Obesogammarus crassus
(G.O. Sars, 1894)
Common Name:
Thick scud
Synonyms and Other Names:
Gammarus crassus Sars 1894 (objective synonym), Pontogammarus crassus (G.O. Sars), Niphargoides (Pontogammarus) crassus Grimm
Identification:
Obesogammarus crassus is an off-white amphipod with an endopod that is no more than 30% of the length of its exopod (Dobson 2012). The exopod is short and its length is as long as the width of the urosome. This species has dense tufts of setae on uropod 3 and spines on urosome 1 and 2 that form a single central line. The large segment towards the base of the posterior pereopod is expanded and protrudes downwards. Obesogammarus crassus looks similar to Pontogammarus robustoides, but has only a single pair of spines on urosome 2, and has few setae on its posterior pereopod.
Size:
Up to 12 mm in length. Mean breeding female 8.81 mm in length.
Native Range:
Ponto-Caspian basin and Black and Caspian Seas. Nonindigenous Occurrences: Obesogammarus crassus has been found in the Pripyat River, Belarus (Semenchenko and Vezhnovetz 2008). This species occurs in the Szczecin Lagoon and Elbe River in Germany (Grabowski et al. 2007). Obesogammarus crassus is established in the Curonian and Vistula Lagoons in the Baltic Sea (Russia) (Berezina et al. 2011). In the past decade, O. obesus crossed the salinity barrier (5.6 to 6.8 ppt) of the Gulf of Gdansk (Poland) in the Baltic Sea (Dobrzycka-Krahel et al. 2016). In Western Europe, this species is known to be introduced through ballast water transport (Holdich and Pöckl 2007). It was introduced into Lithuania in the 1960’s/70’s and is now widespread in large rivers and lakes throughout the country (Arbaciauskas et al. 2017).
Studies suggest that Obesogammarus crassus has been introduced outside of the Ponto-Caspian basin through the “central corridor of dispersal”, on the following route: Dnieper River to Vistula River to Oder River to Elbe River to Rhine River, and consequently into the Baltic Sea and Western Europe (Bij de Vaate et al. 2002).
This species is not currently in the Great Lakes region but may be elsewhere in the US. See the
point map
for details.
Ecology:
Obesogammarus crassus is a scud native to the Ponto-Caspian basin. Although this species inhabits the limnetic zone in its native region, it is part of the nekton-benthic ecofunctional group (Olenin et al. 2010); thus it can inhabit both benthic and limnetic zones. Obesogammarus obesus prefers soft substrate (sand and mud) and macrophytes (Borza et al. 2017). Obesogammarus crassus lives in oligohaline water bodies; however, it tolerates both fresh and brackish waters (Jazdzewski et al. 2004; Grabowski et al. 2007; Meßner and Zettler 2018). It inhabits a higher range of salinity in its native range (12–34 ppt) than its nonindigenous range (<0.5–19 ppt) (Holopainen et al. 2016; Paiva et al. 2018). Favorable conditions for O. obesus osmoregulation are greatest in a salinity of around 7 psu, relative to 3.4 or 0.3 psu, but individual abundance did not differ between any of the concentrations in the Baltic Sea (Dobrzycka-Krahel and Graca 2018). It can tolerate oxygen levels lower than 2 mg/L O2, temperatures up to 30° C, and salinities between 0 and 20 psu (Santagata et al. 2008; Olenin et al. 2010).
Obesogammarus crassus is an omnivorous dietary generalist (Bij de Vaate et al. 2002; Hänfling et al. 2011). Juveniles (<7 mm) are primarily detritivores/algivorous, and adults (>7mm) are omnivorous (consuming plants and other invertebrates equally) (Berezina et al. 2017). Due to its ability to tolerate various oxygen levels, temperature, salinity, and its flexible diet, it is predicted that it can inhabit a broad range of ecological living conditions (Bij de Vaate et al. 2002). Obesogammarus crassus has a relatively short life span and generation time (Bij de Vaate et al. 2002). It does not grow rapidly, but has an early sexual maturity. The female carries the eggs in a brood pouch and the average brood size is 25.33 (Kurandina 1975). This species has a breeding period of 7 months and has an average of 3 generations per year. Compared to other amphipods that have extended geographical ranges into Central Europe from either the Ponto-Caspian basin or North America, Obesogammarus crassus has intermediate fecundity (Grabowski et al. 2007).
Means of Introduction:
Obesogammarus crassus has a moderate probability of introduction to the Great Lakes (Confidence Level: High) Potential Pathway(s): Transoceanic shipping (ballast water)
Currently, this species has not been found near waters connected to the Great Lakes, although it occurs in waters that have direct trade connections with the Great Lakes, such as the Baltic Sea (Sala et al. 2000; NBIC 2009). Ballast water may be a potential vector for the introduction of Obesogammarus crassus (Ricciardi and Rasmussen 1998). It should be noted that where Obesogammarus crassus is introduced, it is frequently inoculated in high numbers by ballast water exchange (Grabowski et al. 2007). The distribution of this species has already spread extensively beyond its native range; it has been introduced to western European waters via ballast water transport (Holdrich and Pöckl 2007). However, Obesogammarus crassus experiences complete mortality under flow through, full strength seawater for 24 hours (Santagata et al. 2008). It was also stocked into freshwater basins Ukraine, Modlavia, and Lithuania in the 1950’s and 1960’s as a food source for fishes (Konopacka and Jazdzewski 2002).
