Effects of an invasive crayfish on trophic relationships in north‐temperate lake food webs

Abstract

Summary 1. The introduction of invasive species is one of the main threats to global biodiversity, ecosystem structure and ecosystem processes. In freshwaters, invasive crayfish alter macroinvertebrate community structure and destroy macrophyte beds. There is limited knowledge on how such invasive species‐driven changes affect consumers at higher trophic levels. 2. In this study, we explore how the invasive rusty crayfish Orconectes rusticus, a benthic omnivore, affects benthic macroinvertebrates, as well as the broader consequences for ecosystem‐level trophic flows in terms of fish benthivory and trophic position (TP). We expected crayfish to decrease abundance of benthic macroinvertebrates, making most fish species less reliant on benthic resources. We expected crayfish specialists (e.g. Lepomis sp. and Micropterus sp.) to increase their benthic dependence. 3. In 10 northern Wisconsin lakes, we measured rusty crayfish relative abundance (catch per unit effort, CPUE), macroinvertebrate abundance, and C and N stable isotope ratios of 11 littoral fish species. We used stable isotope data and mixing models to characterise the trophic pathways supporting each fish species, and related trophic structure to crayfish relative abundance, fish body size and abiotic predictors using hierarchical Bayesian models. 4. Benthic invertebrate abundance was negatively correlated with rusty crayfish relative abundance. Fish benthivory increased with crayfish CPUE for all 11 fish species; posterior probabilities of a positive effect were >95%. TP also increased slightly with crayfish CPUE for some species, particularly smallmouth bass, largemouth bass, rock bass and Johnny darter. Moreover, both fish body size and lake abiotic variables explained variation in TP, while their effects on benthivory were small. 5. Rusty crayfish abundance explained relatively little of the overall variation in fish benthivory and TP. Although rusty crayfish appear to have strong effects on abundances of benthic macroinvertebrates, energy flow pathways and trophic niches of lentic fishes were not strongly influenced by invasive rusty crayfish.

Comparing the effects of introduced signal crayfish and native noble crayfish on the littoral invertebrate assemblages of boreal lakes

“…This result is consistent with a study by Ruokonen et al (2014) who found that macroinvertebrate density was not reduced by invasive signal crayfish in large boreal lakes. However, our results differ from those reported by Nilsson et al (2012) who found that macroinvertebrate abundance was negatively affected by invasive rusty crayfish (Orconectes rusticus) in 10 Wisconsin lakes. This discrepancy might be accounted for by the generally low abundance of crayfish in boreal lakes (CPUE typically <<10 individuals; Erkamo et al 2010, Sandström et al 2014, including our study lakes (Table S1), compared to the large catches of O. rusticus typically reported from North American lakes (Kreps et al 2012, Nilsson et al 2012.…”

The introduced signal crayfish and native noble crayfish have different effects on sublittoral macroinvertebrate assemblages in boreal lakes

“…These results are consistent with those of a spatial comparative study by Ruokonen et al (2014) from Lake Päijänne, which found that signal crayfish affected macroinvertebrate community composition and strongly reduced species richness, and snail density and richness. Moreover, they found comparable overall macroinvertebrate densities between crayfish and noncrayfish sites in line with results in IV but in contrast with previous studies (Nilsson et al 2012, Twardochleb et al 2013. Although snail richness showed temporal stability between sites, macroinvertebrate and snail densities indicated crayfish status effects through the years studied.…”

Are the effects of an invasive crayfish on lake littoral macroinvertebrate communities consistent over time?

“…Even though this contrasts with some previous studies Nilsson et al, 2012;Twardochleb et al, 2013), Ercoli et al (2015) found no differences in littoral benthic macroinvertebrate densities between smaller Finnish lakes with crayfish and without crayfish, suggesting any effect of signal crayfish on overall numerical abundance of littoral benthic macroinvertebrates in boreal lakes is probably weak.…”