Acoustic mapping of benthic sediments

There is an increasing demand for knowledge of habitats, communities and distribution patterns of the seafloor for impact assessment, conservation and ecological studies. The European Union Water Framework directive will require a lot of effort to be met. In this study acoustic mapping of benthic communities and the factors that may influence the acoustic data has been examined, as well as the usage of sediment profile images (SPI). The survey area is located outside the town of Drøbak in the Oslofjord. An acoustic map of the area was made and four different acoustic classes were detected. Sampling of sediment and fauna from three of the four classes was made. SPI pictures were also taken from three of the classes. Sediment composition seemed to have no apparent affect on the acoustic data, the high concentration of organic carbon suggests that it might be the infauna that is the biggest contributor to the differences in the acoustic data. The faunal composition had a high similarity between the stations, but there was spread that followed the acoustic classes to some degree. Some of the shortcomings of the acoustic method have also been noted, and steps to compensate for this in the future are mentioned. The SPI pictures were in accordance with pictures made by others from the same area. Both SPI and acoustic mapping are cost effective methods for remote sensing of the seabed, but they will not replace traditional ground truthing, merely compensate and improve it