Invasion History

First Non-native North American Tidal Record: 1941
First Non-native West Coast Tidal Record: 1941
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Stenothoe valida was described from Rio de Janeiro, Brazil by Dana in 1853. This amphipod was found and named by Costa in Naples, Italy, in the same year, and later recorded from many warm-water ports around the world (Barnard 1953). The small size of the animal, and the diversity and taxonomic difficulty of the genus, means it has been frequently overlooked, and its native range is unknown. Its known range includes both sides of the North Atlantic (Colombia to North Carolina; Senegal to southern England, Fox and Bynum 1975; Lincoln 1979; Hirayama 1988; US National Museum of Natural History 2011); the Mediterranean Sea (Bellan-Santini et al. 1993); Brazil; South Africa (Hirayama 1988); the Indian Ocean (Ledoyer 1967; Sivaprakasam 1969); the Northwest Pacific (Japan and Korea, Hirayama 1988; Kim and Kim 1991); and the Southwest Pacific (New Guinea, Australia, New Zealand, Chilton 1924; Atlas of Living Australia 2015).

Stenothoe valida has apparently extended its range northward in recent years. In the North Sea, it was collected on submerged shipwrecks off Belgium in 2005 (Zintsen et al. 2008) and on floating seaweed at the island of Helgoland, Germany in 1998 (Franke and Gutow 2003). On the coast of New England, in 2000-2013, S. valida was recorded in Buzzards Bay and the Gulf of Maine (MIT Sea Grant 2000-2008; Wells et al. 2014). This amphipod may have been overlooked, due to its similarity with the native S. minuta (Bousfield 1973), so we do not currently consider it introduced here.

North American Invasion History:

Invasion History on the West Coast:

Stenothoe valida was first collected on the West Coast in San Francisco Bay, California sometime before 1941 (Light 1941, cited by Carlton 1979). It has been collected primarily in harbors and bays, usually among hydroids on man-made structures. In San Francisco, it is known from Central, South, and San Pablo Bays (Carlton 1979; Cohen and Carlton 1995; Cohen et al. 2005). In 1951-1953, it was collected in dock fouling in Newport Bay and Los Angeles Harbors (Barnard 1953; Barnard and Reish 1959), and in 1961 in Bahia de San Quintin, Mexico (Carlton 1979; USNM 109156, US National Museum of Natural History 2007). More recently, it was found in: Humboldt Bay in 2000 (Boyd et al. 2002); Channel Islands Harbor in 2000 (Cohen et al. 2002); Marina Del Rey in 2000 (Cohen et al. 2002); and Monterey Harbor, Oceanside Harbor, and Mission Bay in 2011 (California Department of Fish and Wildlife 2014).

Invasion History in Hawaii:

Chilton (1924) reported a collection of Stenothoe valida from the Hawaiian Islands. Followed by a report from Barnard (1970) of S. valida specimens collected from transplanted black coral (Antipathes irregularis) in deep water off Oahu, which showed some atypical features. More definite records are from 1996 in Pearl Harbor; 2000 in Kaneohe Bay (Coles et al. 2002a); and 2002 in Molokai, Kauai, and Maui (Coles et al. 2004). Stenothoe valida is now well-established around the Hawaiian Islands. In 1997, it was found in the lagoon of Midway Island (Defelice et al. 1998).


The family Stenothoidae is distinguished by having coxal plates 2-4 greatly enlarged, covering the basal segments of most of the appendages. The abdomen is flexed downward. They are sometimes called 'seed-amphipods', for their laterally-compressed elliptical shape. The eye is relatively large. Antenna 1 is less than 1/2 body length and is slightly longer than Antenna 2.

In Stenothoe valida, Gnathopod 2 is larger than Gnathopod 1 in the female, and is sexually dimorphic, but does not differ greatly in size. Gnathopod 1, in both sexes, has segment 4 (merus), reaching the distal end of segment 5 (carpus). In the male, segment 6 (the propodus) has a large tooth, adjacent to a deep excavation near the insertion of segment 7, the dactyl. The palm and the opposing surface of the dactyl are both densely covered with setae. The female's Gnathopod 2 lacks the large distal tooth, the excavation, and has only a few, short setae on the palm. In the female, coxa plate 2 is much larger than in the male. Pereiopods 5-7 have segment 4 (merus) enlarged, with a curved, blade-like postero-distal tip. Uropod 1 extends beyond Uropod 2 and is lined with short, fine comb-like spines. Both Uropods 1 and 2 are biramous. Uropod 3 has a thick peduncle, shorter than the single 2-segmented ramus. The distal end of segment 1 bears a spine facing outward; segment 2 resembles a thick-tapered spine. The telson is oval, with 3-4 pairs of marginal spines. Adults are 4-6 mm in size. Description based on: Barnard 1953, Hirayama 1988, Bellan-Santini et al. 1993, Chapman 2007, LeCroy 2011; Lincoln 1979; Krapp-Schickel 2013, and Krapp Schickel 2015). Krapp-Schickel (2015) suggests that S. valida is very likely a complex of closely related species/


