Zooplankton of the Great Lakes
Site created by: Ryan Wheeler
Kingdom - Animalia
Suborder - Gammaridea
Also known as: “Scuds”
The genus Gammarus is extremely broad. Its 204 described species represent 67% of the species in the Gammaridae Family. As such, the differences between each species are often minute.
The body of Gammarus fasciatus is laterally compressed, contains 13 segments, and is divided into three sections; pereon, pleosome, and urosome. Its head has two sets of antennae and medium-sized kidney-shaped eyes. The pleosome and urosome each have three pairs of legs and the pereon has seven pairs of legs.
Gammarus fasciatus is distinguished from other similar-looking Amphipods by the presence of accessory flagellum on the first antennae (Figure 1), the absence of dorsal spines (Figure 2), and a sharp angle above the first antennae attachment (Figure 3). Hyallela azteca is very similar in morphology to Gammarus fasciatus and both can be found in the Laurentian Great Lakes (Figure 4)
The Gammarus genus is widely distributed throughout fresh, saline, lentic, and lotic waters within Palearctic and Nearctic climates. (Vainola et al. 2008) However, Gammarus fasciatus is non-native but present in freshwater lakes and streams within the Midwest and Northeastern portions of North America (Vainola et al. 2008)
Gammarus fasciatus is an abundant member of benthic communities in the Great Lakes region and often aggregate amongst Dreissena colonies and areas of abundant detritus material (VanOverdijk et al. 2003)
Gammarus fasciatus is a benthic filter-feeder that primarily feeds on detritus material and live plant matter (Stewart et al. 1998)
Dreissena colonies enhance Gammarus fasciatus feeding by creating spaces between their shells for detritus to collect (Stewart et al. 1998). These spaces also provide protection from Gammarus predators (Stewart et al. 1998). Also, Dreissena excretion increases nutrient availability for benthic algae which eventually become additional food for Gammarus fasciatus (Stewart et al. 1998).
Gammarus fasciatus reproduces sexually during the summer (Kestrup and Ricciardi 2010). The offspring are sexually mature within two months of birth (Kestrup and Ricciardi).
(Figure 1) – Accessory flagellum on first antennae
(Figure 2) – Absence/presence of dorsal spines. Gammarus fasciatus left, Hyallela azteca right.
(Figure 3) – Sharp angle above first antennae
(Figure 4) – Morphological similarities. Gammarus fasciatus left, Hyallela azteca right.
Stewart, T.W., Miner, J.G. & Lowe, R.L. (1998) Quantifying mechanism for zebra mussel effects on benthic macroinvertebrates: Organic matter production and shell-generated habitat. Journal of the North American Benthological Society, 17, 81-94.
Van Overdijk, C.D.A., Grigorovich, I.A., Mabee, T., Ray, W.J., Ciborowski, J.J.H. & Macisaac, H.J. (2003) Microhabitat selection by the invasive amphipod Echinogammarus ischnus and native Gammarus fasciatus in laboratory experiments and in Lake Erie. Freshwater Biology, 48, 567-578.