Invasion History

First Non-native North American Tidal Record: 1995
First Non-native West Coast Tidal Record: 1995
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Crangonyx floridanus was described from the Florida peninsula and is known from scattered locations in South Carolina, the Florida Panhandle, and Louisiana (Bousfield 1958; Holsinger 1972; U.S. National Museum of Natural History 2015). This species probably has a broader native distribution in the Southeastern US. In 1995, Crangonyx sp. were collected in the Sacramento-San Joaquin Delta, California. Specimens collected in 1998-1999 were identified as C. floridanus. This amphipod is now widespread in the Delta, and has had scattered reports in the interior of California (Graening et al. 2012). In 1989, C. floridanus was first collected in Japan, and soon had colonized many inland rivers and lakes in central Honshu (Morino et al. 2004; Tojo et al. 2010).

North American Invasion History:

Invasion History on the West Coast:

Crangonyx sp. were collected in surveys in freshwater wetlands of the Sacramento-San Joaquin Delta in routine surveys in 1995. In a 1998-1999 study of invertebrates associated with aquatic plants, C. floridanus was identified, mostly at sites in the western end of the Delta (Toft et al. 2002; Toft et al. 2003). Later collections were made further upriver, at Lindseys Slough and Clifton Court Forebay, but also at sites close to the central San Francisco Bay and San Pablo Bay (Simas Creek and Wildcat Creek, Richmond; Graening et al. 2012). Two of the reported sites, the Tuolumne River in Stanislaus County and Hangtown Creek in Eldorado County are in the Central Valley and Sierra foothills, respectively (Graening et al. 2012).

Invasion History Elsewhere in the World:

Crangonyx floridanus was first noticed in Japan in a pond in Chiba prefecture in 1989 and sent to American researchers for identification. After it was recognized as the North American C. floridanus, it was found to be widespread in central Honshu, including the vicinity of Tokyo and tributaries of Tokyo and Sagami Bays (Morino et al. 2004). In 2005, it was discovered in the Chikuma River, Nagano Prefecture, which flows into the Sea of Japan (Tojo et al. 2010). Transport with aquatic plants or stocked fishes are likely vectors (Morino et al. 2004). n 2020, this amphipod was collected in a pond and several rivers in Ireland (Baars et al. 2021). eDNA markers have been developed for detection of this species and C. pseudogracilis in Europe  (Bommerlund et al. 2023).


The body of Crangonyx floridanus is moderately compressed and smooth, lacking spines on the urosome segments. Coxal plates 1-4 are deep and lined with short setae, with Coxa 4 being larger, having a convex posterior edge and a mucron (small spine) on the ventro-posterior corner. The head is small, with a rounded anterior lobe, and lacking a ventral antennal sinus. The eyes are medium-sized and oval. Antenna 1 is 2X longer than Antenna 2, and bears a 2-segment accessory flagellum, characteristic of the Crangonyctidae.

Gnathopod 1 is smaller than gnathopod 2; both are subchelate, with the dactyl (segment 7) folding against the propodus (segment 6). Both gnathopods are larger and more robust in males than females. In females, the propodus and carpus (segment 5) are roughly equal, but in males, the propodus of both gnathopods is more than 2X as long as the carpus. The palms of both gnathopods are lined with many spines, larger in the male than in the female. Pereiopod 6 is the longest. The posterior ventral corners of the abdominal plates (pleons) end in small teeth. Uropods 1 and 2 are biramous, with the rami roughly equal, while Uropod 3 has the inner ramus reduced to a scale-like structure. In males, the outer ramus of Uropod 2 is lined with large, comb-like spines. Females reach a maximum size of 10 mm; males 8 mm. Description based on: Bousfield 1963, Holsinger 1972, Bousfield 1973, Morino et al. 2004, and Chapman 2007.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Gammaridea
Family:   Crangonyctidae
Genus:   Crangonyx
Species:   floridanus


Potentially Misidentified Species

Crangonyx pseudogracilis
Crangonyx pseudogracilis is native to the Atlantic Coast from the Saint Lawrence River to the Delaware and Hudson Rivers, and to the Great Lakes Basin (Holsinger 1972; Bousfield 1973). It has been introduced to the Columbia River and estuary (Sytsma et al. 2004), and to upland creeks in the drainage of Morro Bay, California (Bottoroff et al. 2003, cited by Graening et al. 2012).

Crangonyx richmondensis
Crangonyx richmondensis is presumed native to three broad areas in North America, northern California to Alaska, the Great Lakes and eastern Canada, and the Atlantic Coastal Plain, from Maine to Florida (Holisinger 1972; Bousfield 1973; Graening et al. 2012).



Crangonyx floridanus is a free-living, freshwater amphipod. Sexes are separate, the young are brooded, and development is direct (Bousfield 1973). In populations introduced to the Chikuma River, Japan, brooding females were seen year-round, even at winter water temperatures of 0-5C. Females began to bear eggs at ~4.5 mm length, and the numbers of eggs increased with body size, with up to 83 eggs for a female of ~7 mm length. The mean egg number per female was 35.5. Egg development time decreased with increasing temperature, for 25 days at 4C to 8-9 days at 25C. Females bear multiple broods, with new eggs deposited in the brood pouch before the young are released (Tojo et al. 2010).

