The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Blackfordia virginica
Blackfordia virginica
(Black Sea jellyfish)

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Blackfordia virginica Mayer, 1910

Common name: Black Sea jellyfish

Synonyms and Other Names: Blackfordia manhattensis Mayer, 1910 (synonym)

Taxonomy: available through www.itis.govITIS logo

Identification: Blackfordia virginica, is a relatively small translucent hydrozoan (jellyfish). The medusa of Blackfordia virginica is dome-shaped, a little taller than a hemisphere, with a rounded apex. The jelly in the bell is thick, and composes nearly half the height of the bell. There are usually four radial canals that form ‘X’ pattern across the bell, and a prominent ring canal around the base of the bell. This jellyfish has approximately 80 small tentacles with typically a single statocyte (a balance sensory receptor) between each tentacle (Mills and Rees 2000, Bardi and Marques 2009). Detailed photographs of specifc diagnostic characteristics used to identify Blackfordia virginica medusa are given in Jaspers et al. (2018).

The hydroid colonies (polyp stage) of Blackfordia virginica are extremely small (measured at typically 0.5-2 mm) creeping, and arise from a stolon. The stems sometimes have weak annular rings and are occasionally branched with 2-3 hydrothecae (cup-shaped extensions) on each stem. Polyps possess small, webbed tentacles (Mills and Sommer 1995, Mills and Rees 2000, Bardi and Marques 2009).

Size: polyp stage 0.5-2 mm; medusae 10-14 mm (Mills and Sommer 1995, Mills and Rees 2000).

Native Range: Black Sea (Mills and Sommer 1995).

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Blackfordia virginica are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
CA197020053Lower Sacramento; San Francisco Bay; San Pablo Bay
LA200920091Eastern Louisiana Coastal
VA199320102Lower Chesapeake Bay; Mattaponi

Table last updated 9/24/2021

† Populations may not be currently present.

Ecology: Blackfordia virginica has a complex life cycle of sexual and asexual reproduction. Sexually mature adult B. virginica release eggs and sperm into the water where after fertilization, about four days, hatch as free-swimming (planular) larvae (Kimber 2014). The planular larvae will settle and form small (0.5-2 mm) benthic polyps, which grow in a creeping fashion. Thydroid colonies (polyp stage) reproduce asexually by budding to achieve a stacked colony (Mills and Sommer 1995, Bardi and Marques 2009). The polyps have shown a preference for settling on the undersides of surfaces, but will also grow on submerged aquatic vegetation or barnacle shells (Wintzer et al. 2011).

When conditions are favorable for the medusae (typically in the spring when plankton begin to bloom), Gonophores bud off the stems of the polyps, and each one releases a single planktonic medusa. These newly released medusae are small at approximately 1 mm in diameter, but will eventually grow to their 14 mm adult length and reach sexual maturity, developing either ovaries or testes (Mills and Sommer 1995, Bardi and Marques 2009, Kimber 2014).

Polyps have only been reported from estuarine habitats, over a salinity range of 3-22 PSU (Wintzer et al. 2011), but the medusae have been found in open ocean waters. The medusa feeds on zooplankton: barnacle nauplii, copepods, mysids, fish  larvae and eggs (Mills and Sommer 1995; Bardi and Marques 2009, Wintzer et al. 2013). 

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 waters of California, Oregon, South Carolina, and Virginia. Reported from Delaware and Louisiana.

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.


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)

Bardi, J. and A.C. Marques. 2009. The invasive hydromedusae Blackfordia virginica Mayer, 1910 (Cnidaria: Blackfordiidae) in southern Brazil, with comments on taxonomy and distribution of the genus Blackfordia. Zootaxa 2198: 41-50 

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.

Jaspers, C., B. Huwer, N.Weiland-Bräuer, and C. Clemmesen. 2018. First record of the non-indigenous jellyfsh Blackfordia virginica (Mayer, 1910) in the Baltic Sea. Helgoland Marine Research 72(1):13. https://doi.org/10.1186/s10152-018-0513-7.

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.

Mills, C.E. and J.T. Rees. 2000. New observations and corrections concerning the trio of invasive hydromedusae Maeotias marginata (=M. inexpectata), Blackfordia virginica, and Moerisia sp. in the San Francisco Estuary. Scientia Marina, 64 Suppl. 1: 151-155.

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

Wintzer, A.P., Meek, M.H., Moyle, P.B., and B. May. 2011. Ecological insights into the polyp stage of non-native hydrozoans in the San Francisco Estuary, Aquatic Ecology 45: 151-161. 

Author: Fuller, P. and Daniel, W.M.

Revision Date: 10/1/2019

Citation Information:
Fuller, P. and Daniel, W.M., 2021, Blackfordia virginica Mayer, 1910: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=1050, Revision Date: 10/1/2019, Access Date: 9/24/2021

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.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2021]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [9/24/2021].

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