Invasion History

First Non-native North American Tidal Record: 2000
First Non-native West Coast Tidal Record: 2000
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

The taxonomic and biogeographic history of Pseudosphaeroma spp. are still being worked out. This genus was historically thought to be restricted to the Southern Hemisphere, with Pseudosphaeroma campbellensis Chilton 1909 being described first from the subantarctic Campbell Islands, about 600 km south of New Zealand (Chilton 1909, cited by Poore 1981). Subsequently, P. campbellensis was reported from the North and South Islands, as a possible species complex, or as a single species showing phenotypic variation (Hurley and Jansen 1977, cited by Poore 1981). Isopods identified as P. campbellensis were found in Port Philip Bay, Australia (Harrison 1984), but were later found to be an unidentified species, and are regarded as a probable introduction (Bruce and Wetzer 2008). In 2000, specimens of Pseudosphaeroma sp. A were found in San Francisco Bay, California (CA) and subsequently in Morro Bay, Tomales Bay, and Humboldt Bay, CA and Coos Bay, Oregon (Bruce and Wetzer 2008; Davidson 2006; California Department of Fish and Wildlife 2014). Morphologically, the California specimens correspond to the 'nodular form' of Pseudosphaeroma from New Zealand (Bruce and Wetzer 2008).

North American Invasion History:

Invasion History on the West Coast:

Pseudosphaeroma sp. A was first reported from Coyote Point Marina, in South San Francisco Bay, California (CA) in September 2000 (Bruce and Wetzer 2008). In subsequent sampling it was reported from the Carquinez Bridge Buoy (Cohen and Chapman 2005), several sites in San Pablo Bay (Cohen and Chapman 2005; California Academy of Sciences 2015) and the central Bay (Richmond, San Francisco) (Bruce and Wetzer 2008). In 2002, it was collected at Alan Sieroty State Park, Millerton Point, on Tomales Bay (Bruce and Wetzer 2008). In 2003, it was collected in Coos Bay, Oregon, where it was present throughout the Bay, on marsh banks, woody debris, and sandstone terraces, often in association with the introduced isopod Sphaeroma quoianum (Davidson 2006). In August 2008, it was collected in Morro Bay, CA (Bruce and Wetzer 2008); and in 2011, it was collected in Humboldt Bay, CA (California Department of Fish and Wildlife 2014). Likely vectors include ballast water and hull fouling.

Invasion History Elsewhere in the World:

In 1975, five specimens, then identified as Pseudosphaeroma campbellensis, were collected on barnacle-encrusted pilings in Port Philip Bay, Victoria, Australia (Harrison 1984). These specimens are now considered to represent an unidentified species, resembling P. tuberculatum, described from Tristan da Cunha, a mid-Atlantic Island off South Africa (Bruce and Wetzer 2008). At least one specimen of an unidentified Pseudosphaeroma specimens is known from the Galapagos Islands (Bruce and Wetzer 2008).


Specimens of Pseudosphaeroma sp. A found on the West Coast of North America were originally identified as P. campbellensis (Chilton 1909, described from New Zealand) (Cohen et al. 2005; Davidson 2006; Brusca et al. 2007; Graening and Rogers 2013), but P. campbellensis is now regarded as a complex of at least three species (Bruce and Wetzer 2008). West Coast specimens belong to the New Zealand 'nodular' form, characterized by large tubercles on the pleotelson. The body outline is broad and oval, but more pointed towards the tail. In males, the tip of the pleotelson is turned upward. The body is strongly convex in cross section, and in side view. The eyes are prominent. The rostrum is not visible in a dorsal view. In a ventral view, the epistome is broadly rounded. The lateral portions of Peraonites 5, 6 and 7, are sharply bent posteriorly. In the 'nodular' form, males have a broken ridge of nodules on Peraonites 6 and 7. Males have one pair of very prominent tubercles on the pleon and two pairs on the pleotelson.

Antenna 1 of P. campbellensis has a flagellum of 13 segments, extending back to Peraeonite 1, while Antenna 2's flagellum has 11 segments, and extends to Pereaonite 2. Pleopod 3 has three coupling hooks. Pleopod 2 has an appendix masculina, which is 1.3 times the length of the endopod, and club-like. The rami of the uropod have rounded apices, and end at a level with pleotelson. Males from Tomales Bay, California and of the 'nodular' New Zealand form reached 5.2 mm in size (Bruce and Wetzer 2008). California specimens of Pseudosphaeroma sp. A are 'often light green' in color (Brusca et al. 2007). In Oregon, this isopod can be greenish-black, gray, or bright green, but probably varies with diet and/or background (Davidson 2006). The above description is based on: Poore 1981, Harrison 1984, and Bruce and Wetzer 2008.

As noted above, isopods previously identified as P. campbellensis from New Zealand, California, and Australia, represent at least three species. The type form of P. campbellensis, was described from Campbell Island, at 52°S, a subantarctic island well south of New Zealand proper. On New Zealand, there is a 'smooth' and a 'nodular' form of Pseudosphaeroma which appear to be distinct species, separate from P. campbellensis. Specimens from California appear to belong to New Zealand 'nodular’ form (Bruce and Wetzer 2008). 'Pseudosphaeroma campbellensis' reported from Port Phillip Bay, Australia (Harrison 1984) resembles P. tuberculatum, described from the island of Tristan da Cunha, off South Africa (Bruce and Wetzer 2008). Additional species are known from New Zealand (P. callidum), South Africa (P. barnardi), Brazil (P. jakobi), Argentina (P. platensis), Chile (P. lundae), and the Galapagos Islands (undescribed) (Bruce and Wetzer 2008, Appeltans et al. 2015).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Isopoda
Suborder:   Flabellifera
Family:   Sphaeromatidae
Genus:   Pseudosphaeroma
Species:   sp. A