Crangonyx floridanus is known from warm-temperate habitats, including its native region, the Gulf Coast interior (Florida-Louisiana), and introduced ranges in the Sacramento-San Joaquin Delta (Toft et al. 2002; Graening et al. 2012), and southern Japan (Morino et al. 2004). In Japan, it survives temperatures from 2C to 27C (Tojo et al. 2010). It was initially found in cypress swamps, ponds, and cave pools (Bousfield 1963). In the Delta, it occurred among the roots of floating Water Hyacinth (Eichornia crassipes), in preference to native Pennywort (Hydrocotyle umbellata). In Japan, C. floridanus inhabits a wide range of freshwater habitats, including lakes and rivers (Morino et al. 2004; Tojo et al. 2010). Its salinity tolerance is unknown, but the wide range of locations in the Delta suggests that it can probably survive salinities at least through the oligohaline range (0-5 PSU) (Toft et al. 2002; Graening et al. 2012).

Crangonyx floridanus is probably omnivorous, like many free-living gammarids, feeding on algae, detritus, and occasionally on invertebrates and carrion (Barnes 1983). Tojo et al. (2010) maintained this amphipod in culture on Phragmites detritus. The chief predators are fishes. In the Sacramento-San Joaquin Delta, this amphipod was eaten by non-native fishes: Bluegill (Lepomis macrochirus); Largemouth Bass (Micropterus salmoides); and Striped Bass (Morone saxatilis).


Aquatic plants, detritus. algae, invertebrates

Trophic Status:




General HabitatNontidal FreshwaterNone
General HabitatFresh (nontidal) MarshNone
General HabitatGrass BedNone
General HabitatTidal Fresh MarshNone
General HabitatUnstructured BottomNone
General HabitatSwampNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Life History

Tolerances and Life History Parameters

Minimum Temperature (ºC)2Field, Chikuma River, Japan (Tojo et al. 2010)
Maximum Temperature (ºC)27Field, Chikuma River, Japan (Tojo et al. 2010)
Minimum Salinity (‰)0Crangonyx floridanus is a freshwater amphipod.
Minimum Length (mm)3Males mature at 3 mm,females at 5 (Holsinger 1972).
Maximum Length (mm)10Females reach 10 mm, males 8 mm (Holsinger 1972).
Broad Temperature RangeNoneWarm temperate-Subtropical
Broad Salinity RangeNoneNontidal Limnetic-Tidal Limnetic

General Impacts

Crangonyx floridanus is locally common in freshwater portions of the Sacramento-San Joaquin Delta, and is a frequent food item for fishes (Toft et al. 2002). However, impacts on fish populations have not been reported.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
P090 San Francisco Bay 1995 Def Estab
G170 West Mississippi Sound 0 Native Estab
S100 St. Helena Sound 1983 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Baars, Jan-Robert ; Minchin, Dan; Feeley, Hugh B.; Brekkhus, Sondre; Mauvisseau, Quentin (2021) The first record of the invasive alien freshwater amphipod Crangonyx floridanus (Bousfield, 1963) (Crustacea: Amphipoda) in two Irish river systems, BioInvasions Records 10: In press

Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Bommerlund, Julie; Baars, Jan-Robert; Schrøder-Nielsen, Audun; Brys. Rein; Mauvisseau, Christophe; Hugo J.; de Boer, Christophe; Mauvisseau, Quentin (2023) eDNA-based detection as an early warning tool for detecting established and emerging invasive amphipods, BioInvasions Records 12: Published online

Bousfield, E. L. (1963) New fresh-water amphipod crustaceans from Florida, National Museum of Canada, Natural History Papers 18(3): 1-9

Bousfield, E.L. (1958) Freshwater amphipod crustaceans of glaciated North Amerca., Canadian Field-Naturalist 72(2): 55-113

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

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

Graening, G. O.; Rogers, D. Christopher; Holsinger, John R.; Barr, Cheryl; Bottorff, Richard (2012) Checklist of inland aquatic Amphipoda (Crustacea: Malacostraca) of California, Zootaxa 3544: 1-27

Holsinger, J. R. (1972) <missing title>, US Environmental Protection Agency, Washington DC. Pp. 1-89

Morandini; Andre’ C.; Stampar, Sergio N.; . Maronna, Maximiliano M,; da Silveira, Fabio l. (2017) All non-indigenous species were introduced recently? The case study of Cassiopea (Cnidaria: Scyphozoa) in Brazilian waters, Journal of the Marine Biological Association of the United Kingdom 97(2): 321-328

Morino, Hiroshi; Kusan, Harumi; Holsinger, John R. (2004) Description and distribution of Crangonyx floridanus (Crustacea: Amphipoda: Crangonyctidae) in Japan, an introduced freshwater amphipod from North America, Contributions of the Biological Laboratory of Kyoto University 29: 371-381

Sytsma, Mark D.; Cordell, Jeffrey R.; Chapman, John W.; Draheim, Robyn, C. (2004) <missing title>, Center for Lakes and Reservoirs, Portland State University, Portland OR. Pp. <missing location>

Toft, Jason D.; Cordell, Jeffrey R.; Fields, Wayne C. (2002) New records of crustaceans (Amphipoda, Isopoda) in the Sacramento/San Joaquin Delta, California, and application of criteria for introduced species, Journal of Crustacean Biology 22(1): 190-200

Toft, Jason D.; Simenstad, Charles A.; Cordell, Jeffrey R.; Grimaldo, Lenny F. (2003) The effects of introduced water hyacinth on habitat structure, invertebrate assemblages, and fish diets., Estuaries 26(3): 746-758

Tojo, Koji; Tanaka, Yoshiki; Kuranishi, Ryoichi B.; Kanada, Shoji (2010) Reproductive biology and adaptability of the invasive alien freshwater amphipod Crangonyx floridanus (Crustacea: Amphipoda, Crangonyctidae), Zoological Science 27(6): 522-527

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database. <missing description>