Benthic Habitats Thematic Assessment

Cumulative effects assessment for benthic habitats

It should be noted that the Sankey plots and associated narratives in this thematic assessment are an illustrative representation of a complex set of interactions between DAPSIR components at the coarse North-East Atlantic scale and should be considered and interpreted alongside the supporting full thematic assessment narrative. The Sankey plots should thus be applied with caution and not considered or used as the sole basis for management decisions.

A range of human activities contribute pressures which cumulatively have the potential to affect the state of benthic habitats and associated ecosystem services (which have consequences for societal drivers, e.g., food, energy, space, health, biodiversity). Physical disturbance to the seabed, physical loss, climate change, ocean acidification, inputs of other substances, litter, nutrients, organic matter, other forms of energy, non-invasive species, and mortality and injury of species are the predominant pressures. Following a Driver-Activity-Pressure-State-Impact-Response (DAPSIR) framework and a weighting exercise, an indicative assessment of cumulative effects has been undertaken (see: CEMP Guideline for details) as a first step to describing potential pathways of cumulative causes and consequences of change in the ecosystem linking these to impacts on ecosystem services. 

The Benthic Habitats thematic assessment describes the connectivity between the relevant DAPSIR components, and the sections on activities and pressures provide an overview of the evidence available on some of the interactions between these pressures and benthic ecosystems. Sankey diagrams provide a schematic of potential impact pathways describing cumulative causes and consequences of change in the ecosystem, demonstrating that multiple human activities are contributing to multiple pressures which can lead to multiple and cumulative impacts on the state of benthic habitats and the associated ecosystem services (see: CEMP Guideline for details). A better understanding of this complexity in the causes and consequences of cumulative effects from human activities on ecosystem state and ecosystem services is critical in order to apply the ecosystem approach explicitly and target management measures appropriately.

The evidence underpinning the analyses described in this section are drawn from the Driver, Activity, Pressure, State, Impact and Response sections of this thematic assessment, and should thus be read and interpreted alongside the extended narratives provided therein. The sections on Human Activities and Pressures in this thematic assessment provide detail on the threats that the left-hand side of the Sankey plot (Figure CE.1a) pose to benthic habitats. The State section of this thematic assessment provides detail on ecosystem state, shown in the centre of the Sankey plot (Figure CE.1a) illustrated for benthic habitats. The right-hand side of Figure CE.1a incorporates the impact on ecosystem service scores to present the Activity, Pressure, State and Impact components of the benthic habitat ‘ecosystem’ in a single plot. This is consistent with NEAES operational objective S7.O3 on “ecosystem services and natural capital […] to recognise, assess and consistently account for human activities and their consequences in the implementation of ecosystem-based management”.

Figure CE.1a shows the complex combinations of humans and pressures on state changes (left-hand side) and state changes on ecosystem services (right-hand side); however, there is currently insufficient understanding and evidence to be able to directly track from left to right, hence the single bar in the centre. This should be a focus of study to inform future assessments. 

Overall, the confidence in the evidence for the weighted bow-tie analysis outputs presented in this benthic habitat thematic assessment is described as medium for evidence and medium / low for degree of agreement. The confidence assessment does not currently account for regional or biogeographical variability. The sensitivity of benthic ecosystem components to pressures will vary depending on exposure to ambient environmental variables such as depth, temperature and hydrodynamic conditions (e.g., localised tidal regimes). Additionally, separate confidence assessments have been applied to each module.

Figure CE.1a: Impact potential of benthic habitats to exposure to pressures from human activities in the North-East Atlantic. Columns left to right: Activity, Pressure, State, Environmental Impact, Ecosystem Service. Derived from Exposure score (Extent x Frequency of pressure) x Degree of Impact score (in terms of whether the impact is acute or chronic). Pressures with a low Degree of Impact score have been removed for clarity. ‘Impact’ in this context does not consider the persistence of the pressure or the resilience of the ecosystem associated with that pressure. Were these parameters to be included, the relative contribution for some pressures will most likely increase. For example, at the NEA scale, non-indigenous species have a small spatial footprint and thus score relatively low in this Figure, but if their persistence and the resilience of the ecosystem to their presence is considered, they score more highly in the relative ranking. Links are weighted to indicate relative contribution to impact. A wider link = greater potential for impact

NOTE: Confidence in Activity/Pressure impacts, apart from Fish and shellfish harvesting and Climate change, is Low. It should be noted that the Sankey plots and associated narratives in this thematic assessment are an illustrative representation of a complex set of interactions between DAPSIR components at the coarse North-East Atlantic scale and should be considered and interpreted alongside the supporting full thematic assessment narrative., The Sankey plots should thus be applied with caution and not considered or used as the sole basis for management decisions.

