Meiofaunal communities in the Clarion-Clipperton Zone: geographic distribution and link with environmental conditions

Polymetallic nodule mining in the abyss is a nascent industry hoping to meet the growing worldwide demand for metallic minerals. Given that prospective mining is likely to have a profound impact on deep seafloor communities, knowledge on their wider geographic distribution is pivotal in order to provide sound guidelines for environmentally sustainable mining practices. We therefore studied benthic meiofaunal communities spread along four prospective mining areas and one non-mining Area of Particular Environmental Interest in the Clarion-Clipperton Zone (CCZ) of the east Pacific Ocean. Meiobenthic abundance in the upper sediment layer followed an eastward increase in particulate organic matter input, indicating their dependence upon water-column processes. Additionally, standing stock was clearly correlated with the degree of nodule coverage at the different prospective mining areas, with high nodule coverage leading to less sediment volume and thus lower numbers. Future nodule removal through mining activities might therefore lead to an increase in numbers for smaller-sized benthic taxa.In terms of community composition, nematodes were the most abundant meiobenthic taxon, yet showed no pronounced variation in diversity or genus composition between the different mining and non-mining areas. Assemblages were typically dominated by a few genera accounting for the majority of community totals, as well as a large number of rare genera contributing only little to overall abundances. Dominant genera were widely spread within the CCZ and shared among all sampled areas, whereas rare genera were usually limited to one area. The same trend was present when looking at the level of morphospecies, implying that it might be mainly those taxa with a more limited spatial distribution that will be affected by changes in their habitat and/or reduced connectivity between different areas.