Gammarus tigrinus -

The Tiger scud is native to brackish North American waterways with salinities ranging from 1 to 20-25 PSU ^{[2, 3]}. Its natural range extends from the St. Lawrence River in Quebec to Florida. The species is common or dominant on the bottom in intertidal areas. It prefers large, still, or slow-moving bodies of water ^[4] and soils covered with reed grass, hard substrate or sand ^{[2, 3]}.

First observation in Belgium

It has long been assumed that the first Tiger scud collected in Belgium came from the ‘Grote Put van Ekeren’ (Antwerp) in April 1996 ^[5]. However, this species turned out to be widespread in water samples taken in 1991 from four different canals in De Kempen ^[6]. However, its presence was not previously established as the samples were only identified at the genus level. This made it impossible to distinguish them from the native amphipods, such as Gammarus duebeni or Gammarus pulex ^[6].

Spreading in Belgium

The Tiger scud is characterised by a broad tolerance to salt and occurs in Flanders in water with a salt concentration between 0.03 and 9.6 PSU ^[7]. By way of comparison, the seawater of the North Sea has a salinity of about 35 PSU. Its tolerance to different salinities has helped the Tiger scud become the most common amphipod in Flanders today ^[7-9]. Since 1999, it has been found in almost all polder waters in Flanders. In the study area, the Tiger scud is also found along the Ghent-Terneuzen Canal and brackish polder waters ^[10]. No data is available on the recent distribution (past five years).

Spreading in neighbouring countries

In 1931, the Tiger scud was discovered in the brackish English waterways around Droitwich and Coventry (near Birmingham). These individuals were used to officially describe the species ^[11].

Based on testimonies from fishermen in Lough Neagh (Northern Ireland) who claimed that amphipods damaged their nets, scientists suspected that this species was already present in Ireland before 1931. If so, it would have been introduced into Ireland’s Bann River via ballast water from American ships during World War I. Today, the Tiger scud dominates Northern Ireland’s waterways of Lough Neagh, Lough Erne and the mouth of the River Bann ^[4].

In 1957, English individuals were bred in Germany and deliberately released into the German Weser River and its source river, the Werra, to replace the indigenous amphipod that had disappeared due to salt pollution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{[3, 12]}. These Tiger scuds migrated in 1967 via the mouth of the Weser and the mouth of the Ems to the Baltic Sea, where they have been found since 1979 ^{[3, 13]}. The species benefits from the low salinity of the Baltic Sea. Since 2005, this amphipod occupied the Vistula Lagoon (between Poland and Russia), the Bay of Puck and the Gulf of Finland ^[14]. In 2003, Gammarus tigrinus was found for the first time in the north of the Baltic Sea, where it is still expanding its range ^[15-19].

The initial introduction into Europe took place before 1931, probably via the ballast water of transport ships ^[4]. Also, subsequent deliberate introductions have taken place, such as in Germany, where they tried to replace the indigenous amphipods that had disappeared due to pollution ^[12], or in the Netherlands, as a result of a scientist’s misjudgement, where it was thought that the species could not survive in the wild ^[20].

How the Tiger scud has reached Belgian waters is still a matter of conjecture ^[26]. The species might have reached the Belgian waterways from the Netherlands via the Meuse or the Zuid-Willemsvaart Canal ^[5]. There are two hypotheses for the introduction into the Grote Put of Ekeren. A first possibility is that the Tiger scud was imported together with fish from the Netherlands. An alternative hypothesis is that recreational divers or water birds that had been diving in Dutch waters brought unwittingly this non-native species with them during a subsequent dive in the Grote Put of Ekeren ^[5].

In comparison to some of our native species (Gammarus duebeni and Gammarus zaddachi ^[7]), the Tiger scud has a short life cycle and it is already mature after one and a half months. Moreover, adult specimens can reproduce up to 16 times a year and thus produce several generations in one season. Our native species, on the other hand, need up to six months to mature. The first generation of the year – born in spring – can therefore reproduce at the earliest in autumn. Since temperatures are lower in autumn, the eggs will develop slower. Moreover, the specimens that are already mature in spring only have one to four reproductive cycles per year ^[12].

In addition, the Tiger scud is characterised by a high salt tolerance: at optimal temperatures, the species can survive in salinities of between 0.3 and 11 PSU ^[27]. Some scientists even state that the species can tolerate salt concentrations of up to 29.5 PSU ^[12]. By comparison, the seawater of the North Sea has a salinity of about 35 PSU. They are also more resistant to low concentrations of oxygen and varying temperatures ^{[28, 29]} compared to the two native species ^{[7, 12, 22]}. At the same time, Tiger scuds have less difficulty surviving in polluted areas or areas heavily influenced by human activities. As these areas are becoming more common, this too reduces the relative success of our native species ^[30].

