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1 March 2005 The effects of 2 coexisting crayfish on an Appalachian river community
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Crayfish can act as keystone species and ecosystem engineers in small streams, but their effects in large rivers are not well known. Two species of crayfish, Orconectes cristavarius and Cambarus chasmodactylus, coexist in the South Fork of the New River in western North Carolina. We used gut-content analyses and an enclosure–exclosure experiment to investigate the influence of both species of crayfish on sediment accumulation and benthic invertebrates. Crayfish guts contained mostly sediment and vegetative detritus. However, C. chasmodactylus guts contained significantly more detritus and animal matter than O. cristavarius guts, and O. cristavarius guts contained significantly more sediment than C. chasmodactylus guts. In the field experiment, sediment volume was lower in open baskets and cage controls, which were exposed to crayfish and benthic-feeding fish, than in enclosures containing only crayfish. Sediment volume was highest in fish/crayfish exclosures. Despite their effect on sediment accumulation, crayfish did not significantly affect the density of any invertebrate taxon. No clear relationship was found between chironomid density and enclosure–exclosure treatment, but chironomid density was positively correlated with sediment volume. Damselflies (Calopteryx maculata) tended to be more abundant in crayfish enclosures than in open treatments and cage controls, and cyclopoid copepods tended to be more abundant in O. cristavarius enclosures than C. chasmodactylus enclosures. The significant differences in the diets of the 2 species of crayfish were not associated with differences in their effects on invertebrates. Our results suggest that these 2 species of crayfish may be functionally redundant in this community, despite differences in diet. Furthermore, the lack of pronounced crayfish effects on invertebrate taxa suggests that the effects of crayfish may not be as strong in large rivers as in small streams.

Brian S. Helms and Robert P. Creed "The effects of 2 coexisting crayfish on an Appalachian river community," Journal of the North American Benthological Society 24(1), 113-122, (1 March 2005).<0113:TEOCCO>2.0.CO;2
Received: 22 May 2003; Accepted: 5 November 2004; Published: 1 March 2005

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