Invasion History

First Non-native North American Tidal Record: 1946
First Non-native West Coast Tidal Record: 1946
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Monocorophium uenoi was described from the Sea of Japan and is also known from locations on Japan's Pacific coast and the Seto Inland Sea (Nagata 1960; Hirayama 1965; Aikins and Kikuchi 2002). It also occurs on the coast of China, along the East China Sea, and Hong Kong (Huang 2001; Hirayama 1986). Monocorophium uenoi has been introduced to the Northeast Pacific from Humboldt Bay, California to Bahia San Quintin, Mexico (Barnard and Reish 1959; Carlton 1979; Bousfield and Hoover 1997; Boyd et al. 2002; Chapman 2007). This species is also reported from Chile (Gonzalez 1991), and was recently found associated with oysters in the Netherlands (Faasse 2014). Likely vectors for its spread include ballast water, hull fouling, and exports of Pacific oysters (Crassostrea gigas) from Japan (Barnard and Reish 1959; Carlton 1979; Faasse 2014).

North American Invasion History:

Invasion History on the West Coast:

The earliest reported collection of Monocorophium uenoi is from Newport Bay, California (CA) in 1946 (USNM specimen, cited by Carlton 1979). The distribution of this amphipod along the West coast is spotty, and mostly occurs where oysters have been planted in the past (Newport Bay) or are actively cultured. It was collected in 1950 in Morro Bay, CA (Barnard 1952, cited by Carlton 1979), but was not found in a 2005 survey (Needles and Wendt 2013). This species was reported from Monterey Harbor, CA (Barnard 1966, cited by Carlton 1979); Elkhorn Slough, CA in 1977 (Carlton 1979; Wasson et al. 2001); Bolinas Lagoon, CA (Page and Stenzel 1975, cited by Carlton 1979); Tomales Bay, CA in 1964 (Johnson and Juskevice 1965, cited by Carlton 1979); Bodega Harbor, CA (Standing 1975, cited by Carlton 1979); and Humboldt Bay, CA in 2000 (Boyd et al. 2002). In San Francisco Bay, M. uenoi was collected in 1976 (CAS-IZ 123419.00, California Academy of Sciences 2015), from South San Francisco Bay, but was not reported in subsequent large invasion inventories (e.g. Carlton 1979; Cohen and Carlton 1995). It was found at Coast Guard Island in the central Bay in 2004 (Cohen et al. 2005) and San Pablo Bay in 2011 (Foss 2011). Graening et al. (2012) list records from the Sacramento River, as well. While most records are from bays with oyster culture, occurrences from Goleta, Gaviota, and Point Conception are from kelp beds on the open coast (Barnard 1961, cited by Carlton 1979), perhaps due to ship or boat fouling, ballast water (Carlton 1979) or natural dispersal.

Invasion History Elsewhere in the World:

Monocorophium uenoi was reported from several locations on the coast of central Chile by Gonzales (1991), but does not give information on specific dates, habitats, or possible vectors. However, this region is an area of intense aquaculture (Castilla et al. 2005). In 2012, M. uenoi was found closely associated with Pacific Oysters in Yeserke, the Netherlands, but was not found in other nearby locations (Faasse 2014).


Monocorophium uenoi has a slender, depressed body with small, separated coxal plates, a fused urosome segment, and a distinct dorso-lateral notch. In males, the rostrum is long, ending about equally or just beyond the optical lobes, and Antenna 2 is longer and heavier than Antenna 1. In females, the rostrum is short, not exceeding the anterior lobes, and Antenna 2 is only slightly longer, but more robust than Antenna 1. In males, segment 1 of the peduncle of Antenna 1 is bluntly serrate and has 3 ventral spines. In the female, segment 1 has 3 stout spines, and segments 1-3 have many more setae than in the male. In males, segment 4 is somewhat inflated and has a very large distal tooth on the posterior side and 1-2 smaller teeth. Segment 5 (male) also has a distal process, but it is triangular and blunt. In females, segment 4 has 3 pairs of strong spines on the posterior surface and segment 5 has a stout median spine.

