Description: Mining of polymetallic nodules in abyssal seafloor sediments promises to address the growing worldwide demand for metallic minerals. Given that prospective mining operations are likely to have profound impacts on deep seafloor communities, industrial investment has been accompanied by scientific involvement for the assessment of baseline conditions and provision of guidelines for environmentally sustainable mining practices. Benthic meiofaunal communities were studied in four prospective mining areas of the Clarion–Clipperton Zone (CCZ) in the eastern Pacific Ocean, arranged in a southeast–northwest fashion coinciding with the productivity gradient in the area. Additionally, samples were collected from the Area of Particular Environmental Interest no. 3 (APEI-3) in the northwest of the CCZ, where mining will be prohibited and which should serve as a “source area” for the biota within the larger CCZ. Total densities in the 0–5 cm upper layer of the sediment were influenced by sedimentary characteristics, water depth and nodule density at the various sampling locations, indicating the importance of nodules for meiofaunal standing stock. Nematodes were the most abundant meiobenthic taxon, and their assemblages were typically dominated by a few genera (generally 2–6) accounting for 40 %–70 % of all individuals, which were also widely spread along the CCZ and shared among all sampled license areas. However, almost half of the communities consisted of rare genera, each contributing less than 5 % to the overall abundances and displaying a distribution which was usually restricted to a single license area. The same observations (dominant and widely spread versus rare and scattered) could be made for the species of one of the dominant genera, Halalaimus, implying that it might be mainly these rare genera and species that will be vulnerable to mining-induced changes in their habitat.

Description: The deep-sea mining industry is currently at a point where large-sale, commercial polymetallic nodule exploitation is becoming a more realistic scenario. At the same time, certain aspects such as the spatiotemporal scale of impacts, sediment plume dispersion and the disturbance-related biological responses remain highly uncertain. In this paper, findings from a small-scale seabed disturbance experiment in the German contract area (Clarion-Clipperton Zone, CCZ) are described, with a focus on the soft-sediment ecosystem component. Despite the limited spatial scale of the induced disturbance on the seafloor, this experiment allowed us to evaluate how short-term (〈 1 month) soft-sediment changes can be assessed based on sediment characteristics (grain size, nutrients and pigments) and metazoan meiofaunal communities (morphological and metabarcoding analyses). Furthermore, we show how benthic measurements can be combined with numerical modelling of sediment transport to enhance our understanding of meiofaunal responses to increased sedimentation levels. The lessons learned within this study highlight the major issues of current deep-sea mining-related ecological research such as deficient baseline knowledge, unrepresentative impact intensity of mining simulations and challenges associated with sampling trade-offs (e.g., replication).

Description: An understanding of the forces controlling community structure in the deep sea is essential at a time when its pristineness is threatened by polymetallic nodule mining. Because abiotically defined communities are more sensitive to environmental change, we applied occurrence- and phylogeny-based metrics to determine the importance of biotic versus abiotic structuring processes in nematodes, the most abundant invertebrate taxon of the Clarion–Clipperton Fracture Zone (CCFZ), an area targeted for mining. We investigated the prevalence of rarity and the explanatory power of environmental parameters with respect to phylogenetic diversity (PD). We found evidence for aggregation and phylogenetic clustering in nematode amplicon sequence variants (ASVs) and the dominant genus Acantholaimus , indicating the influence of environmental filtering, sympatric speciation, affinity for overlapping habitats and facilitation for community structure. PD was associated with abiotic variables such as total organic carbon, chloroplastic pigments equivalents and/or mud content, explaining up to 57% of the observed variability and providing further support of the prominence of environmental structuring forces. Rarity was high throughout, ranging from 64 to 75% unique ASVs. Communities defined by environmental filtering with a prevalence of rarity in the CCFZ suggest taxa of these nodule-bearing abyssal plains will be especially vulnerable to the risk of extinction brought about by the efforts to extract them.

Description: The increasing demand for metals is pushing forward the progress of deep‐sea mining industry. The abyss between the Clarion and Clipperton Fracture Zones (CCFZ), a region holding a higher concentration of minerals than land deposits, is the most targeted area for the exploration of polymetallic nodules worldwide, which may likely disturb the seafloor across large areas and over many years. Effects from nodule extraction cause acute biodiversity loss of organisms inhabiting sediments and polymetallic nodules. Attention to deep‐sea ecosystems and their services has to be considered before mining starts but the lack of basic scientific knowledge on the methodologies for the ecological surveys of fauna in the context of deep‐sea mining impacts is still scarce. We review the methodology to sample, process and investigate metazoan infauna both inhabiting sediments and nodules dwelling on these polymetallic‐nodule areas. We suggest effective procedures for sampling designs, devices and methods involving gear types, sediment processing, morphological and genetic identification including metabarcoding and proteomic fingerprinting, the assessment of biomass, functional traits, fatty acids, and stable isotope studies within the CCFZ based on both first‐hand experiences and literature. We recommend multi‐ and boxcorers for the quantitative assessments of meio‐ and macrofauna, respectively. The assessment of biodiversity at species level should be focused and/or the combination of morphological with metabarcoding or proteomic fingerprinting techniques. We highlight that biomass, functional traits, and trophic markers may provide critical insights for biodiversity assessments and how statistical modeling facilitates predicting patterns spatially across point‐source data and is essential for conservation management.

