Use of x-ray images and a contrasting agent to study the behavior of animals in soft sediments

Abstract

We developed a means of observing and recording the burrowing behavior of animals in soft sediments by using X-ray images. The poor contrast between animal burrows and sediment was compensated for by the addition to sediment of a dense inert compound, molybdenum carbide. This contrasting agent allowed us to quantify the development in space and over time of burrows made by a variety of small animals, as well as to determine the exact location and orientation of animls in a burrow system. Nymphs of the mayfly Hexagenia are confirmed to be very active burrowers in comparison with other sympatric insect taxa and are thus likely to be key animals in influencing community irrigation and bioturbation rates. The considerable variation observed in the depth of burrows constructed by various taxa could influence their potential exposure to vertically stratified food particles and sedimentary contaminants. We also used the contrasting agent in the field to demonstrate that burrow structures could be observed in situ. The radiographic technique we tested should be useful in determining the influence of animals on the physics and chemistry of sedimentary deposits, as well as the impact of sedimentary contaminants on the burrowing and feeding of benthic animals in either marine or freshwater systems.