Invasion History

First Non-native North American Tidal Record: 1894
First Non-native West Coast Tidal Record: 1965
First Non-native East/Gulf Coast Tidal Record: 1894

General Invasion History:

Gonionemus vertens is native to the North Pacific, from Vietnam to the southern Sea of Okhotsk in the Western Pacific, and from Puget Sound, Washington to the Aleutian Islands in the Eastern Pacific (Edwards 1976; Naumov, in Golikov et al. 1976; Mills et al. in Carlton 2007). Asian populations are reported to cause more severe stings, both as polyps and medusae, than those on the Pacific coast of North America (Edwards 1976). Edwards noted considerable local variation in morphology of medusae, but considers this to be environmental or genetic differences at the sub-specific level. It is possible that several cryptic species are present over its broad Pacific range. Medusae of G. vertens appeared suddenly in 1894 in Woods Hole, Massachusetts near the Marine Biological Laboratory, and then appeared in a number of lagoons and harbors in Europe, often near marine laboratories. This hydrozoan is prone to sporadic 'blooms' of medusae, followed by disappearances, while its polyp phase is easily overlooked – hence Edwards (1976) title, 'A study in erratic distribution'.

North American Invasion History:

Invasion History on the West Coast:

On the West coast, a population of G. vertens was found in a lagoon on the campus of the University of California at Santa Barbara, far south of its normal range, first appearing in 1965 (Edwards 1976).

Invasion History on the East Coast:

In 1894, G. vertens appeared in the Eel Pond lagoon, adjacent to the Marine Biological Laboratory in Woods Hole, Massachusetts, where it had not been seen previously. It was subsequently found in eelgrass beds (Zostera marina) in surrounding locations, including Hadley Harbor in the Elizabeth Islands, Vineyard Haven, and Muskeget Island (Mayer 1910; Sumner et al. 1913a). The medusa was also collected in Noank, Connecticut in Long Island Sound (Mayer 1910). It became a frequent experimental animal at Woods Hole, but disappeared after a massive, widespread, eelgrass die-off in 1931. Edwards (1976) considered it extinct on the East Coast, but Gosner (1978) noted it as 'erratic' since the 1930s. Recently, this medusa has re-appeared in tidal salt ponds on Cape Cod and Martha’s Vineyard, where it stung researchers. In 2006, G. vertens was discovered in Farm Pond, Martha's Vineyard, and later in Menemsha Pond (Friends of Farm Pond 2012). In 2010, it was found in Sedge Lot Pond, adjacent to Waquoit Bay in Mashpee (Kehrl 2011). Gonionemus vertens appears on a checklist for Cobscook Bay, Maine, but no details are provided (Trott 2004). Edwards (1976) suggests that a possible vector for this hydrozoan was shellfish research by the US Fisheries Commission, which included rearing and stocking of Pacific Clams (Protothaca staminea), or more likely, oysters from Europe, possibly including the 'Portuguese' Oyster (Crassostrea angulata), with which the polyp could have been carried from Asia. Ballast water or hull fouling is less likely, as they could not account for the highly localized distribution on the East Coast. In June, 2016, several specimens of G. vertens were discovered in New Jersey estuaries, in Shrewsbury River, Manasquan Bay, and Barnegat Bay (Goldman 2016; Gaynor et al. 2016). Genetic barcoding indicated that these specimens were a close match with G. vertens from China (Gaynor et al. 2016). Severe stinging, due to this jellyfish, has not been reported in New Jersey, to our knowledge.

The recent occurrence, since the 1990s, of severely stinging G. vertens in Martha's Vineyard and Waquoit Bay waters may represent a cryptic invasion of the more severely stinging Northwest Pacific form of this hydrozoan (Govindarajan and Carman 2015).

Invasion History Elsewhere in the World:

