In its native habitat (Rhine River), Apocorophium lacustre is found in lower littoral and sublittoral regions and on boulder (10-50 cm diameter) substrate (Faasse and van Moorsel 2003). Distribution patterns suggest that A. lacustre is associated with greater depths and faster water velocity (Krodkiewska et al. 2020). In the Upper Mississippi River, A. lacustre was found associated with hard, stable substrates such as rocks and snags; in the Ohio River, where cobble and boulder habitats were less available, it colonized primarily sand and snags. This species is epibenthic and typically associated with inorganic substrates, aquatic vegetation, or zebra mussel colonies (Grigorovich et al. 2008).

Scuds are found in waters with DO ranging from 1.2-6.9 mg/L (Llansó and Sillett 2009). Apocorophium lacustre is described as salt-tolerant (Evans et al. 2004), from 0-30 ppt (Wolf et al. 2009), and euryhaline, but it tends to be found in the least saline environments (Faasse and van Moorsel 2003). A. lacustre has been observed in areas with mean water temperatures as low as 1°C and as high as 31.4°C (Harmeson and Schnepper 1965; Llansó and Sillett 2009).

Food Web

Apocorophium lacustre is a detritus, suspension, and surface-deposit feeder (Llansó and Sillett 2009; Power et al. 2006) making it a moderately dietary generalist with a flexible diet. Gut content analysis indicates that its diet is composed of bacteria, protozoa, algae, and detritus (Quebbeman and Keller 2023). A. lacustre is a suitable prey item for many aquatic predators, from the micro-predator flatworm Euplana gracilis to the shovelnose sturgeon Scaphirhynchus platorynchus (Seibert et al. 2011; Janiak et al. 2017). A. lacustre has the potential to alter food webs through competition with native mussels for food and habitat (USACE 2013; Barrera et al. 2020).

Life History

Apocorophium lacustre reproduces sexually and is sexually dimorphic, with males larger than females. The male locates potential partners using antennae to detect pheromones, riding or carrying the female until she is ready to molt (Ruppert et al. 2004). Like other amphipods, A. lacustre broods its young in the marsupium, a strategy associated with enhanced colonization success. Embryos brood on the female’s underside and hatch out as crawling juveniles (USACE 2013). Individuals undergo a maximum of 20 molts and have a one-year-long life cycle (Ruppert et al. 2004).