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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: scud

Synonyms and Other Names: Chaetogammarus ischnus (Stebbing, 1899), Chaetogammarus tenellus (G. O. Sars, 1914)

Taxonomy: available through www.itis.gov

Identification: Echinogammarus ischnus has a laterally compressed body and lacks dorsal teeth. The eyes are kidney shaped and twice as long as they are wide.  The rostrum is short and triangular. This species is distinguishable from native gammarid amphipods (particularly Gammarus fasciatus) by its telson, whose outer rami (branches) are elongated and the inner rami are vestigial (approximately 1/7 the length of the outer pair). The telson is also cleft to the base and each lobe has two dorsal and three apical spines. Echinogammarus ischnus exhibits strong sexual dimorphism, with males having larger bodies and proportions than females. Male 2nd antennae are very setose and are almost the same length as the 1st antennae, while female 2nd antennae are visibly shorter than the 1st (Kohn and Waterstraat 1990; Witt et al. 1997).

Size: Adult length ranges from 6 to 15 mm for males and 5 to 13 mm for females (Kohn and Waterstraat 1990; Witt et al. 1997; Nalepa et al. 2001).

Native Range: Ponto-Caspian region, in both the Black Sea drainage and the Caspian Sea drainages (Cristescu et al. 2004).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

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

Ecology: Echinogammarus ischnus is a euryhaline species that is most common in large northern rivers of the Black and Caspian Sea drainages (Kohn and Waterstraat 1990; Cristescu et al. 2004). Echinogammarus ischnus is known to live and reproduce in waters ranging in salinity from 0 to 18 psu (Mordukhai-Boltovskoi 1964; Dediu 1980). It has been recorded at depths ranging from 0 to 300 m (typically <50 m) on mud, silt, sand, rock, Dreissena mussels and under wrack (Kohn and Waterstraat 1990; Witt et al. 1997; Nalepa et al. 2001; Grigorovich et al. 2003; Kley and Maier 2005). Its occurrence and density in the upper St. Lawrence River is positively correlated with current velocity and the availability of gravel-sized sediment (Palmer & Ricciardi 2004). It can tolerate highly eutrophic conditions and temperatures up to an absolute maximum of 33–35°C, with a thermal optimum around 27°C (Kohn and Waterstraat 1990; Wijnhoven et al. 2003; Romanenko et al. 2020). Because E. ischnus is a species from the Ponto-Caspian region that has high environmental variability, it and other invaders may benefit from future warming from climate change in the Great Lakes region (Casties et al. 2018).

Echinogammarus ischnus only reproduces sexually and has no resting stages. Brood size varies from 2–51 eggs. Breeding often occurs in spring and summer and ends in the fall, but may occur twice throughout the year in warm, thermally stable waters (Witt et al. 1997; Kley and Maier 2003; Kley and Maier 2006).

Echinogammarus ischnus feeds on deposits, including those associated with zebra mussels, and preys on other macroinvertebrates such as chironomids, other amphipods, or its own species (Krisp and Maier 2005; Limen et al. 2005). In general, E. ischnus is more carnivorous than amphipods such as Gammarus fasciatus and Hyalella azteca (Limen et al. 2005). It is consumed by fish, including Acipenser fulvescens (Lake Sturgeon), Perca flavescens (Yellow Perch), and Neogobius melanostomus (Round Goby) (González and Burkhart 2004; Bailey 2015; Bruestle et al. 2019).

Means of Introduction: Echinogammarus ischnus was almost certainly introduced in ballast water (Witt et al. 1997). Its subsequent introduction to a port in Lake Superior (Grigorovich et al. 2003) was likely caused by a separate introduction in ballast water, either from a saltwater vessel or a domestic freighter from another freshwater port.

Status: This species has expanded its range outside the Great Lake drainages into the Mississippi River drainage.

Great Lakes:
Established where recorded in Lakes Erie, Huron, Ontario, and Michigan. It is assumed to not yet be established in Lake Superior because only two populations have been found to date (Grigorovich et al. 2003; Trebitz et al. 2010).