In Europe, Gonionemus vertens medusae were first reported in aquaria at Dove Marine Laboratory, in Cullercoats, on the North Sea coast near Scotland (in 1913, Edwards 1976). There have been many subsequent records, many of them from aquaria in marine laboratories or private homes, but these often contained stones gathered from nearby shores. Several of the laboratories had been engaged in oyster research (Edwards 1976). Elsewhere in Europe, G. vertens medusae (and later, polyps) were found in 1929 at Callot, France, near Roscoff in Brittany (Teissier 1965, cited by Edwards 1976), again in an area of heavy oyster cultivation. Other appearances in Europe were at Ostend, Belgium in 1946; the island of Sylt, Germany in 1947; the Rammekenshoek creek, near Middelburg, the Netherlands in 1960; and Lake Grevelingen, the Netherlands (Edwards 1976; Bakker 1980; Wolff 2005). Further north, medusae were found in the Oslofjord, Norway in 1921; the Gullmar Fjord, Sweden in 1930; and the more northern Hardangerfjord, Norway in 1958 and Trondheimsfjord, Norway in 1969 (Tambs-Lyche 1964; Edwards 1976; Hopkins 2002). Gonionemus vertens appeared in the outer Baltic at Frederikshavn, Denmark in 1960, but did not become established (Edwards 1976; Jensen and Knudsen 2005). In the Mediterranean, there are some early records, from 1876 to 1950, from the French coast and Adriatic (Edwards 1976; Bouillon et al. 2004), but we have not found more recent reports and are uncertain of its establishment. Edwards (1976) considered oyster culture, particularly the 'Portuguese' oyster (C. angulata), introduced from Asia in the 16th-17th century, to be the likeliest vector for the introduction of this hydrozoan to Europe.

In September 2008, medusae of G. vertens were found in an aquarium filled with benthic organisms collected near Mar de Plata, Argentina, the first record of this hydrozoan in the Southwest Atlantic. Shipping is the likely vector of this introduction (Rodriguez et al. 2014b).

In June 2016, G. vertens was found in the Berre Lagoon on the Mediterranean coast of France. In July 2017, this jellyfish was associated with severe stinging of swimmers, including several cases of anaphylactic shock. Environmental restoration of the lagoon, including the recovery of Eelgrass (Zostera marina) may have favored the establishment of G. vertens. Past pollution may have also contributed to abnormalities in the medusae (Marchessaux et al. 2017).


Gonionemus vertens (Clinging Jellyfish) is a hydrozoan with a small, solitary polyp, but a conspicuous medusa stage. The polyp is rounded, with a conical hypostome and 4 to 6 tentacles. The base of the polyp lacks hydrorhizae (rootlets, for attachment). The polyp is often embedded in detritus, or clinging to the substrate with its tentacles. It produces creeping, mobile frustules (which develop into new polyps) or medusae by budding from the lower part of the hydranth. The polyps can also degenerate into cysts. The polyp is less than 1 mm in height.

The medusa has a flattened hemispherical umbrella, with a nipple-shaped manubrium, and four radial canals. The manubrium ends with four folded lips, just inside the opening of the umbrella. The gonads form folded sacs, following most of the length of the marginal canals. The medusa has 60-80 tentacles, each sharply bent at the tip, and bearing an adhesive pad. Medusae are up to 20 mm (rarely to 40 mm) in diameter. The gonads are orange, brownish orange, or reddish, while the umbrella is golden-brown, and the tentacle bulb has a brilliant emerald-green spot. They cling to vegetation, such as eelgrass or seaweeds during bright daylight, but may swim to the surface at night or on cloudy days. A frequent mode of swimming in G. vertens (and the source of the species name) is pulsing towards the surface, flipping near the surface, and then sinking upside down with tentacles extended (description from: Edwards 1976; Naumov in Golikov et al. 1976; Gosner 1978; Bakker 1980; Bouillon et al. 2004; Mills et al., in Carlton 2007).

Gonionemus 'vertens' may be a species complex, with animals from the Northeast and Northwest Pacific differing in small details of morpholgy, and notably, in the strength and toxicity of stinging. Earlier records in New Eng;lnd and Europe, classified as G. vertens or G. murbachi were not associated with severe stings. Recent appearances in Massachusetts, New Jersey, and Sweden have been associated with a strong-stinging form genetically related to Chinese (Yellow Sea, Bohai Sea) medusae (Govindarajan et al. 2016, 2917, 2018)


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Cnidaria
Class:   Hydrozoa
Subclass:   Hydroidolina
Suborder:   Limnomedusae
Family:   Olindiidae
Genus:   Gonionemus
Species:   vertens


Gonionemus oshoro (Uchida, 1912)
Gonionemus murbachi (Mayer, 1901)
Haleremita cumulans (Schaudinn, 1894)
Cosmetira salinarum (Du Plessis, 1879)
Gonionemus vertens (Agassiz, 1862)

Potentially Misidentified Species



Gonionemus vertens has a small, inconspicuous hydroid stage and a semi-planktonic medusa stage. The tiny hydroid (~1 mm in diameter) apparently occurs among benthic debris and algae on rocks, shells, and vegetation. It presumably feeds on small zooplankton or epibenthos. As it grows, it buds off creeping frustules, which move away and develop into new polyps and medusae (Edwards 1976; Naumov in Golikov et al. 1976; Bouillon et al. 2004; Mills et al., in Carlton 2007). Polyps may reproduce asexually for long periods of time, without producing medusae, and then suddenly produce jellyfish blooms, as has been noted for the related Freshwater Jellyfish Craspedacusta sowerbii (Acker and Muscat 1976).

