Description: Polymetallic nodules in deep-sea habitats of the Pacific Ocean will be subject to commercial exploitation in the near future but the potential effects of such mining activities on benthic life are difficult to assess. Here we present results from a recent revisit onboard RV SONNE (leg SO242/2) to the site of the “DISturbance and reCOLonization experiment” (DISCOL), a large scale benthic impact study initiated in 1989 in a polymetallic nodule area in the Peru Basin (tropical south-eastern Pacific). The area was artificially disturbed by a plow harrow to simulate manganese nodule extraction. In 2015, Meiofauna samples were collected and analysed at two different spatial scales in the framework of the JPI Oceans' programme ‘Ecological Aspects of Deep-Sea Mining’ to study the response and recovery rate of benthic faunal communities. At a macroscale, meiofauna densities and community composition were compared between two stations within the DISCOL experimental area (DEA) and three undisturbed reference stations. No long-term disturbance effects could be identified, most likely because high sediment heterogeneity in the disturbed and reference sites resulted in large variation in meiofauna communities. However, additional ROV push core sampling at selected microhabitats within the disturbance tracks (white patches, ripple crests and ripple valleys) revealed significant differences at a microscale for two out of three tracks. Meiofauna abundances were significantly reduced at all sites compared to outside track control samples with the exception of ripple valleys. Lowest densities were found at the white spot habitats where disturbances in 1989 exposed deeper sediment layers and where lowest pigment and organic matter contents were found. The study demonstrates that physical disturbances as they will be associated with mining will most likely result in long-term impacts on meiofauna communities in nodule areas. However, the results also show that detailed investigations at small spatial scales may be required to discriminate disturbance effects on meiofauna communities from natural variability.

Description: Investigations carried out during leg SO242/2 of RV SONNE to the DISCOL experimental area in Sep. 2015 show that the removal of the reactive surface layer by disturbances created in 1989 is still reflected in altered microbial standing stocks and activities. Based on measurements of microbial carbon assimilation rates (inorganic carbon uptake, oxygen uptake, leucine uptake) and the carbon and nitrogen content of the sediment, we estimated the time needed post-disturbance for microbial regrowth and community turnover to reach initial population sizes. According to these calculations, microbial cell numbers are expected to recover in less than a year. Surprisingly, 26 years after the disturbance, population sizes still do not reach the level found at reference sites. Also the community structure still differs at the disturbed sites. Various explanations for the lack of growth are possible: Grazing, viral lysis, removal of manganese nodules, and a lack of labile organic matter are some of the potential mechanisms which may limit microbial population growth, in spite of the relatively high carbon assimilation rates.

Description: Leg SO242/2 of an RV SONNE expedition to the DISturbance and reCOLonization (DISCOL) area in the manganese nodule ecosystem area of the Peruvian Basin in the framework of JPI Oceans program ‘Ecological aspects of deep-sea mining’ and MIDAS investigated the faunal and biogeochemical response and recovery to both recent (~5 weeks prior) and historical (~26 yrs prior) nodule removal and seafloor disturbances. Recently published by MIDAS partners, epifauna studies conducted within the Clarion Clipperton Fracture Zone (CCZ) as part of the same projects have shown the potential importance of manganese nodules as suitable hard substrate ‘islands’ onto which stalked fauna, such as deep sea sponges and crinoids, can settle and develop (Vanreusel et al., 2016). At the DISCOL site, 27 deep sea incirrate octopi were observed actively feeding around the edges of Manganese nodules at depths of approx. 4100 m, using crevices between nodules as sites of refuge, and in two instances brooding eggs directly onto the stalks of dead deep sea fauna. Interestingly, no incirrate octopi were observed during any of the recent MIDAS / JPI Oceans cruises to the CCZ, Observed individuals represent at least two species, with several being identified as Vulcanoctopus sp. The majority appear to belong to the recently observed ‘Casper’ species, recorded by Remote Operated Vehicles from several locations within the Hawaiian archipelago, and as yet, undescribed. Together with the recent Hawaiian observations, these new data increase the depth range of incirrate octopi by several hundreds of meters. Additionally they represent the first observations of incirrate octopi using other fauna as a brooding substrate. Though the knock-on impacts on stalk supported small megafauna communities has been a known consideration for several decades (though better understood following MIDAS and JPI Oceans investigations) the potential impacts on larger semi-pelagic mobile fauna such as octopi has not been considered to date. In this study we show that potentially the loss of nodules will have direct impacts on these larger megafauna. Tantalisingly, the observations of the incirrate octopi in the Hawaiian archipelago were made in areas also abundant in stalked fauna. Survey dives within these manganese crust rich regions of seafloor covered considerably less area than the DISCOL work carried out during SO242/2, and therefore there is the potentiality that stalks in these commercially interesting ecosystems represent habitat resources at risk from mining activities.