Status:
Not established in North America, including the Great Lakes Obesogammarus crassus has a high probability of establishment if introduced to the Great Lakes (Confidence Level: High).
Due to its ability to tolerate a broad range of oxygen levels, temperatures, salinities, and its flexible omnivorous diet (See Ecology), it is very likely that Obesogammarus crassus will establish if introduced to the Great Lakes. Where established, Obesogammarus crassus, has outcompeted various native species (Bij de Vaate et al. 2002). Furthermore, the Great Lakes climate is similar to that of this species’ native range in the Ponto-Caspian basin. The salinity, oxygen level, and temperature in the Great Lakes is suitable for the survival of Obesogammarus crassus. Because this species can tolerate waters with salinities as low as 0 psu, it is likely able to survive the freshwaters of the Great Lakes. The Caspian and Black Seas temperature ranges from 12.1° to 16.1°C, while that of the Great Lakes ranges from 5.9° to 13.7°C (U.S. EPA 2008). It has established populations in the Vistula Lagoon, Poland which freezes over in winter and is eutrophic (Dobrzycka-Krahel and Graca 2018). Due to the wide temperature and salinity tolerances of this species, it is likely to benefit from environmental changes predicted for the Great Lakes due to the effects of climate change. Most of the nonindigenous species that have been established in the Great Lakes since 1985 are native to the Ponto-Caspian region (Ricciardi and MacIsaac 2000).
Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...
Environmental | Socioeconomic |
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Obesogammarus crassus has the potential for high environmental impact if introduced to the Great Lakes. Where established, Obesogammarus crassus, has outcompeted various native species (Bij de Vaate et al. 2002). The presence of Obesogammarus crassus, Pontogammarus robustoides, and Dreissena polymorpha in the Curonian Lagoon resulted in a severe reduction in the relative abundance of the former community and even population extinction within the ecosystem (Zaiko et al. 2011). However, the species identity of the populations that faced extinction is unknown. Whether the introduction of Obesogammarus crassus alone caused the reduction in the relative abundance of the former community is not specified. Where it is introduced, there is a significant reduction in native species, especially in the Curonian Lagoon (Zaiko et al. 2011). The relative abundance of the species that dominated the former community was significantly reduced. The populations of certain species faced extinction within this particular community. In the lower and upper reaches of the Pripyat River, Obesogammarus crassus comprises 80% of the total species abundance (Semenchenko and Vezhnovetz 2008). In the Vistula estuary, O. obesus was the dominant gammarid, comprising 41% of individuals recorded in 2009–2011. No native gammarids were recorded during this time (Dobrzycka-Krahel et al. 2019).
There is little or no evidence to support that Obesogammarus crassus has the potential for significant socio-economic impacts if introduced in the Great Lakes.
Establishment of Obesogammarus crassus has not been known to cause a hazard or threat to human health, damage to infrastructure, or negative impacts on water quality. It has not been documented that this species is detrimental to markets or economic sectors, recreational activities or associated tourism, or the perceived aesthetic or natural value of the areas it inhabits.
There is little or no evidence to support that Obesogammarus crassus has the potential for significant beneficial effects if introduced in the Great Lakes.
It was historically stocked in some areas and is reportedly a food source for many species of farmed fish (Szaniawska 2018), but there are no reports concluding that it has any significant value as a prey for wild or farmed fish.
Management:
Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.* *Ballast water regulations applicable to this species are currently in place to prevent the introduction of nonindigenous species to the Great Lakes via shipping. See Title 33: Code of Federal Regulations, Part 151, Subparts C and D (33 CFR 151 C) for the most recent federal ballast water regulations applying to the Great Lakes and Hudson River.
Note: Check federal, state/provincial, and local regulations for the most up-to-date information.
Control
Biological
There are no known biological control methods for this species.
Physical
In an experiment performed by Santagata et al. (2008), Obesogammarus crassus experienced 100% mortality after 3 hours with empty-refill ballast water exchange and after 24 hours with flow-through exchange with full strength seawater.
Chemical
There are no 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.
References
(click for full reference list)
Author:
Li, Jane S. , C. Patel, and A. Bartos
Contributing Agencies:
Revision Date:
8/27/2021
Citation for this information:
Li, Jane S. , C. Patel, and A. Bartos, 2024, Obesogammarus crassus (G.O. Sars, 1894): 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=3615&Potential=Y&Type=2&HUCNumber=DGreatLakes, Revision Date: 8/27/2021, 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.