Accurate quantification of the influence of benthic macro- and meio-fauna on the geometric properties of estuarine muds by micro computer tomography

Abstract

This paper describes the novel application of high resolution micro computer tomography (microCT) to the quantification of the properties of marine biogenic structures. CT scanning has been used to examine sediments in the past but the resolution of most previous techniques has been dependent upon commercial medical CT scanners which only have a slice thickness of ≥ 0.625 mm. In addition adequate software has not previously been available to rapidly quantify all the properties of biogenic structures. The microCT technique developed here used a standard core sample of estuarine sediment and new software was developed to calculate the axial variation of the following burrow parameters: number, diameter, volume, surface area and density. The increased resolution has resulted in the first quantification of meiofaunal burrow structures. A test core has shown, as an example, that the total volume of burrows created by macrofaunal organisms decreased from 827 mm 3, within the top 15 mm of the core, to 204.2 mm 3 at a depth 60 –75 mm within the core. Total burrow surface area decreased from 1883 mm 2 to 512 mm 2, for these depth ranges, respectively and burrow diameter ranged from 2.37–2.58 mm, remaining fairly constant between depths. Meiofaunal burrow structures decreased from 1.3–0.1 mm 3 within the top 6 mm of the core with burrow surface area decreasing from 33.52–3.4 mm 2. Again, burrow diameter remained relatively constant, ranging from 0.23–0.25 mm. Quantification to this resolution is required to identify the impact of infaunal organisms on factors such as oxygen penetration, vertical and horizontal (across burrow walls) gradients in redox conditions and chemical/nutrient speciation and flux. The quantification of these burrow properties will improve the ability to examine the interrelationships between chemical, physical and biological processes and their role in ecological functioning. The present study indicates that there is potential for further development of this software to allow more detailed analysis of burrow structures and surface features including parameters such as burrow length, shape and sediment surface roughness.