The medusae are released at about 1.5 mm in diameter. By day, at least in bright daylight, they cling to Eelgrass (Zostera marina) or other vegetation, and swim in the water column by night, swimming to the surface, and drifting down with spread tentacles, to catch zooplankton. The medusae shed eggs, which settle on the bottom and develop into polyps (Edwards 1976). Little information is available on the temperature and salinity requirements of this hydrozoan, but it has not been reported from strongly brackish habitats.


Zooplankton, isopods, amphipods

Trophic Status:




General HabitatGrass BedNone
General HabitatCoarse Woody DebrisNone
General HabitatUnstructured BottomNone
General HabitatOyster ReefNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Life History

Tolerances and Life History Parameters

Maximum Temperature (ºC)27Field data, Berre Lagoon (Marchessaux et al. 2017)
Minimum Salinity (‰)20Field data, Berre Lagoon (Marchessaux et al. 2017)
Minimum Width (mm)1.5Medusa, after release (Edwards 1976)
Maximum Width (mm)20Maturing at 7 mm (Edwards 1976), rarely reaching 40 mm (Naumov, in Golikov et al. 1976)
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

After its appearance in Woods Hole, Massachusetts (MA) in 1894, until its disappearance in the 1930s, Gonionemus vertens was a frequent experimental animal for embryological and other research, and for teaching (Edwards 1976). After its reappearance in MA salt ponds, from 2006 on, its major impact has been stinging researchers, and in at least one case, causing serious health symptoms.

Health- Gonionemus vertens has stung researchers working in Farm Pond, Martha's Vineyard, MA (Friends of Farm Pond 2012), and Sedge Lot Pond (part of Waquoit Bay), in Mashpee, MA (Kehrl 2011). Some of these people suffered muscle cramps, chest tightness, and swollen throats, and received hospital treatment (Kehrl 2011). This jellyfish is not likely to be abundant in areas heavily used by swimmers, but could affect casual waders and people gathering shellfish near eelgrass beds. The occurrence of severely stinging G. vertens may be due to a cryptic invasion of the more venomous Northwest Pacific form of this hydrozoan (Govindarajan and Carman 2015). One severe case of anaphylactic shock was repoeted in 2015 in the Lagune de Berre, Mediterranean France. However, stings were rare, and usually not severe, so the impact could not be estimated, (Marchessaux et al. 2022).

