Original paper

Food spectra and consumption rates of four amphipod species from the North-West of Russia

Berezina, Nadezhda

Abstract

Microscopic analysis of the gut contents of four native and invasive gammaridean amphipods Gammarus lacustris, Gammaracanthus loricatus, Gmelinoides fasciatus, Pontogammarus robustoides showed that these species are omnivorous to varying degrees. Mean percentage contribution to the gut content varied significantly between the food categories and between different-sized specimens for all species. Detritus was the major item in guts of juveniles of all species, contributing 70-100 % in entire mass of gut content. Contribution of this food category in guts of adults significantly decreased where proportion of animal food significantly increased. Distinct size-dependent differentiation in food preferences was found for P. robustoides, whereby juveniles are preferably detritivorous, mid-sized specimens choose macrophytes as a favorite food and large specimens are predators. The relationship between consumption rates (CR, %) and wet weight of consumer body was approximated by exponential function. During predation, the diurnal consumption rate of all species ranged between 6 and 63 % of body weight, being the lowest (5-22 %) for the large species G. loricatus. The amount of consumed matter essentially increased when macrophytes (CR = 14-84 %) or detritus (CR = 46-103 %) were offered as food items. The predation index, the difference between losses in number of prey due to predation and the physiological requirements of a predator (G. loricatus case study), increased with an increasing density of prey and reached at maximum 50 %. Significant decreases in daily consumption rates of G. loricatus preying upon oligochaetes, chironomids and small amphipods were obtained at a decrease in prey availability. These results indicate high variability of consumption rates in the amphipods related to type, availability and amount of food.

Keywords

amphipodsgut contentconsumption ratespredatory and non-predatory feedingprey densityfood availability