Invasion History

First Non-native North American Tidal Record: 1991
First Non-native West Coast Tidal Record: 1991
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Paradexamine SD1 does not correspond to any known species, and is of unknown origin. There are 46 known species of Paradexamine (Appeltans et al. 2015), mostly in Australian waters, but with outliers along the coasts of Asia, South America, and Africa (Barnard and Karaman 1991). In 1991, Paradexamine SD1 was collected on Catalina Island, California (Cadien 2007) and in 1993-1994, it was collected in San Francisco Bay (Cohen and Carlton 1995). It is well-established in saline waters of Central and South San Francisco Bay, outer San Pablo Bay (Foss 2009), and along the coast of southern California (Cohen et al. 2002; Ranasinghe et al. 2005; California Department of Fish and Wildlife 2014).

North American Invasion History:

Invasion History on the West Coast:

In 1991, Paradexamine SD1 was collected on Catalina Island, California (CA). Cadien (2007) suggested that it had arrived on the hull of a yacht. In 1993-1994, it was collected in San Francisco Bay, CA (Cohen and Carlton 1995). In 1998-2000, it was found in harbors on the coast of southern California from Channel Islands Harbor and Oxnard to San Diego Bay (Cohen et al. 2002; Cohen et al. 2005; Ranasinghe et al. 2005). Likely vectors include hull fouling of recreational boats or commercial ships and ballast water.


Paradexamine SD1 does not correspond to any known species, and a detailed description is not available, so we will present generic characteristics. The body is laterally compressed and arched with a distinct rostrum. Coxae 1-4 are deeper than their length. Pereiopods 5-7 have segment 2 expanded into shield-like plates. One or more of the posterior pereonites and all of pleonites bear posterior-dorsal median teeth. Pleonites 1-3 bear lateral and dorsal keels. Urosome segments 2 and 3 are fused (Barnard and Karaman 1991; Chapman 2007). The strong pleonal and urosomal armature of this species makes it stand out from other local dexaminoids (Cadien 2007). Adults of Paradexamine SD1 are ~ 5 mm long (Chapman 2007).

Barnard and Karaman (1991) list more than 30 species of Paradexamine worldwide, and Myers and Lecroy (2009) described 9 more species from the Great Barrier Reef. The name of the Australian species, P. churinga has been applied to Paradexamine SD1, but the features of the California form do not quite fit those of any described species (Cadien 2007). The genus is most diverse in the Australian region, but species are known from South America, Japan, Korea, China, and Fiji (Barnard and Karaman 1991; Huang 2001; Kim et al. 2006; Myers and Lecroy 2009).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Gammaridea
Family:   Dexaminidae
Genus:   Paradexamine
Species:   sp.


Paradexamine cf. churinga? (Cohen et al., 2002)

Potentially Misidentified Species



Paradexamine sp. SD1 is found associated with marine fouling communities, often on or among algae and marine invertebrates (Cadien 2007). In gammarid amphipods, sexes are separate, the young are brooded, and development is direct (Bousfield 1973). Little is known about the life history of species in this genus (Myers and LeCroy 2009). In California waters, it is found in bays and harbors, and is associated with algal turf and fouling communities (Cadien 2007; Chapman 2007). We have not found information on the feeding of amphipods in this genus, but omnivory is common in free-living gammaridian amphipods.


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

Tolerances and Life History Parameters

Maximum Length (mm)None5 (Chapman 2007)
Broad Temperature RangeNoneWarm-temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

No impacts have been reported for Paradexamine sp. on the West Coast.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-VI Pt. Conception to Southern Baja California 1991 Def Estab
NEP-V Northern California to Mid Channel Islands 1993 Def Estab
P050 San Pedro Bay 2000 Def Estab
P020 San Diego Bay 1998 Def Estab
P030 Mission Bay 1998 Def Estab
P027 _CDA_P027 (Aliso-San Onofre) 1998 Def Estab
P040 Newport Bay 1998 Def Estab
P060 Santa Monica Bay 1998 Def Estab
P062 _CDA_P062 (Calleguas) 2000 Def Estab
P090 San Francisco Bay 1993 Def Estab
P023 _CDA_P023 (San Louis Rey-Escondido) 2011 Def Unk
NEP-VI Pt. Conception to Southern Baja California 1991 Def Estab
P058 _CDA_P058 (San Pedro Channel Islands) 1991 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Appeltans, W. et al. 2011-2015 World Registry of Marine Species. <missing URL>

Barnard, J. Laurens; Karaman, Gordan S. (1991) The familes and genera of marine gammaridean Amphipoda, (except marine Gammaroidea). Part 1., Records of the Australian Museum Supplement 13: 1-417

Bousfield, E.L. (1973) <missing title>, Comstock Publishing Associates, Ithaca, NY. Pp. <missing location>

Cadien, Donald B. 2007 Dexaminoidea of the NEP (Equator to Aleutians, intertidal to abyss): a review.. <missing URL>

California Department of Fish and Wildlife (2014) Introduced Aquatic Species in California Bays and Harbors, 2011 Survey, California Department of Fish and Wildlife, Sacramento CA. Pp. 1-36

Chapman, John W. (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of California Press, Berkeley CA. Pp. 545-611

Cohen, A. N. and 11 authors (2005) Rapid assessment survey for exotic organisms in southern California bays and harbors, and abundance in port and non-port areas., Biological Invasions 7: 995-1002

Cohen, Andrew N. and 12 authors (2002) Project report for the Southern California exotics expedition 2000: a rapid assessment survey of exotic species in sheltered coastal waters., In: (Eds.) . , Sacramento CA. Pp. 1-23

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>

Foss, Stephen (2009) <missing title>, California Department of Fish and Game, Sacramento CA. Pp. <missing location>

Huang, Zongguo (Ed.), Junda Lin (Translator) (2001) Marine Species and Their Distributions in China's Seas, Krieger, Malabar, FL. Pp. <missing location>

Kim, Young Ho; Eun, Ye; Lee, Kyung Sook (2006) Two new records of Dexaminidae (Crustacea: Amphipoda) from Korea, Korean Journal of Systematic Zoology Molluscan Research 22(1): 37-49

Myers, Alan A.; Lecroy, Sara E. (2009) Dexaminidae, Zootaxa 2260: 393-424

Pierce, Richard W., Carlton, James T., Carlton, Deborah A., Geller Jonathon B. (1997) Ballast water as a vector for tintinnid transport, Marine Ecology Progress Series 149: 295-297

Ranasinghe, J. Ananda and 6 authors. (2005) The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities, Biological Invasions 7: 679-686