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.

The DISCOL study involving a long-term, large-scale, disturbance-recolonization experiment in the abyssal South Pacific Ocean was devised to achieve a better understanding of the rate, sequence, and direction of benthic community re-establishment after severe anthropogenic disturbance of the seabed similar to that expected to result from deep sea floor mining. The project is funded by the German government and has been in progress since February, 1989, when the experiment was initiated during a two-month cruise aboard FS SONNE. After site selection and baseline assessments, a circular area of the seabed was impacted using a specially designed disturber device and then examined during an ini tial post-impact sampling series. The DISCOL site was sampled again during a second cruise in September, 1989, about six months after the impact was created. A third cruise of the recently rebuilt and enlarged FS SONNE will again visit the site in January-February, 1992, in order to carry out another post-impact sampling series three years after the disturbance. Bottom sediment and biota samples, photo/video images, and other data obtained during the first two cruises are continuing to be evaluated, but some initial results have become available and are summarized in this paper. Experimental studies on large scales have rarely been attempted or successfully carried out in the challenging deep-sea milieu, but are vital to understanding biological processes and evaluating impacts resulting from ocean mining and other future industrial incursions into this largest and least understood of marine environments. INTRODUCTION The DISCOL (disturbance-recolonization) experiment in a manganese nodule area of the southeastern Pacific Ocean is funded by the German Federal Ministry for Research and Technology and has been in progress since February, 1989, when a circular 10.8 km2 area of the sea floor at depths near 4150 m and located approximately 650 km southeast of the Galapagos Islands (Figure 1) was selected as the for a large-scale and long-term study.1,2 The site was divided into eight pre-shaped sectors, each consisting of a central and a peripheral region separated by a 350 m wide buffer zone. Five central and five peripheral sector regions, designated according to their compass position prefixed by a C or P respectively, were randomly selected for concentrated study (sectors labelled in Figure 1). After taking a series of pre-impact baseline samples (DISCOL 1/1) to serve as controls, the DISCOL Experimental Area (DEA) was intentionally disturbed with a specially designed eight meter wide "plow harrow" device during the later part of February and in early March of 1989. 3,4 The disturber device was towed across the DEA center a total of 78 times on diametric courses which resulted in a central region of densely clustered plow tracks surrounded by a less severely affected peripheral region as shown in Figure 2.

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Consideration of mining-related environmental effects and the associated deep research programs have developed in parallel with deep-sea mining technology and are expected to continue to do so in the future Three major phases of environmental research may be recognized:monitoring of pre-pilot mining tests,performance of small- to large scale experiments, andmonitoring of pilot mining operations. Although the third phase still lies a number of years ahead of us, we should utilize the time available and prepare now for monitoring a pilot mining operation. Ocean miners and oceanographers should consider common strategies in close communication and collaboration, well in advance of the approaching commercial and environmental challenges. We propose establishing a permanent and multi disciplinary steering group at the international level for the purpose of formulating, developing and executing a comprehensive plan addressing all further needed environmental research, mining impact evaluation, and risk assessment. Introduction - ocean mining and the Environment The development of the still nascent deep sea mining industry has from its very beginnings been accompanied by deliberations on mining related environmental effects. Although most of the early research activities focused on characterizing nodule deposits in relation to various physical, geological, chemical, and biological parameters of the abyssal environment limited impact and risk assessment studies were also conducted in conjunction with tests of several commercial technologies. Thirty years ago, Mero wrote in the introduction to his book1 that "the sea is a major storehouse of the minerals which serve as the foundation of an industrial society". He also referred to the 1958 Geneva Law of the Sea Conference which adopted among others a document entitled "Convention on fishing and conservation of the living resources of the high seas". This convention, however, was not directed toward a general conservation of nature, but took a more anthropocentric approach which viewed conservation as "rendering possible the optimum sustainable yield from those resources so as to secure a maximum supply of food and other marine resources". Since the time of Mero's writing, deep-sea mining has developed in great strides marked by pre-pilot mining tests (PPMT):In 1970, manganese nodules were recovered from 750m depths of the Blake Plateau in the Atlantic Ocean off the coast of Florida by Deep sea Ventures Inc.(DVI).2.3In March, 1978, nodules were successfully brought up from 5000m depths of the Pacific Ocean by the Ocean Management Inc. (OMI) consortium.4In November, 1978, nodules were mined from 4500m depths in the Pacific Ocean, again by DVI which had by that time formed the Ocean Mining Associates (OMA) consortium.5In 1979, Preussag AG, under contract to the Saudi-Sudanese Red Sea Commission, pumped metalliferous muds from 2200m depths of the Atlantis II Deep of the Red Sea.8 Each of these major technology tests was accompanied by limited environmental investigations. If one reflects upon the evolution of environmental thought and the functional stages of research in relation to deep ocean mining, several past, present, and future phases may be recognized.