Figure CE.1b: Unweighted assessment of the contribution by climate change and greenhouse gas emissions to pressures affecting benthic habitats in the North-East Atlantic. Columns left to right: Activity, Pressure, State, Environmental Impact, Ecosystem Service

Figure CE.1a and CE.1b demonstrate the complex relationships which the collective pressures from human activities exert on the quality status of benthic habitats. This complexity suggests that, while single-issue responses may be effective, in order to fully apply ecosystem-based management OSPAR needs to consider the causes and consequences of changes in ecosystem state more holistically, namely: 

• recognise that any measures to reduce impacts, while critical to ecosystem health, could have potential consequences for our ability to maintain ecosystem services to meet society’s needs, which in turn has consequences for the viability of human activities in the North-East Atlantic;
• recognise that pressures may have additive, multiplicative, synergistic or antagonistic interactions when combined, with implications for the nature of the threats posed to benthic habitats and how best to manage those threats.

Methodology

See: CEMP Guideline: Cumulative effects assessment for the QSR 2023 (Bow Tie Analysis)

A modified bow-tie analysis (Cormier et al., 2018; Cormier et al., 2019) was developed to identify and connect all the DAPSIR components, integrating them into either a pressure (e.g., underwater sound, litter, hazardous substances, eutrophication) or a biodiversity receptor-focused analysis of the causes and consequences of change (e.g., pelagic habitats, benthic habitats, fish, marine birds, marine mammals). For the biodiversity assessments the APS connections are weighted to determine which are the most important, using an adaptation of the ODEMM pressure assessment (Robinson et al., 2013; Knights et al., 2015) focusing on:

1. Exposure module: spatial extent and frequency for all activity pressure combinations on state, to generate exposure weightings;
2. Impact potential module: spatial extent, frequency of occurrence and impact potential for all activity pressure combinations on state, to generate impact potential weightings;
3. Risk module: spatial extent, frequency of occurrence, impact potential for all activity pressure combinations on state, combined with pressure persistence and ecosystem resilience, to generate risk weightings.

The SI (ecosystem services) connections are weighted to determine which are the most important (Cornacchia, 2022).

The impact potential and ecosystem services outputs are combined and presented in Sankey diagrams (Figure CE.1).

Confidence in this weightings exercise for benthic habitats has been assessed in accordance with the QSR 2023 guidance. Confidence is based on two criteria to communicate degree of uncertainty in the key findings: (i) level of evidence (determined by considering the type, amount, quality, and consistency of evidence (i.e. Robust, Medium, or Limited)), and (ii) degree of agreement (i.e., High, Medium, or Low).

Exposure module:

Confidence Assessment: Evidence – Medium; Consensus – Medium

Pressures from human activities have been demonstrated in the assessments for this QSR to be widely distributed in the OSPAR Maritime Area. The presence of pressures does not automatically lead to impacts. However, in the first instance, consideration of the spatial and temporal extents of pressures provides a useful basis for our consideration of cumulative effects within a risk-based approach (in line with the North-East Atlantic ecosystem principle and strategic approach). 

The exposure module describes how much pressure from human activities exists in the North-East Atlantic. It considers the spatial extent and frequency of human activity pressure combinations which have been identified as important for benthic habitats (derived from spatial extent score multiplied by frequency score). Exposure relates only to the pressure cell in the DAPSIR schema (Figure CE.1). Consideration of exposure in isolation provides a coarse cross-cutting assessment to provide an early identification which enables OSPAR to develop management strategies for pressures in order to prevent / minimise impacts.

The thematic assessments for Hazardous Substances, Eutrophication, Marine Litter, Offshore Industry, Human Activities, Climate Change and the Ocean Acidification Other Assessment describe pressures on benthic habitats. The Radioactive Substances Committee Thematic Assessment identifies inputs of radionuclides from a range of human activities but has concluded that there are no significant radiological impacts on biodiversity from the current levels of radionuclides.

