Behavior of Gammarus aequicauda (Crustacea, Amphipoda) during predation on Artemia (Crustacea, Anostraca): New experimental results

Gammarus aequicauda and Artemia spp. are abundant crustacean species in Crimean hypersaline lakes. G. aequicauda preys on Artemia but there was no quantitative data on this before the current study. Predation of G. aequicauda on adult Artemia was studied in experiments with two different approaches evaluating (a) the time balance of the feeding process and (b) the grazing intensity. The threshold prey concentration, when consumption began to increase with increasing concentration, was approximately 15 ind./L in 200-ml vessels and about 5 ind./L in 500-ml vessels. When the Artemia abundance reached 20–25 ind./L, there was no further influence on the gammarid consumption rate. There was a significant negative correlation between the consumption rate of gammarids and Artemia abundance. According to study results, an individual G. aequicauda may eat up to 20–24 Artemia/day. Our study suggests that (a) G. aequicauda is an omnivorous species and can significantly suppress populations of its prey. (b) The two experimental approaches used to study the feeding of gammarids on Artemia produced similar results, and both may be used to quantitatively assess relations in a “prey–predator” system. (c) The abundance of predators and prey, as well as the experimental vessel volume, may influence the feeding rate. (d) The presence of plant food resources such as the leaves of Ruppia does not influence on the predatory feeding rate of G. aequicauda. (e) The rate of prey consumption by G. aequicauda is not constant and depends nonlinearly on prey and predator abundance. (f) Cannibalism occurs in the presence of plant resources only, but not in the presence of Artemia. (g) Other gammarids react to the capture of Artemia by one of them. They swim up to the successful individual and try to take some part of the prey.