The Marine Life Information Network

Global warming

Middle emission scenario (by the end of this century 2081-2100) benchmark of:

• A 3°C rise in SST, NBT (coastal to the shelf seas) and surface air temperature (in eulittoral and supralittoral habitats).

• A 1°C rise in Deep-sea habitats (>200 m) off the continental shelf.

• A 2°C rise in surface air temperature in intertidal habitats exclusive to Scotland.

High emission scenario (by the end of this century 2081-2100) benchmark of:

• A 4°C rise in SST, NBT (coastal to the shelf seas) and surface air temperature (in eulittoral and supralittoral habitats).

• A 1°C rise in Deep-sea habitats (>200 m) off the continental shelf, and

• A 3°C rise in surface air temperature in intertidal habitats exclusive to Scotland.

Extreme emission scenario (by the end of this century 2081-2100) benchmark of:

• A 5°C rise in SST and NBT (coastal to the shelf seas),

• A 6°C rise in surface air temperature (in eulittoral and supralittoral habitats).

• A 1°C rise in Deep-sea habitats (>200 m) off the continental shelf, and

• A 5°C rise in surface air temperature in intertidal habitats exclusive to Scotland.

Global warming results from the retention of thermal energy within the atmosphere and hence the ocean by ‘greenhouse’ gases, such as CO₂ and CH₄ (amongst others).  Since the industrial revolution (in the 1800s) the average temperature of the globe has risen by 1°C and the CO₂ concentration in the atmosphere is currently the highest it has been in the last 800,000 years (at over 400 ppm) (Palmer et al., 2018; IPCC, 2019).  Since the 1970s, the ocean has absorbed ca 93% of the extra heat (Laffoley & Baxter, 2016).  As a result, models predict varying increases in average air and sea surface temperature, depending on the greenhouse gas emission scenario used, well beyond the end of this century (Palmer et al., 2018; IPCC, 2019). 

Comments. Air temperature is included for marine species /habitats in the eulittoral and supralittoral that will be exposed to air when emersed.  SST = Sea surface temperature; NBT = Near bottom temperature.

Marine heatwaves

Middle emission scenario benchmark: A marine heatwave occurring every three years, with a mean duration of 80 days, with a maximum intensity of 2°C.

High emission scenario benchmark: A marine heatwave occurring every two years, with a mean duration of 120 days, and a maximum intensity of 3.5°C.

A marine heatwave can be defined as a period when SST exceeds its local 99^th percentile, based on daily observations of satellite data (Frölicher et al., 2018), and occurs when air temperatures exceed the seasonal average (Garrabou et al., 2009).  Marine heatwaves have already doubled in frequency since the 1860 - 1880 baseline, and it is very likely that 84-90% of marine heatwaves occurring from 2005-2016 are attributable to anthropogenic temperature rises (Frölicher et al., 2018).  Marine heatwaves are expected to increase in frequency, duration, extent and intensity, with climate models predicting that the frequency of marine heatwaves will increase 50-fold for RCP 8.5 and 20-fold for RCP 2.6 by 2081-2100 relative to 1850-1900 (IPCC, 2019). Marine heatwaves can be caused by a range of factors, such as:

• air-sea heat flux when the surface temperature reaches anomalously high temperatures such as the heatwave experienced in the Mediterranean in the summer of 2003 (Smale et al., 2019),

• a decrease in heat loss and a reduction in cold advection which caused a persistent (2013-2016 ) warm heat anomaly ‘the Blob’ in the NE Pacific (Bond et al., 2015), and

• El Nińo events in the tropical Pacific (Holbrook et al., 2019).

For example, the Mediterranean heatwave of 2003 saw air temperatures soar to 3-6°C above mean seasonal temperatures, lasting from early June until mid-August, and led to occurrence of a marine heatwave where mean and maximum SSTs were between 1 and 3^OC higher than average which saw widespread mortality on rocky reefs (Garrabou et al., 2009). Heatwaves caused by increased air-sea heat flux due to significantly warmer summer temperatures are the most likely heatwaves that the UK will face in the future (D. Smale, pers. comms.).  These heatwaves generally only impact shallow water habitats (≤ 50 m).

