The dynamics of predation on Gammarus spp. (Crustacea : Amphipoda)

Gammarus spp. (Crustacea: Amphipoda) are widespread throughout a diverse ra nge of marine, freshwater and estuarine/brackish habitats, often dominating benthic macroinvertebrate communities in terms of both numbers and/or biom ass. Gammarus spp. are the dominant macroinvertebrate prey items of many fi sh, whether as a seasonal food source or a year-round staple. Selective pre dation by fish on Gammarus spp, is often linked to parasitism and the body size of the prey. Gammarus spp. populations are under increasing threat fro m both pollution and replacement/displacement by introduced species. Loss o f populations and species invasions/replacements could have significant imp acts on native predator species if the predator(s) cannot successfully adap t their feeding patterns to cope with non-indigenous Gammarus prey species. Despite this, many fish predation studies do not identify Gammarus prey to species level. This lack of precision could be important, as Gammarus spp, exhibit wide variations in physiochemical tolerances, habitat requirements , abilities to invade and susceptibility to replacement. Although rarely ac knowledged, the impacts of nonpiscean predators (particularly macroinverteb rates) on Gammarus prey species may frequently be stronger than those exert ed by fish. A major aim of this review is to ascertain the current importan ce of Gammarus as a prey species, such that the implications of changes in Gammarus spp, populations can be more accurately assessed by interested gro ups such as ecologists and fisheries managers. We also review the dynamics of Gammarus spp. as prey to a diverse array of mammals, birds, amphibians, insects, flatworms, other crustaceans such as crabs and crayfish and, perha ps most importantly, other Gammarus spp.