With Turgeon et al. (1988) as a guide, we conducted a review of the literature about all reported introduced aquatic, nonindigenous mollusks in the United States. We also identified species that are nonindigenous to Florida (Table 5). Four more species, Pomacea bridgesi, Melanoides tuberculatus, M. turriculus, and Tarebia granifera are species that we consider introduced and nonindigenous but were not identified as such by Turgeon et al. (1988). Clench and Turner (1956) described the freshwater mollusks of Alabama, Georgia, and Florida. Additional information may be obtained from Feinberg (1979) and Stange (1990).
Recently, the edible brown mussel (Perna perna; Linnaeus,1758), was identified as having been introduced into the coastal waters of Texas (Hicks and Tunnell 1993; Carlton 1992b). However, no evidence of this species' expansion into Florida waters exists, and we therefore omitted the species from our accounts.
The following species of mollusks have been identified in the literature as aquatic and nonindigenous to Florida.
Corbiculidae
Asiatic Clam or corbicula (Corbicula fluminea) Müller 1774. The North American literature contains references to four species of nonindigenous clams in the genus Corbicula: Corbicula fluminea, C. manilensis, C. fluminalis, and C. leana that, however, may represent a single species, C. fluminea, with several varieties (Smith et al. 1979; Britton and Morton 1979). Corbicula fluminea is presently in Eurasia, in Southeast Asia, in Africa, in Australia, in the Pacific Islands, in South America, and in North America (Britton and Morton 1979). Clench (1970) and Gottfried and Osbourne (1982) discussed the presence of C. manilensis in southern Florida. Counts (1991) provided a compendium of zoological records of this species in North America.
Corbicula was first collected in North America as empty shells in Namaimo, Vancouver Island, British Columbia, in 1924 (Counts 1981; Britton 1979; Britton and Prezant 1986). It was first discovered in the United States in 1938 by Burch (1944) in the sand and gravel banks of the Columbia River, Washington. Later, Hanna (1966), Fox (1971a,b), and Morton (1973) identified the occurrence of this mollusk with the arrival of immigrant Chinese laborers in the United States. In the Orient, many people eat corbicula (Miller and McClure 1931). Details on the spread of this species in the United States into the southern Atlantic area are summarized by Dundee and Harman (1963),Dundee (1974), and Sinclair (1971a and b). Isom (1986) also traced the spread of this species from the West Coast through the lower Midwest and the southeastern United States. The distribution and occurrence of this species in Florida was summarized by Bass and Hitt (1974a).
Heinsohn (1958) was one of the first investigators of the introduction and life history of the Asian clam. More recently McMahon (1983) traced the chronological spread of the clam in the United States and concluded that the mussel was moved from the Northwest to the Midwest (Ohio River) in the late 1950's by unknown pathways. Heinsohn (1958) listed tourist curiosity, the bilge waters of pleasure boats, fishing bait, or aquarium hobbyists as possible pathways of introduction. After its initial introduction in the Midwest, the Asian clam spread through natural pathways southward and then eastward into Florida in the early 1960's. Counts (1986) summarized the present zoogeographic distribution and chronology of the invasion of this species on a state-by-state basis from museum records and discussed in detail many pathways that may have assisted in the rapid spread of corbicula. He incorrectly blamed the spread of this species from the western coast to the eastern coast of Florida on movement through the Cross-Florida Barge Canal; however, the canal was never completed.
Studies by Dreier (1977) and Thompson and Sparks (1977) indicated that migrating waterfowl were a probable means of spreading the species over long distances. The clam cannot survive even a short time in the digestive tract of waterfowl, however, Dundee et al. (1967) discovered that live terrestrial snails can be transported for short distances tangled in the feathers of some birds such as woodcocks. Rees (1965) in summarizing the works of others also found that birds can transport live snails. Sinclair and Isom (1963) discovered that live corbicula may be transported long distances in sand and gravel for construction. Fox (1970) reported that corbicula is sold in some states (e.g., in California) as bait to anglers who sometimes dump their unused bait. Abbott (1975) reported that corbicula is also sold by pet stores for aquaria. Although the pathways of spread may vary, corbicula may expand its range slowly and over short distances of its own accord. However, fast expansion of the range over great distances would have to be implemented by humans.
Corbicula can tolerate a wide range of water temperatures. Mattice and Dye (1976) reported that the upper 50% tolerance limits in continuous exposures were between 24 and 34 C when acclimation temperatures ranged from 5 to 30 C. The lower tolerance limits were between 2 and 12 C when acclimation temperatures ranged from 15 to 30 C. The expansion of corbicula northward is probably limited by low temperatures in winter (McMahon 1983). Some populations of this clam are farther north than expected, however, they are associated with anthropogenic warm-water discharges from power plants or with other thermal water discharges.
