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A long term, large scale, disturbance decolonization experiment with relevance to the environmental effects of deep-sea mining is described. The study is funded by the West German government and was launched in the abyssal eastern tropical South Pacific Ocean in February-March, 1989. After obtaining pre-impact baseline environmental data, a 10.8 km circular area of seafloor was disturbed using a specially designed "plow-harrow" device. An initial post-impact sampling series was carried out immediately after disturbance and the site was revisited in September, 1989, for renewed post-impact sampling six months after the disturbance. Plans call for repeated visits to the site at two year intervals in order to monitor the anticipated slow decolonization process until the area is inhabited by a new, stabilized community. INTRODUCTION The search for new sources of raw materials and recent advancements in technology have spurred mankind to penetrate further and deeper into the oceans. Over the past several decades, international mining consortia have carried out extensive exploration and prospecting activities to locate and delineate economically viable ferromanganese nodule deposits on the ocean floor. Some claims have been filed and exploration licenses awarded under several coexisting legal regimes for promising areas at abyssal depths in the Pacific and Indian Oceans. Although commercial mining is currently not envisioned until the next century, warnings have been issued about potentially harmful and long term effects of deep sea mining upon the abyssal ecosystem. Some of the most severe potential effects of ocean mining so far foreseen are associated with the sediment and community disturbance caused by the mining collector as it passes across a deposit harvesting nodules. The impact upon the benthic community in the path of the collector and the related impacts resulting from dispersion and resettling of the sediment plume have been the subject of a number of studies. Most such investigations have focused on the pre-pilot mining tests of 1978-79 which provided limited and inconclusive data due to the restricted temporal and spatial extent of the tests themselves. Other efforts have sought to extrapolate data obtained in small scale laboratory or modeling studies which introduce their own inherent uncertainties. Large scale in situ investigations of the effects of a seabed disturbance and of the nature of the decolonization process had not previously been attempted. As a result of funding provided by the Federal Ministry for Research and Technology (Bundesministerium for Forschung und Technologies or BMFT) of the Federal Republic of Germany (FRG), the first large scale experiment involving disturbance and decolonization at abyssal depths was initiated at a site in the eastern South Pacific Ocean near an existing FRG mining claim in February-March of 1989. The acronym OISCOL (for disturbance - decolonization experiment) was-applied to this pioneering effort.

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