ABSTRACT:

Future human activities in the deep-sea will have diverse impacts on the abyssal seafloor. Mapping the affected areas with deep-tow systems provides a clear view of the extents and intensities of impacts and is an excellent method for monitoring the megabenthos, one of the important components of the abyssal community. The German DISCOL and ECOBENT studies demonstrated the suitability of the megafauna as indicator organisms for detecting environmental changes. Megafauna can, for example, be used to identify impacts of deep seabed mining activities. New data on the taxon Holothuroidea provides additional insight into the recolonisation process taking place during the experiment.

INTRODUCTION

During the last decades the deep-sea was used for dumping of wastes such as radioactive materials and munitions (Thiel et al., 1998), and in the future, mining of mineral resources will impact large areas of the currently poorly known and understood abyssal seafloor. All these human activities should be accompanied by environmental studies to assess their impacts on the deep-sea ecosystem. The first step should be thorough baseline studies including mapping the seafloor with photo/video systems. During the last thirty years, photography in marine science has changed from pure observation of the seafloor to an effective tool for acquiring geological and biological information. Seafloor surface structures can be determined in photographs and video recordings, and the density and distribution patterns of the deep-sea megabenthos can be quantitatively assessed. With the help of photo and video systems, large areas can be visualised and characterised in terms of their bottom structures and megafauna associations. These allow researchers to identify areas sensitive to human impacts. The megabenthos consists of large animals (> 40 mm) occurring in low densities which makes it generally difficult to assess by the usual methods of sampling, e.g. by grab samplers or corers.

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