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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: tiger scud

Synonyms and Other Names: Tigermärle (SE); Gefleckter Flussflohkrebs, Getigerter Bachflohkrebs (DE); Kielz tygrys (PL); Leväkatka (FI); Tijgervlokreeft (NL) [translates as tiger scud]  

Taxonomy: available through www.itis.gov

Identification: Amphipods in the family Gammaridae have accessory flagellae on their 1st antennae and also display well-developed third uropods (biramous appendages on the posterior abdomen). Mature male G. tigrinus typically have relatively long and curly 2nd antennae, distinct setae on their pereopods (walking legs), and 2-5 groups of posterior marginal setae on the 2nd peduncular (basal) segment of their 1st antennae. Females have fewer setae on the antennae and pereopods (Bousfield 1969; Grigorovich et al. 2005). See Bousfield (1969) for a detailed description.

Size: Length varies greatly with temperature, salinity, and type of food. In Saginaw Bay, Lake Huron, males average 10.5 mm and females average 7.6 mm in length (Grigorovich et al. 2005).

Native Range: This species is native to the Atlantic coast of North America.

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: This euryhaline species tolerates salinities from 0–25‰, pH 6–10, relatively eutrophic conditions, hypoxic habitats, and warmer temperatures (mortality occurs at 32–34°C) in saltier water than other gammarid species (Bousfield 1969; Barlocher and Porter 1986; Winn and Knott 1992; MacNeil et al. 2003; Wijnhoven et al. 2003; Grigorovich et al. 2005). Gammarus tigrinus prefers rivers and shallow lakes in turbid, low salinity habitats, but can colonize lower depths (to approximately 20 m) if displaced by competitors from preferred littoral habitat (Dodson et al. 1989; MacNeil et al. 2003; Grigorovich et al. 2005).  In Lake Huron, it mostly occurs in very shallow areas on silty sand, on Cladophora, or in macrophyte beds (Grigorovich et al. 2005). Densities in Lake Huron average 280 m^-2 while those in some European habitats can reach 103 m_^-2 (Chambers 1977; Grigorovich et al. 2005; Wawrzyniak-Wydrowska and Gruszka 2005).

Gammarus tigrinus is omnivorous. It filter feeds suspended organic matter and can also directly consume zooplankton, plants, algae, detritus, and even its own young (Hunte and Myers 1984; Grigorovich et al. 2005). 

Reproducing adults occur in freshwater in the Great Lakes. In Saginaw Bay, reproductive females carry 32 embryos on average and populations contain many more juveniles and females than males, probably because males have shorter life spans (Grigorovich et al. 2005). Gammarus tigrinus often matures in a few months, reproduces quickly, and produces 3-16 generations annually (Chambers 1977; Grigorovich et al. 2005). Reproduction can be triggered at any time of year if ambient 10°C temperature increases by 15–16°C (Ginn et al. 1976).

Means of Introduction: Very likely introduced in ballast water (Grigorovich et al. 2005). Populations of G. tigrinus in the Great Lakes are genetically similar to those from the Hudson River estuary (Kelly et al. 2006).

Status: Not established yet, may be introduced (U.S. EPA 2008).

Impact of Introduction: A) Realised: In many wetland habitats along the Great Lakes’ perimeter G. tigrinus is already the second most abundant amphipod after G. pseudolimnaeus (Grigorovich et al. 2005).

B) Potential: G. tigrinus has extensively colonized European waters, spreading at rates of around 40 km per year along the Baltic Sea coast, and covering approximately 1000 km in total from 1975 to 1998 (Grigorovich et al. 2005).

G. tigrinus has eliminated some native species in parts of the Rhine River and the Baltic Sea; it is frequently a superior predator in comparison to indigenous species such as G. duebenii, G. zaddachii, and G. pulex (Grigorovich et al. 2005). It coexists in Ireland with the native opossum shrimp Mysis relicta through mutual predation (Bailey et al. 2006). However, the latter has been forced to change its use of microhabitat, exposing itself more to fish predation due to the presence of the invader (Bailey et al. 2006). G. tigrinus preys on relatively small Crangonyx pseudogracilis in Ireland, and could similarly prey on it in the Great Lakes (Dick 1996; Grigorovich et al. 2005). The potential for negative impacts on the native amphipod community in the Great Lakes due to predation and competition with the invader is high (Dick 1996; Grigorovich et al. 2005). G. tigrinus can exclude C. pseudogracilis from better water quality habitat when the two co-occur but in poor water quality this may not be the case (MacNeil et al. 2001).

This species can act as an intermediate host to the acanthocephalan Paratenuisentis ambiguus, whose definitive host is Anguilla rostrata (Samuel and Bullock 1981).

Remarks: In the Netherlands, the Ponto-Caspian amphipod Dikerogammarus villosus is eliminating G. tigrinus, a previously successful invader in this region (Dick and Platvoet 2000).

References: (click for full references)

Bailey, R.J.E., J.T.A. Dick, R.W. Elwood, and C. MacNeil. 2006. Predatory interactions between the invasive amphipod Gammarus tigrinus and the native opossum shrimp Mysis relicta. Journal of the North American Benthological Society 25(2): 393-405.