Climate Change and Ocean Acidification pressures have been identified as important for benthic habitats. 

Input of other substances; input of nutrients and organic matter; input of litter; physical disturbance to the seabed; input of radioactive substances; input and spread of NIS; extraction of species; and input of other forms of energy are also identified as important and rank highly for exposure, demonstrating the ubiquitous nature of some of these pressures in the North-East Atlantic.

The exposure scores support the importance that OSPAR places on these pressures in the North-East Atlantic Environment Strategy:

• Strategic Objective 1 to tackle eutrophication by limiting inputs of nutrients and organic matter (and the work of the Hazardous Substances and Eutrophication Committee (Eutrophication Thematic Assessment). 
• Strategic Objective 2 to prevent pollution by hazardous substances and the work of the Hazardous Substances and Eutrophication Committee (Hazardous Substances Thematic Assessment).
• Strategic Objective 3 to prevent pollution by radioactive substances and the work of the Radioactive Substances Committee (Radioactive Substances Committee Thematic Assessment) 
• Strategic Objective 4 to prevent inputs and significantly reduce marine litter (Marine Litter Thematic Assessment) and the work of the Environmental Impacts of Human Activities Committee (Human Activities Thematic Assessment) 
• Strategic Objective 5 to protect and conserve marine biodiversity and ecosystems (this Benthic Habitats thematic assessment, the work of the Biodiversity Committee, including the other biodiversity thematic assessments (Pelagic Habitats Thematic Assessment, Fish Thematic Assessment, Marine Mammals Thematic Assessment, Marine Birds Thematic Assessment, Food Webs Thematic Assessment).
• Strategic Objective S7.02 to develop a coordinated management approach to ensure the number of non-indigenous species introduced via human activity is minimised and where possible reduced to zero.
• Strategic Objective 9 to safeguard the structure and functions of the seabed / marine ecosystems by preventing significant habitat loss and physical disturbance (this Benthic Habitats thematic assessment and the work of the Biodiversity Committee).
• Strategic Objectives 10 to raise awareness of climate change and ocean acidification; 11 to facilitate adaptation to the impacts of climate change and ocean acidification; and 12 to mitigate climate change and ocean acidification.

Multiple human activities have been identified as exerting these pressures in the North-East Atlantic. Any actions to manage these pressures to prevent or reduce impacts on state either individually or cumulatively (collectively) will need to consider if and how these human activities might best be targeted (and the consequences for the associated drivers and ecosystem services) within an Ecosystem Approach.

Impact potential module:

Confidence Assessment: Evidence – Medium; Consensus – Medium / Low

The impact potential is incorporated with the exposure module (spatial extent and frequency) of pressures from specified human activities. Impact potential here relates to the generic interaction in terms of a pressure’s likely effects on the ecological component, categorised as low potential for significant impact, chronic impact or acute impact (Robinson et al., 2013). Figure CE.1 shows the combined weighted scores for exposure and impact potential. 

Any activity-pressure combination with a low Degree of Impact score was filtered out, following discussion with the expert group. For example, the input of radionuclides has been filtered out based on the conclusions in the Radioactive Substances Committee Thematic Assessment , as the available evidence shows that these have a low potential for resulting in a significant impact. Other pressures filtered out as having low potential for significant impact are inputs of other forms of energy from marine aquaculture, oil and gas extraction and subsea cables.

The relative ranking of pressures changes when impact is considered (Figure CE.1a). Physical disturbance to the seabed from multiple activities ranks highest (as it is the most widespread and frequently occurring pressure), as does physical loss of habitats. Climate change and ocean acidification pressures are considered highly important for benthic habitats (see the Climate Change Thematic Assessment for details of contributing human activities and the Ocean Acidification Other Assessment ) and the climate change section, but there is low confidence in incorporating these pressures directly into weighted bow- tie analyses (Figure CE.1a), so they are shown separately in Figure CE.1b. The Pressures section of this thematic assessment describes the importance of pressures on benthic habitats and corroborates the importance of seabed disturbance and climate change pressures. Although the weighted bow-tie analysis has identified relative rankings for other pressures, the OSPAR Benthic Habitats Expert Group considers that limited evidence exists to confirm these relative rankings. It is thus concluded that the other pressures shown in Figure CE.1a should be considered of equal importance until further evidence can be provided (i.e., input of other substances, input of nutrients, input of organic matter, input of litter, mortality and injury of wild species, input of other forms of energy, input and spread of NIS, and others).

