africa (Brown et al. 1982). The reproduce at Spring Lake. date of first introduction of this species to the river is unknown, but likely dates to Cygnus atratus (Latham), black swan.— the first arrival of Europeans to central This large swan is a native of Australia Texas. and Tasmania. Individuals occasionally have been observed along the San Marcos Anser cygnoides (L.), Chinese or River, but no specimens have been seen African goose.—Several of these recently. Observed specimens likely distinctly marked domestic geese have originated from domestic sources, but the been observed along the upper San date of first introduction is unknown. Marcos River since 1998. African geese actually are domesticated descendants of Mammals the Asiatic or Chinese goose (Brown et al. 1982). Both white (Chinese goose) and Myocaster coypus (Molina), nutria.— brown (African goose) forms have been The only introduced mammal known from seen on the river. The date of introduction the upper San Marcos River is the nutria. is unknown, but it is presumed to be No specific population estimate has been recent. made for the river, but the species is abundant along this stretch of river. This Branta canadensis (L.), Canada large rodent is native to the temperate goose.—This species occurs naturally in portions of South America including the U.S, but domesticated individuals can Argentina, Bolivia, Chile, Paraguay, and be found throughout the year along the Uruguay. Schmidly (1983) reported that upper San Marcos River, particularly the nutria was first introduced into the around Spring Lake and the various parks U.S. in the late 1930s to Avery Island, along the river. Louisiana. They were later introduced to the mainland in 1940 during a hurricane, Cairina moschata (L.) Muscovy duck.— and the species subsequently has spread This duck is a native of southern Texas throughout most of Texas (Hollander et (Hildago, Starr and Zapata counties) al. 1992). Other introductions have (Eitniear et al. 1998) and southward from occurred from releases of animals for the Mexico to South America (Long 1981). It proposed purpose of controlling aquatic has been introduced locally as a domestic vegetation and by disillusioned fur form and a few individuals occasionally farmers who found no market for nutria can be observed at Spring Lake. fur (Smith 1969). The primary impacts to aquatic systems, including the San Marcos Cygnus olor (Gmelin), mute swan.— River, attributed to the nutria include 14 15 destab-ilization of stream banks associated proposed as biological control agents of with burrowing, and eating aquatic such invasive species as Hydrilla vegetation (Atwood 1950; Davis 1974). verticillata, (e.g., Del Fosse et al. 1976). Relatively little is known about the However, such intro-ductions must be specific impacts nutria may have on the carefully evaluated given that some river and its native vegetation. However, introduced insects can have severe Emery (1967) reported observing nutria consequences with respect to native feeding on endangered Texas wild-rice. species and the environment (Sailer 1978, Atwood (1950) presented a detailed life Howarth 1992). Similarly, grass carp history study of the nutria. (Ctenopharyngodon idella Cuvier and Valenciennes) are commonly used to Solutions to the Problem control aquatic vegetation, but these voracious, non-discriminant herbivores Introductions of non-native species into often produce adverse environmental the San Marcos River ecosystem have impacts to systems in which they are occurred for well over 100 years. Our introduced (Courtenay and Stauffer 1984), interpretation of available data on the and their management can be problematic approximate year or decade of exotic (Prentice et al. 1998). Mechanical species known to have been introduced harvesting of aquatic vegetation also can into the river show that new introductions be an effective tool in some have occurred steadily throughout the past circumstances, but it generally requires century (Fig. 2). While the 1960s multiple harvests, and disposal of exhibited the greatest documented number harvested material can be problematic of introductions for any decade, the 1980s (Langeland 1996; Madsen 1997). and 1990s also show substantial numbers Moreover, hydrilla fragments can sprout of species were introduced. Based on this entire new plants (Langeland 1996) and relatively recent surge of introductions, an failure to remove cuttings of hydrilla may argument can be made that past and result in a larger population of this weed. present attempts to prevent introductions As Barrett (1989) noted, mechanical of exotic species have largely failed. Such methods cannot destroy plants at a rate introductions call into question the fast enough to eliminate them, and potential solutions that are available or herbicides often have harmful side effects, must be developed to resolve this such as impairing water quality, killing problem. fish and disrupting ecosystem functioning. Numerous proposals have been made The occurrence of the federally- concerning the management and control of endangered Texas wild-rice in the San exotic species, especially aquatic Marcos River precludes the use of any vegetation (Madsen 1997). However, herbicides in that system. Management of most management and control techniques invertebrate and vertebrate exotic species are not completely effective, and they can poses even more problems than those present unacceptable problems themselves noted for aquatic vegetation (Courtenay (Gallagher and Haller 1990). For and Stauffer 1984). These species often example, various insects have been are highly fecund and are capable of 15 16 movement and escape