Great Lakes Impacts: Hemimysis anomala has moderate environmental impact in the Great Lakes H. anomala has a broader, more flexible diet than other zooplankton native to the Great Lakes (Evans et al., 2018; Marty et al., 2012). Additionally, this species has higher attack rates and lower prey handling times when compared to native species of Mysis (Dick et al., 2012). These characteristics give them a competitive advantage compared to native zooplankton species, and may affect the characteristics of plankton assemblages in the Great Lakes. In a mesocosm experiment, H. anomala predation selected for larger daphnia (Sinclair et al., 2016).
Potential:
Ponto-Caspian mysids differ from the North American mysid, Mysis relicta, in their adaptation to warmer temperatures (Bondarenko and Yablonskaya 1979). Therefore, H. anomala could become abundant in many areas of the Great Lakes, including littoral zones that are currently devoid of mysids. However, increased water clarity in shallow waters may instead inhibit such migration (Ricciardi et al. in press).
Based on its impacts in some European reservoirs (Ketelaars et al. 1999), H. anomala may reduce zooplankton biomass and diversity in invaded areas, with cladocerans, rotifers, and ostracods being most affected. Hemimysis anomala may compete with, or prey upon, other invertebrate predators, such as Bythotrephes longimanus and Leptodora kindti. Its omnivory may also reduce local phytoplankton if small-sized juvenile mysids are abundant (Ketelaars et al. 1999); however, phytoplankton biomass typically increases (sometimes doubling) in lakes following mysid invasions (Borcherding et al. 2006). It is not known whether plankton consumption by H. anomala affects other planktivorous organisms. Dumont and Muller (2010) remarked that there was no decrease in zooplanktonic hydra (Pelmatohydra oligactis) or juvenile roach (Rutilus rutilus) in areas with large H. anomala densities, although this evidence was largely anecdotal. In general, lake productivity seems to influence the degree of mysid impact, with less productive, nutrient-poor lakes being more affected by the competition and predation following mysid invasions (Ricciardi et al. in press).
Hemimysis anomala feeds rapidly, even at low prey densities, and its fecal pellets may alter the local physico-chemical environment (Ketelaars et al. 1999, Olenin and Leppäkoski 1999, Pienimäki and Leppäkoski 2004). A mysid introduction can also increase the biomagnification of contaminants in piscivores through a lengthening of the food chain; for example, concentrations of polychlorinated biphenyls and mercury in fishes have been shown to be higher in lakes containing mysids than in mysid-free lakes (Cabana et al. 1994, cf. Rasmussen et al. 1990). Furthermore, through direct transmission and indirect effects on the food web, introduced mysids may cause increased parasitism by nematodes, cestodes, and acanthocephalans in fishes (Lasenby et al. 1986, Northcote 1991).
There is little or no evidence to support that Hemimysis anomala has significant socio-economic impacts in the Great Lakes.
There is little evidence to support that Hemimysis anomala has significant beneficial effects in the Great Lakes.
Hemimysis anomala is considered a high-energy food source due to its lipid content, which can increase growth rates for planktivores (Borcherding et al. 2006). However, the nutritional value of H. anomala can vary depending on the food source and trophic position of the individual (Marty et al. 2010). A recent caloric density analysis in Lake Ontario indicates that H. anomala appears to be a lower quality food source than native mysid M. diluviana but higher than most zooplankton (Walsh et al. 2010).
In many regions, including the Great Lakes basin, perch (Perca spp. and Morone americana) is known to feed on H. anomala, as is rock bass (Ambloplites rupestris) (Brooking et al. 2010, Lantry et al. 2010). In Lake Ontario, recent surveys indicated that H. anomala was a predominant food item of alewife (Alosa pseudoharengus), an important forage fish, in the sampled area (Lantry et al. 2010). Moreover, stable isotope analysis suggests that H. anomala may be replacing zooplankton in the diet of young yellow perch (Yuille et al. in press). It appears that as H. anomala density increases, this species plays a more substantial role in supporting higher trophic levels (Yuille et al. in press).
However, the net effect of this new prey item on its predators’ populations in the Great Lakes is currently unknown. In some lakes, mysid (Mysis spp.) introductions have preceded the increased growth of salmonids; in contrast, in other lakes they are associated with rapid declines in abundance and productivity of pelagic fishes (Lasenby et al. 1986, Langeland et al. 1991, Spencer et al. 1991). Through its predation on benthic invertebrates and detritus, H. anomala could become a significant part of the local benthic food web in areas containing appropriate habitat and shelter for H. anomala (Kestrup and Ricciardi 2008). Furthermore, analysis of carbon and nitrogen stable isotopes indicate that H. anomala may obtain carbon from both littoral and pelagic sources, potentially linking these two zones in the food web (Marty et al. 2010).