Abundance and morphology of Paleodictyon nodosum, observed at the Clarion-Clipperton Zone

Paleodictyon is an important trace fossil characterised by a regular hexagonal structure and typical of ancient deep-ocean habitats as far back as the Ordovician. It is represented in modern deep-sea settings by Paleodictyon nodosum, known from the Mid-Atlantic Ridge, the South Atlantic, and off eastern Australia. Here we report the occurrence of P. nodosum in the Clarion Clipperton Zone (CCZ), abyssal equatorial Pacific, an area characterised by polymetallic nodule fields. At the study site within the International Seabed Authority northeastern Area of Particular Environmental Interest (APEI-6), P. nodosum appeared as a compact, regular pattern of small circular openings on the seafloor, each pattern interpreted as reflecting the activity of an individual organism. The patterns had a mean size (maximum dimension) of 45 mm?±?16 mm SD (n?=?841) and occurred at a density of 0.33 individuals m?2. Most (82%) were interrupted by nodules, but those that were not displayed both regular (59%) and irregular (41%) forms, the former having equal numbers of rows along the three axes (6 x 6 x 6 and 8 x 8 x 8). In both size and morphology, our Paleodictyon traces were more similar to the Australian examples than to those from the Mid-Atlantic Ridge

Detecting the effects of deep-seabed nodule mining: simulations using Megafaunal Data From the Clarion-Clipperton Zone

The International Seabed Authority (ISA) is in the process of preparing exploitation regulations for deep-seabed mining (DSM). DSM has the potential to disturb the seabed over wide areas, yet there is little information on the ecological consequences, both at the site of mining and surrounding areas where disturbance such as sediment smothering could occur. Of critical regulatory concern is whether the impacts cause “serious harm” to the environment. Using metazoan megafaunal data from the Clarion-Clipperton Zone (northern equatorial Pacific), we simulate a range of disturbances from very low to severe, to determine the effect on community-level metrics. Two kinds of stressors were simulated: one that impacts organisms based on their affinity to nodules, and another that applies spatially stochastic stress to all organisms. These simulations are then assessed using power analysis to determine the amount of sampling required to distinguish the disturbances. This analysis is limited to modelling lethal impacts on megafauna. It provides a first indication of the effect sizes and ecological nature of mining impacts that might be expected across a broader range of taxa. To detect our simulated “tipping point,” power analyses suggest impact monitoring samples should each have at least 500–750 individual megafauna; and at least five such samples, as well as control samples should be assessed. In the region studied, this translates to approximately 1500–2300 m2 seabed per impact monitoring sample, i.e., 7500–11,500 m2 in total for a given location and/or habitat. Detecting less severe disturbances requires more sampling. The numerical density of individuals and Pielou’s evenness of communities appear most sensitive to simulated disturbances and may provide suitable “early warning” metrics for monitoring. To determine the sampling details for detecting the desired threshold(s) for harm, statistical effect sizes will need to be determined and validated. The determination of what constitutes serious harm is a legal question that will need to consider socially acceptable levels of long-term harm to deep-sea life. Monitoring details, data, and results including power analyses should be made fully available, to facilitate independent review and informed policy discussions

Ecology of a polymetallic nodule occurrence gradient: Implications for deep-sea mining

Abyssal polymetallic nodule fields constitute an unusual deep‐sea habitat. The mix of soft sediment and the hard substratum provided by nodules increases the complexity of these environments. Hard substrata typically support a very distinct fauna to that of seabed sediments, and its presence can play a major role in the structuring of benthic assemblages. We assessed the influence of seafloor nodule cover on the megabenthos of a marine conservation area (area of particular environmental interest 6) in the Clarion Clipperton Zone (3950–4250 m water depth) using extensive photographic surveys from an autonomous underwater vehicle. Variations in nodule cover (1–20%) appeared to exert statistically significant differences in faunal standing stocks, some biological diversity attributes, faunal composition, functional group composition, and the distribution of individual species. The standing stock of both the metazoan fauna and the giant protists (xenophyophores) doubled with a very modest initial increase in nodule cover (from 1% to 3%). Perhaps contrary to expectation, we detected little if any substantive variation in biological diversity along the nodule cover gradient. Faunal composition varied continuously along the nodule cover gradient. We discuss these results in the context of potential seabed‐mining operations and the associated sustainable management and conservation plans. We note in particular that successful conservation actions will likely require the preservation of areas comprising the full range of nodule cover and not just the low cover areas that are least attractive to mining

Biological responses to disturbance from simulated deep-sea polymetallic nodule mining