Impact of Introduction: A) Realised: E. ischnus is now among the most abundant non-Dreissena invertebrates in benthic communities in the Lake Ontario, L. Michigan, and L. Erie watersheds, where it has displaced native Gmelinoides fasciatus from many areas (Dermott et al. 1998; Stewart et al. 1998a, 1998b; Nalepa et al. 2001; Ratti and Barton 2003; van Overdijk et al. 2003; Haynes et al. 2005). Habitat heterogeneity in the St. Lawrence River may be promoting the co-existence of both species by allowing them to segregate along physicochemical gradients (Palmer & Ricciardi 2004). It is possible that E. ischnus has benefited from a co-evolved relationship with dreissenid mussels (Ricciardi & MacIsaac 2000). Structural complexity of Dreissena mussel substrate in combination with available nutrition from mussel biodeposits may have given E. ischnus a competitive advantage, stimulating its population expansion in the lower Great Lakes (van Overdijk et al. 2003). However, native amphipods consume dreissenid mussel pseudofeces more than the invader does at some sites, thus mussel habitat structure alone could enhance E. ischnus dominance over native species in the Great Lakes (Limen et al. 2005). E. ischnus in the St. Lawrence may be more susceptible to predation amongst dreissenid mussels than G. fasciatus, and predation may allow for coexistence of introduced and native species (Palmer and Ricciardi 2005). In the Great Lakes, however, E. ischnus is found more frequently amongst introduced mussels where native amphipods obtain refuge from predators amongst macrophytes and Cladophora-encrusted habitats (van Overdijk et al. 2003; Gonzalez and Burkart 2004).

B) Potential: This species has also been introduced to Western Europe and the Baltic Sea (Cristescu et al. 2004). In parts of Germany and Poland, it has reduced or replaced native gammarids (such as G. fossarum, G. roeseli and G. pulex) (Jazdzewski et al. 2004; Kinzler and Maier 2006). In streams in Central Europe, introduced E. ischnus and Dikerogammarus villosus appear to have contributed to declines in some native macroinvertebrates through predation (Krisp and Maier 2005). It is possible that with increasing colonization of D. bugensis in deeper waters of the Great Lakes, E. ischnus may follow (Nalepa et al. 2001). Canal systems promote the dispersal of this species throughout Europe and may aid its further dispersal in North America (Witt et al. 1997).

Remarks: Although there is great genetic variation amongst native populations in the native Ponto-Caspian region, one mitochondrial genotype of this species from the Black Sea has been responsible for invasions from the Rhine River to North America. (Cristescu et al. 2004).

References: (click for full references)

Bailey, K.L. 2015. Changes in the benthic macroinvertebrate community of southwestern Lake Ontario following invasion by Dreissena mussels, the amphipod Echinogammarus ischnus, and the Round Goby Neogobius melanostomus: a longterm (1983-2014) perspective. Unpublished M.S. thesis. State University of New York College at Brockport.

Bruestle, E.L., C. Karboski, A. Hussey, A.T. Fisk, K. Mehler, C. Pennuto, and D. Gorsky. 2019. Novel trophic interaction between lake sturgeon (Acipenser fulvescens) and non-native species in an altered food web. Canadian Journal of Fisheries and Aquatic Sciences 76(1):6-14.

Casties, I., C. Clemmesen, and E. Briski. 2018. Environmental tolerance of three gammarid species with and without invasion record under current and future global warming scenarios. Diversity and Distributions 25(4):603-612.

Cristescu, M.E.A., J.D.S. Witt, I.A. Grigorovich, P.D.N. Hebert, and H.J. MacIsaac. 2004. Dispersal of the Ponto-Caspian amphipod Echinogammarus ischnus: invasion waves from the Pleistocene to the present. Heredity 92(3): 197-203.

Dediu, I.I. 1980. Amphipods of fresh and brackish waters of the southwestern USSR. Shtiintsa, Chi?inau, Moldova.

