TERRESTRIAL AND AQUATIC NEOICHNOLOGICAL LABORATORY EXPERIMENTS WITH THE FRESHWATER CRAYFISH ORCONECTES: TRACKWAYS ON MEDIA OF VARYING GRAIN SIZE, MOISTURE, AND INCLINATION

Abstract

This study records the different types of trackways produced by the freshwater crayfish Orconectes in a controlled environment. Different trackway morphologies were created through the variation of media ( = substrates) grain size, moisture level, and surface inclination in terrestrial and subaqueous settings. Sediment was sieved into clay and silt, very fine-, fine-, and medium-grained sand. A rectangular container filled with sediment was used to run trackway trials on flat and 10° inclined surfaces. All subaqueous tracks were made in a container on a flat surface. Moisture content for the terrestrial trials was determined by removing a sample of moistened sediment, weighing it before and after heating in an oven for 24 hours, and recording the values in percent water weight. Media moisture content had the greatest effect on trackway characteristics. Trackway preservation of individual appendage marks decreased as grain size and moisture content increased; dry clay and silt preserved the most detailed trackways. Intermediate moisture levels created a firm surface that decreased trackway preservation. Crayfish movement through soupy sediment produced continuous furrows to a depth of 1 cm. Trackways of crayfish moving up and down the inclined surface had shorter stride lengths than those made of a flat surface. Subaqueous trackways in fine- and very fine-grained sand preserved the clearest, most consistent trackways. Results from this study can be used to (1) identify trackways of ancient crayfish and (2) infer the relative amount of moisture present at the time the trackway was produced.