Tuesday, June 5, 2007 - 11:45 AM
147

Spatial and Temporal Variation in the Effects of Grazing Fish and Crayfish on Benthic Communities During Stream Drying

John P. Ludlam, Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701 and Daniel D. Magoulick, Department of Biological Sciences, USGS, Arkansas Cooperative Fish and Wildlife Research Unit, University of Arkansas, Fayetteville, AR 72701.

Central stonerollers (Campostoma anomalum) and crayfish (Orconectes meeki) inhabit streams in the Boston Mountains of Arkansas in high densities and can have substantial effects on stream ecosystem structure and function through foraging and ecosystem engineering activities.  Seasonal summer drying is extensive in these systems and may alter interactions between grazers and stream benthic communities.  We examined changes in grazer effects on chlorophyll a, ash free dry mass, and chironomid density during drying using electric exclusions in the Little Mulberry River, Arkansas, to manipulate grazer densities on tiles.  Replicate paired exclusion/open treatments were placed in nine pools for two 30 day periods in early and mid summer.  Exclusion increased chlorophyll a 1.44X, and effects were greater in the second period, but differed among pools.  Grazer effects on ash free dry mass were 2.5X to 8.8X greater in period 2 than period 1 in three of eight pools, and treatment effects were significant in two other pools.  Additionally, after drying, chironomid densities were positively affected by grazer exclusion in four pools.  This study provides evidence that grazing organisms can modify algal abundances, sediment deposition, and insect densities, but these effects vary among pools and during the course of stream drying.