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The establishment of thresholds is integral to environmental management. This paper introduces the use of thresholds in the context of deep-seabed mining, a nascent industry for which an exploitation regime of regulations, standards and guidelines is still in the process of being developed, and for which the roles and values of thresholds have yet to be finalised. There are several options for integrating thresholds into the International Seabed Authority’s regulatory regime, from being stipulated in regulations to being part of a mining contract, each option having its own advantages and disadvantages. Here we explore the range of ways that thresholds can be derived, set out the challenges in translating ecological and management data into thresholds, highlight factors for acceptance and operationalisation of thresholds in deep-seabed mining, and explain the necessity of refining thresholds as knowledge on impacts to features improves. Some comparable marine industries already use thresholds and these could potentially be used as starting points for the development of thresholds for deep-seabed mining. In order to be acceptable to the wide range of deep-seabed mining stakeholders, thresholds need to strike a balance among levels of harm acceptable by society, levels of environmental precaution justifiable by governments, scientific robustness, and operational practicality.

New Zealand’s large offshore region is dominated by the collision of the Pacific and Australian Plates. Gas hydrates have been identified in three areas: the Hikurangi Margin, the Taranaki and Northland Basins, and the Fiordland-Puysegur Margin. The Hikurangi Margin subduction margin to the east of the North Island stands out, displaying numerous indications of highly-concentrated gas hydrate occurrences. This subduction zone constitutes an environment with high fluid flow and rapidly changing pressure–temperature conditions, leading to anomalies such as the occurrence of double-bottom simulating reflections (BSRs). The Taranaki and Northland Basins west of the North Island is New Zealand’s most prominent petroleum province. So far, however, only limited evidence for hydrate occurrence has been found there. BSRs have also been detected south of the South Island along the Fiordland-Puysegur Margin, an incipient subduction zone. It is likely that gas hydrates are present elsewhere along New Zealand’s vast continental margins.

New Zealand’s large offshore region is dominated by the collision of the Pacific and Australian Plates. Gas hydrates have been identified in three areas: the Hikurangi Margin, the Taranaki and Northland Basins, and the Fiordland-Puysegur Margin. The Hikurangi Margin subduction margin to the east of the North Island stands out, displaying numerous indications of highly-concentrated gas hydrate occurrences. This subduction zone constitutes an environment with high fluid flow and rapidly changing pressure–temperature conditions, leading to anomalies such as the occurrence of double-bottom simulating reflections (BSRs). The Taranaki and Northland Basins west of the North Island is New Zealand’s most prominent petroleum province. So far, however, only limited evidence for hydrate occurrence has been found there. BSRs have also been detected south of the South Island along the Fiordland-Puysegur Margin, an incipient subduction zone. It is likely that gas hydrates are present elsewhere along New Zealand’s vast continental margins.

SERPENT visited the Borgsten Dolphin semisubmersible drilling rig at Hurricane Exploration’s Lancaster and Whirlwind drilling sites, West of Shetland in 2010. The work at Lancaster was an opportunity to investigate recovery of biodiversity at the drilling site which had been studied by SERPENT nine months previously. At Whirlwind an assessment of biodiversity and initial study of the effects of disturbance were carried out. At Lancaster background environment data were collected; temperature, salinity and oxygen profiles and seabed current speed and direction. Video surveys and sample collection were used to map disturbance and quantify biodiversity. The size of the area characterised as completely covered by drill cuttings had reduced in the nine months since the initial drilling disturbance commenced. The abundance and diversity of megafaunal organisms was more consistent with distance from the well in 2010 suggesting evidence of some recovery (return to background) from the 2009 situation. There was also some evidence of recolonization in the macrofauna close to the well with organisms present, even in the samples closest to the well. There may however be a change in the macrofaunal community composition, but in order to determine such a change further analysis including a higher number of samples would be essential. Two visits were made to the nearby but slightly deeper Whirlwind site, where the same background data were collected and an assessment made of the initial effects of disturbance. The megafaunal organisms observed at Whirlwind were similar to Lancaster. The extent of complete cuttings coverage of the seabed at reached a maximum of 70m from the well. There was visible evidence of disturbance (incomplete coverage) reaching beyond the extent of the 100 m video surveys to the SE, W and NW of the well, otherwise incomplete coverage of the seabed reached between 10 and 40m beyond the complete coverage (visit 2). The vertical accumulation of cuttings was mea