Regional Impacts

NA-ET3Cape Cod to Cape HatterasEconomic ImpactHealth
This medusa has stung researchers working in Farm Pond and Menemsha Pond, Martha's Vineyard, MA (Friends of Farm Pond 2011), and Sedge Lot Pond, in Mashpee, MA (Kehrl 2010). Some of these people suffered muscle cramps, chest tightness, and swollen throats, and received hospital treatment (Kehrl 2010).
N190Waquoit BayEconomic ImpactHealth
This medusa has stung salt marsh researchers working in Sedge Lot Pond, in Mashpee, MA. These people suffered muscle cramps, chest tightness, and swollen throats, and received hospital treatment (Kehrl 2010; Govindarajan and Carman 2015).
N195_CDA_N195 (Cape Cod)Economic ImpactHealth
This medusa has stung researches working in Farm Pond and Menemsha Pond, Martha's Vineyard, MA (Friends of Farm Pond 2011; Govindarajan and Carman 2015).
MAMassachusettsEconomic ImpactHealth
This medusa has stung researches working in Farm Pond and Menemsha Pond, Martha's Vineyard, MA (Friends of Farm Pond 2011; Govindarajan and Carman 2015)., This medusa has stung salt marsh researchers working in Sedge Lot Pond, in Mashpee, MA. These people suffered muscle cramps, chest tightness, and swollen throats, and received hospital treatment (Kehrl 2010; Govindarajan and Carman 2015).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-4a None 0 Native Estab
NWP-3b None 0 Native Estab
NWP-4b None 0 Native Estab
NEP-II Alaska south of the Aleutians to the Alaskan panhandle 1903 Native Estab
NEP-III Alaskan panhandle to N. of Puget Sound 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 1894 Def Estab
MED-II None 2016 Def Unk
NEA-II None 1913 Def Estab
NWP-2 None 0 Native Estab
NWP-3a None 0 Native Estab
NEA-IV None 1929 Def Estab
AR-V None 1958 Def Estab
B-II None 1960 Def Unk
M010 Buzzards Bay 1894 Def Estab
M040 Long Island Sound 1910 Def Unk
B-I None 1921 Def Estab
N195 _CDA_N195 (Cape Cod) 1910 Def Estab
NA-ET2 Bay of Fundy to Cape Cod 1973 Def Estab
N010 Passamaquoddy Bay 1973 Def Unk
NEP-VI Pt. Conception to Southern Baja California 1965 Def Estab
P065 _CDA_P065 (Santa Barbara Channel) 1965 Def Estab
NWP-5 None 0 Native Estab
N190 Waquoit Bay 2000 Def Estab
MED-VII None 1894 Def Unk
MED-III None 2013 Def Unk
SA-I None 2008 Def Estab
N180 Cape Cod Bay 2010 Def Unk
M030 Gardiners Bay 2011 Def Unk
M070 Barnegat Bay 2016 Def Unk
M060 Hudson River/Raritan Bay 2016 Def Estab
AR-IV None 2017 Def Estab
N130 Great Bay 2017 Def Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1901 Def Unk
S206 _CDA_S206 (Vero Beach) 1901 Def Unk

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Ahyong, Shane T. (2010) New species and new records of Caridea (Hippolytidae: Pasiphaeidae) from New Zealand, Zootaxa 2372(2372): 341-357

Acker, Thomas; Muscat, Anne M. (1976) The ecology of Craspedacusta sowerbii Lankester, a freshwater hydrozoan, American Midland Naturalist 95(2): 323-336

Alves, Douglas Ferandes Rodrigues; Marcondes Lima, Daniel Jose, Hiorse, Gustavo Luis; Martinez, Pablo Ariel; Dolabella, Sivio Santana; Barros-Alves, (2018) Morphological and molecular analyses confirm the occurrence of two sympatric Lysmata shrimp (Crustacea, Decapoda) in the southwestern Atlantic, Zootaxa 4526(1): 41-55

Bakker, C. (1980) On the distribution of Gonionemus vertens A. Agassiz (Hydrozoa, Limnomedusae), a new species in the eelgrass beds of Lake Grevelingen (S. W. Netherlands), Hydrobiological Bulletin 14(3): 186-195

Bouillon, J. D.; Medel, M. D.; Pages, F.; Gili, J. M.; Boero, F/\.; Gravili, C. (2004) Fauna of the Mediterranean Hydrozoa, Scientia Marina 68(Suppl. 2.): 1-449

Carlton, James T. (Ed.) (2007) The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon Fourth Edition, Completely Revised and Expanded, University of California Press, Berkeley. Pp. <missing location>

Eddy,Elizabeth N. ; Roman, Charles T. (2016) Relationship between epibenthic invertebrate species assemblages and environmental variables in Boston Harbor’s intertidal habitat, Northeastern Naturalist 23(1): 45-66

Edwards, C. (1976) A study in erratic distribution: the occurrence of the medusa Gonionemus in relation to the distribution of oysters, Advances in Marine Biology 14: 251-284

Friends of Farm Pond 2012 <i>Gonionemus vertens</i>- New to the Vineyard. <missing URL>

Goldman, Jeff 6/10/2016 Possible dangerous 'clinging jellyfish' found along Jersey Shore, report says. <missing URL>

Golikov, A. N. and 7 other editors. (1976) <missing title>, Nauk, Leningrad. Pp. <missing location>

Gosner, Kenneth L. (1978) A field guide to the Atlantic seashore., In: (Eds.) . , Boston. Pp. <missing location>

Govindarajan, Annette F.; Carman, Mary R. (2016) Possible cryptic invasion of the Western Pacific toxic population of the hydromedusa Gonionemus vertens (Cnidaria: Hydrozoa) in the Northwestern Atlantic Ocean, Biological Invasions 18(2): 463-469

Gravili, Cinzia; Di Camillo, Cristina Gioia; Piraino, Stefano; Boero, Ferdinando (2013) Hydrozoan species richness in the Mediterranean Sea: past and present, Marine Ecology 34(Suppl. 1): 41-62