The gnathopods are not especially large or conspicuous in this genus. Segment 5 of Gnathopod 1 is slightly longer than segment 6, and the dactyl (segment 7) is twice as long as the palm of segment 6. On Gnathopod 2, segment 2 is longer than segment 5 and the dactyl bears 3 prominent, unequal teeth. Pereiopods 3 and 4 are very short, with a very broad segment 5, which partially covers segment 6. As noted above, the urosome segments are fused, but with a prominent lateral notch. Uropod 1 has short, unequal rami, each with 3-4 outer marginal spines. Uropod 2 is short, with the rami unequal, and the inner ramus often bare. Uropod 3 is uniramous, with the ramus longer than the peduncle. Adults are 2-5 mm long (Hirayama 1986; Chapman 2007). Centers of the pleonites and the segments of Antenna 2 are dark brown, mottled with white. There is a patch of pigment between the eyes, but it does not extend to the back of the head. The borders of the pleonites and most of the appendages are white (as shown in Faasse 2014). The description is based on: Crawford 1937, Hirayama 1986, Bousfield and Hoover 1997, Chapman 2007, and Faasse 2014.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Gammaridea
Family:   Corophiidae
Genus:   Monocorophium
Species:   uenoi


Corophium uenoi (Stephensen, 1932)
Monocorophium uenoi (Bousfield and Hoover, 1997)

Potentially Misidentified Species

Crassicorophium bonellii
A species of uncertain taxonomic status, not reported from the Northeast Pacific, possibly a parthenogenetic form of M. acherusicum or M. insidiosum, reported from high latitudes of the Northern and Southern Hemispheres, including the Northwest Pacific (Bousfield and Hoover 1997, Chapman 2007).

Monocorophium acherusicum
Native to the North Atlantic, introduced to Pacific (Bousfield and Hoover 1997; Chapman 2007).

Monocorophium californiensis
A species of uncertain taxonomic status, not reported from northeast Pacific, possibly a parthenogenetic form of M. acherusicum or M. insidiosum, reported from high latitudes of the Northern and Southern Hemispheres, inlduding the northWest Pacific (Bousfield and Hoover 1997, Chapman 2007).

Monocorophium carlottensis
Northeast Pacific native, Puget Sound to Prince William Sound (Bousfield and Hoover 1997; Chapman 2007)

Monocorophium insidiosum
Native to the North Atlantic, introduced to the Pacific (Bousfield and Hoover 1997; Chapman 2007).

Monocorophium oaklandense
Possibly an intersex form of M. insidiosum (Chapman 2007)



Monocorophium uenoi is a gammarid amhipod which inhabits soft and hard substrates, as epifauna and infauna (Hirayama 1986; Larson et al. 2009; Faasse 2014). Gammarid amphipods have separate sexes, brooded embryos, and direct development (Bousfield 1973).

In its native range, M. uenoi tolerates a wide range of temperatures, including temperatures as high as 30 C (Hirayama 1986; Aikins and Kikuchi 2002). The extent of its salinity tolerance is not clear, but it has been collected from a range of locations. For instance, it was collected in parts of Humboldt Bay receiving freshwater drainage (Boyd et al. 2002), and in San Pablo Bay and the lower Sacramento River (Graening et al. 2012), as well as 'open sea' locations off southern California (Barnard 1969b). Habitats include intertidal muddy sandflats, oyster beds, mussel beds, seaweeds (Hirayama 1986; Larson 2009, Faasse 2014), and kelp holdfasts on the open coast (Barnard 1969b). Corophiid amphipods secrete threads of 'amphipod silk', to which the detritus is attached, to form its tubes. When the amphipods are abundant, the tubes form a mass in which the openings point outward or upward (Barnard et al. 1988). The tubes can be formed on the sediment surface, or attached to fouling on vertical surfaces such as rocks or pilings, or other fouling organisms (Barnard 1958).

Like other corophiid amphipods, M. uenoi is probably capable of feeding on phytoplankton, detritus and benthic microalgae on the sediment surface, and grazing on filamentous epiphytic algae growing on seaweeds and seagrasses (Bousfield 1973). In the Gamo Lagoon, Japan, M. uenoi fed on diatoms growing on the surface of the red alga Gracilaria vermiculophylla (Aikins and Kikuchi 2002). Fishes and shrimps are likely predators.


