DISCOL: A Long-Term, Large-Scale, Disturbance-Recolonization Experiment in the Abyssal Eastern Tropical South Pacific Ocean

Abstract

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.

Has Phytodetritus Processing by an Abyssal Soft-Sediment Community Recovered 26 Years after an Experimental Disturbance?

“…The DEA is a 10.8 km 2 large circular area (Bluhm, 2001) that was plowed diametrically 78 times in 1989 (Foell et al, 1990(Foell et al, , 1992 to induce a disturbance that would mimic small-scale mining of polymetallic nodules. We deployed newly designed benthic incubation chambers that enabled us to include larger megafauna in pulse-chase studies.…”

Response of deep-sea macrobenthos to a small-scale environmental disturbance

“…In the deep-sea environment such as CIB, the production of sediment organic matter is low (Nath & Mudholkar, 1989) and hence benthic biota has to rely on the particulate organic matter that is produced in the euphotic zone. The benthic community has presumably adapted to the prevailing conditions at deep-sea and any disturbance to their environment will certainly bring major changes in the composition and abundance of benthos (Thistle et al 1985;Foell et al 1990). …”

The Benthic Megafaunal Assemblages of the CCZ (Eastern Pacific) and an Approach to their Management in the Face of Threatened Anthropogenic Impacts

“…The environmental impact studies that have been conducted on nodule ecosystems in the CCZ, the Indian Ocean and the Peru basin (e.g., Amos et al, 1977;Ozturgut et al, 1980;Tilot, 1989;Foell et al, 1990;Thiel et al, 1991Thiel et al, , 2001Bluhm et al, 1995;Fukushima, 1995;Tkatchenko et al, 1996;Radziejewska, 1997;Schriever et al, 1997;Trueblood et al, 1997;Shirayama, 1999;Fukushima et al, 2000;Chung et al, 2001;Oebius et al, 2001;Sharma et al, 2001) mostly focused on alterations to the sediment-nodule interface and impacts to epibenthic faunal communities over very localized areas, compared to the size and the number of areas to be mined. Several reviews (e.g., Smith, 1999;Sharma, 2015;Jones et al, 2017) concluded that there is a lack of information on the potential impact of sediment burial at the scale of the CCZ and that there would be considerable long-term negative effects on the ecosystem.…”