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Gammaridea
Family:   Stenothoidae
Genus:   Stenothoe
Species:   valida


Stenothoe assimilis (Chevreux, 1908)
Stenothoe validus (Dana, 1853)
Probolium polyprion (Costa, 1853)
Probolium megacheles (Heller, 1866)
Montagua miersii (Haswell, 1880)
Montagua longicornis (Haswell, 1880)
Probolium miersii (Chilton, 1885)
Stenothoe adhaerens (Chilton, 1891)
Stenothoe valida (Della Valla, 1893)
Stenothoe miersii (Stebbing, 1906)
Stenothoe ornata (Barnard, 1930)

Potentially Misidentified Species

Stenothoe estacola
Northeast Pacific native, found in Southern California associated with the sabellariid Phragmatopoma califonrica (Chapman 2007).

Stenothoe gallensis complex
Described from the Indo-Pacific, now widely distributed in the Atlantic, introduced to Hawaii and New Zealand (Bellan-Santini et al. 1993; Carlton and Eldredge 2009; LeCroy 2011). The species-complex contains at least 8 named species, several of which occurin both the Indo-Pacific and Atlantic (Krapp-Schickel 2015)

Stenothoe georgiana
Northwest Atlantic native, Virginia to Tortugas and Brazil (LeCroy 2011).

Stenothoe minuta
Northwest Atlantic native, Cape Cod to Georgia (Bousfield 1973).



Stenothoe valida is a small marine gammaridean amphipod, usually associated with fouling communities, fouling organisms such as sponges and tunicate, corals, algae, or seagrasses (Lewis 1992; Lecroy 2011; Krapp-Schickel and Vader 2015). Sexes are separate, the young are brooded and development is direct (Bousfield 1973). Females in Barbados carried 10-20 eggs. Juveniles actively swam and walked, while adults tended to be more sedentary, staying in cavities and barnacle shells, defending these territories (Lewis 1992).

Stenothoe valida is known from cold-temperate to tropical climates, and polyhaline to euhaline salinities (Lincoln 1979; Hirayama 1988; Cohen et al. 2005). This amphipod tends to be strongly associated with live or dead sessile organisms that provide refuge. In Los Angeles Harbor, it was found among colonies of the hydroid Ectopleura crocea (Barnard 1953), while in Humboldt Bay, it was found around mussels (Mytilus trossulus) and tunicates. Other hosts include the hydrozoan coral Millepora complanata and empty barnacle shells in Barbados; seagrasses and sponges in Florida (LeCroy 2011); and floating seaweeds in the North sea, Germany (Franke and Gutow 2003). Stenothoe valida is common in dock, buoy, and ship fouling (Woods Hole Oceanographic Institution 1952; Carlton 1979).  It is a suspension feeder - animals sit in place, with uropods pressed against a surface and the body pointed upward at a 30-degree angle, with the antennae and gnathopods in motion, and periodically wiped across the mouthparts (Lewis 1992).


Phytoplankton, detritus

Trophic Status:

Suspension Feeder



General HabitatCoarse Woody DebrisNone
General HabitatMarinas & DocksNone
General HabitatCoral reefNone
General HabitatVessel HullNone
General HabitatRockyNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)20Field data, Port Sonoma, CA, San Pablo Bay (Cohen et al. 2005)
Maximum Salinity (‰)40Approximate maximum salinity, Mediterranean Sea
Minimum Length (mm)2.1Females, Males 2.5 mm, Barbados (Lewis 1992)
Maximum Length (mm)6Mediterranean (Krapp-Schickel 2013)
Broad Temperature RangeNoneCold temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

