Common name: freshwater jellyfish
Synonyms and Other Names: peach blossom fish (China)
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Identification: Craspedacusta sowerbyi is a hydrozoan (Phylum Cnidaria, Class Hydrozoa), which is most easily identified when it takes the form of a small, bell-shaped jellyfish, known as a hydromedusa. The hydromedusa measures about 5–25 mm in diameter, and is translucent with a whitish or greenish tinge (Peard, 2002; Pennak, 1989). It possesses five opaque-white canals, which form the gastrovascular cavity; four are radial and one is medially dorsoventral. Tentacles of varying lengths protrude from the upper margin of the velum, arranged with three to seven short tentacles between longer ones (Pennak, 1989; Slobodkin and Bossert, 1991). Freshwater jellyfish exhibit four very long tentacles, each parallel to a radial canal at the edge of the velum. Shorter tentacles facilitate feeding, while the longer ones give stability for swimming. The total number of tentacles varies from 50 to 500 (Pennak, 1989). Conspicuous swarms of hydromedusae appear sporadically, but are only one part of the animal's life cycle. Craspedacusta sowerbyi more often exist as microscopic podocysts (dormant "resting bodies"), frustules (larvae produced asexually by budding), planulae (larvae produced sexually by the hydromedusae), or as sessile polyps, which attach to stable surfaces and can form colonies consisting of two to four individuals and measuring 5 to 8 mm (Angradi, 1998; Acker and Muscat, 1976; Pennak, 1989; Peard, 2002).
Size: hydromedusa is 5–25 mm in diameter
Native Range: Craspedacusta sowerbyi is indigenous to the Yangtze River valley in China, where it can be found in both the upper and lower river valley (Slobodkin and Bossert, 1991).
Interactive maps: Point Distribution Maps
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Craspedacusta sowerbyi was first described from specimens collected in 1880, from water-lily tanks in Regents Park, London. Competing descriptions were published simultaneously by Lankester and by Allman, who called the species Limnocodium victori (Slobodkin and Bossert, 1991). Polyps discovered in Philadelphia were initially described as a separate species, but were later determined to be a form of C. sowerbyi (Boulenger and Flower, 1928).
Excluding the colder states of Alaska, Montana, North and South Dakota, and Wyoming, freshwater jellyfish has been recorded throughout the United States (Deacon and Haskell, 1967; DeVries, 1992; Eldredge, 1994; Peard, 2002). It is most common in the eastern temperate states (DeVries, 1992).
Freshwater jellyfish are now common in temperate climates almost globally, occurring frequently in North and South America, Eurasia and Australia (Acker and Muscat, 1976; Pennak, 1989). Although it has been recorded in tropical locations, including the Hawaiian island of Maui, the states of Nuevo Leon and Sinaloa, Mexico and the Natal Midlands, South Africa, its extent and status in tropical climates is not well known (Edmondson, 1940; Guajardo et al., 1987; Rayner, 1988; Eldredge, personal communication, 2002, Moreno-Leon, personal communication, 2007).
Great Lakes Region: Craspedacusta sowerbyi was discovered in the Huron River near Ann Arbor, MI, in 1933, and in Lake Erie shortly thereafter (Mills et al., 1993). It has since been recorded in Lake Huron and Lake St. Clair, as well as dozens of inland lakes and streams throughout the region, in the states of IL, IN, MI, MN, NY, OH, PA, and WI. In Canada, freshwater jellyfish have been known in Quebec since 1955 and in Ontario since 1980 (Peard, 2002).
Ecology: Craspedacusta sowerbyi occupies a range of freshwater habitats. In its native range, it typically inhabits shallow pools along the Yangtze River, sometimes coexisting with a related species, C. sinensis, which occurs in the upper river valley (Slobodkin and Bossert, 1991). In this environment, changing conditions in the main river system expose jellyfish to fluctuating water levels, temperatures and plankton populations. Where it is introduced, C. sowerbyi is most commonly found in shallow, slow moving or stagnant artificial water bodies such as ornamental ponds, reservoirs, gravel pits, and quarries (Pennak, 1956; DeVries, 1992; Peard, 2002). It has also been reported in large river systems, including the Allegheny, Ohio and Tennessee River systems, natural lakes, aquaria, and ornamental ponds (Beckett and Turanchik, 1980; DeVries, 1992; Peard, 2002).
