Taxonomic name: Sphaeroma quoianum (=S. quoyanum H. Milne-Edwards, 1840)
Synonyms: Sphaeroma pentodon, Sphaeroma quoiana, Sphaeroma quoianum Milne Edwards, 1840, Sphaeroma quoyana, Sphaeroma quoyanum, Sphaeroma verrucauda
Common names: Australasian isopod (English), Australian-New Zealand boring isopod (English), burrowing Australian isopod (English), burrowing isopod (English), mud-dwelling isopod (English), New Zealand burrowing isopod (English), New Zealand isopod (English), New Zealand pillbug (English)
Organism type: crustacean
The burrowing isopod, Sphaeroma quoianum, invades estuarine environments and causes increased erosion rates as well as significant damage to maritime structures. The reproductive patterns, high densities, and rapid colonisation rates make Sphaeroma quoianum a significant invasive species to local estuarine systems. When densities of Sphaeroma quoianum are high this isopod has the ability to increase erosion amounts up to 240%, as is the case in California.
Sphaeroma quoianum has a stout, thick body with paddle-like appendages that are sharply serrated in the hind region. S. quoianum tends to be darkly coloured gray or sandy brown with black patterns throughout. S. quoianum can grow up to 15mm in length. Powerful mandibles aid in forming the burrows which S. quoianum is so well known for (Rotramel 1975a ).
Sphaeroma quoianum do not consume the material excavated from burrows (Rotramel, 1975a), but likely create burrows to be less vulnerable to epibenthic predators and to reduce environmental stress (Davidson, 2008).
coastland, estuarine habitats, wetlands
Sphaeroma quoianum inhabits wetland marshes within estuarine environments and is found predominately between salinity levels of 5 and 30 (Davidson, 2008). Within these habitats themselves S. quoianum resides within burrows created in the marsh banks (composed of mud, clay, or peat). The system of interconnected burrows within the bank weakens the substratum, which in turn accelerates erosion. S. quoianum is also found in wooden structures, sandstone or other friable rock, and various other materials such as Styrofoam floats (used in floating docks) along shorelines (Davidson, 2008). S. quoianum is often found in empty barnacle tests in its native range (Hass & Kott, 1998).
The burrowing tendencies of Sphaeroma quoianum have lead to an increase in erosion rates by as much as 240% of many estuarine environments as well as damage to docks, wooden structures, levees and dikes (Carlton, 2001; Talley et al., 2001, Davidson, 2008). Burrowing by S. quoianum into polystyrene floats, such as Styrofoam, also disperses microscopic polystyrene particles into local waterways (Carlton, unpublished). An increased loss of marsh plants also occurs due to the invasion of S. quoianum (Talley et al., 2001).
Through their burrowing activities, S. quoianum creates extensive networks of burrows which are utilised by a variety of estuarine and semi-terrestrial species. Davidson et al. (2009) found that S. quoianum were associated with higher densities, richness and diversity of fauna in some substrates. Additionally, some species were able to survive at higher tidal levels than normal by using burrows as refuges.
Burrow microhabitats appeared to support greater proportions of non-native fauna than native fauna in Coos Bay, Oregon (Davidson et al., 2009). Thus burrows created by S. quoianum could be an important factor in the establishment and spread of other non-native species (Davidson et al., 2009).
Introduced to the United States along with Sphaeroma quoianum is a commensal isopod Iais californica from New Zealand which lives directly on S. quoianum. The U.S. native isopod Gnorimosphaeroma oregonensis also plays host to I. californica but unlike S. quoianum actively removes it (Rotramel, 1975b).
Native range: Australia, New Zealand.
Known introduced range: United States.
Higher densities of S. quoianum have been observed in vertical banks compared with sloped banks. Thus restoration efforts should use sloped banks where possible, in order to reduce colonisation rates and erosion impacts (Talley et al., 2001).
Recent work by Davidson et al. (2008) on substrate preference of S. quoianum demonstrated that they colonise a wide range of substrata, but have a clear preference for decayed wood. A potential control method could involve outplanting a preferred substrate such as wood and removing it once it had been colonised. By continuing to do this over several seasons it may be possible to reduce S. quoianum populations, thereby reducing their impacts. Further research by Davidson et al. will investigate the success of different management strategies.
Sphaeroma quoianum is capable of feeding using plumose setae on the pereopods to filter currents generated by its pleopods (Rotramel, 1975a). S. quoianum, as well as other members of the Sphaeroma genus, does not consume wood products but rather feeds on microalgae and detritus (Rotramel, 1975a).
Sphaeroma quoianum adults are thought to reproduce continuously though peak reproduction occurs in late spring and early summer. The brood size increases from 19.5 in fall to 64 in spring (Schneider, 1976).
Sphaeroma quoianum undergoes direct development. Females carry fertilized eggs within a marsupium and the young disperse as fully formed juveniles. Often juveniles remain at the terminal end of the burrow for an unknown amount of time, until they are likely expelled by the adult. Growth rates for S. quoianum are highest in spring at approximately 1.5mm per month. Normal growth rates average 0.64mm per month and juveniles become reproductive after 6 months. The life-span of S. quoianum is between 1.5 to 2 years (Schneider, 1976).
Reviewed by: Timothy M. Davidson, Aquatic Bioinvasion Research and Policy Institute, Portland State University.
Principal sources: Davidson, T.M., Shanks, A.L. & Rumrill, S.S. 2009. The composition and density of fauna utilizing burrow microhabitats created by a non-native burrowing crustacean (Sphaeroma quoianum). Biological Invasions. in press.
Davidson, T.M. 2008. Prevalence and distribution of the introduced burrowing isopod, Sphaeroma quoianum, in the intertidal zone of a temperate northeast pacific estuary
(Isopoda, Flabellifera). Crustaceana 81(2): 155-167.
Davidson, T.M., Rumrill, S.S. & Shanks, A.L. 2008. Colonization and substratum preference of an introduced burrowing crustacean in a temperate estuary. Journal of Experimental Marine Biology and Ecology 354: 144–149.
Talley, T. S., Crooks, J. A., and Levin, L. A. 2001. Habitat utilization and alteration by the invasive, burrowing isopod, Sphaeroma quoyanum, in California salt marshes, Marine Biology 138, 561-573.
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Thursday, 5 June 2008