Macroinvertebrate colonization dynamics on artificial substrates along an algal resource gradient

Riparian canopy removal and land use may introduce multiple stressors that can alter food and habitat for stream organisms, but the influence of these alterations on macroinvertebrate colonization dynamics is less well known. A field study involving the simultaneous placement and removal of artificial substrates was performed to examine how macroinvertebrate colonization rates might vary with algal accumulation within a perennial stream segment in eastern Ohio, USA. The study was conducted over a 60-day summer colonization period in three reaches that were selected to represent an algal resource gradient according to canopy cover and agricultural nutrient sources in the riparian corridor. Total nitrogen, water temperatures, and mean algal biomass from substrates increased along the resource gradient represented by the study sites. Total macroinvertebrate biomass and the abundance and biomass of scrapers also increased according to the gradient. Correlation results indicated that chlorophyll a biomass, rather than time or temperature, was better related to the abundance and biomass of most primary consumers on substrates. These results suggest that the combined effects of elevated temperatures and nutrients can result in relatively rapid algal accrual that may alter the colonization and establishment of macroinvertebrate communities in streams subjected to gradients of riparian disturbances.