Blackfordia virginica
(Black Sea jellyfish)
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Blackfordia virginica Mayer, 1910

Common name: Black Sea jellyfish

Taxonomy: available through www.itis.govITIS logo

Size: polys - 1-2mm; medusae 10 mm (Mills and Sommer 1995).

Native Range: Black Sea (Mills and Sommer 1995).
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Nonindigenous Occurrences: Petaluma and Napa rivers in the San Francisco Bay area, California (Mills and Sommer 1995). Established in Coos Bay, Oregon (Ruiz 2000). Chesapeake Bay, Virginia (Mills and Sommer 1995).  East coast of North American prior to 1910 (Thiel 1935).

Means of Introduction: One researcher has concluded, based on genetics, this species is native to the Black Sea and was likely transported to the East Coast of North America prio to 1910 in ship ballast water (Thiel 1935; Mills and Sommer 1995).  Specimens deposited at the California Academy of Sciences reveal this species was collected in the early 1970s in the Bay area, but was misidentified as Phialidium sp.  One collection was of 150 to 200 individuals from the Napa River in September 1970.  A second contained eight individuals from the Petaluma River in September 1974.  Therefore, it is likely that this species has been in the San Francisco Bay area and has gone undetected for over 20 years (Mills and Sommer 1995).

Status: Established in California.  Reported from Virginia.

Impact of Introduction: Unknown.

Remarks: Unlike the other Black Sea jellyfish introduced into this area, both males and females of this species have been collected (Mills and Sommer 1995).  Also introduced to the Ganges River in Calcutta, India in 1926 (Carlton 1985).

References: (click for full references)

Carlton, J.T.  1985.  Transoceanic and interoceanic dispersal of coastal marine organisms: The biology of ballast water.  Oceanogr. Mar. Biol. Ann. Ref. 23:313-371.

Mills, C.E., and F. Sommer. 1995.  Invertebrate introductions in marine habitats: two species of hydromedusae (Cnidaria) native to the Black Sea, Maeotias inexspectata and Blackfordia virginica, invade San Francisco Bay.  Marine Biology 122:279-288.

Theil, M.E.  1935.  Zur Kenntnis der Hydromedusenfauna des Schwarzen Meeres.  Aool. Anz 111:161-174.

Author: Fuller, P.

Revision Date: 4/3/2006

Citation Information:
Fuller, P., 2018, Blackfordia virginica Mayer, 1910: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 4/3/2006, Access Date: 1/22/2018

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.

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Page Last Modified: Thursday, December 21, 2017


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Citation information: U.S. Geological Survey. [2018]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [1/22/2018].

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