Small-humped scud, Dikerogammarus villosus balatonicus Ponyi, Gammarus haemobaphes

This species can be distinguished from other Dikerogammarus species by morphological features of the second (lower) pair of antennae and of the first and second urosomal segments. In D. haemobaphes, the peduncle and flagellum of antenna 2, as well as the gnathopods, are characterized by short bristles rather than dense, long bristles. Urosomes 1 and 2 of D. haemobaphes have a shallow dorsal protuberance tipped with two spines instead of the pointed dorsal protuberance seen in other species of Dikerogammarus. Additionally, in contrast to the morphologically similar D. villosus, no color variation is exhibited by this species (Müller et al. 2002). However, these distinguishing features apply mainly to adult males and are less diagnostic in females and juveniles.

Adult male: average 16 mm (range 9–21 mm); adult female: average 11 mm (range: 7–15 mm); stage 2 egg: average 0.43 mm (Bacela et al. 2009; Kinzler et al. 2009).

Nonindigenous occurrences: Widespread in Europe in inland and coastal brackish waters (Bij de Vaate et al. 2002) and is established in the North and Baltic Seas (Casties et al. 2016). Dikerogammarus haemobaphes was first reported in the United Kingdom in 2012 (Gallardo and Aldridge 2015).

Dikerogammarus haemobaphes is a dietary generalist (Bij de Vaate et al. 2002), feeding on detritus, sediments, unicellular and filamentous algae, and other small crustaceans. Its predation intensity on animal food sources such as chironomids, oligochaetes, crustaceans, and mayflies increases during the summer months when water temperatures are higher (van der Velde et al. 2009). Cannibalism within this species is significantly higher (~50%) than that of other European gammarid species (Kinzler et al. 2009).

Dikerogammarus haemobaphes is frequently found in association with another Ponto-Caspian mass invader, Dreissena polymorpha, preferring to settle on living zebra mussel shells over other substrate types (Muskó 1993; 1993; Bij de Vaate et al. 2002; Wawrzyniak-Wydrowska and Gruszka 2005; Kobak et al. 2009). Dreissenid shell surface properties are thought to attract D. haemobaphes, with a distinct preference shown for living mussels over empty shells as well as clean shells over varnished shells (Kobak and Zytkowicz 2007). Additionally, the living mussel shells serve as a better habitat for prey items, including chironomids (Botts et al. 1996; Ricciardi et al. 1997; Stewart et al. 1998; Mörtl and Otto-Rothhaupt 2003). Dikerogammarus haemobaphes also consumes mussel detritus (Verstijnen et al. 2019). There was also a positive correlation between D. bugenis and D. haemobaphes in deep-water areas (>3m) of Volga River reservoirs (Kurina and Seleznev 2019).

The reproductive period of D. haemobaphes lasts from April to October, with the production of spring, summer, and autumn (overwintering) generations, each with 3–5 cohorts (Bacela et al. 2009; Kurina 2017). The autumn (overwintering) generation begins to reproduce in April, and by mid May its progeny (spring generation) appear. At this point, population size structure is strongly bimodal due to the presence of the parental generation. In June, the spring generation begins to reproduce and the autumn generation dies off. In early July, the summer generation is released and rapidly matures, giving rise to the next autumn generation. As in many other gammarid species, mean size of mature individuals, mean size of breeding females, and fecundity declines over subsequent generations (autumn to spring to summer) (Muskó 1993; Bacela et al. 2009).

Male to female sex ratios are generally close to 1:1, with intersex individuals (able to both lay and fertilize eggs in a brood pouch) representing roughly 1% of the population (Bacela et al. 2009). The maturity index (minimal size/mean size of gravid females) of D. haemobaphes is low (~0.67), indicating this species reaches maturity at a relatively young age. Clutch size varies from 5 to 128 eggs, with mean estimates ranging from 20–52 eggs (Kurandina 1975;  Kititsyna 1980; Muskó 1993; Bacela et al. 2009). Clutch size has been observed to increase with female body length according to a log-linear relationship, with both clutch and body size varying in different habitats (e.g., mean brood sizes of 35 and 52 in river and reservoir populations, respectively) (Bacela et al. 2009). The partial fecundity index (mean clutch size/mean breeding female size) for D. haemobaphes reported in this same study is relatively high, with values of 3.3 for river females and 4.3 for reservoir females. These variations in size and fecundity based sampling location are possibly due to differences in predation pressure and/or hydrological conditions such as water velocity (Adams et al. 1989).

Potential pathway(s) of introduction: Trans-oceanic shipping (ballast water)

Dikerogammarus haemobaphes has been proposed to be able to survive partial to complete ballast water exchange due to one reported natural occurrence in 17 ppt salinity waters (Grigorovich et al. 2003), but other estimates of this species’ salinity tolerance are more restrictive (0—8 ppt) (Holopainen et al. 2016). Based on the former, Grigorovich et al. (2003) assessed D. haemobaphes as having a high Great Lakes invasion risk mediated by both BOB and NOBOB vessels. However, the closely related European invader D. villosus, which has a higher salinity tolerance, exhibited 0% survival after 24 hours in 34 PSU empty-refill and flow-through salinity treatments (Santagata et al. 2008), suggesting that D. haemobaphes may be similarly impacted by current ballast water regulations.

Dikerogammarus haemobaphes has a high probability of establishment if introduced to the Great Lakes (Confidence level: Moderate).