These two factors – rapid reproduction and broad tolerance to environmental conditions – make it easy for the Tiger scud, like many other non-native species, to establish and thrive

Thanks to its broad salt tolerance, the Tiger scud can survive in both fresh and brackish waters. Previous reports stating that this species cannot reproduce in extremely freshwater ^[12] are disputed, as the species can be abundant in freshwater ^[31].

Its tolerance to a variety of salt concentrations may have had an important influence on its distribution pattern in Flanders, where the salinity of the water has decreased over the past 20 years. The Tiger scud was found increasingly often and in greater numbers in water where the salinity had decreased. Some authors claim that the decline in native populations is related to this decrease in salinity, and to a lesser extent to competition with the Tiger scud ^[7].

After the introduction of the Tiger scud, native amphipods in the Rhine, Dutch waterways and Baltic Sea had a hard time surviving ^{[12, 22]}. The Tiger scud has a competitive advantage: it can reproduce faster and is more resistant to a variety of environmental factors. Moreover, this omnivore can feed on smaller native amphipods ^{[12, 14]}. Since predator-prey relationships are very important, the arrival of the Tiger scud has a major impact on the ecosystem. Not only does its prey experience higher predator stress, but the original predators experience a decrease in their food source, causing a decline in their populations too. Thus, the influence of a single species spreads through the entire food web ^[32].

The Tiger scud has had both a positive and a negative impact on fisheries. After its introduction in Germany and the Netherlands, the species was used as fish food ^[33]. A disadvantage is the damage that Tiger scuds cause to fishing nets ^{[12, 21]}.

When the Germans introduced the Tiger scud into the Weser river in 1957, they unwittingly brought an unwelcome guest with them. The parasite Paratenuisentis ambiguus was present inside the Tiger scud. The parasite’s primary hosts are eels and they only make use of the Tiger scud to complete its reproductive cycle ^[34]. In German rivers and lakes, this parasite has been found to cause problems for eels

The Tiger scud is a relatively small amphipod (4 to 11 mm) ^[35] and feeds primarily by filtering organic material from the water column. As an omnivore, it consumes animals, plants, algae and dead organic material ^[14].

The name tigrinus refers to the somewhat darkly striped pattern in freshly caught individuals. However, this striped pattern quickly disappears when the animals are preserved in formaldehyde or alcohol, which makes it no easy task to distinguish the smaller specimens from other species of amphipod ^[5]. During the summer phase, adult male specimens can be recognised by the presence of frizzled hairs on their antennae, legs and hind protrusions ^{[11, 21]}.

[1]          World Register of Marine Species (WoRMS) (2020). Gammarus tigrinus Sexton, 1939. [http://www.marinespecies.org/aphia.php?p=taxdetails&id=102296] (2020-11-17).

[2]          Kelly, D.W.; Maclsaac, H.J.; Heath, D.D. (2006). Vicariance and dispersal effects on phylogeographic structure and speciation in a widespread estuarine invertebrate. Evolution 60(2): 257-267. [www.vliz.be/en/imis?module=ref&refid=205863]

[3]          Kelly, D.W.; Muirhead, J.R.; Heath, D.D.; Maclsaac, H.J. (2006). Contrasting patterns in genetic diversity following multiple invasions of fresh and brackish waters. Mol. Ecol. 15(12): 3641-3653. [http://www.vliz.be/en/imis?module=ref&refid=205876]

[4]          Costello, M.J. (1993). Biogeography of alien amphipods occurring in Ireland, and interactions with native species. Crustaceana 65(3): 287-299. [www.vliz.be/en/imis?module=ref&refid=205695]

[5]          Vercauteren, T.; Wouters, K.; Van de Poel, D. (1999). Eerste melding van de Tijgervlokreeft (Gammarus tigrinus Sexton, 1939) in België. Berichten over macrofauna en biol. kwal. v. oppervlaktewateren in de Prov. Antwerpen 11: 1-9. [www.vliz.be/en/imis?module=ref&refid=206084]

[6]          Messiaen, M.; Lock, K.; Gabriels, W.; Vercauteren, T.H.; Wouters, K.; Boets, P.; Goethals, P.L.M. (2010). Alien macrocrustaceans in freshwater ecosystems in the eastern part of Flanders (Belgium). Belg. J. Zool. 140(1): 30-39. [http://www.vliz.be/en/imis?module=ref&refid=206040]