thus making their intentional, non-malicious releases by ill- management a difficult, if not impossible, informed individuals who want to beautify process. In addition, management or supplement the biotic diversity of an activities may conflict with sport and aquatic ecosystem. Given these many recreational uses and legal water rights. sources of introduction, regulatory action Once these species become established, alone clearly cannot be completely they essentially become permanent effective in stopping the flow of non- residents. native species into ecosystems. Regulations applicable to the Relatively few efforts are made to introduction of exotic species in Texas educate the general public on the potential waters were reviewed by Howells (1999). environmental and legal ramifications of These regulations include 31 TAC introducing exotic species into public §§57.111-57.130 concerning harmful or waters. Many people view the potentially harmful exotic fish, shellfish introduction of exotic species as serving a and aquatic plants, and 31 TAC §57.251, positive benefit, and they are generally §§57.257-57.260 concerning the unaware that such actions seldom produce introduction of fish, shellfish, or aquatic a desirable outcome. In our view, one of plants into public waters. Comparable the most important means for eventually laws apply at the federal level (Peoples et halting the spread and introduction of al. 1992; U.S. Office of Technology exotic species is public education. Assessment 1993; Clugston 1986). Both Educational efforts relating to the dangers the Executive Order 11987 (42 USC of exotic species can be achieved through 4321) and Nonindigenous Aquatic mass media announcements, development Nuisance Prevention and Control Act of of educational kiosks, developing 1990 (P.L. 101-646) address the import programs for presentation to schools, and and export of exotic species of plants and providing information pamphlets and animals. In February 1999, President Bill posters for dissemination through pet Clinton signed Executive Order 13112 shops and other sources. Two educational that tasks federal agencies to prevent the kiosks previously have been erected along introduction of invasive species and the upper San Marcos River in recent provide for their control in order to years that address, in part, the potential minimize undesirable impacts. Although impacts of exotic species. A greater effort such regulations may appear to be also must be made to properly address efficacious at face value, few people are exotic species in the popular literature. even vaguely familiar with these state and Presently, educational articles on exotic federal laws. Moreover, such laws often species for the benefit of the general are not enforced because violators are public are only infrequently published. In seldom caught. Exotic species addition, popular literature addressing introductions have originated as escapees exotic species sometimes presents from aquacultural sources, released pets conflicting information that the lay public and plants by aquarists, released and must decipher. For instance, an Texas escaped bait by fishermen, releases from Parks and Wildlife article (Shook 1997) attempts to supplement sport fishing, and heralds the presence of Rio Grande 16 17 cichlids in non-native habitats for their The situation may well exist that exotic sport fishing value, while in the same species will never be successfully issue readers are alerted to the highly managed or controlled in the river as long invasive and deleterious nature of water as such dams alter the normal ecological hyacinth and other exotic species (Castillo functioning of this unique aquatic 1997). Clearly, educational efforts ecosystem. Exotic species occur in many regarding exotic species must not only be other aquatic systems in Texas including more unified in their message to the some of the other large-volume springs public, but they must be more widely (Bowles and Arsuffi 1993). Many of the disseminated and placed in a broader non-native species introduced into the San variety of mass media if they are to reach Marcos River also occur in these systems. and effectively influence the target Thus, the information presented in this audience. Environ-mentally conscious paper can be used as a model for groups, such as The Nature Conservancy, comparison with other spring systems in have been at the forefront in educating the Texas in an effort to better understand the general public on exotic species. magnitude of the existing exotic species Recently, nearly an entire issue of Nature problem. Conservancy magazine was devoted to The arguments against introducing non- exotic species issues (Nature Conservancy native species into freshwater ecosystems, 1999). Similarly, an informative article recommendations for increased on exotic species recently was published enforcement of existing regulations, and in the San Antonio (Texas) Express-News emphasis on public education and (Verrengia 1999). vigilance are not new (Shaffland 1986; Beyond the obvious necessity of public Clugston 1986; Kohler and Courtenay education and legal enforcement is 1986). However, we find our-selves still addressing the physical functioning of making these same arguments as we ecosystems themselves. For instance, as venture into a new millennium. Clearly, stated by Vitousek et al. (1996), damming we have far to go in fully addressing the and impoundment of streams alters natural problem of exotic species. Although the disturbance cycles, such as flooding and number of exotic species we report here is scouring, that normally occurs in these high for a single aquatic ecosystem, there