PARENT SESSION
Poster Session #23: Fish, Lakes, Streams, and Wetlands.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
113
Ontogenetic variation in the effects of crayfish in a warmwater stream benthic community.
HOEKSTRA, JON1, SOLUK, DANIEL1, 1
ABSTRACT- Variation in the size structure of populations may alter interspecific interactions and influence community structure. For example, juvenile and adult crayfish differ in their diet and in other ecologically important traits. We used an in situ experiment to contrast the effects of adult and juvenile crayfish (Orconectes propinquus) on other benthic stream invertebrates. The following treatments were maintained for 20 days in 0.25 m2 flow-through cages: exclosure, ambient (accessible to crayfish), adult-only (1 male), juvenile-only (6 young of year), and enclosure (1 adult + 6 juveniles). Crayfish likely influenced the abundance of other invertebrates through a mixture of trophic and nontrophic effects; sediment accumulation was reduced by 50-80 percent in cages with crayfish compared with exclosures (P<0.05). Macroinvertebrate density was 29 percent lower in enclosures than in exclosures (P<0.05). Densities of Chironomidae, Tabanidae, and Elmidae were reduced in the presence of crayfish, whereas Caenidae and Heptageniidae showed positive responses to some crayfish treatments. Adult-only and juvenile-only treatments generated equivalent effects on most responses, an unexpected result given known differences between the size classes in diet and predatory efficiency. Combined effects of juveniles and adults in enclosures were generally weaker than predicted given the magnitude of adult-only and juvenile-only effects. In addition, juvenile growth rates were lower in enclosures than in juvenile-only cages (P<0.05), suggesting that adults interfered with juveniles in enclosure cages.
KEY WORDS: ontogenetic variation, predation, bioturbation, Decapoda