[7]          Boets, P.; Lock, K.; Goethals, P.L.M. (2011). Shifts in the gammarid (Amhipoda) fauna of brackish polder waters in Flanders (Belgium). J. Crust. Biol. 31(2): 270-277. [http://www.vliz.be/en/imis?module=ref&refid=211034]

[8]          Boets, P.; Brosens, D.; Lock, K.; Adriaens, T.; Aelterman, B.; Mertens, J.; Goethals, P.L.M. (2016). Alien macroinvertebrates in Flanders (Belgium). Aquat. Invasions 11(2): 131-144. [http://www.vliz.be/en/imis?module=ref&refid=285591]

[9]          Boets, P.; Brosens, D.; Lock, K.; Adriaens, T.; Aelterman, B.; Mertens, J.; Goethals, P.L.M. (2016). Alien macro-invertebrates in Flanders, Belgium [https://www.gbif.org/dataset/3c428404-893c-44da-bb4a-6c19d8fb676a]

[10]        Boets, P.; Lock, K.; Goethals, P.L.M. (2011). Using long-term monitoring to investigate the changes in species composition in the harbour of Ghent (Belgium). Hydrobiologia 663(1): 155-166. [http://www.vliz.be/en/imis?module=ref&refid=201947]

[11]        Sexton, E.W. (1939). On a new species of Gammarus (G. tigrinus) from Droitwich Disctrict. J. Mar. Biol. Ass. U.K. 23(2): 543-551. [http://www.vliz.be/en/imis?module=ref&refid=205864]

[12]        Pinkster, S.; Smit, H.; Brandse-de Jong, N. (1977). The introduction of the alien amphipod Gammarus tigrinus Sexton, 1939, in the Netherlands and its competition with indigenous species. Crustaceana, Suppl. 4: 91-105. [http://www.vliz.be/en/imis?module=ref&refid=206041]

[13]        Gollasch, S.; Nehring, S. (2006). National checklist for aquatic alien species in Germany. Aquat. Invasions 1(4): 245-269. [http://www.vliz.be/en/imis?module=ref&refid=142431]

[14]        Grigorovich, I.A.; Kang, M.; Ciborowski, J.J.H. (2005). Colonization of the Laurentian Great Lakes by the amphipod Gammarus tigrinus, a native of the North American Atlantic Coast. J. Great Lakes Res. 31(3): 333-342. [http://www.vliz.be/en/imis?module=ref&refid=206039]

[15]        Grabowski, M.; Konopacka, A.; Jazdzewski, K.; Janowska, E. (2006). Invasions of alien gammarid species and retreat of natives in the Vistula Lagoon (Baltic Sea, Poland). Helgol. Mar. Res. 60(2): 90-97. [http://www.vliz.be/nl/catalogus?module=ref&refid=100420]

[16]        Herkül, K.; Kotta, I.; Kotta, J.; Orav-Kotta, H. (2006). Effects of physical disturbance, isolation and key macrozoobenthic species on community development, recolonisation and sedimentation processes. Oceanologia 48S: 267-282. [http://www.vliz.be/nl/catalogus?module=ref&refid=296767]

[17]        Paavola, M.; Laine, A.O.; Helavuori, M.; Kruafvelin, P. (2008). Profiling four brackishwater harbours: zoobenthic composition and invasion status. Boreal Env. Res. 13: 159-175. [http://www.vliz.be/nl/catalogus?module=ref&refid=296768]

[18]        Kotta, J.; M., P.; T., K.; Lehtiniemi, M.; Malavin, S.A.; Reisalu, G.; Panov, V.E. (2013). Is a rapid expansion of the invasive amphipod Gammarus tigrinus Sexton, 1939 associated with its niche selection: a case study in the Gulf of Finland, the Baltic Sea. Aquat. Invasions 8(3): 319-332. [http://www.vliz.be/nl/catalogus?module=ref&refid=296769]

[19]        Herkül, K.; Lauringson, V.; Kotta, J. (2016). Specialization among amphipods: The invasive Gammarus tigrinus has narrower niche space compared to native gammarids. Ecosphere 7(6). [http://www.vliz.be/nl/catalogus?module=ref&refid=296773]

[20]        Nijssen, H.; Stock, J.H. (1966). The amphipod, Gammarus tigrinus Sexton, 1939, Introduced in the Netherlands (Crustacea). Beaufortia 13(160): 197-206. [http://www.vliz.be/en/imis?module=ref&refid=206039]

[21]        Stock, J.H.; Nijssen, H. (1967). De ingevoerde vlokkreeft, Gammarus tirinus Sexton, 1939, krijgt vaste voet in Nederland. Het Zeepaard 27(1): 2-5. [http://www.vliz.be/en/imis?module=ref&refid=115130]