ecosystems. As a result, construction of is a realistic possibility of additional dams often can be correlated with the species being introduced into the San successful invasion of non-native species Marcos River ecosystem. The trend into lotic ecosystems (Vitousek et al. reported in this paper substantiates this 1996). The upper San Marcos River has prediction, and the problem could become three dams upstream of its confluence worse if steps are not taken to prevent with the Blanco River, and three flood future introductions. The ultimate control dams have been constructed in the solution must include a combination of a tributaries that feed the river (Poole and wide range of educational programs, Bowles 1999). The impounded areas funded research into potential and actual behind these dams provide habitat for impacts to ecosystem structure and many of the exotic species listed herein. functioning, enforcement of existing 17 18 regulations at all governmental levels, and aceae) from Texas. Sida 166:365- removal and management of offending 371. species when possible and practical. Atwood, E.L. 1950. Life history studies of Regrettably, such solutions are not readily nutria, or coypu, in coastal Louisiana. at hand and ultimately resolving the Journal of Wildlife Management 14: 249-265 problem of exotic species introductions Bailey, L.H. 1949. Manual of cultivated will not be accomplished soon. plants, revised edition. Macmillan Company, Toronto, 1,116 pp. Barrett, S.C.H. 1989. Waterweed invasions. Scientific American 261:90-97. Acknowledgements Barron, J.C. 1964. Reproduction and apparent over-winter survival of the We thank David E. Lemke, Southwest suckermouth armored catfish, Texas State University, Bob Howells, Roy Plecostomus sp., in the headwaters of Kleinsasser, and Kevin Mayes, Texas the San Antonio River. Texas Journal of Science 16:449-450. Parks and Wildlife Department, and Bob Botts, P.S., J.M. Lawrence, B.W. Witz, and Edwards, University of Texas-Pan C.W. Kovach. 1990. Plasticity in American for reviewing earlier versions of morphology, proximate composition, this paper. Karim Aziz, Texas Parks and and energy content of Hygrophila Wildlife Department, prepared the map of polysperma (Roxb.) Anders. Aquatic the San Marcos River. Botany 36:207-214. Bowles D.E., and T.L. Arsuffi. 1993. Karst References aquatic ecosystems of the Edwards Plateau region of central Texas, USA: Abbott, R.T. 1950. Snail invaders. Natural a consideration of their importance, History 59:80-85. threats to their existence, and efforts Abbott, R.T. 1952. A study of an for their conservation. 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individuals of Corbicula fluminea Corbicula manilensis (Philippi) in (Müller) (Bivalvia: Corbiculacea). Texas. Nautilus 85: 35-36. American Mala-cological Bulletin Murray, H.D. 1972. Freshwater mussels in (Special Edition) 2:151-166. Lake LBJ, Texas. Bulletin of the Meffe, G.K., and F.F. Snelson, Jr. (eds.). American Malacological Union, 1989. Ecology and evolution of 1971:36-37. livebearing fishes (Poeciliidae). Murray, H.D., and D. Haines. 1969. Prentice Hall, Englewood Cliffs, NJ, Philophthalmus sp. (Trematoda) in 453 pp. Tarebia granifera and Melanoides Metcalf, A.L. 1966. Corbicula manilensis in tuberculatus in south Texas. Annual the Mesilla Valley of Texas and New Reportof the American Malacological Mexico. Nautilus 80:16-21. Union, pp. 44-45. Metcalf, A.L., and R. Smartt. 1972. Records Murray, H.D., and A. Stewart. 1968. of introduced mollusks: New Mexico Establishment of a trematode cycle in and western Texas. Nautilus 85:144- Tarebia granifera (Lamarck) in 145. Texas. Annual Report of the Mitchell, A. J., M. J. Salmon, D. G. Huffman, American Malacological Union, pp. A. E. Goodwin, T. M. Brandt. 2000. 17-18. Prevalence and pathogenicity of a Nature Conservancy. 1999. July-August. heterphyid trematode infecting the The Nature Conservancy, Arlington, gills of an endangered fish, the VA, 42 pp. fountain darter, in two central Texas Neck, R.W. 1984. Occurrence of the striped spring-fed rivers. Journal of Aquatic ram’s horn snail, Marisa cornuarietis Animal Health 12:283-289. in Central Texas (Ampullariidae). Morizot, C., S.W. Calhoun, L.L. Clepper, Nautilus 98:119-120. M.E. Schmidt, J.H. Williamson, and Nelson, E.N., and R.W. Couch. 1985. G.J. Carmichael. 1991. Multispecies History and distribution of Myrio- hybridization among native and phyllum aquaticum in North America. introduced centrarchid basses in In: Anderson L.W.J. (ed.) central Texas. Transactions of the Proceedings of the first international American Fisheries Society 120:283- symposium on watermilfoil (Myrio- 289. phyllum spicatum) and related Morton,C.V.1967. Ceratopteris thalictroides, Haloragaceae species, pp. 19-26. a fern new to Texas. American Fern Vancouver, British Columbia, Journal 57: 13-14. Canada, July 23 and 24, 1985. Muoneke, M.I. 1988. Tilapia in Texas Penfound, W.T., and T.T. Earle. 1948. The waters. Inland Fisheries Data Series biology of the water hyacinth. No. 9, Texas Parks and Wildlife Ecological Monographs 18:447-472. Department, Austin, TX, 44 pp. Peoples, R.A., J.A. McCann, and L.B. Murray, H.D. 1964. Tarebia granifera and Starnes. 1992. Introduced organ- Melanoides tuberculata in Texas. isms: policies and activities of the Annual Report of the American U.S. Fish and Wildlife Service. In: Malacological Union, pp. 15-16. Rosenfield A and Mann R (eds). Murray, H.D. 1977a. The introduction and Dispersal of living organisms into spread of thiarids in the United aquatic ecosystems, pp. 325-352. States. Biologist 53:133-135. Maryland Sea Grant, College Park, Murray, H.D. 1971b. New records of MD.

