Feeding behaviour, predatory functional responses and trophic interactions of the invasive Chinese mitten crab (Eriocheir sinensis) and signal crayfish (Pacifastacus leniusculus)

Abstract

SUMMARY1. Freshwaters are subject to particularly high rates of species introductions; hence, invaders increasingly co-occur and may interact to enhance impacts on ecosystem structure and function. As trophic interactions are a key mechanism by which invaders influence communities, we used a combination of approaches to investigate the feeding preferences and community impacts of two globally invasive large benthic decapods that co-occur in freshwaters: the signal crayfish (Pacifastacus leniusculus) and Chinese mitten crab (Eriocheir sinensis). 2. In laboratory preference tests, both consumed similar food items, including chironomids, isopods and the eggs of two coarse fish species. In a comparison of predatory functional responses with a native crayfish (Austropotamobius pallipes), juvenile E. sinensis had a greater predatory intensity than the native A. pallipes on the keystone shredder Gammarus pulex, and also displayed a greater preference than P. leniusculus for this prey item. 3. In outdoor mesocosms (n = 16) used to investigate community impacts, the abundance of amphipods, isopods, chironomids and gastropods declined in the presence of decapods, and a decapod >gastropod >periphyton trophic cascade was detected when both species were present. Eriocheir sinensis affected a wider range of animal taxa than P. leniusculus. 4. Stable-isotope and gut-content analysis of wild-caught adult specimens of both invaders revealed a wide and overlapping range of diet items including macrophytes, algae, terrestrial detritus, macroinvertebrates and fish. Both decapods were similarly enriched in 15 N and occupied the same trophic level as Ephemeroptera, Odonata and Notonecta. Eriocheir sinensis d 13 C values were closely aligned with macrophytes indicating a reliance on energy from this basal resource, supported by evidence of direct consumption from gut contents. Pacifastacus leniusculus d 13C values were intermediate between those of terrestrial leaf litter and macrophytes, suggesting reliance on both allochthonous and autochthonous energy pathways. 5. Our results suggest that E. sinensis is likely to exert a greater per capita impact on the macroinvertebrate communities in invaded systems than P. leniusculus, with potential indirect effects on productivity and energy flow through the community.

Predatory impacts of alien decapod Crustacea are predicted by functional responses and explained by differences in metabolic rate

“…Predicting and explaining predatory impacts of alien decapod Crustacea 2831 leniusculus also had a higher maximum feeding rate than A. pallipes on all prey items, in accord with previous studies using G. pulex as prey (Haddaway et al 2012;Rosewarne et al 2016) and the general pattern emerging from FR studies in invasion ecology (Dick et al 2017). However, this difference was only significant on chironomid prey, and differences were generally small in magnitude (up to 1.3 times higher in P. leniusculus) relative to the differences observed between E. sinensis and the two crayfish species.…”

“…Rosewarne et al (2016) reported that E. sinensis had a higher FR than P. leniusculus and A. pallipes. However, we demonstrate that relative impact of E. sinensis may be much greater than previously thought, with an attack coefficient up to 6.7 times, and maximum feeding rate up to 3.0 times, that of a similarly sized crayfish (Table 2).…”

“…For example, E. sinensis had an especially high maximum feeding rate on amphipods: at least 2.9 times greater than the crayfish. Accordingly, in mesocosm experiments amphipods were the only prey group that E. sinensis affected more strongly than P. leniusculus (Rosewarne et al 2016). Amphipods and other motile taxa may be amongst the least affected by crayfish in the field (Crawford et al 2006;Mathers et al 2016), so we would expect their FRs to be low.…”

“…Evidence from mesocosms and field manipulations suggests E. sinensis may cause similar declines in macroinvertebrate populations through predation (Yu and Jiang 2005;Rudnick and Resh 2005;Rosewarne et al 2016). However, our knowledge of these predatory impacts and their underlying mechanisms remains incomplete, especially for E. sinensis (Rosewarne et al 2016).…”

“…More recent advancement of E. sinensis populations has created zones of overlap with P. leniusculus, and sympatry between E. sinensis and A. pallipes is also possible (Rosewarne et al 2016). Thus, it is important to understand the relative ecological impacts of these species to appreciate how ecosystems have changed (or might change) as these species meet and replace each other.…”