Effects of an Omnivorous Crayfish (Orconectes Rusticus) on a Freshwater Littoral Food Web

Abstract

Cascading trophic interactions are important in many freshwater pelagic food webs, but their importance in more complex, omnivore—rich littoral—zone food webs is less well known. We tested the existence of a trophic cascade involving omnivorous crayfish (Orconectes rusticus), macroinvertebrates, periphyton, and macrophytes using 9—m2 cages in the littoral zone of Plum Lake, Wisconsin, USA. Treatments in the replicated (N = 4) experiment were crayfish enclosures, crayfish exclosures, and cageless references. During June—September, we measured macrophyte shoot numbers, macroinvertebrate numbers, and periphyton (on plastic strips) chlorophyll a, and dry mass (DM). We expected that crayfish foraging would directly reduce abundance and change species composition of macrophytes and macroinvertebrates and would indirectly enhance periphyton abundance by reducing the abundance of grazing snails. In enclosures, macrophyte and snail (but not nonsnail macroinvertebrate) densities declined significantly throughout the experiment, whereas densities of macrophytes, snails, and nonsnail macroinvertebrates increased in exclosures and cageless references. Some of the reduction in macrophytes resulted from nonconsumptive fragmentation of macrophytes by crayfish. Consistent with the cascading trophic interactions model, periphyton chlorophyll a per unit surface area increased in enclosures, but declined in exclosures. Periphyton quality (as indexed by chlorophyll a/DM) also increased in enclosures relative to exclosures and cageless references. However, because of large reductions in macrophyte surface area (which periphyton colonizes) in enclosures, total amount of periphyton chlorophyll a in enclosures (relative to exclosures) probably declined while periphyton quality per unit surface area and periphyton quality increased. Thus, the impacts of crayfish omnivory on periphyton, expressed in two conflicting indirect effects, confirm the possibility that omnivory can complicate cascading trophic predictions. Overall, results support the existence of strong trophic interactions in the littoral zone, in which omnivorous crayfish control abundance of macrophytes, snails, and periphyton.

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

“…The high predation level of sediment-dwelling Chironomid larvae in the crayfish treatments (81 to 87%) is likely to be higher than in natural environments due to the relatively shallow depth of sediment in the pools, and therefore less opportunity to escape predation. As slow moving species, snails are highly vulnerable to crayfish predation (Lodge et al, 1994;. This was apparent in the current study, with the exception of B. tentaculata which increased in abundance, presumably as a consequence of reproduction by adults, or perhaps hatching of eggs present on plants at the start of the experiment.…”

Comparing the ecological impacts of native and invasive crayfish: could native species’ translocation do more harm than good?

“…Charlebois and Lamberti 1996; Nyström et al 2001;Bobeldyk and Lamberti 2010). This would be expected as crayfish are known to prey heavily upon algivorous snails (Lodge et al 1994;Parkyn et al 1997;Nyström et al 2001;Bjurström 2009), thereby releasing algae from grazing pressure and facilitating primary production. There are still too few examples to provide a quantitative test of the generality of this phenomenon, highlighting the need for empirical studies to include the effects of crayfish on multiple related ecosystem components.…”

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).…”