Dermott, R., J. Witt, Y.M. Young, and M. Gonzalez. 1998. Distribution of the Ponto-Caspian amphipod Echinogammarus ischnus in the Great Lakes and replacement of native Gammarus fasciatus. Journal of Great Lakes Research 24(2): 442-452.

Duggan, J.P., and S.N. Francoeur. 2007. Relative abundance of native and invasive amphipods in western Lake Erie in relation to dreissenid mussel encrustation and algal cover. Journal of Freshwater Ecology 22(2): 201-212.

GLMRIS. 2012. Appendix C: Inventory of Available Controls for Aquatic Nuisance Species of Concern, Chicago Area Waterway System. U.S. Army Corps of Engineers.

Gonzalez, M.J., and G.A. Burkart. 2004. Effects of food type, habitat, and fish predation on the relative abundance of two amphipod species, Gammarus fasciatus and Echinogammarus ischnus. Journal of Great Lakes Research 30: 100-113.

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., A.V. Korniushin, D.K. Gray, I.C. Duggan, R.I. Colautti, and H.J. MacIsaac. 2003. Lake Superior: an invasion coldspot? Hydrobiologia 499: 191-210.

Haynes, J.M., N.A. Tisch, C.M. Mayer, and R.S. Rhyne. 2005. Benthic macroinvertebrate communities in southwestern Lake Ontario following invasion of Dreissena and Echinogammarus. Journal of the North American Benthological Society 24(1): 148-167.

Jazdzewski, K., A. Konopacka, and M. Grabowski. 2004. Recent drastic changes in the gammarid fauna (Crustacea, Amphipoda) of the Vistula River deltaic system in Poland caused by alien invaders. Diversity and Distributions 10(2): 81-87.

Kang, M., J.J.H. Ciborowski, and L.B. Johnson. 2007. The influence of anthropogenic disturbance and environmental suitability on the distribution of the nonindigenous amphipod, Echinogammarus ischnus, at Laurentian Great Lakes coastal margins. Journal of Great Lakes Research 33(Special Issue 3): 198-210.

Kestrup, A.M., and A. Ricciardi. 2009a. Environmental Heterogeneity limits the local dominance of an invasive freshwater crustacean. Biological Invasions 11: 2065-2105.

Kestrup, A.M., and A. Ricciardi. 2009b. Are interactions among Ponton-Caspian invaders driving amphipod species replacement in the St. Lawrence River? Journal of Great Lakes Research 35: 392-398.

Kestrup, A.M., T.A.J. Dick, and A. Ricciardi.  2011a. Interactions between invasive and native crustaceans: differential functional responses of intraguild predators towards juvenile hetero-specifics. Biological Invasions 13: 731-737.

Kestrup, A.M., S.H. Thomas, K. van Rensburg, A. Ricciardi, and M.A.Duffy. 2011b. Differential infection of exotic and native freshwater amphipods by a parasitic water mold in the St. Lawrence River. Biological Invasions 13: 769-779.

Kinzler, W., and G. Maier. 2006. Selective predation by fish: a further reason for decline of native gammarids in the presence of invasives? Journal of Limnology 65(1): 27-34.

Kley, A., and G. Maier. 2003. Life history characteristics of the invasive freshwater gammarids Dikerogammarus villosus and Echinogammarus ischnus in the river Main and the Main-Donau canal. Archiv für Hydrobiologie 156(4): 457-469.

Kley, A., and G. Maier. 2005. An example of niche partitioning between Dikerogammarus villosus and other invasive and native gammarids: a field study. Journal of Limnology 64(1): 85-88.

Kley, A., and G. Maier. 2006. Reproductive characteristics of invasive gammarids in the Rhine-Maine-Danube catchment, south Germany. Limnologica 36(2): 79-90.

Kohn, J., and A. Waterstraat. 1990. The amphipod fauna of Lake Kummerow (Mecklenburg, German Democratic Republic) with reference to Echinogammarus ischnus Stebbing, 1899. Crustaceana 58(1): 74-82.