Craspedacusta sowerbyi is able to reproduce both sexually and asexually. Mature hydromedusae reproduce sexually by broadcasting gametes into the water. Fertilized eggs grow into ciliated planulae (larvae), which then settle and metamorphose into the polyp form. Polyps are capable of budding to produce hydromedusae, as well as either daughter polyps that remain attached to the parent, forming a colony, or frustule larvae which move to new locations before metamorphosing into new polyps (Pennak, 1989; Slobodkin and Bossert, 1991; Peard, 2002).
Hydromedusae are produced only sporadically, and a given location may go several years between blooms (Peard, 2002). Blooms are thought to be temperature dependent, requiring water of at least 25° C, and are most common in summer and fall (Kato and Hirabayashi, 1991; Dodson and Cooper, 1983; Anonymous, 1997; McGaffin, 1997; Peard, 2002). Other factors that may affect hydromedusa blooms include zooplankton populations, alkalinity, and calcium carbonate (Acker and Muscat, 1976; Koryak and Clancy, 1981; McCullough et al., 1981; Angradi, 1998). The more cold tolerant polyp form may have a wider distribution than the hydromedusa form, but because it is inconspicuous and easily overlooked, its range is difficult to determine (Kato and Hirabayashi, 1991; Angradi, 1998). Polyps overwinter by contracting into resting bodies called podocysts, which are essentially dormant cellular balls surrounded by a protective chitin-like membrane that allows them to withstand more extreme conditions than the active forms (Peard, 2002). When conditions are favorable, the podocysts grow into polyps again.
Like other cnidarians, C. sowerbyi is an opportunistic predator, feeding on small organisms that come within its reach. Both polyp and hydromedusa forms use nematocysts (stingers) to capture prey. Polyps are able to camouflage themselves by secreting a sticky mucous that adheres particles to their body (Pennak, 1989; Peard, 2002).
Means of Introduction: Initially, C. sowerbyi was probably transported with ornamental aquatic plants, especially water hyacinth (Eichhornia crassipes), from its native region in China (Slobodkin and Bossert, 1991). An introduction at Fena Lake, Guam may have accompanied introduction of tilapia following dam construction in 1952. The first sightings of C. sowerbyi at Fena Lake were in 1970 (Belk and Hotaling, 1971). In the United States, polyps and resting bodies are probably translocated accidentally with stocked fish and aquatic plants or by waterfowl (Angradi, 1998; Wynett and Wynett, pers. comm. 1998). Pennak (1956) noted that new reservoirs and ponds (less than 40 years) exhibited the majority of hydromedusa blooms known at that time.
Status: Craspedacusta sowerbyi is apparently established throughout most of the United States. Since the first record in 1880, it has been recorded in 44 states and the District of Columbia (Pennak, 1989; DeVries, 1992; Peard, 2002). In Colorado, only two populations have been reported, so the species may not be established there (Pennak, 1956; DeVries, 1992; Peard, 2009). The presence of C. sowerbyi in Maui, Hawaii was confirmed in 1938, however its status in Hawaii is unknown. There have been no documented observations of C. sowerbyi in Hawaii for at least 15 years (Edmondson, 1940; Eldredge, personal communication 2002).
Impact of Introduction: The impact of this widespread jellyfish is unclear. Dodson and Cooper (1983) proposed Craspedacusta sowerbyi's preference for predatory zooplankton, such as the rotifer Asplanchna, could influence relative zooplankton species structure. Spadinger and Maier (1999) agreed with theorized affects on zooplankton communities finding that C. sowerbyi hydromedusae prefer larger zooplankton (0.4–1.4 mm) and vigorous prey such as copepods. Under laboratory conditions and in 4 mm of water, C. sowerbyi polyps apparently killed and fed on striped bass larvae (Dendy, 1978). Dumont (1994) speculated that C. sowerbyi may consume fish eggs, but Spadinger and Maier (1999) note that it is generally not considered an important predator of eggs or small fish . Crayfish are considered the only important predator of the hydromedusa phase (Pennak, 1989; Slobodkin and Bossert, 1991).
References: (click for full references)
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McKercher, L., D. O'Connell, P. Fuller, J. Liebig, J. Larson, T.H. Makled and A. Fusaro
Revision Date: 5/28/2013
McKercher, L., D. O'Connell, P. Fuller, J. Liebig, J. Larson, T.H. Makled and A. Fusaro. 2016. Craspedacusta sowerbyi. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=1068 Revision Date: 5/28/2013
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