Pseudosphaeroma campbellensis (Chilton, 1909)

Potentially Misidentified Species

Pseudosphaeroma campbellensis
Described from Campbell Islands, subantarctic (Chilton 1909, cited by Bruce & Wetzer 2008)

Pseudosphaeroma lundae
Chile (Bruce and Wetzer 2008)

Pseudosphaeroma sp. 'B'
'Smooth form', New Zealand (Bruce & Wetzer 2008)



Pseudosphaeroma sp. A is a an isopod found in sheltered, shallow brackish and marine waters (Cohen et al. 2005; Davidson 2006; Brusca et al. 2007; Graening and Rogers 2013). Sexes are separate, fertilization is internal, and young are brooded. We have not found information on life history, seasonal population dynamics, or fecundity. However, this isopod has reached high densities in Coos Bay (Davidson 2006), and probably in other West Coast estuaries.

Pseudosphaeroma sp. A is found in sheltered, shallow brackish and marine waters (Cohen et al. 2005; Davidson 2006; Brusca et al. 2007; Graening and Rogers 2013). In San Francisco Bay it was collected at salinities down to 18.5-25.0 PSU (Cohen et al. 2005; Cohen and Chapman 2005). Pseudosphaeroma 'campbellensis' in New Zealand tolerated 24-hour exposures to 10-30C and salinities from 2.2-61 PSU. When exposed to a steady temperature increase, these isopods had a lethal temperature of 42C, and survived 24 hours of air exposure at 10 and 20C, and 70 and 100% humidity. This species showed greater tolerance of temperature, salinity extremes, and air exposure than isopod species inhabiting open coasts (Jansen 1971). We do not have information on the feeding of Pseudosphaeroma spp., but most sphaeromatids are herbivores, often scraping microalgae form surfaces (Brusca et al. 2007).

Trophic Status:




General HabitatCoarse Woody DebrisNone
General HabitatRockyNone
General HabitatMarinas & DocksNone
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Salinity RangeHyperhaline40+ PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Tidal RangeMid IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Temperature (ºC)30Highest temperature tested for long-term survival. In short-term experiments, heating at 1 C/min, 90% of animals died at 42 C (Jansen 1971).
Minimum Salinity (‰)2.2Direct transfer, 24 hr survival, 10-20 C, Jansen 1971
Maximum Salinity (‰)61Direct transfer, 24 hr survival, 10-30 C, Jansen 1971
Maximum Length (mm)5.2Males, California and New Zealand (Bruce and Wetzer 2008)
Broad Temperature RangeNoneWarm-temperate-Cold temperate
Broad Salinity RangeNoneOligohaline-Euhaline

General Impacts

No ecological impacts have been reported for Pseudosphaeroma sp. A on the West Coast of North America. However, this isopod has been seen in high densities in Coos Bay, Oregon (Davidson 2006), and may be abundant in other West coast estuaries.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NZ-IV None 0 Native Estab
NZ-VI None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 2000 Def Estab
P110 Tomales Bay 2002 Def Estab
P090 San Francisco Bay 2000 Def Estab
P170 Coos Bay 2003 Def Estab
NEP-IV Puget Sound to Northern California 2003 Def Estab
P093 _CDA_P093 (San Pablo Bay) 2004 Def Estab
P070 Morro Bay 2008 Def Estab
P130 Humboldt Bay 2011 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Ahyong, Shane T.; Wilkens, Serena L. (2011) In the wrong place- Alien marine crustaceans: Distribution, biology, impacts, Springer, Dordrecht, Netherlands. Pp. 451-485

Appeltans, W. et al. 2011-2015 World Registry of Marine Species. <missing URL>

Bruce, Niel L.; Wetzer, Regina (2008) New Zealand exports: Pseudosphaeroma Chilton, 1909 (Isopoda: Sphaeromatidae), a Southern Hemisphere genus introduced to the Pacific coast of North America, Zootaxa 1908: 51-56

Brusca, Richard C.; Coeljo, Vania R. Taiti, Stefano (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of Calfiornia Press, Berkeley CA. Pp. 503-542

California Academy of Sciences 2005-2015 Invertebrate Zoology Collection Database. <missing URL>

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

Cohen, Andrew N. and 10 authors (2005) <missing title>, San Francisco Estuary Institute, Oakland CA. Pp. <missing location>

Cohen, Andrew N.; Chapman, John T. (2005) <missing title>, San Francisco Estuary Institute, San Francisco. Pp. <missing location>

Davidson, Timothy M. (2006) <missing title>, University of Oregon, MS Thesis, Eugene. Pp. <missing location>

Graening, G. O.; Rogers, D. Christopher (2013) Checklist of inland aquatic Isopoda (Crustacea: Malacostraca) of California, California Fish and Game 99(4): 176-192

Harrison, K. (1984) Some sphaeromatid isopods (Crustacea) from southern and south-western Australia, with the description of a new genus and two new species, Records of the Western Australia Museum 11(3): 259-286

Harrison, K.; Ellis, J. P. (1991) The genera of the Sphaeromatidae (Crustacea: Isopoda): a key and distribution list, Invertebrate Taxonomy 5: 915-952

Jansen, K. P. (1971) Ecological studies on New Zealand Sphaeromatidae (Isopoda, Flabellifera), Marine Biology 11: 263-285

Poore, Gary C. B. (1981) Marine Isopoda of the Snares Islands, New Zealand- 1. Gnathidae, Valfvifera, Anthiuridea, and Flabellifera., New Zealand Journal of Zoology 8: 331-348