No impacts have been reported for Stenothoe valida throughout its range.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-VI Pt. Conception to Southern Baja California 1951 Def Estab
NEP-V Northern California to Mid Channel Islands 1941 Def Estab
NEP-IV Puget Sound to Northern California 2000 Def Estab
CAR-III None 0 Crypto Estab
NA-ET3 Cape Cod to Cape Hatteras 2013 Crypto Estab
NEA-II None 0 Crypto Estab
MED-III None 1857 Crypto Estab
MED-VII None 0 Crypto Estab
NWP-4b None 0 Crypto Estab
SP-XXI None 1924 Def Estab
CAR-VII Cape Hatteras to Mid-East Florida 0 Crypto Estab
NA-ET2 Bay of Fundy to Cape Cod 2000 Crypto Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Crypto Estab
AUS-X None 1924 Crypto Estab
EA-IV None 1955 Crypto Estab
WA-V None 1955 Crypto Estab
SA-II None 1852 Crypto Estab
CAR-IV None 0 Crypto Estab
NWP-3a None 0 Crypto Estab
NWP-4a None 1991 Crypto Estab
CAR-II None 0 Crypto Estab
MED-II None 1925 Crypto Estab
MED-V None 0 Crypto Estab
M010 Buzzards Bay 2000 Crypto Estab
P050 San Pedro Bay 1951 Def Estab
P130 Humboldt Bay 2000 Def Estab
NEA-V None 0 Crypto Estab
P040 Newport Bay 1951 Def Estab
P060 Santa Monica Bay 2000 Def Estab
P062 _CDA_P062 (Calleguas) 2000 Def Estab
P090 San Francisco Bay 1941 Def Estab
NZ-IV None 0 Crypto Estab
NZ-VI None 0 Crypto Estab
AUS-XI None 0 Crypto Estab
EA-V None 0 Crypto Estab
CIO-II None 0 Crypto Estab
EA-III None 0 Crypto Estab
N170 Massachusetts Bay 2000 Crypto Estab
P093 _CDA_P093 (San Pablo Bay) 1941 Def Estab
SP-IX None 0 Crypto Estab
N100 Casco Bay 2013 Crypto Estab
N120 Wells Bay 0 Crypto Estab
N130 Great Bay 2013 Crypto Estab
P080 Monterey Bay 2011 Def Estab
P023 _CDA_P023 (San Louis Rey-Escondido) 2011 Def Estab
P030 Mission Bay 2011 Def Estab
WA-IV None 0 Crypto Estab
WA-I None 1953 Crypto Estab
NA-ET4 Bermuda 0 Crypto Estab
AUS-VIII None 1977 Crypto Estab
SP-I None 0 Crypto Estab
MED-VI None 0 Crypto Estab
CIO-V None 1978 Crypto Estab
SEP-C None 2015 Def Estab
NEA-IV None 0 Crypto Estab
CIO-III None 0 Crypto Estab
NWP-3b None 0 Crypto Estab
SP-XVI None 0 Crypto Estab
AUS-IV None 0 Crypto Estab
NEA-III None 0 Crypto Estab
MED-IV None 2015 Crypto Unk
P062 _CDA_P062 (Calleguas) 2015 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
767384 Ruiz et al., 2015 2012 2012-08-15 Tomales- Call Box 401, Bodega Bay, California, USA Def 38.1793 -122.9104
767450 Ruiz et al., 2015 2013 2013-07-29 Mission Bay Yacht Club, Mission Bay, CA, California, USA Def 32.7778 -117.2485
767469 Ruiz et al., 2015 2013 2013-08-04 Bahia Resort Marina, Mission Bay, CA, California, USA Def 32.7731 -117.2478
767596 Ruiz et al., 2015 2013 2013-09-05 Launch Ramp, Morro Bay, CA, California, USA Def 35.3577 -120.8508
767660 Ruiz et al., 2015 2013 2013-07-16 Naval Base Point Loma, San Diego Bay, CA, California, USA Def 32.6886 -117.2343
767699 Ruiz et al., 2015 2013 2013-07-25 Navy Ammo Dock, Pier Bravo, San Diego Bay, CA, California, USA Def 32.6939 -117.2276
767739 Ruiz et al., 2015 2013 2013-07-18 NAB Fiddlers Cove, San Diego Bay, CA, California, USA Def 32.6524 -117.1486
768028 Ruiz et al., 2015 2012 2012-08-27 Port of San Francisco Pier 31, San Francisco Bay, CA, California, USA Def 37.8078 -122.4060
768160 Ruiz et al., 2015 2012 2012-09-05 Port of Oakland, San Francisco Bay, CA, California, USA Def 37.7987 -122.3228


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