This clam is now in 35 states (Counts 1991). It is a freshwater species that does not enter brackish water (Haertel and Osterberg 1967; Sickel 1979). The taxonomy, significant effects, physiological ecology, life history, control measures, and future use of this species were discussed by McMahon (1983). It is a burrowing (infaunal) bivalve with a small byssus during only the first year of life. For the first 2 years, it is a protandric consecutive hermaphrodite (Morton 1977) that cannot tolerate exposure to greater-than-10% salinities for 10 days (Evans et al. 1979). However, it has a 20% survival rate in 80-day exposures to water with gradually increasing salinity.
Corbicula may create accumulations of dead shells and seriously impede water flow in irrigation canals that require dewatering and cleaning (Eng 1979). It fouls municipal water-treatment facilities, infests water-intake areas in which it damages centrifugal pumps, clogs main straining screens, and contributes to bad tastes and odor even after chemical treatment of the water (Ingram 1959; Ray 1962; Sinclair 1974; Smith et al. 1979). It has fouled raw water lines and reduced the efficiency of water-treatment plant operations (Sinclair 1964) and power plants (Page et al. 1986). The problems from corbicula in gravel for making cement are discussed by Sinclair and Isom (1961, 1963). While the concrete sets, the live clams move to the top and leave a void that weakens the set concrete product. Corbicula is also a major problem in cooling systems of power-generation plants where it fouls condensers and restricts water flows (McMahon 1983).
Corbicula populations were as dense as 5,000 clams/m2 (Heinsohn 1958) in California, 12,000/m2 (O'Kane 1976) in Texas, and 131,000 on sand bars in California (Eng 1979). When the concentration of clams reaches this level, native benthic communities are stressed from limitations of space and suspended food resources. Habitat invasion of this species may be the cause of declining abundances and elimination of native unionids and shaeriid endemics (Cooper and Johnson 1980; Boozer and Mirkes 1979; A.H. Clarke 1988; Fuller and Imlay 1976; Gardner et al. 1976; Sickel 1973; Taylor and Hughart 1981). Other studies revealed that corbicula has little or no effect on native species (Isom 1974; Kraemer 1979; Klippel and Parmalee 1979; Taylor 1980a&b). Some investigators concluded that, if the native environment was not already changed by human activities and the native flora and fauna were not already stressed, corbicula could not displace native species (Isom 1974; Fuller and Imlay 1976; Leff et al. 1990; Klippel and Parmalee 1979; Kraemer 1979; Taylor 1980a). Corbicula has an advantage over many native species because it tolerates anthropogenic activities and because it has an unusually high reproductive capacity, high growth rate, and short generation time that allow it to quickly adapt to disturbed environments (McMahon 1983). McMahon (1983) summarized the physiological ecology of Corbicula; its environmental need for substrate, salinity, and osmoregulation; temperature; exposure to air; general life history; and control measures.
Although most experts feel that the introduction of corbicula was economically and ecologically undesirable, Sinclair and Isom (1963) pointed out some benefits: its use as an index organism in pollution studies, as a local food for fishes and wildlife (Villadolid and Del Rosario 1930), as a fish bait (Metcalf 1966), and as possible food for ducks (Keup et al. 1963). Bass and Hitt (1974b) studied the food habits of many native fishes in Florida where the Asiatic clam is present and found that only the redear sunfish (Lepomis microlophus) eats this exotic and other species of fishes eat only a small amount of the clam.
Dreissenidae
Zebra Mussel (Dreissena polymorpha; Pallas, 1771). This species was introduced into the Great lakes in the ballast water of ships in 1988 (Herbert et al.1989). It has been spread by barge traffic into all major East Coast rivers of this country that are connected through canals to the Great Lakes. At first it was believed to be intolerant of the warm water in the southern parts of the United States, but now that it is established in the lower Mississippi River, there is some concern that it could survive in Florida if it were introduced. The species is also well established in the Tennessee River from where barge traffic will carry it south into the Tombigbee River system; establishment in Alabama and Georgia seems unavoidable (personal observation). The impact of this species on native species, especially rare and endangered shellfish species, is of particular concern. Because this species seems not to have spread into Florida, it is not be further discussed in this report.
Thiaridae
Thiarid Snail or Quilted Melania (Tarebia granifera-Thiara; (Lamarck 1758)). Three species of the Family Thiaridae in Florida were probably introduced incidentally with aquatic plants (Abbott 1950). Members of this family are in freshwater in the tropical and subtropical areas of the world. Some may occur in brackish waters. A synonym for this species is Tarebia lateritia (Lea; Thompson 1984). The thiarid snail is native to the Orient, the Far East, the western Pacific Islands, Madagascar, and east of India throughout Malaysia and the Philippines to the Society Islands and north to the Ryukyu Islands and Hawaii (Pace 1973). It was probably imported with exotic water plants and tropical fishes into California in 1936 (Abbott 1950).