Ocean acidification

Middle emission scenario benchmark: a further decrease in pH of 0.15 (annual mean) and a corresponding 35% increase in H+ ions with no coastal aragonite undersaturation and the aragonite saturation horizon in the NE Atlantic, off the continental shelf, at a depth of 800 m by the end of this century 2081-2100.

High emission scenario benchmark: a further decrease in pH of 0.35 (annual mean) and corresponding 120% increase in H+ ions, seasonal aragonite saturation of 20% of UK coastal waters and North Sea bottom waters, and the aragonite saturation horizon in the NE Atlantic, off the continental shelf, occurring at a depth of 400 m by the end of this century 2081-2100.

Increased CO₂ concentrations in the atmosphere are absorbed by the ocean.  Increased CO₂ concentrations affect the carbonate chemistry of seawater, and result in a reduction in pH, changes in the carbonate saturation and, potentially, hypercapnia (CO₂ poisoning) in marine organisms.  Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s, leading to a 25% increase in H⁺ ions (Jacobson, 2005). However, the pH of surface waters are highly variable over time (Fig. 5), which reflects seasonal cycles in photosynthesis, respiration and water mixing (Ostle et al., 2016). 

Marine calcifiers may be particularly at risk, especially as waters suffer from seasonal aragonite undersaturation, leading to the dissolution of calcium carbonate.  Aragonite saturation state is influenced by dissolved inorganic carbon (DIC) concentration, pressure and temperature so that deep waters, which have high levels of DIC, high pressure and low temperatures, will be the first habitats to face undersaturation (C. Ostle pers. comms.). 

Sea-level rise

Middle emission scenario benchmark: a 50 cm rise in average UK sea-level rise by the end of this century (2081-2100).

High emission scenario benchmark: a 70 cm rise in average UK by the end of this century (2018-2100).

Extreme scenario benchmark: a 107 cm rise in average UK by the end of this century (2018-2100).

Sea-level rise results from a combination of the thermal expansion of seawater and ice melt (e.g. ice sheets and glaciers).  Sea-levels have risen 1-3 mm yr^-1 in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006).  The global mean sea-level has risen by 0.16 m (a range of 0.12-0.21 m) between 1902 and 2015 (IPCC, 2019).  The rate of rise in 2006-2015 is unprecedented compared to the last century, during which period, sea-level rise has been dominated by melting ice-sheets and glaciers (IPCC, 2019).

A rise in sea-level increases the water depth at the shore and results in increased wave and tidal energy along the shore, due to the increase in fetch and reduction in wave attenuation (Pethick, 2001; Crooks, 2004; Fujii, 2012).  As a result, coastal landforms (e.g. subtidal bedforms, intertidal flats, saltmarshes, shingle banks, sand dunes, cliffs and coastal lowlands) migrate along and parallel to the shore to maintain their position with the coastal energy gradient (Cooks, 2004; Fujii, 2012).  Sedimentary habitats are dynamic and liable to adapt to sea-level rise, except where hard structures (e.g. cliffs and artificial structures) prevent their natural movement, where existing intertidal areas are likely to be submerged, eroded, or moved (coastal squeeze).

Temperature changes - local

A decrease or an increase in 5°C for one month, or 2°C for one year.

Events or activities increasing or decreasing local water temperature. This is most likely from thermal discharges, e.g. the release of cooling waters from power stations. This could also relate to temperature changes in the vicinity of operational sub-sea power cables. This pressure only applies within the thermal plume generated by the pressure source. It excludes temperature changes from global warming which will be at a regional scale (and as such are addressed under the climate change pressures).

Comments. The increase and decrease in temperature are assessed separately.

Salinity changes - local

A decrease or an increase in one MNCR salinity category outside the usual range of the biotope/habitat for one year.

Events or activities increasing or decreasing local salinity. This relates to anthropogenic sources/causes that have the potential to be controlled, e.g. freshwater discharges from pipelines that reduce salinity, or brine discharges from salt caverns washings that may increase salinity. This could also include hydromorphological modification, e.g. capital navigation dredging if this alters the halocline or erection of barrages or weirs that alter freshwater/seawater flow/exchange rates. The pressure may be temporally and spatially delineated derived from the causal event/activity and local environment.

Comments. The increase and decrease in salinity are assessed separately.

