Megabenthic Community Structure Within and Surrounding the DISCOL Experimental Area 26 Years After Simulated Manganese Nodule Mining Disturbance.

The current supplies of many high technology elements from land-based sources are at capacity, such as copper, nickel and yttrium. Potential future sources of some of these elements include the deep sea manganese nodule fields of the Atlantic, Indian and Pacific oceans. Large swathes of deep-sea seafloor are covered with high densities of 5 – 25 cm diameter nodules – agglomerations of manganese, iron and trace metals. In the 1980's these manganese fields were first seriously considered as mining targets, and the ''DISturbance and reCOLonization (DISCOL) experiment was started in the South Pacific, to simulate the likely environmental impacts of mining. In September 1989, 'RV Sonne', deploying a custom-built plough device, removed manganese nodules from the seafloor surface by ploughing them down into the sediment. This removal of nodules (and therefore hard substrate) was considered to likely be the most significant environmental impact of any future mining efforts. 78 plough tracks of 8 – 16m width were made across a 10.8 km diameter circular area centered on 7°04.4´S 88°27.6´W. Megafauna abundances were assessed prior and post ploughing, both within the disturbed area and at reference stations 6 km from the disturbed area.

Research cruises in the 1990s investigated the short-term temporal impact ploughing had on the faunal community in the DISCOL area. Cruises conducted 3 and 7 years after disturbance showed that megafaunal communities within ploughed areas remained quite distinct from those observed pre-disturbance or in the reference areas.

In 2016 the 'RV Sonne' revisited the DISCOL site with two research cruises, as part of the 'JPI-Oceans' programme. Here we report the current megafaunal community structures observed by SO242-2 within the DISCOL area, and the slow recovery rates of many taxa 26 years after the initial experimental disturbance, and provide images of the long term impact of experimental disturbances at the seafloor.