In 1937, a dealer brought the snail to Tampa and sold it to aquarists as the "Philippine Horn of Plenty" (Roessler et al. 1977). The same dealer probably contaminated Lithia Springs, Florida, while cleaning his tanks and replenishing his plant stocks. Abbott (1952) was the first person to report that this species was in the wild in Florida. As many as 400 individuals/m2 have been in Lithia Springs where it is still common on the sandy bottom of the spring (Abbott 1950). The snail cannot survive in water below 21.1 C; therefore, its natural spread to other nearby waters has been hindered. Abbott (1952) reports that this species prefers shallow riffles of fast flowing freshwater streams. The thiarid snail is a moderately important species because it can serve as the first intermediate host for the sheep liver fluke (Clonorchis sinensis) and for the human lung fluke (Paragonimus westermani) that causes a disease that is known as paragonimiasis (Abbott 1950). Because the parasite is presently not in this country, most foods that could contain the parasite are usually cooked, and the uncertainty that North American crayfishes would serve as intermediate hosts significantly lessens the threat to humans. However, this species is ecologically significant because it tends to replace native Goniobasis (Elimia spp.) species and become very abundant.
Thiaridae
Red Rimmed Melania (Melanoides tuberculata; Muller 1774). This species is native to a large part of Africa, to the eastern Mediterranean, and throughout India, Southeast Asia, Malaysia, and southern China north to the Ryukyu Islands of Japan and south and east through the Pacific Islands to Northern Australia and the New Hebrides (Pace 1973). This species was introduced into Florida (Dundee 1974; Burch and Tottenham 1980 a,b; Burch 1982) and is now widely distributed throughout the state. It is most common in rivers, streams, canals, and springs and can flourish in brackish water with salinity from 0 to 30 ppt (Roessler et al. 1977). First recorded in Florida in 1969 (Clench 1969; Russo 1974), this species was in the St. Johns River at population densities of 10,000/m2 in 1976 (Thompson 1984). This snail, like the others of established families in Florida, may replace the native Goniobasis (Elimia spp.). New populations of the red rimmed melania have been in freshwater canals of Dade and Collier counties and in the saline mangrove areas adjacent to Biscayne Bay in the Matheson Hammock-Snapper Creek Area of Coral Cables (Roessler et al. 1977). Although trematode larvae were not discovered in these snails, the extension of range of the red rimmed melania into brackish and marine waters increases the possibility of the spread of avian trematode infection because of the many potential intermediate crustacean hosts in the mangrove habitat (Roessler et al. 1977). The life history and cycle of the red rimmed melania is described by Abbott (1950). Its habitat requirements and distribution are described by Roessler et al. (1977). Murray (1971) reported that this species is a known intermediate host for the trematodes of human lung fluke (Paragonimus westermani) and of sheep lung fluke--also from the Orient. The adult lung fluke causes what is known as paragonimiasis by attacking the lungs and causing symptoms not unlike tuberculosis or broncho-pneumonia. It also attacks the brain and causes symptoms that are similar to the symptoms of infantile paralysis and meningitis. The chance of human infection in Florida is remote because of normal sanitation in the state. The transfer of aquatic vegetation around the state, however, will probably spread it throughout the canals and brackish waters of southern Florida.
Faune Melania (Melanoides turricula; Lea, 1850). This species is native to the Philippines and has been introduced into springs and spring-fed streams in Florida. It is in Alexander Springs, Lake County; Blue Springs and the Withlacoochee River, Marion County; and Eureka Springs, Hillsborough County. Melanoides tuberculata and M. turricula may be ecological varieties of a single species. In Florida, the two snails are ecologically segregated. Melanoides tuberculata is usually in quiet, euthrophic, turbid habitat, whereas M. turricula is in cleaner, oligotrophic springs and runs (Thompson 1984).
Piliidae
Giant or Colombian Ramshorn (Marisa cornuarietis; Linnaeus, 1758). This species is native to the lowlands of northern South America, Trinidad (Baker 1930) and has also been reported from Costa Rica and the islands of Tobago and Grenada and the drainage system of the Magdelena and Orinoco rivers (Michelson 1956). In the recent literature, it is sometimes classified under the genus Ceratodes (Robins 1971).
This large freshwater tropical snail was introduced from northern South America and southern Central America into southern Florida. The snail can reach a diameter of 5.7 cm. Its ability to completely denude vegetated areas may be undesirable (Hunt 1958). The exact date and means of introduction are unknown. In Florida, it is abundant in canals, marshes, and ponds in Palm Beach, Broward, Dade and Monroe counties (Robins 1971).