Description: This dataset contains sedimentary parameters pigments (Chlorophyll a, Pheophorbide, Pheophytin) measured from Multicorer (MUC) samples from the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Germany) and Global Sea Mineral Resources (GSR, Belgium) license areas in the Clarion Clipperton Fracture Zone collected on onboard the RV Sonne during expeditions SO268 (Leg1 and Leg2) in 2019. Values are given in their respective units (SI) and have been collected and measured by the Marine Biology Research Group of Ghent University (Belgium).

Description: This dataset contains sedimentary parameter grain size distribution measured from Multicorer (MUC) samples from the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Germany) and Global Sea Mineral Resources (GSR, Belgium) license areas in the Clarion Clipperton Fracture Zone collected on onboard the RV Sonne during expeditions SO268 (Leg1 and Leg2) in 2019. Values are given in their respective units (SI) and have been collected and measured by the Marine Biology Research Group of Ghent University (Belgium).

Description: This dataset contains sedimentary parameters total nitrogen (TN) and total organic carbon (TOC) measured from Multicorer (MUC) and Remotely Operated Vehicle (ROV) samples from the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Germany) and Global Sea Mineral Resources (GSR, Belgium) license areas in the Clarion Clipperton Fracture Zone collected on onboard the RV Sonne during expeditions SO268 (Leg1 and Leg2) in 2019. Values are given in their respective units (SI) and have been collected and measured by the Marine Biology Research Group of Ghent University (Belgium).

Description: This dataset contains sedimentary parameters total nitrogen (TN) and total organic carbon (TOC) measured from Multicorer (MUC) samples from the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Germany) and Global Sea Mineral Resources (GSR, Belgium) license areas in the Clarion Clipperton Fracture Zone (CCFZ) collected on onboard the Norwegian Island Pride during expeditions Mangan21 in 2021. Total organic carbon (TOC) and total nitrogen (TN) was quantified by combustion of freeze-dried samples with the Flash 2000 NC Sediment Analyser. These data were collected to quantify nutrients in the CCFZ and to correlate these values to observed levels of biodiversity. Values are given in their respective units (SI) and have been collected and measured by the Marine Biology Research Group of Ghent University (Belgium).

Description: This dataset contains sedimentary parameters pigments (Chlorophyll a, Pheophorbide, Pheophytin) measured from Multicorer (MUC) samples from the Global Sea Mineral Resources (GSR, Belgium) license area in the Clarion Clipperton Fracture Zone (CCFZ) collected on onboard the Norwegian Island Pride during expeditions Mangan21 in 2021. Pigment analysis was completed according to Van Heukelem and Thomas (2001). After addition of 90% acetone, freeze-dried samples were sonicated and extracted overnight at 4°C. After filtration, the extract was injected into an Agilent HPLC with fluorescence detector (type 1200 Infinity II, Agilent Technologies, Diegem, Belgium) equipped with an Eclipse XDB C8 column. The sum of Chl-a and phaeopigment concentrations was calculated and is referred to as the Chloroplast Pigment Equivalent (CPE). These data were collected to quantify primary productivity in the CCFZ and to correlate these values to observed levels of biodiversity. Values are given in their respective units (SI) and have been collected and measured by the Marine Biology Research Group of Ghent University (Belgium).

Description: This dataset contains sedimentary parameter grain size distribution measured from Multicorer (MUC) samples from the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Germany) and Global Sea Mineral Resources (GSR, Belgium) license areas in the Clarion Clipperton Fracture Zone (CCFZ) collected on onboard the Norwegian Island Pride during expeditions Mangan21 in 2021. Grain size analysis was completed using laser diffraction (Malvern Mastersizer Hydro 2000 G). These data were collected to characterize the sediment in the CCFZ and to correlate these values to observed levels of biodiversity. Values are given in their respective units (SI) and have been collected and measured by the Marine Biology Research Group of Ghent University (Belgium).