It is a Ponto-Caspian amphipod identified as having high probability of invasion if introduced to the Great Lakes (Ricciardi and Rasmussen 1998; Grigorovich et al. 2003; U.S. EPA 2008); listed as invasive in Baltic Sea. The climatic conditions of the native (Ponto-Caspian) and introduced (Baltic) ranges of D. haemobaphes are very similar to those of the Great Lakes. While D. haemobaphes is able to survive in moderately wide temperature and salinity ranges, as well as hypoxic conditions, it is primarily a freshwater, riverine species (see Ecology). Its westward spread through all major European river systems connecting the Ponto-Caspian with the Baltic may have been limited by salinity levels to inland water courses (see Bij de Vaate et al. 2002). Nevertheless, its physiological tolerances are well within conditions occurring in the Great Lakes. Increased salinization as a potential effect of climate change (Rahel and Olden 2008) may be inconsequential to this species’ establishment in the Great Lakes, as it tolerates salinities up to 8 ppt (Holopainen et al. 2016). Arbaciauskas (2002) hypothesized that oxygen concentration is the principal limiting factor in determining the survival and sustainability of populations of Ponto-Caspian amphipods. Therefore, anoxic conditions, as present in the central basin of Lake Erie (Summers 2001), may prevent D. haemobaphes from establishing in some regions of the Great Lakes. Dikerogammarus haemobaphes constitutes a food base for multiple fish genera (Kelleher et al. 1998; Kostrzewa and Grabowski 2003; Grabowska and Grabowski 2005), though the extent to which this predation will have an effect on potential populations in the Great Lakes is unknown.

Feeding plasticity, high reproductive capacity, relatively small eggs, short egg development time, fast sexual maturation, brooding, and production of multiple generations per year are factors thought to contribute to the invasion success of this species (Bij de Vaate et al. 2002; Bacela et al. 2009). Dikerogammarus haemobaphes fecundity is moderate compared to that of the invasive gammarids D. villosus and P. robustoides (Bacela et al. 2009), but it is high in relation to invasive European gammarids as a group (Grabowski et al. 2007a). The autumn generation typically overwinters, but in thermally polluted waters (e.g., hydroelectric cooling water discharge), this species may reproduce year round (Kiticyna 1980); therefore, warming waters as a result of climate change could be beneficial to its invasion success.

Invasive dreissenid mussels are likely to facilitate the establishment of D. haemobaphes in the Great Lakes, as this amphipod preferentially colonizes living zebra mussel shells over other substrate types, including empty shells and stones, in the Ponto-Caspian and other newly invaded regions. It also consumes the detritus of dreissenid mussels (see Ecology).

The dispersal rate of D. haemobaphes across Europe is similar to that of many other Ponto-Caspian invasive amphipods (e.g., D. villosus), spreading across the entire European continent in roughly 50 years (Bij de Vaate et al. 2002). Dikerogammarus haemobaphes has outcompeted and displaced native European gammarids, but has also experienced declines in European waterways following expansion of congeneric amphipod Dikerogammarus villosus (Jazdzewski et al. 2004, 2005; Kinzler et al. 2009), which is believed to be the superior competitor and invader to D. haemobaphes (Dodd et al. 2014).  For example, D. haemobaphes spread slowly up the Sava river (0.9 km/yr) and was quickly overtaken and displaced by D. villosus (Žganec et al. 2018). However, there is evidence to suggest that the two species may be able to coexist in environments with sufficient habitat. The expansion of D. haemobaphes in the River Danube was not greatly affected by D. villosus due to the abundance of both high and low velocity habitats, suggesting potential co-existence of the species as they can inhabit varying velocities (Borza et al. 2017). More information on the relationship between the two species is needed to determine if the establishment of D. haemobaphes in the Great Lakes would be diminished by D. villosus. Recent studies have found both positive and negative relationships between the two gammarids. Dikerogammarus haemobaphes perceives the chemical stimuli of D. villosus as a threat and avoids it. In contrast,  D. villosus is attracted to the alarm cues of D. haemobaphes and follows it, which displaces both species further and can actually enhance the spread of D. haemobaphes (Kobak et al. 2016; Rachalweski et al. 2019).

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

Environmental	Beneficial

There is little or no evidence to support that Dikerogammarus haemobaphes has the potential for significant socio-economic impacts if introduced to the Great Lakes.

No socio-economic impacts of Dikerogammarus haemobaphes have been documented within its European and invaded ranges.

There is little or no evidence to support that Dikerogammarus haemobaphes has the potential for significant beneficial effects if introduced to the Great Lakes.

Dikerogammarus haemobaphes constitutes a food base for perches, gobies, and eels (Kelleher et al. 1998; Kostrzewa and Grabowski 2003; Grabowska and Grabowski 2005). It was intentionally stocked in large European rivers prior to the 1970s to enhance the fish fauna (Jazdzewski 1980; Bij de Vaate et al. 2002).

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
There are no known physical control methods for this species

Chemical
The following control methods have been reported for the congeneric D. villosus, and thus will likely be effective for D. haemobaphes as they have similar environmental tolerances. Dikerogammarus villosus is highly sensitive to fluoride toxicity, and is expected to have low invasion risk in freshwater systems with 1.5 mg F-/L (10x the average background level) (Gonzala et al. 2010). Carbonated water led to narcosis in all D. villosus specimens within a few seconds (Sebire et al. 2018).
Hot water and steam are highly effective at controlling D. villosus. Immersion in 40°C water for 10 seconds led to 100% mortality of D. villosus (Shannon et al. 2018). Alternatively, a 90°C hot water spray 10 cm away for a duration of 5 seconds resulted in 100% mortality of D. villosus (Bradbeer et al. 2021). Steam (>100°C) killed all D. villosus within 10 seconds and 3 broad-spectrum disinfectants killed all specimens within 120 seconds at the lowest dose (1%) and in 15 seconds for the highest dose (4%) (Bradbeer et al. 2020). However, all of these methods are likely to result in the death of many non-target organisms.

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