Guerra-Garcia, José Manuel and 21 authors (2023) Quick spreading of the exotic amphipod Laticorophium baconi (Shoemaker, 1934): another small stowaway overlooked?, Mediterranean Marine Science 24(3): 644-665

Hopkins, C.C.E. (2002) Invasive aquatic species of Europe: Distribution, impacts, and management, Kluwer Academic Publishers, <missing place>. Pp. 240-253

Jensen, Kathe R.; Knudsen, Jorgen (2005) A summary of alien marine benthic invertebrates in Danish waters., Oceanological and Hydrobiological Studies 34 (suppl. 1): 137-161

Kazyak (1998) Pocomoke River Basin: Environmental Assessment of Stream Conditions, Maryland Department of Natural Resources, Annapolis. Pp. <missing location>

Kehrl, Brian (7/30/2011) Mini jellies in Sedge Lot Pond pack a mega punch, Falmouth Enterprise <missing volume>: published online

Kennedy, C. R.; DiCave (1998) Gyrodactylus anguillae: The story of an appearance and a disappearance, Folia Parasitologica 45: 77-78

Mayer, A. G. (1910) Medusae of the World., In: (Eds.) . , Washington, D.C.. Pp. 231, 276-278

Mills, Claudia; Marques, Antonio; Migotto, Alvaro E; Calder, Dale R.; Hand, Cadet (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of California Press, Berkeley CA. Pp. 118-168

Oliveira, Otto M. P. and 24 authors (2016) Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters, Zootaxa 4194: 1-256

Pongparadon, Supattra; Zuccarello, Giuseppe C.; Prathep, Anchana (2017) High morpho-anatomical variability in Halimeda macroloba (Bryopsidales, Chlorophyta) in Thai waters, Phycological Research 65: 136-145
doi: 10.1111/pre.12172

Provan, Jim; Booth, David; Todd, Nicola P. ; Beatty, Gemma E.; Maggs, Christine A. (2008) Tracking biological invasions in space and time: elucidating the invasive history of the green alga Codium fragile using old DNA., Diversity and Distributions 39: 43-50

Rodriguez, Carolina S.; Pujol, María Gabriela; Mianzan, Hermes W.; Genzano, Gabriel N. (2014) First record of the invasive stinging medusa Gonionemus vertens in the southern hemisphere (Mar del Plata, Argentina), Latin American Journal of Aquatic Research 42(3): 653-657

Saraiva, A. (1995) Pseudodactylogyrus anguillae (Yin and Sprosion 1948, Gussev 1965) and P. bini (Kikuchi 192, Gussev 1965) Monogenea: Monopisthocotylea in Portugal, Bulletin of the European Association of Fish Pathologists 15(3): 81-83

Smith, Ralph I. (1964) <missing title>, Systematics-Ecology Program, Marine Biological Laboratory, Woods Hole, Massachusetts. Pp. <missing location>

Sumner, Francis B., Osburn, Raymond C., Davis, Bradley M. (1913a) A biological survey of the waters of Woods Hole and vicinity. Part I. Section I. Physical and Zoological. Section II. Botanical, Bulletin of the Bureau of Fisheries 31: 1-544

Tambs-Lyche, Hans (1964) Gonionemus vertens L. Agassiz (Limnomedusae)- A zoogeographical puzzle, Sarsia 10(15): 1-8

Todd, Eric S.; Kier, Andrew; Ebeking, Alfred W. (1966) Gonionemus vertens Agassiz, (Hydrozoa, Limnomedusae) in southern California, Bulletin of the Southern California Academy of Sciences 65(4): 205-210

Torres, Gladys (1990) [Presence of Limnoria sp.maarine woodboirers in the prinicipal ports of Ecuador (Crustacea:Isopoda: Flabellifiera)], Acta Oceanografica del Pacifico 6(1): 68-71

Trott, Thomas J. (2004) Cobscook Bay inventory: a historical checklist of marine invertebrates spanning 162 years., Northeastern Naturalist 11(Special issue 2): 261-324

Wolff, W. J. (2005) Non-indigenous marine and estuarine species in the Netherlands., Zoologische Verhandelingen 79(1): 1-116

Young, Craig S; Gobler, Christopher J. (None) Coastal ocean acidification and nitrogen loading facilitate invasions of the non-indigenous red macroalga, Dasysiphonia japonica, Biological Invasions <missing volume>: 1367-1391(