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Pimentel, D., L. Lach, R. Zuniga, and D. Schmidly, D.J. 1983. Texas mammals east Morrison. 2000. Environmental and of the Balcones Fault Zone. Texas economic costs of nonindigenous A&M University Press, College species in the United States. Station, TX, 400 pp. Bioscience 50:53-65. Schwartz, M.W. 1997. Defining indigenous Pointier, J.P., R.N. Incani, C. Balzan, P. species: an introduction. In: L.O. Chrosciechowski, and S. Prypchan. Luken and J.W. Theiret (eds.). 1994. Invasion of the rivers of the Assessment and management of plant littoral central region of Venezuela by invasions, pp 7-17. Springer-Verlag, Thiara granifera and Melanoides New York. tuberculata (Mollusca: Proso- Seaman, D.E., and W.A. Porterfield. 1964. branchia: Thiaridae) and the absence Control of exotic weeds by the snail of Biomphalaria glabrata, snail host Marisa cornuarietis. Weeds 12:87- of Schistosoma mansoni. Nautilus 92. 107: 124-128. Shafland, P.I. 1986. A review of Florida’s Poole, J., and D.E. Bowles. 1999. Habitat efforts to regulate, assess and manage characterization of Texas wild-rice exotic fishes. Fisheries 11:2025. (Zizania texana Hitchcock), an Shafland, P.L., and W.M. Lewis. 1984. endangered macrophyte from the San Terminology associated with Marcos River, Texas, USA. Aquatic introduced organisms. Fisheries Conservation: Freshwater and Marine 9:17-18. Ecosystems 9:291-302. Shook, P. 1997. A Texas original. Texas Prentice, J.A., W.J. Dean, M.S. Reed, and Parks & Wildlife (February):12-13. E.W. Chilton, II. 1998. Movement Simberloff, D. 1996. Impacts of introduced of triploid grass carp among small species in the United States. hydropower impoundments of the Consequences 2:13-24. Guadalupe River, Texas. Pro- Sinclair, R.M. 1971. Annotated bibliography ceedings of the Annual Conference of on the exotic bivalve Corbicula in Southeastern Association of Fish and North America, 1900-1971. Wildlife Associations 52:49-61. Sterkiana 43:11-18. Robins, C.H. 1971. Ecology of the Smith, C.S., and J.W. Barko. 1990. Ecology introduced snail, Marisa cornuarietis of Eurasian watermilfoil. Journal of (Ampul-lariidae) in Dade County, Aquatic Plant Management 28:55-64. Florida. Biologist 53:136-152. Smith, G. 1969. The fur that failed. Florida Rose, F.L., R.W. Manning, T.R. Simpson, Wildlife 22:4-5. and S. Jenkins. 1998. A sustaining Spencer, W., and G. Bowes. 1985. population of the Florida red-bellied Limnophila and Hygrophila: a re- turtle, Pseudemys nelsoni (Reptilia: view and physio-logical assessment Emydidae) in Spring Lake, Hays of their weed potential in Florida. County, Texas. Texas Journal Journal of Aquatic Plant Management Science 50:89-92. 23:7-16. Rosen, D. J. 2000. Cryptocoryne beckettii Strayer, D.L. 1999. Effects of alien species (Araceae), a new aquatic plant in on freshwater mollusks in North Texas. Sida 19:399-401. America. Journal of the North Sailer, R.I. 1978. Our immigrant insect American Benthological Society fauna. Bulletin of the Entomological 18:74-98. Society of America 24:3-11. Sutton, D.L. 1985. Biology and ecology of

