Status: Not established in North America, including the Great Lakes. Dikerogammarus villosus has a high probability for establishment if introduced to the Great Lakes (Confidence level: Moderate).
Dikerogammarus villosus has not yet been recorded in the Great Lakes, but this species has a history of successful invasions throughout Europe (Devin et al. 2001). In addition to a physiology that facilitates ballast water transport (relatively wide temperature and salinity tolerance), this species possesses many advantageous life history traits conducive to successful invasions, including: short generation time, rapid growth rate, female-biased sex ratio, early sexual maturity, high fecundity, brooding, production of multiple generations per year, exceptional predatory and competitive capabilities, ecological plasticity, and large size compared to related species (Dick and Platvoet 2000; Bruijs et al. 2001 Bij de Vaate et al. 2002; Wijnhoven et al. 2003; Devin et al. 2004). These characteristics, combined with abundant potential food sources, make D. villosus a species expected to have high potential for spread if introduced to the Great Lakes ecosystem (Ricciardi and Rasmussen 1998; Dick and Platvoet 2000; MacIsaac et al. 2001; Dick et al. 2002; Grigorovich et al. 2003; Devin et al. 2003, 2004). Its propagule pressure during the shipping season (May-October) is likely to be high, as this period overlaps with D. villosus’ reproductive peak (May/June) (Pöckl 2009). Following introduction, this species is also likely to spread by hitchhiking on recreational gear, boats, or trailers, as was a probable vector for its introduction to Lake Garda, Italy (Casellato et al. 2006).
Sieracki et al. (2014) described D. villosus as having a high invasion probability in ports of all 5 Great Lakes and is predicted to become rapidly widespread once introduced (Sieracki et al. 2014). The dispersal rate of this species across Europe is similar to that of many other Ponto-Caspian invasive amphipods (e.g., Dikerogammarus haemobaphes), spreading across the entire European continent in roughly 50 years (Bij de Vaate et al. 2002). Its spread and establishment in Great Britain is attributed to genetic founder effects and enemy release as invading shrimp had no parasites or predators to inhibit their expansion relative to their native range (Arundell et al. 2015).
In its invaded range in Europe, D. villosus has highly variable and unpredictable individual activity patterns relative to indigenous gammarids (Gammarus fossarum, G. pulex, and G. roseli) which promotes its invasion success by coping with new environmental conditions (Bierbach et al. 2016). In a laboratory experiment, Dikerogammarus villosus relied on a potential predator's diet rather than its species as a cue to avoid predation, thus likely facilitating their recognition of allopatric predators and increasing survival in newly invaded habitat (Jermacz et al. 2017b). This species also sustains its growth rate despite long-term predator presence due to its highly efficient anti-predator strategies (Jermacz et al. 2017a), including a harder exoskeleton, better shelter utilization, aggregation techniques, and enhanced metabolic sustainability while minimizing oxidation damage (Jermacz and Kobak 2018; Mennen and Laskowski 2018; Jermacz et al. 2020). Dikerogammarus villosus also exhibits variable morphology and coloration (Nesemann et al. 1995), which could facilitate its concealment and establishment in new environments.
Climatic conditions (e.g., temperature, precipitation, seasonality) and abiotic factors (e.g., pollution, water temperature, salinity, pH, nutrient levels and current) relevant to the success of D. villosus in its native and introduced ranges are similar to those in the Great Lakes. Kurikova et al. (2016) lists D. villosus as having high invasive potential to the Great Lakes based on climate-match data with their native range. Kramer et al. (2017) reports intermediate values of niche centrality for D. villosus in the Great Lakes, which indicates that climate conditions often, but not completely overlapped with its predicted niche. This species also is able to greatly reduce its oxygen demand at temperatures around 1°C, making it likely to overwinter in the Great Lakes (Wijnhoven et al. 2003; Becker et al. 2016).
Increased water temperature as a result of climate change is likely to enhance breeding, as has been observed with its relative D. haemobaphes (Kititsyna 1980). Despite D. villosus having broad environmental tolerances, particularly with respect to high salinity, it is not known to survive in waters warmer than 35°C and may not typically survive prolonged exposure to temperatures in excess of 27°C (Bruijs et al. 2001; Wijnhoven et al. 2003; van der Velde et al. 2009; Maazouzi et al. 2011). In contrast, food intake increased significantly for females as temperatures increased from 15–25°C due to a decrease in food handling time, which suggests predation pressure may increase due to climate change (Pellan et al. 2016). Some disparity in reported temperature tolerances for this species could be attributed to the two genetically distinct populations of D. villosus that occur in Europe. The western population has a higher temperature range tolerance and the eastern is more sensitive to sudden changes in temperature. However, there is potential for a new “super-hybrid” to form the two populations that has an even wider range of thermal tolerance and would pose an even bigger invasion threat (Hupalo et al. 2018).
A strong ecological connection exists between D. villosus and other Great Lakes invaders from the Ponto-Caspian, such as Dreissena polymorpha; under the theory of “invasional meltdown,” it has been predicted that invasion of the D. villosus will be facilitated by these companion species (Ricciardi and Rasmussen 1998; Dick and Platvoet 2000, 2002; Devin et al. 2003). For instance, beds of D. polymorpha may facilitate establishment of this large amphipod by providing colonization substrate (Dick et al. 2002; Devin et al. 2003). Dreissena bugensis beds are also a food source and habitat for D. villosus (Verstijnen et al. 2019). This species is also chemically attracted to the waters scented by D. polymorpha and thus the mussels may facilitate their invasion and establishment into new areas (Rolla et al. 2019). In Lake Balaton, Hungary, it uses Phragmites australis leaves as substrate and food source (Karádi-Kovács et al. 2015).