This report covers the work of the SERPENT Project at the deep water Lagavulin well in the Faroe-Shetland Channel (FSC). As with all deep-sea environments, scientific knowledge about this area is limited. The surveys will investigate how sediment conditions and animal communities around the drilling location change from the baseline to a disturbed situation. Our field results will be compared to previous model predictions of sedimentation at Lagavulin. The baseline sediment is fine and does not have the heterogeneous grain sizes of sediment found in shallower depths in the Faroe-Shetland Channel (e.g. at Rosebank). A total of 18 animal species were observed living on or associated with the seabed at Lagavulin, with megafaunal representatives (i.e. those animals greater than 10 mm) from at least 7 animal groups (phyla). There were species common to other shallower sites (>900m) within the cold water area of the FSC, but no species were common to sites investigated below 600m depth. After drilling and cementing the tophole section drill spoil (cuttings, mud and cement) was found to extend to nearly 150 m from the centre of drilling (down current; S direction). Approximately 33,750 m2 of seabed was disturbed. It was not possible to determine the vertical height of drill spoil. A new image complexity method was successfully trialled in this study to measure the extent of drill spoil. Lagavulin had a low number of visible animals, particularly as many species live partially burrowed into the sediments. The number of seabed animals (non-mobile) found at Lagavulin was very low close to the drill site. It is most likely that these animals were covered with drill cuttings, as 60mm deep cuttings were measured at 20m distant from drilling. There was no evidence that the distribution of mobile animals was affected by drilling.

This report covers the work of the SERPENT project at the deep water exploration well Dalsnuten in the Norwegian Sea (1452 m depth). The study was designed to investigate the general benthic diversity (mega- and macrofauna) at the location and the disturbance on the seabed resulting from drilling activities and the effects of these activities on the benthic environment, the megafaunal and macrofaunal organisms. The seabed at Dalsnuten experiences a low current regime with the sediment consisting of homogeneous fine silt. A total of 78 species, of which 35 are megafauna (<1 cm) and 43 are macrofaunal (≥ 0.5 mm) were recorded. The megafauna was present in low numbers but the species were typical for the deeper cold waters of the Norwegian. The macrofauna samples were dominated numerically by protozoan species such as foraminifera. Disturbance appeared variable with complete coverage of the seabed with drill cuttings reaching as far as 60 m from the well and partial coverage as far as 100 m. Barium concentrations in surface sediments were elevated but decreased with distance. Megafaunal abundance was also significantly reduced and the community structure altered with very few animals observed in a 50 m radius of the well. Approximately 15,000 m2 of seabed were disturbed. A possibly new species of the amphipod genus Neohela was discovered.

The SERPENT Project, Scientific & Environmental ROV Partnership using Existing iNdustrial Technology, is a collaboration between world leading scientific institutions and companies associated with the oil and gas industry. SERPENT is hosted at the National Oceanography Centre, Southampton (NOCS), one of the worlds’ largest research and teaching organisations specialising in deep-sea science and oceanography. SERPENT encompasses a scientific network of academic partners across the world (USA, Canada, Brazil, Africa, Australia), linked to a network of major oil and gas operators and contractors. The project centres around the opportunistic use of ROVs (Remotely Operated Vehicles) in operational settings during periods of stand-by time. The project also aims to maximise the scientific benefit of environmental data collected as part of routine offshore operations and environmental surveys. Through access to ROVs and such environmental data scientists at NOCS and from the wider SERPENT partnership aim to improve the scientific understanding of the deep-sea's biodiversity in all its aspects. This document presents the cruise reports for SERPENT missions carried out from 2008 to 2010 and includes a history of all previous SERPENT missions.

The SERPENT Project, Scientific & Environmental ROV Partnership using Existing iNdustrial Technology, is a collaboration between world leading scientific institutions and companies associated with the oil and gas industry. SERPENT is hosted at the National Oceanography Centre, Southampton (NOCS), one of the worlds’ largest research and teaching organisations specialising in deep-sea science and oceanography. SERPENT encompasses a scientific network of academic partners across the world (USA, Canada, Brazil, Africa, Australia), linked to a network of major oil and gas operators and contractors. The project centres around the opportunistic use of ROVs (Remotely Operated Vehicles) in operational settings during periods of stand-by time. The project also aims to maximise the scientific benefit of environmental data collected as part of routine offshore operations and environmental surveys. Through access to ROVs and such environmental data scientists at NOCS and from the wider SERPENT partnership aim to improve the scientific understanding of the deep-sea's biodiversity in all its aspects. This document presents the cruise reports for SERPENT missions carried out from 2008 to 2010 and includes a history of all previous SERPENT missions.

