Observations of Freshwater Jellyfish, Craspedacusta sowerbyi 

 Lankester (Trachylina: Petasidae), in a West Virginia Reservoir 



Ted R. Angradi 



U.S. Department of Agriculture, Forest Service 



Timber and Watershed Laboratory, 



Parsons, West Virginia 26287 



ABSTRACT. — A swarm of medusae of the freshwater jellyfish 

 Craspedacusta sowerbyi was observed in a cove of a West Virginia 

 reservoir in August and September, 1995. Medusae were abundant 



(>1000/iTr) but extremely localized. Distribution of medusae in the 

 cove did not appear to be linked to water chemistry. Size of medusae 

 ranged from 6-21 mm in diameter and increased significantly with dis- 

 tance from the center of abundance, suggesting that the localized distri- 

 bution of medusae resulted from dispersion rather than from environ- 

 mentally-induced aggregation. Measurements of mean diameter of 

 medusae on separate dates indicated a growth rate of about 0.2 mm/d, 

 and a medusa life cycle of approximately 102 days. 



The freshwater jellyfish Craspedacusta sowerbyi Lankester 1880 is an 

 exotic species first observed (as medusae) in the United States in 1908 (Kramp 

 1950, Pennak 1989). Native to the Yang-tse River system in China (Kramp 

 1950), C sowerbyi has been reported from many localities worldwide between 



45° north and 45° south latitude (Acker and Muscat 1976, Pennak 1989). True 

 freshwater jellyfishes are few, limited to about a dozen species worldwide 

 (Hutchinson 1967, Pennak 1989). 



Craspedacusta sowerbyi has been reported from 3 1 states and the Dis- 

 trict of Columbia; it has not been reported from northern New England, the 

 Northern Rocky Mountains, or the Northern Great Plains (DeVries 1992). In 

 West Virginia there are records of C. sowerbyi from Barbour, Fayette, Mercer, 

 Monogalia, Wayne, and Wood counties (Reese 1940, Lytle 1962, Koryak and 

 Stafford 1981, and D. Tarter, Marshall University, personal communication). 



Craspedacusta sowerbyi has two life stages, a free-swimming medusa 

 (10-20 mm diameter), and a sessile hydroid polyp (1 mm long, Acker and Mus- 

 cat 1976). Lytle (1959) reviewed the developmental biology of the species. 

 Medusae of C. sowerbyi appear sporadically in lentic and even less frequently in 

 lotic ecosystems in the United States (Acker and Muscat 1976, Beckett and 

 Turanchik 1980, DeVries 1992). Usually a swarm of medusae appears in sum- 



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