Consumption of macroinvertebrates by invasive and native gammarids: a comparison

Abstract

The Ponto-Caspian gammarids Dikerogammarus villosus SOVINSKIJ and Echinogammarus ischnus STEBBING have invaded Central-European streams in the early 1990s. Declines in macroinvertebrates have been observed since the arrival of invasive species. To elucidate the predatory impact of gammarids on the macroinvertebrate community, we conducted laboratory experiments with macroinvertebrate prey taxa and native and invasive gammarids as predators. Dikerogammarus villosus, which is known to be a strong predator, consumed more and a broader range of prey than E. ischnus or the native gammarids, Gammarus pulex L. and Gammarus roeseli GERVAIS. Echinogammarus ischnus consumed a somewhat higher amount of prey organisms than G. pulex and a higher number and a broader range than G. roeseli. Adult D. villosus consumed up to 25 mg macroinvertebrate biomass (wet weight) per day which corresponds to approximately 1/3 of their own biomass. Chironomid larvae were preferred by all gammarids tested. Taking into account that gammarids density may surpass 1000 ind m-2, our results suggest that the predatory behaviour of invasive gammarids, in particular of D. villosus, may have contributed to the decline of some macroinvertebrate taxa in some European streams

Density and temperature dependent feeding rates in an established and an alien freshwater gammarid fed on chironomid larvae

“…This assumption is supported by earlier investigations, in which D. villosus showed a remarkable broad prey spectrum encompassing macro-invertebrates from various taxonomic groups (Dick et al 2002;van Riel et al 2006). Gammarus roeselii instead seems to be limited to more soft-bodied invertebrates, such as some dipteran larvae (Krisp & Maier 2005). However, results of weighing of males and females indicated that D. villosus specimens are slightly heavier than G. roeselii specimens of the same size (Fig.…”

“…Coincidently with the arrival of D. villosus a decline of several native macro-invertebrates, including native and established gammarids such as Gammarus roeselii Gervais, 1835, was observed Kley & Maier 2006;van Riel et al 2006). Laboratory studies suggested that D. villosus is markedly carnivorous feeding on a variety of prey types from different taxonomic groups (Dick et al 2002;Krisp & Maier 2005). Isotope analyses even suggested that D. villosus could be placed on the same trophic level as some fish species (Marguillier 1998).…”

“…More recent investigations of feeding ecology, morphology and biomarkers have shown that freshwater gammarids are omnivorous, feeding on a variety of food (Dick 1996;MacNeil et al 1997;Dick & Platvoet 1996, 2000Krisp & Maier 2005;Platvoet et al 2006;Maazouzi et al 2007;Mayer et al 2008). Although omnivory seems widespread in freshwater gammarids, differences in preferred food types or feeding modes seem likely.…”

“…Although numerous investigations demonstrated that, besides feeding on leaves and detritus, freshwater gammarids are cannibals and predators (e.g., reviewed in MacNeil et al 1997) little is known about the quantity of prey one gammarid can consume per time unit. Krisp & Maier (2005) studied the consumption rate of four gammarid species at high prey density and observed that each individual of these gammarids consumed prey of approximately one third of its own biomass per day.…”

“…We chose chironomid larvae since these belong to the preferred prey organisms of gammarids and since they are consumed entirely (Dick et al 2002;Krisp & Maier 2005). Our expectation was that feeding rate is particularly high in the invasive D. villosus since this species is known to exert a high impact on native food webs (van Riel et al 2006).…”