Contrasting Effects of Sand Burial and Exposure on Invertebrate Colonization of Leaves

Abstract

Leaf detritus in streams fills dual resource roles as habitat and as food. Unless retained by some structural component, detritus gets transported to downstream reaches out of the local system. Low gradient sandy-bottomed streams retain leaf detritus via burial in sand, but this mechanism of retention limits the availability of detritus as a resource for the benthic community. We hypothesized that burial of leaf litter in sand would impact invertebrate colonization by reducing density and richness on leaf litter. We conducted a short-term experiment (i.e., 2 wk) in a sandy-bottom stream in which leaves were subject to either burial in sandy substrate, exposure to the water column, or a sequential combination of both. Results showed that 2 wk burial of leaf litter significantly impacted the colonization of benthic invertebrates. Burial or exposure status of leaves at the time of collection represented the major factor influencing invertebrate abundances on leaf litter. Leaves exposed to the water column had the highest abundance of invertebrates, dominated by collector-gatherers, that suggests the primary role of leaf litter as refugia in this system. Burial of leaf litter in sand had a significantly negative effect on invertebrate colonization of leaf litter. Furthermore, no difference existed in invertebrate colonization on leaf litter that had never been buried versus leaf litter that had been buried for 1 wk and then exposed and collected after a week in the water column. This suggests short-term burial of leaf litter does not influence colonization by invertebrates once leaf litter is exposed to the water column. The results of this study suggest that the benthic colonization on newly exposed leaf litter is rapid, potentially due to a lack of habitat structure availability in the sandy-bottomed stream.