SERPENT visited the Borgsten Dolphin semisubmersible drilling rig at Hurricane Exploration’s Lancaster and Whirlwind drilling sites, West of Shetland in 2010. The work at Lancaster was an opportunity to investigate recovery of biodiversity at the drilling site which had been studied by SERPENT nine months previously. At Whirlwind an assessment of biodiversity and initial study of the effects of disturbance were carried out. At Lancaster background environment data were collected; temperature, salinity and oxygen profiles and seabed current speed and direction. Video surveys and sample collection were used to map disturbance and quantify biodiversity. The size of the area characterised as completely covered by drill cuttings had reduced in the nine months since the initial drilling disturbance commenced. The abundance and diversity of megafaunal organisms was more consistent with distance from the well in 2010 suggesting evidence of some recovery (return to background) from the 2009 situation. There was also some evidence of recolonization in the macrofauna close to the well with organisms present, even in the samples closest to the well. There may however be a change in the macrofaunal community composition, but in order to determine such a change further analysis including a higher number of samples would be essential. Two visits were made to the nearby but slightly deeper Whirlwind site, where the same background data were collected and an assessment made of the initial effects of disturbance. The megafaunal organisms observed at Whirlwind were similar to Lancaster. The extent of complete cuttings coverage of the seabed at reached a maximum of 70m from the well. There was visible evidence of disturbance (incomplete coverage) reaching beyond the extent of the 100 m video surveys to the SE, W and NW of the well, otherwise incomplete coverage of the seabed reached between 10 and 40m beyond the complete coverage (visit 2). The vertical accumulation of cuttings was mea

This report covers the work of the SERPENT Project at the deep water Lagavulin well in the Faroe-Shetland Channel (FSC). As with all deep-sea environments, scientific knowledge about this area is limited. The surveys will investigate how sediment conditions and animal communities around the drilling location change from the baseline to a disturbed situation. Our field results will be compared to previous model predictions of sedimentation at Lagavulin. The baseline sediment is fine and does not have the heterogeneous grain sizes of sediment found in shallower depths in the Faroe-Shetland Channel (e.g. at Rosebank). A total of 18 animal species were observed living on or associated with the seabed at Lagavulin, with megafaunal representatives (i.e. those animals greater than 10 mm) from at least 7 animal groups (phyla). There were species common to other shallower sites (>900m) within the cold water area of the FSC, but no species were common to sites investigated below 600m depth. After drilling and cementing the tophole section drill spoil (cuttings, mud and cement) was found to extend to nearly 150 m from the centre of drilling (down current; S direction). Approximately 33,750 m2 of seabed was disturbed. It was not possible to determine the vertical height of drill spoil. A new image complexity method was successfully trialled in this study to measure the extent of drill spoil. Lagavulin had a low number of visible animals, particularly as many species live partially burrowed into the sediments. The number of seabed animals (non-mobile) found at Lagavulin was very low close to the drill site. It is most likely that these animals were covered with drill cuttings, as 60mm deep cuttings were measured at 20m distant from drilling. There was no evidence that the distribution of mobile animals was affected by drilling.

This report covers the work of the SERPENT project at the deep water exploration well Dalsnuten in the Norwegian Sea (1452 m depth). The study was designed to investigate the general benthic diversity (mega- and macrofauna) at the location and the disturbance on the seabed resulting from drilling activities and the effects of these activities on the benthic environment, the megafaunal and macrofaunal organisms. The seabed at Dalsnuten experiences a low current regime with the sediment consisting of homogeneous fine silt. A total of 78 species, of which 35 are megafauna (<1 cm) and 43 are macrofaunal (≥ 0.5 mm) were recorded. The megafauna was present in low numbers but the species were typical for the deeper cold waters of the Norwegian. The macrofauna samples were dominated numerically by protozoan species such as foraminifera. Disturbance appeared variable with complete coverage of the seabed with drill cuttings reaching as far as 60 m from the well and partial coverage as far as 100 m. Barium concentrations in surface sediments were elevated but decreased with distance. Megafaunal abundance was also significantly reduced and the community structure altered with very few animals observed in a 50 m radius of the well. Approximately 15,000 m2 of seabed were disturbed. A possibly new species of the amphipod genus Neohela was discovered.

