Invasion History

First Non-native North American Tidal Record: 1988
First Non-native West Coast Tidal Record: 1988
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Caprella drepanochir is native to the Northern Pacific, ranging from China, Japan and Russia to the subarctic seas off Alaska, including Prince William Sound (Mayer 1903; Laubitz 1970; Chapman, in Ruiz et al. 2000). It appears to be a recent introduction to bays on the West Coast of the US, from Willapa Bay, Washington to San Francisco Bay, California (Ferraro and Cole 2007; Watling and Carlton, in Carlton 2007; Carr et al. 2011).

North American Invasion History:

Invasion History on the West Coast:

Caprella drepanochir is native to Alaskan waters, but appears to be a recent introduction to bays on the continental US West Coast. One guidebook for the Pacific Northwest considers it 'unlikely to be found in our region' (Kozloff 1996). However, it was discovered in Coos Bay, Oregon in 1988, and is abundant there (Carlton 1989; Watling and Carlton, in Carlton et al. 2007; Maciejeski 2008). This caprellid has also been reported from Willapa Bay, Washington (in 1996, Ferraro and Cole 2007), Humboldt Bay, California (James T. Carlton, 2006, personal communication; Wilson 2011) and San Francisco Bay, California (in 2006, Christopher Brown, personal communication, Carr et al. 2011). In all of these bays, it is now an abundant part of the fouling community, occurring on manmade structures (Carlton 1989; Maciejeski 2008; Wilson 2011), mudflat habitats (Ferraro and Cole 2007) and eelgrass (Zostera marina) beds (Carr et al. 2011).  Given the scarcity of intermediate records along the coast, ballast water or fouling transport from the Northern Pacific appears to be the most probable route of introduction (Watling and Carlton, in Carlton 2007). However, all of these occurrences also occur near sites of present or historical rearing of Pacific Oysters (Crassostrea gigas from Japan), so this vector is also possible. One record, from a buoy in Prince Rupert Harbor, British Columbia (Lu et al. 2007), could represent either a natural range extension or anthropogenic transport, either from Alaska or Japan.


Caprellid amphipods have a greatly modified body form, when compared to more familiar gammarid amphipods. The body is elongated (giving rise to the name 'skeleton shrimp'), though the abdomen is compressed. The head is partly fused with the first thoracic segment (called Pereonite 1 in amphipods). The head bears a pair of long antennae 1, somewhat shorter antennae. The 1st antennae (A1) have a 3-segmented peduncle, tipped by a flagellum with multiple segments. The 2nd antennae (A2) may be fringed with long setae, and have 3-4 segments in the peduncle, and a shorter flagellum, usually of 2 segments. A mandibular palp of several segments is present in some genera, arising between the antennae, but this is absent in Caprella. There is a small pair of gnathopods (Gnathopod 1), with small grasping claws with a movable finger, on Pereonite 1. Pereonite 2 bears a much larger pair of gnathopods (Gnathopod 2), which may have conspicuous spines or setae. Pereonites 3 and 4 usually have round or club-shaped gills, while in most species, including Caprella, pereopods are absent. Pereopods 5, 6, and 7 are roughly equal and hook-like, for climbing and attachment, with 6 segments. Females develop oostegites, plates which form a brood pouch. Males are usually larger than females of the same species. Females and immature males can be hard to identify to species level. (Description from: Barnes 1983; Watling and Carlton, in Carlton 2007).

Caprella drepanochir is 9-13 mm long. Except for blunt knobs on anteriorateral regions of pereonites 2, 3, and 4, the body is smooth, though covered with fine sensory hairs. The head does not have an anteriorly directed spine. The antenna 1 flagellum is longer than peduncle segment 3. Antenna 2 is longer than the peduncle of A1 and the flagellum of A1 bears short setae. Gnathopods 1 have a serrated grasping margin. Gnathopods 2 have a very large propodus and dactylus. On the distal edge of the palm of the propodus is a sharp poison tooth, and blunt triangular projection, (creating a narrow notch). The dactylus (finger) is thick, and slightly curved. The gills are circular in males, and broadly rounded in females. Pereopods 5-7 increase in length, posteriorly. The female differs from the male in a number of characteristics, including: having a short pereonite 1 and gnathopod 2; the palm of the propodus has a proximal grasping spine, an accessory spine, and a distal minute poison spine; and the pereiopods are more slender (Description from: Watling and Carlton, in Carlton 2007; Ashton 2012a).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Caprellidea
Infraorder:   Caprellida
Superfamily:   Caprelloidea
Family:   Caprellidae
Genus:   Caprella
Species:   drepanochir


Potentially Misidentified Species



Life History – The males and females of Caprella drepanochir are morphologically distinct. The males are large, more robust, and armed with larger gnathopods. This is likely an adaptation to competition for females and for guarding themselves during molting, which proceeds mating. The young are brooded by the female in an egg-pouch formed by large plates (oostegites) on the 3rd and 4th pereonites (Turcotte and Sainte Marie 2009). Development is direct, with the newborn juveniles having the general form of adults.

Ecology – Caprellids feed in a variety of ways, including filtering small particles from the water, browsing on small filamentous algae, scraping tissue from large algae, scavenging, and predation (Turcotte and Sainte Marie 2009). Caprella drepanochir has been found on a wide range of habitats, including seaweeds, seagrasses, sponges, bryozoans (Watersipora subtorquata), mudflats, and manmade structures such as jetties, buoys, and floating docks (Carlton 1989; Ferraro and Cole 2007; Maciejeski 2008; Carr et al. 2011; Wilson 2011). We have not found experimental information on the temperature and salinity tolerances of C. drepanochir, although its native range suggests that high water temperatures could limit its southern range expansion.


Phtyoplankton, Detritus, Bryozoans, Hydroids

Trophic Status:

Suspension Feeder



General HabitatGrass BedNone
General HabitatCoarse Woody DebrisNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Length (mm)13Watling and Carlton, in Carlton 2007; Ashton 2012a
Broad Temperature RangeNoneCold temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Caprella drepanochir has been found in a variety of habitats in West Coast bays (Ferraro and Cole 2007; Maciejeski 2008; Carr et al. 2011; Wilson 2011); however, impacts on native biota have not been reported.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-5 None 0 Native Estab
NEP-IV Puget Sound to Northern California 1988 Def Estab
NEP-II Alaska south of the Aleutians to the Alaskan panhandle 1890 Native Estab
NEP-V Northern California to Mid Channel Islands 2006 Def Estab
P090 San Francisco Bay 2006 Def Estab
NWP-4b None 0 Native Estab
NWP-6 None 0 Native Estab
P130 Humboldt Bay 2006 Def Estab
P270 Willapa Bay 1996 Def Estab
P170 Coos Bay 1988 Def Estab
NEP-III Alaskan panhandle to N. of Puget Sound 2005 Crypto Estab
NWP-4a None 0 Native Estab
NEP-VI Pt. Conception to Southern Baja California 2011 Def Unk
P023 _CDA_P023 (San Louis Rey-Escondido) 2011 Def Unk

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


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