Commercial-scale mining for polymetallic nodules could have a major impact on the deep-sea environment, but the effects of these mining activities on deep-sea ecosystems are very poorly known. The first commercial test mining for polymetallic nodules was carried out in 1970. Since then a number of small-scale commercial test mining or scientific disturbance studies have been carried out. Here we evaluate changes in faunal densities and diversity of benthic communities measured in response to these 11 simulated or test nodule mining disturbances using meta-analysis techniques. We find that impacts are often severe immediately after mining, with major negative changes in density and diversity of most groups occurring. However, in some cases, the mobile fauna and small-sized fauna experienced less negative impacts over the longer term. At seven sites in the Pacific, multiple surveys assessed recovery in fauna over periods of up to 26 years. Almost all studies show some recovery in faunal density and diversity for meiofauna and mobile megafauna, often within one year. However, very few faunal groups return to baseline or control conditions after two decades. The effects of polymetallic nodule mining are likely to be long term. Our analyses show considerable negative biological effects of seafloor nodule mining, even at the small scale of test mining experiments, although there is variation in sensitivity amongst organisms of different sizes and functional groups, which have important implications for ecosystem responses. Unfortunately, many past studies have limitations that reduce their effectiveness in determining responses. We provide recommendations to improve future mining impact test studies. Further research to assess the effects of test-mining activities will inform ways to improve mining practices and guide effective environmental management of mining activities

Megabenthic ecology of abyssal polymetallic nodule fields

Abyssal polymetallic nodule fields constitute an unusual deep-sea habitat. The mix of soft sediment and the hard substratum provided by nodules increases the complexity of these environments, and is thought to promote the occurrence of some of the most biologically diverse seafloor assemblages in the abyss. This unusual and diverse habitat is potentially subject to imminent large-scale human impacts in the form of seafloor mining. Mining disturbances are likely to extend over extremely large seafloor areas and have a clear potential to drive major changes in the resident fauna. Predicting the nature of such changes remains difficult; the ecology of this remote and vast habitat is poorly understood. The large seafloor areal coverage that can be investigated using photographic surveys presents an opportunity to numerically quantify variation in megafaunal communities inhabiting these abyssal plain environments. In this thesis, the fundamental drivers of megabenthic community variations in abyssal polymetallic nodule fields are explored based on extensive acoustic and imagery data collected using autonomous underwater vehicles. First, baseline ecological patterns of megafaunal distribution are investigated at different factor-operating scales, i.e. different environmental factors, in the proposed conservation zone ‘Area of Particular Environmental Interest 6’ of the Clarion Clipperton Zone (NE Pacific; water depth: 3950-4250 m). Broad-scale (tens of kilometres) variations in seafloor geomorphology appear to control megabenthic standing stock, while fine-scale (tens of meters) variations in nodule occurrence appear more important in the regulation of diversity and community composition. Both of these factors seem to play a key role in the functional structuring of megafauna assemblages across a nodule field. Second, long term effects of disturbance on megafaunal distribution patterns are investigated in the Peru Basin (E Pacific; 3800-4300 m water depth), 26 years after simulated mining impacts were induced during the “DISturbance and reCOLonization” experiment. Distinct ecological patterns are found across different seafloor disturbance levels; i.e. suspension feeder standing stock remains strongly reduced in directly disturbed seafloor areas, suggesting that the megabenthos of the DISCOL area has not yet recovered from simulated mining impacts. The findings of this thesis provide evidence of the habitat heterogeneity of polymetallic nodule field ecosystems, which appears promoted by both geomorphological and nodule occurrence variations across space. The nodule field is likely better considered as a mosaic habitat where nodules act as keystone structures, modulating a continuous community variation across a gradient of this resource. Consequently, successful conservation actions will likely require the preservation of areas comprising the full range of nodule cover and not just the low cover areas that are least attractive to mining

Investigating the benthic megafauna in the eastern Clarion Clipperton Fracture Zone (north-east Pacific) based on distribution models predicted with random forest

The eastern Clarion Clipperton Fracture Zone (CCZ) is a heterogeneous abyssal environment harbouring relatively low abundances of highly diverse megafauna communities. Potential future mining of polymetallic nodules threatens these benthic communities and calls for detailed spatial investigation of megafauna. Based on the predicted probability of occurrence of 68 megafauna morphotypes, a seabed area extending over 62,000 km2 was divided into three assemblages covering an eastern plain area, a deeper western plain area and an area covering both seamount and abyssal hill sites. Richness, estimated as the sum of morphotypes with a predicted probability of occurrence larger than 0.5, amounts to 15.4 of 68 morphotypes. Highest richness was predicted at seamount sites, and lowest richness in the western part of the study area. Combining the predicted probability of megafauna occurrences with bathymetric variables, two seamount habitats and two plain habitats could be defined. One of these megafauna plain habitats corresponds with contiguous nodule fields of high abundance that may be targeted for future mining, showing that prospective nodule fields have a clearly differentiated megafauna assemblage. Monitoring and management schemes, including the delineation of preservation and protection areas within contract areas, need to incorporate this geological and biological heterogeneity

Fully automated image segmentation for benthic resource assessment of poly-metallic nodules

