Spatial distribution of Alitta virens burrows in intertidal sediments studied by axial tomodensitometry

Abstract

Relationships between sediment characteristics and the spatial organization of biogenic structures remain poorly understood, albeit important for characterizing bioturbation impacts and small-scale ecological patterns. Using axial tomodensitometry (CT-scan) and core sectioning, we studied the spatial distribution of Alitta virens burrows in sediment cores from two mudflats with different degrees of exposure along the St Lawrence Estuary, Canada. A variety of burrow morphologies was observed at both sites, with most being I-shaped. Most values measured (organic matter content, mean tomographic intensity, the number and diameter of burrow shafts and the percentage of space they occupy per transverse section) covaried with depth. The more sheltered site had higher organic matter and mud contents, and lower average tomographic intensity values. The spatial distribution of burrow shafts also differed between sites, with the more sheltered site having a higher number of burrow shafts and percentage of biogenic space in the upper sediment column, as well as a greater volume of biogenic structures that were connected to the surface (although intra-site variability was great). Along the horizontal plane and at various depths within sediments, burrow shafts were more randomly distributed at the exposed site, compared to a more even, maximal spacing at the sheltered site. In addition to finding differences in burrow organization at two spatial scales, we found significant correlations between tomographic intensity and (1) the number of burrow shafts, (2) biogenic space and (3) organic matter content. CT-scan data, including tomographic intensity, are useful for examining and comparing biogenic structures in sediment cores.

Characterizations of how species mediate ecosystem properties require more comprehensive functional effect descriptors

“…Whilst context-dependent changes in species behaviour (e.g. in relation to food supply18, tidal periodicity25, temperature26 or photoperiod27) and key features of biogenic structures, including length, diameter, volume and configuration, have been described in detail for individual species282930 and communities31, there is a paucity of information on whether such information is of utility in distinguishing the functional standing of individual species323334. Here, we investigate the functional effect of three co-occurring species of benthic invertebrates, alone and in mixture, using a combination of high-resolution sediment profile imaging and computerized tomography that, together, allow multiple components of particle and fluid transport to be assessed alongside important aspects of burrow morphology at functionally relevant scales (microns to mm).…”