Impacts on the state of habitats across OSPAR will vary depending on the variability of activities and pressures across regional areas, as well as variations in their interactions with different habitat types, for example coastal habitats under highly hydrodynamic regimes against deeper habitats highly sensitive to changes in natural environmental conditions. Most of the data available on the status of habitats and impacts have been evaluated using results from the common and candidate benthic indicators for some of the main activities and predominant associated pressures, in particular physical disturbance caused by bottom trawling and aggregate extraction in benthic habitats, and impacts from nutrients on coastal waters. The evaluation of habitat loss is only available for some areas. Additional impacts from pressures to be included in the next round of assessments will help us to build a wider picture of the interactions and effects on benthic ecosystem status. Impacts from climate change and ocean acidification have not been evaluated with a set of indicators; however, there is a wide range of evidence on the sensitivity of these habitats to climatic drivers and acidification effects, which will be investigated further to improve benthic status assessments.

Risk module:

Confidence Assessment: Evidence – Low; Consensus – Low

Given the low confidence score, the outputs from the risk analyses have not been included in this thematic assessment for QSR 2023. Nevertheless, it is beneficial to consider the agreed outputs of the persistence weightings. Details of the criteria applied in the risk module are described in the CEMP Guideline.

Regional summary of likely cumulative effects:

Confidence Assessment: Evidence – High; Consensus – Medium

Although the weighted bow-tie analyses displayed in the Sankey diagrams have been produced at the North-East Atlantic scale, consideration can be given to where regional differences may arise through cross-referencing with other assessments in QSR 2023.

The Benthic Habitats Thematic Assessment identifies the cumulative pressures for benthic habitats in terms of both exposure and impact , but does not attempt a regional breakdown of pressures :

The list below summarises the main pressures on benthic habitats, with information on associated activities. Please note that activity-pressure combinations scored as low impact based on the current available evidence have been filtered out from the Sankey diagram in Figure CE.1a. The activity-pressure links listed below relate to the unfiltered outputs used in the Exposure assessment. 

• Climate change and ocean acidification pressures;
• Habitat loss and physical disturbance from extraction of oil and gas; restructuring of seabed morphology; tourism and leisure infrastructure; transmission of electricity and communications; aquaculture – marine; coastal protection and flood defence; renewable energy generation; transport infrastructure; fish and shellfish harvesting and extraction of minerals;
• Extraction or mortality of wild species through extraction of oil and gas and fish and shellfish harvesting as well as from transport infrastructure, coastal defence and flood protection;
• Input of nutrients from urban uses, waste water treatment and disposal; industrial uses; transport – shipping; agriculture; extraction of oil and gas; restructuring of seabed morphology; tourism and leisure infrastructure; aquaculture; coastal defence and renewable energy generation; 
• Input of other substances from urban uses; waste water treatment and disposal; industrial uses; transport – shipping; research, survey and educational activities; military operations; agriculture; extraction of oil and gas; restructuring of seabed morphology; tourism and leisure infrastructure; transmission of electricity and communications; aquaculture – marine; coastal protection and flood defence; renewable energy generation and non-renewable energy (Nuclear);
• Input of litter from transport – shipping; extraction of oil and gas; restructuring of seabed morphology; tourism and leisure infrastructure; aquaculture – marine; coastal protection and flood defence and renewable energy generation;
• Input of organic matter from agriculture; extraction of oil and gas; restructuring of seabed morphology; tourism and leisure infrastructure; transmission of electricity and communications; aquaculture – marine; coastal protection and flood defence; renewable energy generation and transport infrastructure;
• Input of NIS from extraction of oil and gas; tourism and leisure infrastructure; transmission of electricity and communications; aquaculture – marine; coastal protection and flood defence; renewable energy generation and transport infrastructure;
• Input of other forms of energy from extraction of oil and gas; tourism and leisure infrastructure; transmission of electricity and communications; aquaculture – marine; coastal protection and flood defence and renewable energy generation;
• Disturbance of species from non-renewable energy generation (Nuclear); extraction of minerals (Aggregate extraction), fish and shellfish harvesting and extraction of minerals.