Krisp, H., and G. Maier. 2005. Consumption of macroinvertebrates by invasive and native gammarids: a comparison. Journal of Limnology 64(1): 55-59.

Limen, H., C.D.A. van Overdijk, and H.J. MacIsaac. 2005. Food partitioning between the amphipods Echinogammarus ischnus, Gammarus fasciatus, and Hyalella azteca as revealed by stable isotopes. Journal of Great Lakes Research 31(1): 97-104.

Mordukhai-Boltovskoi. 1964. Caspian fauna beyond the Caspian Sea. Internationale Revue der gesamten Hydrobiologie und Hydrographie 49(1):139-176. https://doi.org/10.1002/iroh.19640490105.

Nalepa, T.F., D.W. Schloesser, S.A. Pothoven, D.W. Hondorp, D.L. Fanslow, M.L. Tuchman, and G.W. Fleischer. 2001. First finding of the amphipod Echinogammarus ischnus and the mussel Dreissena bugensis in Lake Michigan. Journal of Great Lakes Research 27(3): 384-391.

Nalepa, T.F., L.E. Burlakova, A.K. Elgin, A.Y. Karatayev, G.A. Lang, and K. Mehler. 2020. Abundance and Biomass of Benthic Macroinvertebrates in Lake Michigan in 2015, with a Summary of Temporal Trends. NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI.

van Overdijk, C.D.A., I.A. Grigorovich, T. Mabee, W.J. Ray, J.J.H. Ciborowski, and H.J. MacIsaac. 2003. Microhabitat selection by the invasive amphipod Echinogammarus ischnus and native Gammarus fasciatus in laboratory experiment and in Lake Erie. Freshwater Biology 48(4): 567-578.

Palmer, M.E., and A. Ricciardi. 2004. Physical factors affecting the relative abundance of native and invasive amphipods in the St. Lawrence River. Canadian Journal of Zoology 82: 1886-1893.

Palmer, M.E., and A. Ricciardi. 2005. Community interactions affecting the relative abundances of native and invasive amphipods in the St. Lawrence River. Canadian Journal of Fisheries and Aquatic Sciences 62(5): 1111-1118.

Ratti, C., and D.R. Barton. 2003. Decline in the diversity of benthic invertebrates in the wave-zone of eastern Lake Erie, 1974-2001. Journal of Great Lakes Research 29: 608-615.

Ricciardi, A., and H.J. MacIsaac. 2000. Recent mass invasion in the North American Great Lakes by Ponto-Caspian species. Trends in Ecology and Evolution 13(2): 62-65.

Romanenko, V.D., Y.G. Krot, T.I. Lekontseva, and G.B. Podrugina. 2020. Peculiarities of adaptation of Gammaridae of the reservoirs' littoral zone to water temperature increase. Hydrobiological Journal 56(3):3.

Stewart, T.W., J.G. Miner, and R.L. Lowe. 1998a. Quantifying mechanisms for zebra mussel effects on benthic macroinvertebrates: organic matter production and shell-generated habitat. Journal of the North American Benthological Society 17: 81-94.

Stewart, T.W., J.G. Miner, and R.L. Lowe. 1998b. Macroinvertebrate communities on hard substrates in western Lake Erie: structuring effects of Dreissena. Journal of Great Lakes Research 24: 868-879.

Trebitz, A.S., C.W. West, J.C. Hoffman, J.R. Kelly, G.S. Peterson, and I.A. Grigorovich. 2010. Status of non-indigenous benthic invertebrates in the Duluth-Superior Harbor and the role of sampling methods in their detection. Journal of Great Lakes Research 36(4):747-756. https://doi.org/10.1016/j.jglr.2010.09.003.

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 the water. Aquatic Ecology 37: 151-158.

Witt, J.D.S., P.D.N. Hebert, and W.B. Morton. 1997. Echinogammarus ischnus: another crustacean invader in the Laurentian Great Lakes basin. Canadian Journal of Fisheries and Aquatic Sciences 54(2): 264-268.

Other Resources:
Great Lakes Waterlife

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

Peer Review Date: 2/25/2021

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.