[22]        Szaniawska, A.; Lapucki, T.; Normant, M. (2003). The invasive amphipod Gammarus tigrinus Sexton, 1939 in Puck Bay. Oceanologia 45(3): 507-510. [http://www.vliz.be/en/imis?module=ref&refid=114365]

[23]        Pinkster, S.; Scheepmaker, M.P.C.; Platvoet, D.; Broodbakker, N. (1992). Drastic changes in the amhipod fauna (Crustacea) of Dutch inland waters during the last 25 years. Bijdr. Dierkd. 61(4): 193-204. [http://www.vliz.be/en/imis?module=ref&refid=205909]

[24]        Van Riel, M.C.; van der Velde, G.; Rajagopal, S.; Marguillier, S.; Dehairs, F.; bij de Vaate, A. (2006). Trophic relationships in the Rhine food web during invasion and after establishment of the Ponto-Caspian invader Dikerogammarus villosus. Hydrobiologia 565(1): 39-58. [www.vliz.be/en/imis?module=ref&refid=206042]

[25]        Ba, J.; Hou, Z.; Platvoet, D.; Zhu, L.; Li, S. (2010). Is Gammarus tigrinus (Crustacea, Amphipoda) becoming cosmopolitan through shipping? Predicting its potential invasive range using ecological niche modeling. hydrobiologia 649(1): 183-194. [http://www.vliz.be/nl/catalogus?module=ref&refid=296771]

[26]        Kerckhof, F.; Haelters, J.; Gollasch, S. (2007). Alien species in the marine and brackish ecosystem: the situation in Belgian waters. Aquat. Invasions 2(3): 243-257. [http://www.vliz.be/en/imis?module=ref&refid=114365]

[27]        Savage, A.A. (1982). The survival and growth of Gammarus tigrinus Sexton (Crustacea: Amphipoda) in relation to salinity and temperature. Hydrobiologia 94: 201-212. [http://www.vliz.be/nl/catalogus?module=ref&refid=206054]

[28]        Wijnhoven, S.; Van Riel, M.C.; Van der Velde, G. (2003). Exotic and indigenous freshwater gammarid species: physiological tolerance to water temperature in relation to ionic content of the water. Aquat. Ecol. 37(2): 151-158. [http://www.vliz.be/nl/catalogus?module=ref&refid=58602]

[29]        Lenz, M. (2011). Non-native marine invertebrates are more tolerant towards environmental stress than taxonomically related native species: results from a globally replicated study. Environmental Research 111: 943-952. [http://www.vliz.be/nl/catalogus?module=ref&refid=296776]

[30]        Grabowski, M.; Bacela, K.; Konopacka, A. (2007). How to be an invasive gammarid (Amphipoda: Gammaroidea ) – comparison of life history traits. Hydrobiologia 590(1): 75-84. [http://www.vliz.be/nl/catalogus?module=ref&refid=296783]

[31]        Boets, P. (2019). Persoonlijke mededeling

[32]        Bailey, R.J.; Dick, J.T.; Elwood, R.W.; MacNeil, C. (2006). Predatory interactions between the invasive amphipod Gammarus tigrinus and the native opossum shrimp Mysis relicta. J. N. Am. Benthol. Soc. 25(2): 393-405. [http://www.vliz.be/nl/catalogus?module=ref&refid=296789]

[33]        Piscart, C.; Maazouzi, C.; Marmonier, P. (2008). Range expansion of the North American alien amphipod Gammarus tigrinus Sexton, 1939 (Crustacea: Gammaridae) in Brittany, France. Aquat. Invasions 3(4): 449-453. [http://www.vliz.be/en/imis?module=ref&refid=205888]

[34]        Køie, M. (1991). Swimbladder nematodes (Anguillicola spp.) and gill monogeneans (Pseudodactylogyrus spp.) parasitic on the european eel (Anguilla anguilla). J. Cons. - Cons. Int. Explor. Mer 47(3): 391-398. [http://www.vliz.be/en/imis?module=ref&refid=135845]

[35]        Naylor, M. (2006). Alien species in Swedish seas: Gammarus tigrinus. . Informationscentralerna för Bottniska viken, Egentliga Östersjön och Västerhavet. Sweden. 3 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=207015]

VLIZ Alien Species Consortium (2020). Gammarus tigrinus – Tiger scud. Non-native species of the Belgian part of the North Sea and bordering estuaries anno 2020. Flemish Institute for the Sea (VLIZ). 8 pp.