A Comparison of Benthic Invertebrate Communities in Three Aquatic Habitats of the Hoh River Valley, Olympic National Park, Washington

Macroinvertebrate communities in three aquatic habitats of the Hoh River Valley, Jefferson County, Washington, were characterized and compared. Within-stream and between­ stream habitat differences and similarities were analyzed in a valley-wall tributary (Twin Creek), river off-channel (side channel of the Hoh River) and terrace tributary (Taft Creek). Between-stream differences were found to be significant using a one-way ANOV. Twin Creek and the side channel were similar in most physical characteristics, dominance of benthic functional groups, and general dominance by taxa. The major variable between these two sites was the influence of silt in the side channel. The effects of a high silt load and the process of siltation appear to be responsible for much lower X benthic densities and the absence of scrapers in the side channel. Taft Creek differed from the other sites in physical characteristics and benthic community composition. Twin Creek and the side channel had rock-rubble substrate, higher current velocities and heavy canopy cover, while Taft Creek had homogeneous substrate, reduced current velocities, dense macrophytic growth, and little canopy cover. Mean benthic densities in Taft Creek (103,914 m-2) were much higher than those found in Twin Creek (15,009 m-2) or the side channel (2,983 m-2). The e was a predominance of Diptera (40%) and non-insects (51%) in Taft Creek and Diptera and Ephemeroptera in Twin Creek (42% and 24% respectively) and the side channel (30% and 43% respectively). Collectors were the predominant functional group at all three sites. No significant differences between riffle, reach, and pool habitat types was found in either Twin Creek or the side channel using a one-way ANOV. When comparing taxonomic and functional group composition, however, reach, and riffle habitats were more similar to each other than to pool habitats in both Twin Creek and the side channel