Potential Impacts of Polymetallic Nodule Removal On Deep-Sea Meiobenthos

Deep seabed mining is imminent in the Clarion Clipperton Fracture Zone (CCFZ; northeast Pacific). Seabed collectors will remove the polymetallic nodules and the surrounding surface sediments, both inhabited by meiobenthos, along their path. To determine potential impacts of polymetallic nodule removal, we investigated the importance of nodule presence for sediment abundance, composition and diversity of meiobenthos, nematodes and copepods, and evaluated the existence and composition of nodule crevice meiobenthos in the Global Sea Mineral Resources (GSR) exploration contract area. Nodule-free and nodule-rich sediments displayed high biodiversity with many singletons and doubletons, potentially representing rare taxa. Nodule presence negatively influenced sediment meiobenthic abundances but did not markedly affect community composition or diversity. This is the first report on CCFZ nodule crevice meiobenthos, whose abundance related positively to nodule dimensions. Though dominated by the same taxa, the meio- and nematofauna differed between sediments and nodules regarding community and functional composition. Nevertheless, there were no taxa endemic to the nodule crevices and nodule crevice meiobenthos added only little to total small-scale (~ cm) meiobenthic abundance and diversity. We formulated environmental management recommendations at the contract area and regional (CCFZ) scale related to sampling effort, set-aside preservation and monitoring areas, and potential rehabilitation measures.