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

Abstract

Summary We investigated differences in the abundance, community composition and taxon richness of sublittoral macroinvertebrates in boreal lakes containing introduced invasive signal crayfish (Pacifastacus leniusculus) or native noble crayfish (Astacus astacus). We hypothesised that sublittoral macroinvertebrate assemblages in lakes containing noble crayfish, which reportedly prefer the shallow littoral, would differ little from those in lakes without crayfish, in contrast to assemblages in lakes containing signal crayfish, which reportedly forage at greater depths. In a set of 24 small and medium‐sized Finnish lakes, eight lakes contained signal crayfish, eight had noble crayfish and eight control lakes had no crayfish. At three sites per lake, we sampled macroinvertebrates quantitatively from soft sediment in the sublittoral. The sublittoral macroinvertebrate assemblage in lakes with noble crayfish and control lakes was similar. In contrast, lakes with signal crayfish had a lower density of Trichoptera and Ephemeroptera, as well as a lower density and species richness of Chironomidae, and a lower overall benthic density and taxon richness. In contrast to some previous reports from other habitats, we infer that introduced signal crayfish have stronger negative effects than native noble crayfish on sublittoral macroinvertebrates. Hence, the ecological equivalence or differences of crayfish species cannot be generalised across habitats.

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.…”

“…The results of this temporal study were generally consistent with our previous findings from largescale spatially replicated space-for-time studies in Lake Päijänne (Bjurström et al, 2010;Ruokonen et al, 2014) and in other boreal lakes Ercoli et al, 2015) The overall mean benthic macroinvertebrate densities were similar at the crayfish and non-crayfish sites throughout the study years 2007−2011, as found previously (Bjurström et al, 2010;Ruokonen et al, 2014). 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.…”

“…Signal crayfish were introduced to the Padasjoki study site in 1990, and the population reproduces naturally and supports an important recreational and commercial fishery in the area. The sampled crayfish site is located in the most productive signal crayfish area in Finland representing a regionally high crayfish density (Erkamo et al, 2010;Ruokonen et al, 2014;Ercoli et al, 2015). We selected one additional site at Saalahti (61 • 55 N, 25 • 26 E) where signal crayfish had been recently introduced.…”

“…Studies at various temporal and spatial scales in experimental set-ups, streams and lakes have shown that non-native crayfish can have direct and indirect detrimental effects on benthic macroinvertebrate abundance and species richness, and on snails (Gastropoda) in particular (Nyström, 1999;Twardochleb et al, 2013;Ruokonen et al, 2014;Ercoli et al, 2015). However, few studies (Wilson et al, 2004;McCarthy et al, 2006;Kreps et al, 2012;Hansen et al, 2013;Mathers et al, 2016) have examined the effects of invasive crayfish using data collected over multiple years.…”

The long-term effects of invasive signal crayfish (Pacifastacus leniusculus) on instream macroinvertebrate communities

“…Studies documenting the effect of invasive crayfish in stream ecosystems have identified significant reductions in the biomass and richness of aquatic macrophytes Nyström et al, 2001), and aquatic invertebrates Stenroth and Nyström, 2003;Crawford et al, 2006;Nilsson et al, 2012;Ercoli et al, 2015b).…”