Grazing by a native and an exotic crayfish on aquatic macrophytes

Abstract

1. We compared grazing by native noble crayfish (Astacus astacus) and the exotic signal crayfish (Pacifastacus leniusculus) on seedling or well‐established macrophytes. 2. In a pool experiment, seedlings of emergent Scirpuslacustris and floating‐leaved Potamogetonnatans were heavily grazed by adult signal crayfish, whereas established plants of the same species sustained only minor damage. 3. In a preference experiment two submerged macrophytes (Charavulgaris and Elodeacanadensis), and both seedlings and established plants of S. lacustris and P. natans, were presented pairwise to signal and noble crayfish. There was no significant difference in preference by the two crayfish species. Chara vulgaris was preferred to all other plants presented, established plants of S. lacustris and P. natans were never preferred, and seedlings of P. natans were preferred to established P. natans. 4. An aquarium experiment was conducted in which the consumption of Chara by signal and noble crayfish was measured in relation to water temperature. Signal crayfish consumed significantly more Chara than noble crayfish, especially at higher temperatures. 5. Our results indicate that the signal crayfish is the more voracious grazer especially at higher temperatures. There may be negative effects on vegetation (emergents and floating‐leaved, as well as submerged species) when the signal crayfish is introduced. Chara species are particularly susceptible, since they are preferred by crayfish and the genus includes a large number of rare species. Stocking of crayfish therefore could lead to the decline or removal of submerged species in order of crayfish feeding preferences and could prevent the spread or cause a decline of emergent and floating‐leaved vegetation.

Size-dependent impacts of the endangered white-clawed crayfish (Austropotamobius pallipes) (Lereboullet) on the littoral community

“…Presence of crayfish of Astacus sp. has been associated with reduction in submerged macrophytes (Nyström and Strand, 1996;Nyström et al, 1999), reduced biomass of grazers, particularly gastropods, and shifts in community composition towards predatory invertebrates (Nyström et al, 1999). Some crayfish species are also significant bioturbators, modifying sediment transport and increasing turbidity (Harvey et al, 2011;Johnson et al, 2011), with indirect effects on algae and macrophyte cover (Dorn and Wojdak, 2004;Usio et al, 2009).…”

The Within-Catchment Invasion of the Non-Indigenous Signal Crayfish Pacifastacus Leniusculus (Dana),in Upland Rivers

“…Through a combination of large size, broad feeding habitats and high densities attained, their introduction to new habitats can have a significant impact on the aquatic environment (NYSTRÖM and STRAND, 1996;NYSTRÖM, 2002;DORN and WOJDAK, 2004). The introduction of North American crayfish species into Europe has been partially responsible for severe declines in indigenous European species (HENTTONEN and HUNER, 1999;HOLDICH, ROGERS and REYNOLDS, 1999) through a combination of transfer of crayfish plague Aphanomyces astaci and competitive displacement of native European species.…”

A review of ecological interactions between crayfish and fish, indigenous and introduced

“…High populations and activity of signal crayfish may have negative impacts on resident fish. Signals directly predate on small fish such as stone loach and bullhead (Guan and Wiles, 1997), and on fish fry (Rubin and Svensson, 1993), while alteration of invertebrate communities (Crawford et al, 2006) and cropping of macrophytes by crayfish may put themselves and other denizens at risk (Lodge and Lorman, 1987;Hart, 1993, 1995;Matthews et al, 1993;Nyström and Strand, 1995). Studies have shown that predatory fish interfere with crayfish survival, activity and food consumption, e.g.…”