Macroinvertebrate Assemblages of Submerged Woody Debris in the Elm Fork of the Trinity River, Texas

ABSTRACT

We studied the taxonomic composition and spatial and temporal variability of macroinvertebrates inhabiting coarse woody debris in an 8 km segment of the Elm Fork, a low gradient prairie river in Texas. Seventy-seven macroinvertebrate taxa were collected from submerged wood habitats compared with 38 taxa collected from soft benthic substrata. Assemblages were highly variable spatially and temporally, particularly among seasons. An ordination of species and environmental variables indicated some trends in the longitudinal distribution of flow-dependent species but overall did not find coarse woody debris-inhabiting taxa to have strong associations with many of the selected environmental variables. Significant seasonal differences occurred in the abundances of the Chironomidae (Diptera) with Orthocladiini dominating in the winter and Chironomini and Tanytarsini in the summer and autumn. Data gathered after an extended high flow period in the spring indicated a greater resilience of snag habitats than benthic substrata, with rapid re-colonization of coarse woody debris by macroinvertebrates following the high flow episodes.