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Myriophyllum aquaticum. In: L.W.J. and R. Westbrooks. 1996. Anderson (ed.). Proceedings of the Biological invasions as global first international symposium on environmental change. American water-milfoil (Myriophyllum spic- Scientist 84: 486-478. atum) and related Haloragaceae Wallace, S.A. 1984. The food habits of species, pp. 59-71. Vancouver, redbreast sunfish in the San Marcos British Columbia, Canada, July 23 River, Texas. MS Thesis, Southwest and 24, 1985. Texas State University, San Marcos, Taylor, J.N., W.R. Courtenay, Jr., and J.A. TX, 59 pp. McCann. 1984. Known impacts of Watkins, G.M. 1930. Vegetation of San exotic fishes in the continental United Marcos Springs. MA Thesis, Univer- States. In: W.R. Courtenay, Jr., and sity of Texas, Austin, TX, 53 pp. J.R. Stauffer, Jr. (eds.). Distribution, Whiteside, B.G., and C.C. Berkhouse. 1992. biology, and man-agement of exotic Some collection locations for six fish fishes, pp. 322-373. John Hopkins species. Texas Journal of Science 44: University Press, Baltimore, MD. 494. Tiner, R.W. 1993. Field guide to coastal Whitley, J.R., B. Bassett, J.G. Dillard, and wetland plants of the southeastern R.A. Haefner. 1990. Water plants United States. University of for Missouri ponds. Missouri Massachusetts Press, Amherst, MA, Department of Conservation, 328 pp. Jefferson City, MO, 151 pp. Tilton, J.E., and R.L. White. 1969. Records Williams, M.C. 1980. Purposefully intro- of Menidia beryllina from several duced plants that have become central Texas impoundments. Texas noxious or poisonous weeds. Weed Journal of Science 16:120. Science 28: 300-305. Tupa, D.D., and W.K. Davis. 1976. Population dynamics of the San Marcos salamander, Eurycea nana Bishop. Texas Journal of Science 32: 179-195. United States Department of Agriculture. 1983. Noxious weeds. Federal Register 48: 20037-20047. United States Fish and Wildlife Service. 1995. San Marcos and Comal springs and associated aquatic ecosystems (revised) recovery plan. Albuquerque, NM, 121 pp. United States Office of Technology Assessment. 1993. Harmful non- indigenous species in the United States. U.S. Government Printing Office, Washington, DC, 391 pp. Verrengia, J.B. 1999. Invaders in our midst. San Antonio Express News, October 24. San Antonio, TX. Vitousek, P.M., C.M. D’Antonio, L.L. Loope,

