Patterns in benthic food webs: a role for omnivorous crayfish?

Abstract

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty‐one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment‐dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte‐associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.

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

“…The most widely cited taxa affected by invasive crayfish colonisation are gastropods and bivalves, with reductions in species richness, abundances and biomass widely reported (Weber and Lodge, 1990;Nyström et al, 1996;Stenroth and Nyström, 2003;Dorn, 2013;Ruokonen et al, 2014). Results from this study indicate a significant effect of crayfish on Radix spp.…”

“…The establishment of populations of invasive species within an ecosystem can severely disrupt the structure and functioning of native floral and faunal communities through direct predation, competition and displacement of native species, but also via indirect pathways and the decoupling of trophic dynamics (Nyström et al, 1996;Strayer, 2010;Gutierrez et al, 2014).…”

“…Indirect effects may also be evident within the ecosystem with a removal of macrophyte and algae cover affecting invertebrate populations through the loss of trophic resources and habitat availability Nyström et al, 1996).…”

Socio-economic drivers and non-indigenous freshwater crayfish species in Europe

“…Therefore, indirect metabolic rifts are continuously created by the spread of NICS through direct impacts on ICS and other aquatic biota and structural modification of habitats (i.e. consumption of aquatic macrophyte, bank erosion and undermining as well as substrate disturbance) (Nyström et al, 1996), affecting both biodiversity and the integrity of the ecosystems. Path models for the protection of ICS involving continuous monitoring of both ICS and NICS distribution range, habitat restoration, re-establishment efforts, designation of no-go areas, ark sites and species protection areas (SPAs), prevention of further spread of NICS and 'plague', augmented legislation and better enforcement policies, transboundary co-operation, public education and increased research efforts (see for instance Taugbøl andSkurdal, 1999 andHoldich et al, 2009) have been already proposed.…”

Crayfish Predation Experiments on the Introduced Zebra Mussel, Dreissena Polymorpha, in Ireland, and Their Potential for Biocontrol.

“…Some are known to be keystone predators in aquatic systems LODGE et al, 1994 ;NYSTROM et al, 1996 ;STEWART et al, 1996). Significant impacts on the benthic community have been demonstrated in both laboratory and field studies MATTHEWS et al, 1993).…”