Invasion History

First Non-native North American Tidal Record: 1979
First Non-native West Coast Tidal Record: 1979
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Cladonema pacificum was first described from the Northwest Pacific (Naumov 1957). Introduced specimens have been found in Bodega, California and Panama Bay, Panama.

North American Invasion History:

Invasion History on the West Coast:

Cladonema pacificum is only known from a display aquarium which had been filled with fouling organisms from Bodega Harbor and San Francisco Bay, California. Cladonema polyps and medusae were first observed in the aquaria in 1979. Rees (1982) thought it was likely that C. pacificum (which he identified as the synonymous C. uchidae) had been introduced to the region since he had not observed the species previously. Rees (1982), Cohen and Carlton (1995) and Mills et al. (in Carlton 2007) treat it as established in San Francisco Bay; however, we know of no further records.

Invasion History Elsewhere in the World:

Cladonema pacificum has also been reported from Panama Bay, Panama where it was found in May, July, and December 2006 (Miglietta et al. 2008).


The hydrozoan Cladonema pacificum has a minute attached polyp stage (~0.5 mm tall) and small, but more conspicuous planktonic medusa (up to 3.5 mm) (Naumov 1957; Rees 1982). The polyps have been observed in aquaria, growing on sand grains and the sides of tanks (Rees 1982). In nature, they were found growing on mollusc shells, among rocks and algae in the littoral zone (Naumov 1957). The polyps form creeping, non-branching colonies, with erect stalks bearing four capitate (ending in bulbs) tentacles each (Naumov 1957; Rees 1982). They release a medusa with a bell shape which is wider than it is high. The medusae have nine radial canals, each with a tentacle bulb with one adhesive and one regular tentacle. The largest medusae (3.5 mm in height) reported by Rees (1982) had up to seven tentacles on each bulb, with the ones most distal to the bulb being the oldest, largest and most developed, with scattered nematocyst batteries clearly evident. The tentacles have many branches – ‘those most proximal to the tentacle bulb and most recently formed were adhesive tentacles'. Therefore tentacles underwent a change in development from adherent tentacles, with their large terminal adhesive pad, to regular tentacles as medusae developed and matured. In medusae over 2 mm in height a slight peduncle began to form above the manubrium, which hung almost to the velar (velum) opening. The most mature of Rees' medusae had male gonadal tissue developing on the manubrium (description from: Rees 1982).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Cnidaria
Class:   Hydrozoa
Subclass:   Hydroidolina
Order:   Anthoathecatae
Suborder:   Capitata
Family:   Cladonematidae
Genus:   Cladonema
Species:   pacificum


Cladonema radiatum var. mayeri (Perkins, 1906)
Cladonema uchidai (Hiro, 1958)

Potentially Misidentified Species

Cladonema californicum
Native to California (Rees 1982; Mills et al., in Carlton 2007)

Cladonema myersi
Native to southern California (Rees 1982; Mills et al., in Carlton 2007)

Cladonema radiatum
Native to Atlantic, introduced in Padilla Bay WA (Rees 1982; Mills et al., in Carlton 2007)



Very little is known about the ecology of Cladonema pacificum. Based on the biology of the congeneric C. radiatum, the hydroid colonies produce medusa buds, which in turn develop into medusae that are released (Schuchert 2006). The medusae feed on zooplankton, and when mature release sperm or brood eggs. The eggs are fertilized and released as planula larvae. These planula larvae settle on a suitable substrate and develop into sessile hydroids. Naumov (1957) found the medusae of C. pacificum among littoral algae on rocky shores and the tiny hydroids attached to mollusk shells on the algae and rocks.



Trophic Status:




General HabitatMarinas & DocksNone
General HabitatUnstructured BottomNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Maximum Height (mm)5Medusa height. Hydroids are 0.5 mm tall (Naumov 1957; Rees 1982).
Broad Temperature RangeNoneCold temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

No impacts are known for introduced populations of Cladonema pacificum.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-4a None 1955 Native Estab
NWP-4b None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 1979 Def Estab
P090 San Francisco Bay 1979 Def Estab
SEP-H None 2006 Def Estab
PAN_PAC Panama Pacific Coast 2006 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
30724 Rees 1982; Cohen and Carlton 1995 1979 1979-01-01 San Francisco Bay Def 37.8494 -122.3681


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>

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

Hirai, Eturo (1958) On the species of Cladonema radiatum var. mayeri Perkins), Bulletin of the marine biological station of Asamushi 9: 23-25

Miglietta, Maria Pia; Rossi, Marco; Collin, Rachel (2008) Hydromedusa blooms and upwelling events in the Bay of Panama, Tropical East Pacific., Journal of Plankton Research 30(7): 783-793

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

Naumov, D. V. (1957) [The life cycle of the hydromedusa Cladonema pacifica Naumov.], Doklady Akademii Nauk USSR 112(1-6): 194-195

Naumov, D. V. (1969) <missing title>, Israel Program for Scientific Translations, Jerusalem. Pp. <missing location>

Rees, John T. (1982) The hydrozoan Cladonema in California: a possible introduction from East Asia, Pacific Science 36(4): 439-444

Schuchert, Peter (2006) The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Capitata Part 1., Revue Suisse de Zoologie 113(2): 325-410