Water flow (tidal current) changes - local (including sediment transport considerations)

A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year

Changes in water movement associated with tidal streams (the rise and fall of the tide, riverine flows), prevailing winds and ocean currents. The pressure is therefore associated with activities that have the potential to modify hydrological energy flows, e.g. tidal energy generation devices remove (convert) energy and such pressures could be manifested leeward of the device, capital dredging may deepen and widen a channel and therefore decrease the water flow, canalisation &/or structures may alter flow speed and direction; managed realignment (e.g. Wallasea, England). The pressure will be spatially delineated. The pressure extremes are a shift from a high to a low energy environment (or vice versa). The biota associated with these extremes will be markedly different as will the substratum, sediment supply/transport and associated seabed/ground elevation changes. The potential exists for profound changes (e.g. coastal erosion/deposition) to occur at long distances from the construction itself if an important sediment transport pathway was disrupted. As such these pressures could have multiple and complex impacts associated with them.

Emergence regime changes - local (includes tidal level change considerations)

A change in the time covered or not covered by the sea for a period of ≥ 1 year.

Or

An increase in relative sea level or decrease in high water level for ≥ 1 year.

Changes in water levels reducing the intertidal zone and the associated/dependent habitats. The pressure relates to changes in both the spatial area and duration that intertidal species are immersed and exposed during tidal cycles (the percentage of immersion is dependent on the position or height on the shore relative to the tide). The spatial and temporal extent of the pressure will be dependent on the causal activities but can be delineated. This relates to anthropogenic causes that may directly influence the temporal and spatial extent of tidal immersion, e.g. upstream and downstream of a tidal barrage the emergence would be respectively reduced and increased, beach re-profiling could change gradients and therefore exposure times, capital dredging may change the natural tidal range, managed realignment, salt marsh creation. Such alteration may be of importance in estuaries because of their influence on tidal flushing and potential wave propagation. Changes in tidal flushing can change the sediment dynamics and may lead to changing patterns of deposition and erosion. Changes in tidal levels will only affect the emergence regime in areas that are inundated for only part of the time. The effects that tidal level changes may have on sediment transport are not restricted to these areas, so a very large construction could significantly affect the tidal level at a deep site without changing the emergence regime. Such a change could still have a serious impact. This excludes pressure from sea level rise.

Comments. The benchmark is only relevant to the intertidal, excluding habitats below Chart Datum (CD). The pressure benchmark does not expressly identify the role of ‘desiccation’ but sensitivity to desiccation will be discussed where known or relevant. In application, the majority of intertidal communities are sensitive to changes in emergence, whether it is for one or more hours, or due to changes in sea level and coastal squeeze. The duration assumes that the effects on most communities would probably take a year to become apparent.

Wave exposure changes - local

A change in nearshore significant wave height of >3% but <5% for one year

Local changes in wave length, height and frequency. Exposure on an open shore is dependent upon the distance of open sea water over which wind may blow to generate waves (the fetch) and the strength and incidence of winds. Anthropogenic sources of this pressure include artificial reefs, breakwaters, barrages, and wrecks that can directly influence wave action or activities that may locally affect the incidence of winds, e.g. a dense network of wind turbines may have the potential to influence wave exposure, depending upon their location relative to the coastline.

Comments. Further research is required on the correlation between significant wave height and wave exposure scales. The definition is subject to further revision.

Physical change (to another substratum type)

Benthic species or habitat

• Change in sediment type by one Folk class (based on UK SeaMap simplified classification).
• Change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa.

The permanent change of one marine habitat type to another marine habitat type, through the change in the substratum, including to artificial (e.g. concrete). This, therefore, involves the permanent loss of one marine habitat type but has an equal creation of a different marine habitat type. Associated activities include the installation of infrastructure (e.g. the surface of platforms or wind farm foundations, marinas, coastal defences, pipelines and cables), the placement of scour protection where soft sediment habitats are replaced by hard/coarse substratum habitats, removal of coarse substrata (marine mineral extraction) in those instances where surficial finer sediments are lost, capital dredging where the residual sedimentary habitat differs structurally from the pre-dredge state, creation of artificial reefs, mariculture i.e. mussel beds. Protection of pipes and cables using rock dumping and mattressing techniques. Placement of cuttings piles from oil & gas activities could fit this pressure type, however, there may be additional pressures, e.g. "pollution and other chemical changes" theme. This pressure excludes navigation dredging where the depth of sediment is changed locally but the sediment typology is not changed.

