Conversion factors as determined by relative macroinvertebrate sampling efficiencies of four common benthic grab samplers

Abstract

Collection efficiencies of benthic grab samplers vary depending on the type of substrate sampled and the organism targeted. When benthic invertebrate samples obtained with two or more sampling devices are compared, it is necessary to understand the relative efficiency of each sampler and, if appropriate, apply conversion factors to the data obtained from one or more of the samplers. We used data from field trials to generate substrate- and taxon-specific conversion factors for four common benthic grabs (Shipek, petite Ponar, standard Ekman, and large Ekman). The Shipek grab collected fewer benthic invertebrates per square meters than the other samplers in silt and sand substrates. The large Ekman collected more benthic invertebrates per square meters than other samplers in silt substrate but performed poorly in sand substrate. The petite Ponar and standard Ekman showed similar performance in silt and sand substrates. The wide range of conversion factors generated from our field trials demonstrates the importance of using substrate- and taxon-specific factors when comparing samples collected with different devices.

Keywords:

• conversion factor
• sampler efficiency
• macroinvertebrate
• lake
• benthos
• benthic sample

Acknowledgments

The authors thank the managers of Round Hill Pines Marina and Tahoe City Marina for access to the marinas, and Brant Allen (UC Davis Tahoe Environmental Research Center) for boat and logistics assistance. The project was funded in part by funds to Drs Sudeep Chandra and Geoff Schladow from the California Tahoe Conservancy and Army Corps of Engineers.