Barlocher, F., and C.W. Porter. 1986. Digestive enzymes and feeding strategies of three stream invertebrates. Journal of the North American Benthological Society 5(1): 58-66.

Bousfield, E.L. 1969. New records of Gammarus (Crustacea: Amphipoda) from the middle Atlantic region. Chesapeake Science 10(1): 1-17.

Chambers, M.R. 1977. The population ecology of Gammarus tigrinus in the reed beds of the Tjeukemeer, Netherlands. Hydrobiologia 53(2): 155-164.

Dick, J.T.A. 1996. Post-invasion amphipod communities of Lough Neagh, Northern Ireland: influences of habitat selection and mutual predation. Journal of Animal Ecology 65(6): 756-767.

Dick, J.T.A., and D. Platvoet. 2000. Invading predatory crustacean Dikerogammarus villosus eliminates both native and exotic species. Proceedings of the Royal Society Biological Sciences Series B 267(1442): 977-983.

Dodson, J.J., J.C. Dauvin, and B. D’Anglejan. 1989. Abundance of larval rainbow smelt Osmerus mordax in relation to the maximum turbidity zone and associated macroplanktonic fauna of the middle St. Lawrence estuary, Canada. Estuaries 12(2): 66-81.

Ginn, T.C., W.T. Waller, and G.J. Lauer. 1976. Survival and reproduction of Gammarus spp. (Amphipoda) following short-term exposure to elevated temperatures. Chesapeake Science 17(1): 8-14.

Grigorovich, I.A., T.R. Angradi, E.B. Emery, and M.S. Wooten. 2008. Invasion of the upper Mississippi River system by saltwater amphipods. Fundamental and Applied Limnology 173(1):67-77.

Grigorovich, I.A., M. Kang, and J.J.H. Ciborowski. 2005. Colonization of the Laurentian Great Lakes by the amphipod Gammarus tigrinus, a native of the North American Atlantic Coast. Journal of Great Lakes Research 31: 333-342.

Hunte, W., and R.A. Myers. 1984. Phototaxis and cannibalism in gammaridean amphipods. Marine Biology (Berlin) 81(1): 75-80.

Kelly, D.W., J.R. Muirhead, D.D. Heath, and H.J. MacIsaac. 2006. Contrasting patterns in genetic diversity following multiple invasions of fresh and brackish waters. Molecular Ecology 15(12): 3641-3653.

Kotta, J., H. Orav-Kotta, and K. Herkül. 2010. Separate and combined effects of habitat-specific fish predation on the survival of invasive and native gammarids. Journal of Sea Research 64(3):369-372.

MacNeil, C., E. Bigsby, J.T.A. Dick, H.B.N. Hynes, M.J. Hatcher, and A.M. Dunn. 2003. Temporal changes in the distribution of native and introduced freshwater amphipods in Lough Neagh, Northern Ireland. Archiv fuer Hydrobiologie 157(3): 379-395.

MacNeil, C., J.T.A. Dick, R.W. Elwood, and W.I. Montgomery. 2001. Coexistence among native and introduced freshwater amphipods (Crustacea); habitat utilization patterns in littoral habitats. Archiv fuer Hydrobiologie 151(4): 591-607.

Orav-Kotta, H., J. Kotta, K. Herkül, I. Kotta, and T. Paalme. 2009. Seasonal variability in the grazing potential of the invasive amphipod Gammarus tigrinus and the native amphipod Gammarus salinus (Amphipoda: Crustacea) in the northern Baltic Sea. Biological Invasions 11(3):597-608.

Pinkster, S., H. Smit, and N. Brandse-de Jong. 1977. The introduction of the alien amphipod Gammarus tigrinus Sexton, 1939, in the Netherlands and its competition with indigenous species. Crustaceana Supplement 4:91-105.

Samuel, G., and W.L. Bullock. 1981. Life cycle of Paratenuisentis ambiguous (Acanthocephala, Tenuisentidae). Journal of Parasitology 67(2): 214-217.

Savage, A.A. 2000. Community structure during a 27-year study of the macroinvertebrate fauna of a chemically unstable lake. Hydrobiologia 421: 115-127.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/066F. Available from the National Technical Information Service, Springfield, VA, and http://www.epa.gov/ncea.

Wawrzyniak-Wydrowska, B., and P. Gruszka. 2005. Population dynamics of alien gammarid species in the River Odra estuary. Hydrobiologia 539: 13-25.

Wijnhoven, S., M.C. van Riel, and G. van der Velde. 2003. Exotic and indigenous freshwater gammarid species: physiological tolerance to water temperature in relation to ionic content of t he water. Aquatic Ecology 37: 151-158.

Winn, R.N., and D.M. Knott. 1992. An evaluation of the survival of experimental populations exposed to hypoxia in the Savannah River estuary. Marine Ecology Progress Series 88(2-3): 161-179.

Other Resources:
Great Lakes Waterlife

Author: Kipp, R.M, J. Larson, A. Fusaro,T. Makled, and A. Benson

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.