Highlights • The proposed method automatically assesses the abundance of poly-metallic nodules on the seafloor. • No manually created feature reference set is required. • Large collections of benthic images from a range of acquisition gear can be analysed efficiently. Abstract Underwater image analysis is a new field for computational pattern recognition. In academia as well as in the industry, it is more and more common to use camera-equipped stationary landers, autonomous underwater vehicles, ocean floor observatory systems or remotely operated vehicles for image based monitoring and exploration. The resulting image collections create a bottleneck for manual data interpretation owing to their size. In this paper, the problem of measuring size and abundance of poly-metallic nodules in benthic images is considered. A foreground/background separation (i.e. separating the nodules from the surrounding sediment) is required to determine the targeted quantities. Poly-metallic nodules are compact (convex), but vary in size and appear as composites with different visual features (color, texture, etc.). Methods for automating nodule segmentation have so far relied on manual training data. However, a hand-drawn, ground-truthed segmentation of nodules and sediment is difficult (or even impossible) to achieve for a sufficient number of images. The new ES4C algorithm (Evolutionary tuned Segmentation using Cluster Co-occurrence and a Convexity Criterion) is presented that can be applied to a segmentation task without a reference ground truth. First, a learning vector quantization groups the visual features in the images into clusters. Secondly, a segmentation function is constructed by assigning the clusters to classes automatically according to defined heuristics. Using evolutionary algorithms, a quality criterion is maximized to assign cluster prototypes to classes. This criterion integrates the morphological compactness of the nodules as well as feature similarity in different parts of nodules. To assess its applicability, the ES4C algorithm is tested with two real-world data sets. For one of these data sets, a reference gold standard is available and we report a sensitivity of 0.88 and a specificity of 0.65. Our results show that the applied heuristics, which combine patterns in the feature domain with patterns in the spatial domain, lead to good segmentation results and allow full automation of the resource-abundance assessment for benthic poly-metallic nodules

Fully automated image segmentation for benthic resource assessment of poly-metallic nodules

Schoening T, Kuhn T, Jones DOB, Simon-Lledo E, Nattkemper TW. Fully automated image segmentation for benthic resource assessment of poly-metallic nodules. Methods in Oceanography. Accepted;15-16:78-89

The megafauna community from an abyssal area of interest for mining of polymetallic nodules

Polymetallic nodules increase habitat heterogeneity in some abyssal benthic ecosystems by providing hard substrate. Besides their important role in structuring ecosystems, polymetallic nodules have high grades of valuable minerals and are a target of likely future exploitation, particularly in the Pacific Clarion-Clipperton Zone (CCZ). Mining activities will remove hard substrate and sediment and cause sediment plumes potentially affecting faunal communities over large areas. Long-lived megafaunal assemblages may be particularly vulnerable but data are lacking on the density, biodiversity and community structure in many areas of the CCZ. This study aims to provide megabenthic community baseline data from two physically similar areas (B6S02 and B4S03) located in the contract area of Global Sea Mineral Resources N.V. (GSR). Seafloor images, obtained by an autonomous underwater vehicle are used to characterise the large areas required for robust evaluation of sparse megafauna. Higher altitude images cover a larger area for the same effort but have reduced resolution compared to images obtained closer to the seafloor, leading to difficulties in detecting and identifying individuals. Our comparison of images obtained at different altitudes shows that images taken above 8m altitude underestimate the megafauna density by almost 50%, so images <8m were used for further analysis. We also used multiobserver agreement analysis to improve the megafaunal annotation consistency, and the quality and robustness of the data in this study. The two GSR areas were significantly different in nodule coverage and megafauna composition and a general positive relationship between nodule coverage and megafauna abundance was observed. Differences in the megafaunal composition were primarily caused by differences in echinoderms (asteroids, echinoids, ophiuroids and holothuroids), representing almost 70% of the megafauna

Megafaunal variation in the abyssal landscape of the Clarion Clipperton Zone

The potential for imminent polymetallic nodule mining in the Clarion Clipperton Fracture Zone (CCZ) has attracted considerable scientific and public attention. This concern stems from both the extremely large seafloor areas that may be impacted by mining, and the very limited knowledge of the fauna and ecology of this region. The environmental factors regulating seafloor ecology are still very poorly understood. In this study, we focus on megafaunal ecology in the proposed conservation zone ‘Area of Particular Environmental Interest 6′ (study area centred 17°16′N, 122°55′W). We employ bathymetric data to objectively define three landscape types in the area (a level bottom Flat, an elevated Ridge, a depressed Trough; water depth 3950–4250 m) that are characteristic of the wider CCZ. We use direct seabed sampling to characterise the sedimentary environment in each landscape, detecting no statistically significant differences in particle size distributions or organic matter content. Additional seafloor characteristics and data on both the metazoan and xenophyophore components of the megafauna were derived by extensive photographic survey from an autonomous underwater vehicle. Image data revealed that there were statistically significant differences in seafloor cover by nodules and in the occurrence of other hard substrata habitat between landscapes. Statistically significant differences in megafauna standing stock, functional structuring, diversity, and faunal composition were detected between landscapes. The Flat and Ridge areas exhibited a significantly higher standing stock and a distinct assemblage composition compared to the Trough. Geomorphological variations, presumably regulating local bottom water flows and the occurrence of nodule and xenophyophore test substrata, between study areas may be the mechanism driving these assemblage differences. We also used these data to assess the influence of sampling unit size on the estimation of ecological parameters. We discuss these results in the contexts of regional benthic ecology and the appropriate management of potential mining activities in the CCZ and elsewhere in the deep ocean