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:

In California, amphipods of the genus Leucothoe are often found inside both native and introduced (eg. Ciona spp., Styela plicata) tunicates (Cohen and Carlton 1995; Don Cadien in SCAMIT 2011). Leucothoe nagatai was described by Ishimaru (1985) from Japan. It can be found on the east and west coasts of Japan and on Ulleungdo Island, off the east coast of Korea (Ishimaru 1985; Kim and Kim 1991). It is introduced throughout California, but its date of introduction is uncertain, since it is easily confused with the cryptogenic (i.e. origin unknown) species L. alata and L. spinicarpa. Cohen and Carlton (1995) referred to Leucothoe alata Barnard 1959, described from Newport Bay, CA as a likely introduction with tunicates. It has been reported from Japan, but identifications there are uncertain and further information is needed to determine its true native range. Since tunicates from the Northwest Pacific are widely introduced, Leucothoe spp. may be more widespread than published records indicate.

North American Invasion History:

Invasion History on the West Coast:

The date of Leucothoe nagatai's introduction is uncertain, since it is easily confused with the cryptogenic species L. alata and L. spinicarpa. The earliest record of Leucothoe spp, as far as we are aware, is a collection of L. spinicarpa collected in 1949 off Santa Catalina Island, California (USNM 127572, U.S. National Museum of Natural History 2015). Leucothoe alata was described from Newport Bay, from specimens collected in 1951 (Barnard and Reish 1959). Leucothoe spp. were collected in San Francisco Bay in 1977 and 1993 (Cohen and Carlton 1995), but the amphipods were not identified to species, so their invasion status is uncertain. The first confirmed collection of Leucothoe nagatai on the West Coast was in 1979, in Los Angeles Harbor (Don Cadien, in SCAMIT 2011). In 2011, it was collected by Don Cadien in Newport Bay and by Ron Velarde in San Diego Bay (Don Cadien, in SCAMIT 2011), and in California Fish and Wildlife surveys in Santa Barbara Harbor, Port Hueneme, Avalon Harbor on Santa Catalina Island, Dana Point Harbor, Oceanside Harbor, Mission Bay, and San Diego Bay (California Department of Fish and Wildlife 2014). In California, L. nagatai has been reported from introduced Ciona spp. and Styela plicata, native/introduced Chalinula sp. (sponge), and native Aplidium californicum and Ascidia ceratodes.


Generic traits of species in the genus Leucothoe include a compact body; short antennae with peduncles much larger than the flagella; Antenna 1 being much more robust than Antenna 2; and a greatly enlarged Gnathopod 2 in both sexes (Bousfield 1973; Chapman 2007; White 2011). The rostrum of Leucothoe nagatai is poorly developed, the lateral lobe of the head is broadly rounded, and the eye is oval and medium-sized. Coxa 1 is small and has a rounded anterior corner. Coxae 2-4 are large, ovoid, and wider than tall, while Coxae 5-6 are small and bilobed, and Coxa 7 is smaller and circular. The basal segment of the flagellum of Antenna 1 is much shorter than segment 2, while in L. alata, the basal segment is much longer than segment 2. Antenna 2, though thinner than Antenna 1, is equal or greater in length.

Gnathopod 1 of L. nagatai is shorter and less robust than Gnathopod 2, with the propodus (segment 6) not inflated, and a short dactyl, resembling a small claw, about 10% of the propodus length. Segment 5 of Gnathopod 2 is extended distally to form a curved blade. The propodus (segment 6) is greatly inflated in males, with a palm having 4 large tubercles. The dactyl (segment 7) is large, but does not exceed the length of the palm. In females, the propodus is less inflated and bears setae on the distal end. The 3 pairs of uropods are biramous, decreasing in length from Uropod 1 to Uropod 3. The telson is shield shaped, with a width 1.8 X length. Male specimens were 8-11 mm and females were 7-10 mm. Description based on: Ishimaru 1985, Kim and Kim 1991, Don Cadien, in SCAMIT 2011, and White 2011.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Gammaridea
Family:   Leucothoidae
Genus:   Leucothoe
Species:   nagatai


Potentially Misidentified Species

Leucothoe alata
Described as  L. alata from Newport Bay, California (Barnard 1959). Reports of this amphipod from Japan may be due to confusion with L. nagatai (Ishimaru 1985). The range of this species is poorly known and it could be native to Calfornia waters. Don Cadien (in SCAMIT 2011) noted that he could distinguish the L. alata and L. nagatai by coloration, but did not give details.