Detrtius; Benthic Diatoms

Trophic Status:

Suspension Feeder



General HabitatGrass BedNone
General HabitatCoarse Woody DebrisNone
General HabitatUnstructured BottomNone
General HabitatOyster ReefNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Salinity RangeMesohaline5-18 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Temperature (ºC)30Field, Gamo Lagoon, Japan (Aikins and Kikuchi 2002)
Maximum Length (mm)4.6Adult female (Hirayama 1986)
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

No impacts have been reported for Monocorophium uenoi in its introduced habitats.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-VI Pt. Conception to Southern Baja California 1946 Def Estab
NWP-4a None 0 Native Estab
NWP-3a None 0 Native Estab
NWP-2 None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 1950 Def Estab
NEP-IV Puget Sound to Northern California 2000 Def Estab
P040 Newport Bay 1946 Def Estab
P065 _CDA_P065 (Santa Barbara Channel) 1961 Def Estab
P070 Morro Bay 1950 Def Unk
P080 Monterey Bay 1966 Def Estab
P090 San Francisco Bay 1976 Def Estab
P095 _CDA_P095 (Tomales-Drakes Bay) 1975 Def Estab
P110 Tomales Bay 1965 Def Estab
P112 _CDA_P112 (Bodega Bay) 1975 Def Estab
P130 Humboldt Bay 2000 Def Estab
SEP-B None 1991 Def Estab
P093 _CDA_P093 (San Pablo Bay) 2003 Def Estab
NWP-4b None 0 Native Estab
NEA-II None 2013 Def Estab
NWP-3b None 0 Native Estab
NEA-V None 2007 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
767318 Ruiz et al., 2015 2012 2012-08-13 Coast Guard, Bodega Bay, California, USA Def 38.3126 -123.0512
767327 Ruiz et al., 2015 2012 2012-08-14 Spud Point South, Bodega Bay, California, USA Def 38.3281 -123.0574
767342 Ruiz et al., 2015 2012 2012-08-21 Lucas/Tides, Bodega Bay, California, USA Def 38.3284 -123.0445
767383 Ruiz et al., 2015 2012 2012-08-15 Tomales- Call Box 401, Bodega Bay, California, USA Def 38.1793 -122.9104
767973 Ruiz et al., 2015 2012 2012-08-24 Richmond Marina Bay Yacht Harbor, San Francisco Bay, CA, California, USA Def 37.9134 -122.3523
767995 Ruiz et al., 2015 2012 2012-08-23 Sausalito Marine Harbor, San Francisco Bay, CA, California, USA Def 37.8609 -122.4853
768014 Ruiz et al., 2015 2012 2012-08-28 San Francisco Marina, San Francisco Bay, CA, California, USA Def 37.8071 -122.4341
768027 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
768096 Ruiz et al., 2015 2012 2012-08-29 Coyote Point Marina, San Francisco Bay, CA, California, USA Def 37.5877 -122.3174
768118 Ruiz et al., 2015 2012 2012-09-04 Redwood City Marina, San Francisco Bay, CA, California, USA Def 37.5023 -122.2130
768143 Ruiz et al., 2015 2012 2012-09-06 Loch Lomond Marina, San Francisco Bay, CA, California, USA Def 37.9736 -122.4802
768159 Ruiz et al., 2015 2012 2012-09-05 Port of Oakland, San Francisco Bay, CA, California, USA Def 37.7987 -122.3228
768184 Ruiz et al., 2015 2012 2012-09-07 Jack London Square Marina, San Francisco Bay, CA, California, USA Def 37.7940 -122.2787
768206 Ruiz et al., 2015 2012 2012-08-31 Glen Cove Marina, San Francisco Bay, CA, California, USA Def 38.0663 -122.2130
768219 Ruiz et al., 2015 2012 2012-09-13 San Leandro Marina, San Francisco Bay, CA, California, USA Def 37.6962 -122.1919
768324 Ruiz et al., 2015 2013 2013-08-23 Loch Lomond Marina, San Francisco Bay, CA, California, USA Def 37.9723 -122.4829


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