The seabed of northern Norway was explored using video and multibeam surveys to assess the distribution of megafauna and examine associations of benthic organisms to their physical environment. The study area was initially divided into ten marine landscapes based on seabed morphology and general water mass distribution. In total 195 taxa were observed during video recordings. The highest number of taxa was found within fjord/coast and upper slope landscapes. Multivariate statistical methods were used to relate bottom environment and taxonomic composition and in order to find the relation between faunal groups and landscapes. Detrended Correspondence Analysis indicated four groups of video transects. The most important environmental factors influencing the groupings were depth, and the frequency of occurrence of mud along the transects. Video transects from canyons and the deep slope formed a distinct group based on faunal composition. The three other groups consisted of transects from banks, fans in outer trough areas, and upper slope/slope terraces respectively. Based on the groups defined by DCA a new set of five landscape classes could be defined. The results indicate that broad-scale topographic features and general hydrography are of relevance for the distribution and composition of megafauna. However to be able to define finer-scaled units of “nature types” more factors (quantitative substrate composition, current regime, etc) must be taken into account, and detailed analyses of the video records must be performed.

The seabed of northern Norway was explored using video and multibeam surveys to assess the distribution of megafauna and examine associations of benthic organisms to their physical environment. The study area was initially divided into ten marine landscapes based on seabed morphology and general water mass distribution. In total 195 taxa were observed during video recordings. The highest number of taxa was found within fjord/coast and upper slope landscapes. Multivariate statistical methods were used to relate bottom environment and taxonomic composition and in order to find the relation between faunal groups and landscapes. Detrended Correspondence Analysis indicated four groups of video transects. The most important environmental factors influencing the groupings were depth, and the frequency of occurrence of mud along the transects. Video transects from canyons and the deep slope formed a distinct group based on faunal composition. The three other groups consisted of transects from banks, fans in outer trough areas, and upper slope/slope terraces respectively. Based on the groups defined by DCA a new set of five landscape classes could be defined. The results indicate that broad-scale topographic features and general hydrography are of relevance for the distribution and composition of megafauna. However to be able to define finer-scaled units of “nature types” more factors (quantitative substrate composition, current regime, etc) must be taken into account, and detailed analyses of the video records must be performed.

Epibiosis on four marine benthic invertebrate species was found to be reduced relative to other nearby surfaces, suggesting the existence of an underlying protection against fouling. In all four cases, toxic chemical antifouling defenses were wanting or inconsistent. However, the lack of epibionts could be attributed to the existence of non-toxic protective properties in all instances, viz. periodic emergence and mutual grazing in the gastropod, Littorina littorea, cumulative filtration and an as yet unidentified fouling-reducing property of the periostracum of the bivalve Mytilus edulis, repellency and, possibly, mucus secretion in the colonial ascidian, Cystodytes lobatus, burrowing, periodic emergence (intertidal individuals) and moulting in the crustacean, Carcinus maenas. It seems that such protective systems are often multiple, consisting of several, more or less overlapping, adaptations to reduce fouling. Characteristics of these non-toxic, multiple protection systems and their significance for potential epibionts are discussed.

Epibiosis on four marine benthic invertebrate species was found to be reduced relative to other nearby surfaces, suggesting the existence of an underlying protection against fouling. In all four cases, toxic chemical antifouling defenses were wanting or inconsistent. However, the lack of epibionts could be attributed to the existence of non-toxic protective properties in all instances, viz. periodic emergence and mutual grazing in the gastropod, Littorina littorea, cumulative filtration and an as yet unidentified fouling-reducing property of the periostracum of the bivalve Mytilus edulis, repellency and, possibly, mucus secretion in the colonial ascidian, Cystodytes lobatus, burrowing, periodic emergence (intertidal individuals) and moulting in the crustacean, Carcinus maenas. It seems that such protective systems are often multiple, consisting of several, more or less overlapping, adaptations to reduce fouling. Characteristics of these non-toxic, multiple protection systems and their significance for potential epibionts are discussed.