Description: This study investigates potential impacts connected to the removal of manganese nodules on deepsea sediment biogeochemistry and benthic microbial communities. The study site is located in the DISCOL Experimental Area (DEA) in the Peru Basin where a large scale disturbance experiment has been carried out in 1989. Investigations were performed during RV SONNE cruise SO242/2 in Sep. 2015 in the framework of the JPI Oceans programme ‘Ecological Aspects of deep sea mining’. The focus of the work presented here is on effects on the community structure, activity, and functions of benthic microorganisms. Sediment cores and manganese nodules were sampled in different disturbed and undisturbed areas. Overall, four microhabitats within the initial DISCOL disturbance tracks, a recent disturbance track created by an epibenthic sledge, and reference areas outside the DEA were investigated. Samples for laboratory incubations and analyses were taken with ROV and multicorer while fluxes were studied in situ with autonomous benthic chamber and micro profiler systems. Sediments were characterized by their colour, phytopigments, particulate carbon and nitrogen contents. The microbial activities were evaluated on the basis of diffusive oxygen fluxes, extracellular enzymatic activities, and uptake of radiolabelled compounds (i.e. bicarbonate and leucine). Microbial communities and diversities were characterized via 16S rRNA Illumina tag sequencing. Our data show that areas, where the simulated mining activity removed the reactive surface layer were most affected, even after 26 years. Most microbial and biogeochemical characteristics at these sites still resemble conditions of deeper sediment layers, with strongly reduced microbial abundances, activities of extracellular enzymes involved in organic matter degradation, respiration rates, and inorganic carbon fixation rates. A significant impact was also observed for the bacterial and archaeal community structure and diversity that differed considerably from communities found at reference sites. Similar effects were also identified at another microhabitat, where surface sediments were still present but largely reworked into ripple-like structures. Also here microbial and biogeochemical characteristics were more similar to subsurface layers than to undisturbed sites. We conclude that deep-sea mining reduces microbial activities, and changes their community structure and consequently their function in manganese nodule ecosystems for decades. Differences between microhabitats indicate that strong sediment redistribution and especially the loss of the surface layer represent the strongest impacts. Since microbes represent the basis of a multi-trophic food web, higher trophic levels and larger organisms may also be indirectly affected by the observed changes.

Description: Rapid biodiversity assessment (RBA) refers to time efficient tools that allow to collect information on the present biodiversity in a given area. RBA is never an exhaustive inventory and will not record every species in an area; it would typically target specific groups, such as particular size classes (micro-, meio-, macro- or megafauna), specific taxa or functional groups (specific trophic levels, key species, habitat engineers,..) for which methods will differ according to organism size, habitat and distribution, among other biological characteristics. RBA in terrestrial environments is often based on key taxa (e.g., specific bird or mammal species) that are used as proxies for the health and integrity of ecosystems. In the deep sea however there is no information on key taxa available yet. Furthermore using a rapid method may imply a quality loss in comparison to traditional methods where more time is given to identify specimens to the lowest taxonomic level. Only when RBA methods are guaranteed to give the same or at least similar level of information as the validated taxonomic expert-based methods they can be applied in a monitoring or an Environmental Impact Assessment (EIA) program. If this is not the case, they should be applied with caution, especially in remote deep-sea systems where key taxa or functional groups, or particularly vulnerable taxa or indicator taxa are not yet identified. During MIDAS several emerging RBA tools that are potentially applicable to address effects of deepsea mining on biota living in these ecosystems were tested with a focus on the seafloor-associated biodiversity since here the impacts are expected to be severe due to the removal and disturbance of the substrate. We identified two main categories for rapid biodiversity assessment for sea-floor associated biota. The first category refers to non-invasive, imaging-based techniques such as high resolution video or photographic image surveys. The second category is based on material of collected specimens where the present biodiversity is assessed through molecular and/or morphological techniques. In general, image-based assessments are restricted to larger morphological features. Hence they typically only cover diversity of epifaunal macroscopic organisms (megafauna). On the other hand, imaging techniques also provide visual information over larger stretches of the habitat. Using this information, biodiversity patterns may be connected to characterizations of the natural habitat or mining-related disturbances. The sampling-based methods may allow to combine detailed morphology and molecular analysis of organisms, although some analysis are destructive and do not allow an integrative approach. Their spatial/temporal coverage will be lower within a given time frame, but the methods potentially cover a wide taxonomic/functional representation of groups, and may target both epi- and endofauna, typically with a focus on small organisms. In case of sediment samples, analyses of organisms may be accompanied by detailed physical and chemical analyses at a small spatial scale.

Description: Efforts to satisfy the current need for many high technology elements, such as copper, nickel and yttrium from land-based sources are growing. Potential future sources of some of these elements include the deep sea manganese nodule fields of the Pacific, Atlantic, and Indian oceans. Large swathes of deep-sea seafloor are covered with high densities of 5 – 25 cm diameter nodules – agglomerations of manganese, iron, cobalt, copper, and other 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 tropical Southeast Pacific, to simulate the likely environmental impacts of mining. In September 1989, 'RV SONNE', used a plough device to disturb the top sediment and to remove manganese nodules from the seafloor surface by burying them below the surface. 78 plough tracks of 8 – 16m width were made across a 10.8 km diameter circular area centered at 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. This disturbance and removal of nodules (and therefore hard substrate) is likely to represents the most significant benthic impact experiment carried out at the deep-sea floor to date. 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 megafauna communities within ploughed areas remained quite distinct from those observed predisturbance or in the reference areas. In 2016 the 'RV SONNE' revisited the DISCOL site, as part of the 'JPI Oceans' programme ‘Ecological Aspects of Deep-Sea Mining.’ Here we report the current megafauna community structures observed during expedition SO242-2 within the DISCOL area. 1500 images covering an area of approximately 7400 m² have been analysed. Results show that communities in and near disturbance tracks differ from those found in the undisturbed areas and that the removal of hard substrates from the sediment surface particularly affects the recovery of sessile communities. Over the past 26 years many taxa did not recover, indicating that the experimental disturbances had a long-term effect on seafloor fauna, despite the use of modest disturbance gear compared to mining equipment.