Comments. Tillin & Tyler-Walters (2014a&b) did not consider the change in one Folk class benchmark applicable to hard rock biotopes but did assess the sensitivity of biotopes occurring on softer substrata, including chalk, peat, mud rock, and clay. The simplified Folk class referred to in the benchmark is based on the simplified classification used for UK SeaMap as described by Long (2006).

A change from sediment to hard rock (or vice versa) would affect all types of substratum, and all habitats would be assessed as highly sensitive. This pressure assumes a permanent change, while short-term smothering of substrata with sediment is addressed under smothering (siltation).

Physical loss (to land or freshwater habitat)

Permanent loss of existing saline habitat within the site

The permanent loss of marine habitats. Associated activities are land claim, new coastal defences that encroach on and move the Mean High Water Springs mark seawards, the footprint of a wind turbine on the seabed, and dredging if it alters the position of the halocline. This excludes changes from one marine habitat type to another marine habitat type.

Habitat structure changes - removal of substratum (extraction)

Extraction of substratum to 30 cm (where substratum includes sediments and soft rocks but excludes hard bedrock)

Unlike the "physical change" pressure type where there is a permanent change in sea bed type (e.g. sand to gravel, sediment to a hard artificial substratum) the "habitat structure change" pressure type relates to temporary and/or reversible change, e.g. from marine mineral extraction where a proportion of seabed sands or gravels are removed but a residual layer of the seabed is similar to the pre-dredge structure and as such biological communities could re-colonize; navigation dredging to maintain channels where the silts or sands removed are replaced by non-anthropogenic mechanisms so the sediment typology is not changed.

Abrasion/disturbance at the surface of the substratum

Benthic species /habitats

Damage to surface features (e.g. species and physical structures within the habitat)

Physical disturbance or abrasion at the surface of the substratum in sedimentary or rocky habitats. The effects are relevant to epiflora and epifauna living on the surface of the substratum. In intertidal and sublittoral fringe habitats, surface abrasion is likely to result from recreational access and trampling (inc. climbing) by humans or livestock, vehicular access, moorings (ropes, chains), activities that increase scour and grounding of vessels (deliberate or accidental). In the sublittoral, surface abrasion is likely to result from pots or creels, cables and chains associated with fixed gears and moorings, anchoring of recreational vessels, objects placed on the seabed such as the legs of jack-up barges, and harvesting of seaweeds (e.g. kelps) or other intertidal species (trampling) or of epifaunal species (e.g. oysters). In sublittoral habitats, passing bottom gear (e.g. rock hopper gear) may also cause surface abrasion to epifaunal and epifloral communities, including epifaunal biogenic reef communities. Activities associated with surface abrasion can cover relatively large spatial areas e.g. bottom trawls or bio-prospecting or be relatively localized activities e.g. seaweed harvesting, recreation, potting, and aquaculture.

Penetration and/or disturbance of the substratum below the surface

Benthic species /habitats

Damage to sub-surface features (e.g. species and physical structures within the habitat)

Physical disturbance of sediments where there is limited or no loss of substratum from the system. This pressure is associated with activities such as anchoring, taking of sediment/geological cores, cone penetration tests, cable burial (ploughing or jetting), propeller wash from vessels, and certain fishing activities, e.g. scallop dredging, and beam trawling. Agitation dredging, where sediments are deliberately disturbed by gravity & hydraulic dredging where sediments are deliberately disturbed and moved by currents could also be associated with this pressure type. Compression of sediments, e.g. from the legs of a jack-up barge could also fit into this pressure type. Abrasion relates to the damage of the sea bed surface layers (typically up to 50 cm depth). Activities associated with abrasion can cover relatively large spatial areas and include fishing with towed demersal trawls (fish & shellfish); bio-prospecting such as harvesting of biogenic features such as maerl beds where, after extraction, conditions for recolonization remain suitable or relatively localised activities including seaweed harvesting, recreation, potting, aquaculture. Change from gravel to silt substrata would adversely affect herring spawning grounds.

Loss, removal or modification of the substratum is not included within this pressure (see the physical loss pressure theme). Penetration and damage to the soft rock substrata are considered, however, penetration into hard bedrock is deemed unlikely.