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8 7 6 5 4 3 2 No. of Species Exotic 1 0 9 0 29 39 49 59 69 79 89 9 19 0-19 0-19 - 0-19 -19 920-19 80-19 190 1910-19191 1930-1 194 1950 196 1970 19 1990-2000 Before 1900 Years of Introduction

Figure 2. Exotic species introductions in to the San Marcos Riv er, Texas by decade of occurrence.

26 Table 1. Exotic species of the upper San Marcos River, Texas.

Species Common Name Status1 Origin Source Known/Probable Relative Date Introduced Ecological Impact

Plants

Arundo donax giant reed E Mediterranean Agricultural Before 1900 Medium

Ceratopteris thalictroides floating fern E Southeast Asia Aquarists 1963 Medium

Colocasia esculenta elephant ear E Southeast Asia, Indonesia Ornamental 1920s High

Cryptocoryne beckettii cryptocoryne E Southeast Asia Aquarists 1993 High

Egeria densa giant elodea E South America Aquarists 1930s Medium

Eichhornia crassipes water-hyacinth E South America Ornamental 1930s Medium

Hydrilla verticillata hydrilla E Africa/Asia? Aquarists 1970s High

Hygrophila polysperma Indian hygrophila E Asia, Malaysia Aquarists 1940s High

Limnophila sessiliflora limnophila E India, Southeast Asia Aquarists 1960s? Low

Myriophyllum aquaticum parrot's feather E South America Aquarists 1940s? Low

Myriophyllum spicatum Eurasian water-milfoil E North Africa, Eurasia Aquarists 1950s? Medium

Pistia stratiotes water lettuce E South/East Texas Ornamental 1920s? Low

Potamogeton crispus curled pondweed E Europe Aquarists 1960s? Low

Ranunculus sceleratus cursed buttercup E Europe Ornamental Unknown Low

Rorippa nasturtium-aquaticum water cress E Europe? Food crop? Before 1900 Low

Xanthosoma sagittifolium elephant ear E Central/South America Ornamental Unknown Low Table 1. Exotic species of the upper San Marcos River, Texas.

