Visualization and quantification of marine benthic biogenic structures and particle transport utilizing computer-aided tomography

Computer-aided tomography was used to visualize and quantify biogenic structures (e.g. burrows, shells) in 3 dimensions (3D) by scanning 9 replicate cores obtained from a 41 m deep station in the Gullmarsfjord (Skagerrak, western Sweden). The main objective was to visualize and quantify the biogenic structures and their volumes in the sediment. In addition, the particle transport was studied by adding an aluminum oxide tracer to the sediment-water interface (SWI), which was analysed after 57, 80 and 128 h, in 3 replicate cores each time. A new software programme was developed for rapid and accurate analysis. The fauna in the cores, analysed after scanning, were dominated by the brittle stars Amphiura filiformis and A. chiajei. The volumes of 'active' biogenic structures, defined as connecting to the SWI, were generally greatest close to the interface with some secondary peaks, probably related to the position of the disc chamber of the brittle stars. A mean volume of 560 cm(3) of biogenic structures per m(2) of sediment surface was recorded within the sediment (down to a mean depth of 137 mm, where the biogenic structures ceased to be 'active'). Ejection of particles to the SWI (mounding) was calculated to be between 4 and 40 mm(3) h(-1).