Echinogammarus ischnus (Stebbing, 1899)

Common Name: Scud

Synonyms and Other Names:

Chaetogammarus ischnus (Stebbing, 1899), Chaetogammarus tenellus (G. O. Sars, 1914)



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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).


Great Lakes Nonindigenous Occurrences: Echinogammarus ischnus was first reported in 1994 from the Detroit River (Witt et al. 1997). Archived specimens show that it could have been present in western Lake Erie as early as 1993 (van Overdijk et al. 2003). By 1996, E. ischnus was widely distributed from southern Lake Huron downstream to the mouth of the Niagara River of Lake Ontario (Dermott et al. 1998). It was reported from Lake Michigan in 1998 (Nalepa et al. 2001) and Lake Superior in 2001 (Grigorovich et al. 2003). It is now widespread in southern Lake Huron, the St. Clair River, the Lake Ontario watershed and the upper St. Lawrence River (Dermott et al. 1998; Palmer and Ricciardi 2004). This species expanded its range outside the Great Lake drainages into the Mississippi River drainage. It has been found in the lower half of the Ohio River since 2004 and in the upper portion in 2005 as well as in the upper Mississippi River from the confluence of the Ohio River upriver into Minnesota (Grigorovich et al. 2008).


Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Echinogammarus ischnus are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IL199920163Lake Michigan; Little Calumet-Galien; Pike-Root
IN199920162Lake Michigan; Little Calumet-Galien
MI1995202014Au Gres-Rifle; Carp-Pine; Huron; Kawkawlin-Pine; Lake Erie; Lake Huron; Lake Michigan; Lake St. Clair; Lone Lake-Ocqueoc; Manistee; Muskegon; Ottawa-Stony; Pigeon-Wiscoggin; Saginaw
MN200520202Lake Superior; St. Louis
NY200720165Chaumont-Perch; Lake Erie; Lake Ontario; Niagara River; Seneca
OH199620071Lake Erie
PA200720121Lake Erie
WI200820177Door-Kewaunee; Duck-Pensaukee; Lake Michigan; Lake Superior; Lower Fox; Milwaukee; Peshtigo

Table last updated 3/28/2024

† Populations may not be currently present.


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).


Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental

Echinogammarus ischnus has a moderate environmental impact in the Great Lakes.

Realized:
Following its initial establishment, Echinogammarus ischnus became one of the most abundant non-dreissenid benthic invertebrates in the Lake Ontario, Lake Michigan, and Lake Erie watersheds, where it locally displaced the native amphipod Gammarus fasciatus from many sites (Dermott et al. 1998;  Stewart et al. 1998a,b; Nalepa et al. 2001; van Overdijk et al. 2003; Ratti and Barton 2003; Haynes et al. 2005; Limén et al. 2005). Differences in fecundity and generation time, which appear to favor G. fasciatus, are not sufficient to explain species replacement by E. ischnus (Dermott et al. 1998). Rather, it has been hypothesized that such displacement is due to intraguild predation and competition for resources (Witt et al. 1997; González and Burkhart 2004; Limén et al. 2005; Palmer and Ricciardi 2005; Kestrup and Ricciardi 2009b).

Studies in the St. Lawrence River have shown that E. ischnus and G. fasciatus are mutual (intraguild) predators. Echinogammarus ischnus is generally the superior predator of adult gammarids in waters of higher conductivity (Kestrup and Ricciardi 2009b), but this advantage is offset by G. fasciatus preying more efficiently on E. ischnus juveniles (Kestrup et al. 2011a). Research in central Europe also reports the invasive E. ischnus to be a stronger predator over native gammarids in cases of intraguild predation, suggesting that predation is a probable mechanism of species replacement (Kinzler and Maier 2006).

A mechanism for competitive exclusion of G. fasciatus by E. ischnus is less clear and may be influenced by total or relative amphipod densities (van Overdijk et al. 2003; Kestrup and Ricciardi 2009a) or by differences in the physical environment (Palmer and Ricciardi 2004). For instance, the initial replacement of G. fasciatus by E. ischnus occurred in primarily rocky and dreissenid-covered habitats, while G. fasciatus populations continued to persist on algal and macrophyte-covered substrates (Dermott et al. 1998; Duggan and Francoeur 2007). These two amphipod species may also differ in their responses to abiotic factors such as current velocity or pH, which could affect their relative fitness in different environments (Palmer and Ricciardi 2004). Echinogammarus ischnus typically numerically dominates high flow sites, and its abundance in the St. Lawrence River has been more positively correlated with current velocity than with any other physical attribute (Palmer and Ricciardi 2004). Kang et al. (2007) also encountered E. ischnus more frequently at high energy coastal sites throughout the Great Lakes.

It has been suggested that E. ischnus has potentially benefited from a co-evolved relationship with dreissenid mussels (Ricciardi and MacIsaac 2000). Available nutrition from mussel biodeposits, in combination with the structural complexity of Dreissena mussel substrate, may have given E. ischnus a competitive advantage, stimulating its population expansion in the lower Great Lakes (van Overdijk et al. 2003). However, at some sites, native amphipods have been found to consume more Dreissena pseudofeces than E. ischnus (González and Burkhart 2004). Furthermore, carbon isotopic composition data indicated that the diets of E. ischnus and native Great Lakes amphipod G. fasciatus differ, suggesting that competition for food is an unlikely mechanism of the species replacement (Limén et al. 2005).