It should be noted that some of the activities listed above, even if considered to be high intensity, are very localised, for example aggregate extraction, and proportionally only affect a small area of habitats within a region, whereas other activities have high intensity and are very localised but affect a large proportion of habitats (and have the potential to grow in the near future), for example offshore wind and associated infrastructure. Activities such as fisheries harvesting can generate widespread pressures across most habitat types. 

OSPAR does not have evidence on all human activities, but a regional breakdown of relative intensities for agriculture; aquaculture; extraction of minerals (aggregates); oil and gas; nuclear; renewable energy; fisheries and shipping has been drawn from the supporting evidence for QSR 2023 and is summarised below. The direct influences of the cumulative pressures on benthic habitats from these activities are likely to follow similar trends in intensity within these regions. Pressures spread beyond the spatial extents of the human activities, but insufficient evidence is currently available, so trends in indirect cumulative pressures have not been considered.

The Offshore Industry Thematic Assessment describes:

• low relative intensity of oil and gas sector activity in the Bay of Biscay and Iberian Coast (Region IV) and Wider Atlantic (Region V);
• moderate relative intensity of oil and gas sector activity in Arctic Waters (Region I) and Celtic Seas (Region III);
• high relative intensity of oil and gas sector activity in Greater North Sea (Region II).

The Human Activities Thematic Assessment describes:

• low relative intensity of aggregate extraction sector activity in Arctic Waters (Region I) and Wider Atlantic (Region V);
• moderate relative intensity of aggregate extraction sector activity in Celtic Seas (Region III) and Bay of Biscay and Iberian Coast (Region IV);
• high relative intensity of aggregate extraction sector activity in Greater North Sea (Region II);
• moderate relative intensity of agriculture sector activity in Celtic Seas (Region III) and Bay of Biscay and Iberian Coast (Region IV);
• high relative intensity of agriculture sector activity in Greater North Sea (Region II);
• moderate relative intensity of aquaculture sector activity in Celtic Seas (Region III) and Bay of Biscay and Iberian Coast (Region IV);
• high relative intensity of aquaculture sector activity in Arctic Waters (Region I) and Greater North Sea (Region II);
• low relative intensity of fisheries sector activity in Wider Atlantic (Region V);
• moderate relative intensity of fisheries sector activity in Bay of Biscay and Iberian Coast (Region IV);
• high relative intensity of fisheries sector activity in Arctic Waters (Region I), Greater North Sea (Region II) and Celtic Seas (Region III);
• low relative intensity of offshore renewable energy sector activity in Bay of Biscay and Iberian Coast (Region IV);
• moderate relative intensity of offshore renewable energy sector activity in Celtic Seas (Region III);
• high relative intensity of offshore renewable energy sector activity in Greater North Sea (Region II);
• low relative intensity of tourism sector activity in Arctic Waters (Region I) and Wider Atlantic (Region V);
• moderate relative intensity of tourism sector activity in Celtic Seas (Region III);
• high relative intensity of tourism sector activity in Greater North Sea (Region II) and Bay of Biscay and Iberian Coast (Region IV);
• low relative intensity of transport and shipping sector activity in Wider Atlantic (Region V);
• moderate relative intensity of transport and shipping sector activity in Arctic Waters (Region I);
• high relative intensity of transport and shipping sector activity in Greater North Sea (Region II), Celtic Seas (Region III) and Bay of Biscay and Iberian Coast (Region IV).

The Radioactive Substances Committee Thematic Assessment describes:

• no nuclear sector activity in Wider Atlantic (Region V);
• low relative intensity of nuclear sector activity in Arctic Waters (Region I).
• moderate relative intensity of nuclear sector activity in Bay of Biscay and Iberian Coast (Region IV);
• high relative intensity of nuclear sector activity in Greater North Sea (Region II) and Celtic Seas (Region III).

Regional evidence for trends in the intensity of other human activities and Climate Change and Ocean Acidification was not available in sufficient detail to be used in this assessment.