In February 1958, the snail was abundant in semi-brackish water along 8 km of canal in the middle of the city of Miami westward to the edge of the Everglades (Hunt 1958). During sampling later in the year, the species was well established farther upstream. By July, hundreds of snails of all ages, including eggs, were 1.6 km downstream. When the snail was first reported by Hunt (1958), its total distribution was in a 8 km section of a canal in Dade County that contained drained water from Lake Okeechobee. Since that time, the Colombian ramshorn has spread to all freshwater branches of the system in the Miami area except to heavily polluted waters with industrial wastes (Hunt 1958). This species was also collected in canals along the west boundary of the city limits in Coral Gables, Florida, in February 1957 (Hunt 1958). By 1971, it had spread into the Everglades east of Fort Myers but had not been reported in the national park (Hunt 1958). The introduction was probably by aquarium dumps and by individuals that escaped from wholesalers of aquarium plants and animals. The major means of natural dispersal of this species is by rafting downstream on floating mats of aquatic vegetation (Hunt 1958). The eggs of this species are laid in gelatinous cluster in the water.
A review of the food habits, habitat, daily movements, environmental requirements, and association with other species is described by Robins (1971). Salinity (4.8 ppt) and temperatures of less than 8 C restrict the spread of this species. The establishment of this species in the mangrove swamps of southern Florida is of particular concern (Roessler et al. 1977).
The giant ramshorn is sold to aquarists but recently became unpopular because it damages aquarium plants. This habit may be the reason for its release into the canals by disgruntled aquarists (Hunt 1958). Hunt (1958) and later Blackburn et al. (1971b) suggested the use of this species as a weed-control agent in the canals of southern Florida. Studies revealed that this species retards the growth and flowering of water hyacinths by feeding on the roots of the plants (Robins 1971). The giant ramshorn has also been released in small ponds in the southern United States and in Puerto Rico to control submersed aquatic plants such as hydrilla (Holm et al. 1969). However, it may also feed on desirable plants such as rice (Oryxa spp.), watercress (Nasturtuim officinale), and water chestnuts (Scirpus esculentus). It feeds heavily on Cabomba, Elodea, dwarf saggitaria (Sagittaria spp.), and water cress (Nasturtium officinale). The giant ramshorn is not known to carry human diseases and has been used as food for humans in Puerto Rico (Holm et al. 1969).
Because of its indiscriminate feeding habits, the giant ramshorn has also been used as a biological control agent against snail populations (Biomphalaria glabrata) that are vectors of schistosomiasis (Oliver-Gonzales et al. 1956; Michelson and Augustine 1957). However, a major disadvantage of using this species as a biological control agent is that its sensitivity to temperatures below 8 C restricts its use in southern Florida.
Spiketopped or Brazilian Apple Snail (Pomacea bridgesi; Reeve). This large freshwater tropical snail is native to Brazil, was introduced into southern Florida, and became established in Monroe, Dade, Broward, and Palm Beach counties. It has also been introduced into isolated water bodies as far north as Alachua County (Thompson 1984). The shell is usually greenish with darker and lighter bands. A unicolor yellow form is raised commercially and marketed as the Albino Mystery Snail (Thompson 1984). The spiketopped snail is popular in the aquarium trade. It probably was initially released from fish farms and subsequently by aquarists.
Hale (1964) describes the significant effects of the spiketopped snail on the Everglades population of the apple snail (Pomacea paludosa) and the consequences to the feeding of the rare Everglades kite (Rostrhamus sociabilis) and the limpkin (Aramus guarauna pictus). This exotic snail is seemingly able to displace the native apple snail. The kite does not readily feed on the Brazilian apple snail (Pomacea bridgesi) because it is unable to extract its soft body from the slightly different shape of the shell since the curve of the shell does not conform to the shape of the kite's bill.
Achatinidae
Giant African Snail (Achatina fulica; Ferussac 1821). Information on the giant African snail (Achatina fulica), which is a terrestrial nonindigenous species, is discussed here because it is one of the few nonindigenous species that was eradicated.
The giant African snail is as long as 30 cm and was a food item of the Japanese armed forces during World War II (Lachner et al. 1970). Around 1967 or 1968, a tourist brought the snail into the North Miami area and eventually released it. By fall 1969, the restricted population exploded and the snail was abundant. It destroyed ornamental vegetation and damaged the paint on stucco walls of houses. Although the snail was confined to an area of approximately 40 city blocks, the spraying of a calcium-baited arsenic poison cost $30,000 (Lachner et al. 1970). A second treatment was needed, and the total cost to eliminate the snail was close to one million dollars.
The introduction of the charru mussel (Mytella charruana) into the coastal waters of Florida is discussed in the section on introductions into the marine environment.