It is possible that E. ischnus evades predators more easily than G. fasciatus, particularly on dreissenid-covered substrate (González and Burkhart 2004). In laboratory feeding trials, G. fasciatus was more heavily consumed by Yellow Perch (Perca flavescens) and Round Goby (Neogobius melanostomus) on dreissenid-covered substrate than E. ischnus, while E. ischnus was consumed more heavily on macrophyte beds (González and Burkhart 2004). In contrast, other studies have found no difference between the two species in their vulnerability to predation on dreissenid-covered substrate (Palmer and Ricciardi 2005; Kestrup and Ricciardi 2009a).

Interestingly, E. ischnus and G. fasciatus appear to coexist in the St. Lawrence River, where G. fasciatus remains the dominant amphipod, but E. ischnus remains abundant at some sites (Palmer and Ricciardi 2004, 2005; Kestrup and Ricciardi 2009a,b). Research has suggested that the use of mussel habitat in this location was equal between the two species, and that both species were equally as vulnerable to Round Goby predation, negating two possible mechanisms of species replacement (Kestrup and Ricciardi 2009a). Instead, coexistence in the St. Lawrence River may be the result of habitat heterogeneity, which is thought to allow the species to segregate along physicochemical gradients (Palmer and Ricciardi 2004; Kestrup and Ricciardi 2009b).

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 Gammarus fossarum, G. roeseli, and G. pulex) (Jazdzewski et al. 2004; Kinzler and Maier 2006). In Central European streams, introduced E. ischnus and Dikerogammarus villosus appear to have contributed to declines in certain native macroinvertebrates through predation, E. ischnus being a stronger predator than native gammarids (Krisp and Maier 2005). However it was deemed unlikely that macroinvertebrate predation by E. ischnus has a significant negative impact overall (Krisp and Maier 2005).

It is possible that with increasing colonization of Dreissena bugensis in deeper waters of the Great Lakes, E. ischnus may follow (Nalepa et al. 2001), though 2015 survey data collected from 140 stations in Lake Michigan did not indicate that E. ischnus occurred at deeper sites that contained D. bugensis (Nalepa et al. 2020). Additionally, canal systems have promoted the dispersal of this species throughout Europe and may aid its further dispersal in North America (Witt et al. 1997).

Echinogammarus ischnus has been found to host a parasitic water mold (oomycete) in the St. Lawrence river. This oomycete also parasitizes the Great Lakes native amphipod G. fasciatus, but the effects are less severe, potentially preventing E. ischnus from becoming dominant (Kestrup et al. 2011b).

There is little or no evidence to support that Echinogammarus ischnus has significant socio-economic impacts in the Great Lakes.

There is little or no evidence to support that Echinogammarus ischnus has significant beneficial effects in the Great Lakes.


Management: Regulations (pertaining to the Great Lakes)
There are no known regulations for this species.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
Benthic invertebrates including Echinogammarus ischnus are a major part of the native Yellow Perch (Perca flavescens) and Lake Sturgeon (Acipenser fulvescens) diets (Gonzalez and Burkart 2004; Bruestle et al. 2019). Echinogammarus ischnus has also become prey of the invasive Round Goby, Neogobius melanostomus (Gonzalez and Burkart 2004). The spread of dreissenid-covered substrate across the Great Lakes region has created an ideal habitat for E. ischnus, where it is less susceptible to predation, indicating that efforts to control Dreissena spp. could also aid control of Echinogammarus ischnus (Gonzalez and Burkart 2004). 

A parasitic water mold (oomycete) detected in the upper St. Lawrence river is likely responsible for reducing E. ischnus abundance despite favorable physical and chemical conditions (Kestrup et al. 2011b). The oomycete also infects the native amphipod Gammarus fasciatus, but its effects are significantly less severe than in E. ischnus (Kestrup et al. 2011b).

Physical
Echinogammarus ischnus can tolerate a maximum water temperature between 31.0°C and 32.2°C before irreversible physiological damage and mortality occur (Wijnhoven et al. 2003).

Electron beam irradiation can be used to control microorganisms in aquatic pathways, including E. ischnus (GLMRIS 2012). Electron beam irradiation is a non-selective control method which exposes water to low doses of radiation using gamma-sterilizers or electron accelerators, breaking down DNA in living organisms while leaving behind no by-products (GLMRIS 2012). Ultraviolet (UV) light can also effectively control microorganisms including E. ischnus in water treatment facilities and narrow channels, where UV filters can be used to emit UV light into passing water, penetrating cell walls and rearranging DNA of microorganisms (GLMRIS 2012).

Chemical
There are no known chemical control methods for this species

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.


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 reference list)


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


Contributing Agencies:
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Revision Date: 2/25/2021


Peer Review Date: 2/25/2021


Citation for this information:
Benson, A.J., R.M. Kipp, J. Larson, T.H. Makled, and A. Fusaro, 2024, Echinogammarus ischnus (Stebbing, 1899): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=23&Potential=N&Type=1&HUCNumber=DHuron, Revision Date: 2/25/2021, Peer Review Date: 2/25/2021, Access Date: 3/28/2024

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.