Bythotrephes longimanus has a high environmental impact in the Great Lakes. Bythotrephes reproduce rapidly and consume small zooplankton such as small cladocerans, copepods, and rotifers, potentially competing directly with planktivorous larval fish for food (Berg and Garton, 1988; Evans, 1988; USEPA, 2008; Vanderploeg et al., 1993). At times, its consumption may even exceed that of zooplankton production (Bunnell et al., 2011). Bythotrephes, in combination with zebra mussels, is associated with slower walleye growth. Following invasion by Bythotrephes or zebra mussels, walleye were on average 12% and 14% smaller, respectively, at the end of their first summer, likely due to changes in zooplankton communities (Hansen et al. 2020). It is important to note that predation by Bythotrephes on rotifer predators and competitors has also been shown to reduce both mortality and competition, leading to food web alterations and positive effects on rotifer populations, particularly Conochilus (Pothoven and Vanderploeg 2022; Marshall et al. 2024).
A decline in native cladocerans following the introduction of Bythotrephes has been observed in Lake Huron and Lake Michigan (Barbiero and Tuchman, 2004). In Lake Erie, the detection of Bythotrephes in 1985 was also accompanied by a decline in multiple species of cladocerans (e.g., Eubosmina coregoni, Daphnia mendotae, D. retrocurva), including an almost complete absence of Diaphanosoma spp. wherever Bythotrephes was present in 1986 (Barbiero and Rockwell, 2008). This study further documented a lack of spatial overlap between Bythotrephes and Leptodora (a native water flea). This is in concordance with many other studies which have documented a negative correlation between the abundance of the two species, implying that competition and/or predation from Bythotrephes has played a significant role in declines of Leptodora (e.g., Branstrator, 1995; Fernandez et al., 2009; Foster and Sprules, 2009; Garton et al., 1990; Lehman and Cáceres, 1993; Yan and Pawson, 1997). Interestingly, Leptodora coexists with and often outnumbers Bythotrephes in European lakes, which could be due to higher abundance of available zooplankton prey or lower levels of planktivory in combination with the greater conspicuousness of Bythotrephes (Foster and Sprules, 2009). In Lake Michigan, the decline of D. retrocurva and D. pulicaria populations in contrast to relatively stable populations of D. mendotae has been attributed to the latter’s markedly faster escape responses (Pichlová-Ptácníková and Vanderploeg, 2011).
Some studies have documented an increase in chlorophyll a abundance with the invasion of Bythotrephes, potentially due to a release from grazing following increased predation pressure on zooplankton species (Barbiero and Rockwell, 2009; Hovius et al., 2007). This would imply that Bythotrephes is capable of affecting multiple trophic levels of the freshwater community. However, an increase in Bythotrephes abundance is not always correlated with an increase in chlorophyll a (Foster and Sprules, 2009; Strecker and Arnott, 2008). Notably, Strecker and Arnott (2008) demonstrated that invaded lakes experienced a significant reduction in secondary production, and hence a reduction in resources available in the epilimnion.
In some cases, Bythotrephes has been associated with a shift in cladoceran communities towards larger taxa over small possibly due to Bythotrephes predation of smaller species (Barbiero and Rockwell 2008; Hovius et al. 2007; Yan and Pawson 1997). Vertical migration has also been observed in Daphnia spp. and copepods (e.g., Diacyclops thomasi, Leptomdiaptomus ashlandi, L. minutus) populations following Bythotrephes invasion, indicating that some species may migrate to deeper waters during the day to avoid Bythotrephes predation or competition (Bourdeau et al. 2011; Jokela et al. 2011; Lehman and Cáceres 1993; Arwine et al. 2025). Diel vertical migration may lead to an indirect negative effect on these native prey species, including reduced individual and population growth rates at lower temperatures (Pangle and Peacor, 2006; Pangle et al. 2007).
Potential:
Significant increases in the trophic position of zooplankton (reduced herbivorous cladoceran biomass and increased omnivorous/predatory copepod biomass) and planktivorous fish such as the lake herring (Coregonus artedi) with the introduction of Bythotrephes has the potential to lead to substantial contaminant biomagnification in consumers (Rennie et al., 2011). However, increased mercury concentrations in consumers has not been observed following invasion; this may be attributed to increased foraging and growth efficiencies of consumers or to changes in the feeding habits of omnivorous prey (Rennie et al., 2011).
There is little or no evidence to support that Bythotrephes longimanus has significant socio-economic impacts in the Great Lakes.
The tail spines of Bythotrephes hook on fishing lines, fouling fishing gear. This problem has largely been eliminated with a switch to line/gear types less susceptible to Bythotrephes fouling.
There is little or no evidence to support that Bythotrephes longimanus has significant beneficial effects in the Great Lakes.
Bythotrephes is a food source for fish including yellow perch, white perch, walleye, white bass, alewife, bloater chub, Chinook salmon, emerald shiner, spottail shiner, rainbow smelt, lake herring, lake whitefish, and deepwater sculpin (Branstrator and Lehman 1996; Bur et al. 1986; Makarewicz and Jones 1990). However due to its long tail spine, predation of Bythotrephes is mainly restricted to larger fish and non-gape limited species (Pothoven et al. 2007).