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: Carbon capture and storage is promoted as a mitigation method counteracting the increase of atmospheric CO2 levels. However, at this stage, environmental consequences of potential CO2 leakage from sub-seabed storage sites are still largely unknown. In a 3-month-long mesocosm experiment, this study assessed the impact of elevated pCO2 levels (1,500 to 24,400 µatm) on Cerastoderma edule dominated benthic communities from the Baltic Sea. Mortality of C. edule was significantly increased in the highest treatment (24,400 µatm) and exceeded 50%. Furthermore, mortality of small size classes (0-1 cm) was significantly increased in treatment levels ≥6,600 µatm. First signs of external shell dissolution became visible at ≥1,500 µatm, holes were observed at 〉6,600 µatm. C. edule body condition decreased significantly at all treatment levels (1,500-24,400 µatm). Dominant meiofauna taxa remained unaffected in abundance. Densities of calcifying meiofauna taxa (i.e. Gastropoda and Ostracoda) decreased in high CO2 treatments (〉6,600 µatm), while the non - calcifying Gastrotricha significantly increased in abundance at 24,400 µatm. In addition, microbial community composition was altered at the highest pCO2 level. We conclude that strong CO2 leakage can alter benthic infauna community composition at multiple trophic levels, likely due to high mortality of the dominant macrofauna species C. edule.

Description: With increasing demand for mineral resources, extraction of polymetallic sulphides at hydrothermal vents, cobalt-rich ferromanganese crusts at seamounts, and polymetallic nodules on abyssal plains may be imminent. Here, we shortly introduce ecosystem characteristics of mining areas, report on recent mining developments, and identify potential stress and disturbances created by mining. We analyze species’ potential resistance to future mining and perform meta-analyses on population density and diversity recovery after disturbances most similar to mining: volcanic eruptions at vents, fisheries on seamounts, and experiments that mimic nodule mining on abyssal plains. We report wide variation in recovery rates among taxa, size, and mobility of fauna. While densities and diversities of some taxa can recover to or even exceed pre-disturbance levels, community composition remains affected after decades. The loss of hard substrata or alteration of substrata composition may cause substantial community shifts that persist over geological timescales at mined sites.