Role of Podostemum ceratophyllum Michx. in structuring benthic macroinvertebrate assemblages in a southern Appalachian river

Abstract

Podostemum ceratophyllum Michx. has been associated with extremely high secondary production of benthic macroinvertebrates in open-canopy rapids. We conducted an experiment in the 7th-order Little Tennessee River, North Carolina, to test whether varying amounts of Podostemum influenced macroinvertebrate abundance, biomass, community composition, and functional feeding group structure. The experiment consisted of 3 treatments in which P. ceratophyllum was completely, partially, or not removed from portions of 4 bedrock outcrops at 2 sites. Macroinvertebrates were sampled at 0, 3, and 6 wk post treatment. Complete removal of P. ceratophyllum greatly reduced overall macroinvertebrate abundance and biomass and altered assemblage structure, but had relatively little effect on functional structure. The lack of change in functional feeding group structure was probably a result of the importance of P. ceratophyllum as a substrate for epiphytic algae, and the availability of nearby colonists in undisturbed habitats. We found a strong positive relationship between surface area of Podostemum and total macroinvertebrate abundance and biomass. We estimated that P. ceratophyllum increased surface area by 3 to 4 times over bare bedrock. Podostemum ceratophyllum in the Little Tennessee River serves as an important habitat supporting high abundance and biomass of macroinvertebrates.