Leucothoe Mission Bay
Unidentified species found in Mission Bay, California (Don Cadien, in SCAMIT 2011)

Leucothoe sp San Diego 1
Unidentified species found in San Diego Bay. Gnathopod 1 dactyl long (Don Cadien, in SCAMIT 2011)

Leucothoe spinicarpa complex
Cryptogenic, commensal with tunicates, described from Norway (Chapman 2007), and reported worldwide, including Antarctica. Many amphipods initially identified as L. spinicarpa are separate species (White 2011). The identity of Northeast Pacific specimens is uncertain.

Leucothoides pacifica
Found in sponges and tunicates. Possibly a super-male, non-feeding morph of L. alata (Chapman 2007).



Leucothoe nagatai is probably a sequential hermaphrodite, being female first and then male (Chapman 2007). The young are brooded and development is direct (Bousfield 1973). Leucothoe sp. often inhabit tunicates in male/female pairs, and drive out or kill intruding individuals (Thiel 1999; Don Cadien in SCAMIT 2011). Juvenile Leucothoe may colonize zooids of colonial tunicates, but move to solitary ascidians as they mature (Thiel 1999).

Leucothoe nagatai is known from temperate climates, and its tunicate and sponge hosts are limited to polyhaline-euhaline waters. In California, L. nagatai has been found inside both native and introduced species. Its hosts include the nonindigenous tunicates Ciona spp., Styela plicata, and the native Aplidium californicum, Ascidia ceratodes, and sponges of the genus Chalinula sp., which include native, introduced, and cryptogenic species (Cohen and Carlton 1995; Don Cadien in SCAMIT 2011). This amphipod feeds by filtering the host's respiratory current, and does not consume sponge or tunicate tissues (Don Cadien in SCAMIT 2011). It could be classified as either a commensal or parasite, since it could deprive the host of some food.


Phytoplankton (filterd by sponges and tunicates)

Trophic Status:




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

Tolerances and Life History Parameters

Minimum Length (mm)7Ishimaru 1985; Kim and Kim 1991; White 2011
Maximum Length (mm)10Ishimaru 1985; Kim and Kim 1991; White 2011
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

There are no reported impacts of Leucothoe nagatai.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
P040 Newport Bay 1979 Def Estab
P020 San Diego Bay 2011 Def Estab
NEP-VI Pt. Conception to Southern Baja California 1979 Def Estab
NWP-3b None 0 Native Estab
NWP-4a None 0 Native Estab
P050 San Pedro Bay 0 Def Estab
NWP-4b None 0 Native Estab
P065 _CDA_P065 (Santa Barbara Channel) 2011 Def Estab
P062 _CDA_P062 (Calleguas) 0 Def Estab
P060 Santa Monica Bay 2011 Def Estab
P027 _CDA_P027 (Aliso-San Onofre) 2011 Def Estab
P058 _CDA_P058 (San Pedro Channel Islands) 0 Def Unk
P023 _CDA_P023 (San Louis Rey-Escondido) 2011 Def Estab
P030 Mission Bay 2011 Def Estab
NEP-V Northern California to Mid Channel Islands 1993 Def Estab
P090 San Francisco Bay 2015 Def Estab
NZ-IV None 2015 Def Estab
NZ-IV None 2015 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Barnard, J. Laurens; Reish, Donald J. (1959) Ecology of Amphipoda and Polychaeta of Newport Bay, California, Allen Hancock Foundation Occasional Publications 21: 1-106

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

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, 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>

Ishimaru, Shin-Ichi (1985) A new species of the genus Leucothoe (Amphipoda, Gammaridea, Leucothoidae) from Japan, Proceedings of the Japanese Society of Systematic Zoology 30: 46-52

Kim, Won; Kim, Chae Bae (1991) The marine amphipod crustaceans of Ulreung Island, Korea. Part III, Korean Journal of Zoology Molluscan Research 34: 323-337

Southern California Association of Marine Invertebrate Taxonomists (SCAMIT) (2011) 8 December 2011, Leucothoidae NHMLAC, SCAMIT Newsletter 30(3-4): 5-7

Thiel, M. (1999) Host and population demographics of the ascidian-dwelling amphipod Leucothoe spinicarpa: indication for extended parental care and advanced social behavior, Journal of Natural History 33: 193-206

Thomas, James Darwin; Cadien, Donald B.; White, Kristine N. (2022) Bi-hemispheric distribution and ecology of the commensal amphipod Leucothoe nagatai Ishimaru, 1985 (Crustacea: Leucothoidae), Pacific Science 75(3): 309-321

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.

White, Kristine N. (2011) A taxonomic review of the Leucothoidae (Crustacea: Amphipoda), Zootaxa 3078: 1-113