Grab Samplers for Benthic Macroinvertebrates in the Lower Mississippi River

摘要

The use of any one single type and size of existing grab sampler for gathering representative benthic macroinvertebrate samples from the various habitats within rivers is impractical, if not impossible. Adjusting one sampling gear (grab sampler) to the existing habitat and program objectives appears to be the best approach. Although macroinvertebrate relative catch efficiency (catch by area inscribed by cocked sampler) varies among sampler types, the catch efficiency of a single type varies with substrate, current regime, and bottoms contours to a greater extent. Data from 24 grab samples, eight each taken with the Standard Ponar, Petite Ponar, and Shipek grabs from a backwater habitat were statistically compared using one-way analysis of variance. Total grabs produced 5696 organisms and 24 distinct taxa. A single grab per station is sufficient to characterize the dominant benthic macroinvertebrate standing crop community and is, therefore, recommended for survey level studies. The Shipek grab is the preferred grab in habitats with strong currents; rough bottom morphology; and sands, gravel, or firm clay substrate. Ponar-type grabs are preferred for softer substrates under lower current velocities. This includes most backwater-type habitats, e.g., river borders, abandoned channels, oxbow lakes, and dike fields under low-flow conditions.