Life inside polymetallic nodules

Deep-sea abyssal plains harbour extensive biodiversity, much of which remains undocumented. Polymetallic nodules in the abyssal plains of the Clarion-Clipperton Zone (CCZ), Central Pacific, harbour diverse meiofaunal communities within their crevices, representing an understudied habitat. Given their high concentrations of nickel, copper, and cobalt, nodules are currently one of the primary targets for the extraction of deep-sea mineral resources. Here, we characterise the physical properties of polymetallic nodules, quantify their meiofaunal crevice communities, and compare them to those from the nearby sediments. We show that nodules contain internal cracks and microfossils, that their crevices harbour meiofaunal communities dominated by nematodes and copepods, and that faunal abundance increases significantly with nodule volume. Nodule-crevice nematode and copepod abundances were equivalent to approximately 10% and 25%, respectively, of those recorded in nearby sediments across the two exploration contract areas in the eastern CCZ. Based on 18S rRNA data, nematode and copepod assemblages recovered from nodule crevices differed from those recovered from nearby sediments collected during the same expedition and within the same exploration contract areas. Our findings, therefore, point to the possibility of nodule-associated crevice meiofauna communities and the consequent risk of biodiversity loss associated with nodule removal through potential future commercial mining.