Species Common Name Status Origin Source Known/Probable Relative Date Introduced Ecological Impact

Invertebrates

Corbicula fluminea Asian clam E Asia Invasive/ 1960s? High Bait bucket?

Marisa cornuarietis giant rams-horn snail E Central/South America Aquarists 1983 High

Melanoides tuberculatus red-rimmed melania E Southeast Asia Aquarists 1960s High

Tarebia granifera quilted melania E Southeast Asia Aquarists 1960s High

Fish

Amblopities rupestris rock bass E Central U.S. Sport fish 1897 Medium

Astayanax mexicanus Mexican tetra E South Texas Bait bucket 1920s Medium

Carrasius auratus goldfish R Asia Aquarists Unknown Low

Cichlasoma cyanoguttatum Rio Grande cichlid E South Texas Sport fish 1928 High

Cichlasoma nigrofasciatum convict cichlid R Central America Aquarists 1980s Low

Colosomma sp. pacu R South America Aquarists 1990 Low

Cyprinus carpio common carp E Eurasia Sport fish/ Before 1900 Low Accidental release

Hypostomus sp. suckermouth catfish E Cental/South America Aquarists 1980s? Low

Lepomis auritus redbreast sunfish E Southeastern U.S. Sport fish 1950s? High

Menidia beryllina inland silversides R Atlantic/Gulf Coast Bait bucket? 1990s? Low Table 1. Exotic species of the upper San Marcos River, Texas.

Species Common Name Status Origin Source Known/Probable Relative Date Introduced Ecological Impact

Micropterus dolomieu smallmouth bass E Eastern North America Sport fish 1960s High

Oncorhynchus mykiss rainbow trout R Pacific Northwest U.S Sport fish 1983 Low Accidental release

Oreochromis aureus blue tilapia E Middle East, Africa Aquaculture 1958 High

Oreochromis mossambicus Mossambique tilapia E? Africa Aquaculture 1958 Low

Poecilia formosa Amazon molly E Rio Grande Basin, Aquarists 1955 Low Central/South America

Poecilia latipinna sailfin molly E Atlantic/Gulf Coast Aquarists 1944 Medium

Pseudotropheus sp. Rift-lake cichlid R Africa Aquarists Early 1990s Low

Ptergoplichthys disjunctivus vermiculated highfin R South America Aquarists 1990s Low catfish

Reptiles

Pseudemys nelsoni Florida red-bellied turtle E Florida Aquarists 1990s? Low

Birds

Alopochen aegyptiacus Egyptian goose L Africa Domestic 2000 Low

Anas platyrhynchos Mallard/domestic duck L North America Domestic Unknown Low

Anser anser domestic goose L Europe/North Africa Domestic Unknown Low Table 1. Exotic species of the upper San Marcos River, Texas.

Species Common Name Status Origin Source Known/Probable Relative Date Introduced Ecological Impact

Anser cygnoides Chinese/African Goose L Asia Domestic 1990s? Low

Branta canadensis Canada/domestic goose L North America Domestic After 1930 Low

Cairina moschata Muscovy duck L South Texas, Mexico Domestic Unknown Low

Cygnus atratus black swan L Australia/Tasmania Domestic Unknown Low

Cygnus olor mute swan E Eurasia Domestic After 1910 Low

Myocaster coypus nutria E South America Invasive 1950s? High

1 E = established, R = reported, L = localized

9 8 s 7 6 5 4 3 2 Number of Specie Number 1 0

9 9 9 6 nown 190 193 197 200 k re 1900 0- 0- 0- 0- o Un 190 1910-19191920-1929193 1940-19491950-19591960-1969197 1980-19891990-1999200 Bef Decade of Introduction Figure 2. Exotic species introductions into the San Marcos River, Texas by decade of occurrence.