Changes in suspended solids (water clarity)

A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year.

Changes in water clarity (or turbidity) due to changes in sediment & organic particulate matter and chemical concentrations. It is related to activities disturbing sediment and/or organic particulate matter and mobilizing it into the water column. It could be 'natural' land run-off and riverine discharges or from anthropogenic activities such as all forms of dredging, disposal at sea, cable and pipeline burial, and secondary effects of construction works, e.g. breakwaters. Particle size, hydrological energy (current speed & direction) and tidal excursion are all influencing factors on the spatial extent and temporal duration. Salinity, turbulence, pH and temperature may result in flocculation of suspended organic matter. Anthropogenic sources are mostly short-lived and over relatively small spatial extents. Changes in suspended sediment loads can also alter the scour experienced by species and habitats. Therefore, the effects of scour are also addressed here.

Smothering and siltation rate changes (depth of vertical sediment overburden)

Benthic species/habitat

‘Light’ deposition of up to 5 cm of fine material added to the habitat in a single, discrete event

‘Heavy’ deposition of up to 30 cm of fine material added to the habitat in a single discrete event

When the natural rates of siltation are altered (increased or decreased). Siltation (or sedimentation) is the settling out of silt/sediments suspended in the water column. Activities associated with this pressure type include mariculture, land claim, navigation dredging, disposal at sea, marine mineral extraction, cable and pipeline laying and various construction activities. It can result in short-lived sediment concentration gradients and the accumulation of sediments on the sea floor. This accumulation of sediments is synonymous with "light" smothering, which relates to the depth of vertical overburden. “Light” smothering relates to the deposition of layers of sediment on the seabed. It is associated with activities such as sea disposal of dredged materials where sediments are deliberately deposited on the sea bed. For “light” smothering most benthic biota may be able to adapt, i.e. vertically migrate through the deposited sediment.

“Heavy” smothering also relates to the deposition of layers of sediment on the seabed but is associated with activities such as sea disposal of dredged materials where sediments are deliberately deposited on the sea bed. This accumulation of sediments relates to the depth of vertical overburden where the sediment type of the existing and deposited sediment has similar physical characteristics because, although most species of marine biota are unable to adapt, e.g. sessile organisms unable to make their way to the surface, a similar biota could, with time, re-establish. If the sediments were physically different this would fall under L2. 

Comments. ‘Light’ and ‘Heavy’ smothering are assessed separately.

Litter

Benthic species/habitat

Introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline)

Marine litter is any manufactured or processed solid material from anthropogenic activities discarded, disposed or abandoned (excluding legitimate disposal) once it enters the marine and coastal environment including plastics, metals, timber, rope, fishing gear etc. and their degraded components, e.g. microplastic particles. Ecological effects can be physical (smothering), biological (ingestion, including uptake of microplastics; entangling; physical damage; accumulation of chemicals) and/or chemical (leaching, contamination).

Comments. The sensitivity to litter is not assessed for habitats at present. It was scored ‘No evidence’ by Tillin & Tyler-Walters (2014a&b). Clearly, it is relevant for large macrofauna such as fish, birds and mammals. Further study is required to agree on suitable pressure benchmarks based on current evidence. 

Electromagnetic changes

A local electric field of 1 V/m or a local magnetic field of 10 µT. 

Localized electric and magnetic fields associated with operational power cables and telecommunication cables (if equipped with power relays). Such cables may generate electric and magnetic fields that could alter the behaviour and migration patterns of sensitive species (e.g. sharks and rays).

Comments. The evidence to assess these effects against the pressure benchmark is very limited and the impact of this pressure could not be assessed for benthic species or habitats (Tillin & Tyler-Walters, 2014a&b).

Noise changes

Underwater noise:

Benthic species/habitat

MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year

Increases over and above background noise levels (consisting of environmental noise (ambient) and incidental man-made/anthropogenic noise (apparent)) at a particular location. Species known to be affected are marine mammals and fish. The theoretical zones of noise influence (Richardson et al 1995) are temporary or permanent hearing loss, discomfort & injury; response; masking and detection. In extreme cases, noise pressures may lead to death. The physical or behavioural effects are dependent on a number of variables, including the sound pressure, loudness, sound exposure level and frequency. High amplitude low and mid-frequency impulsive sounds and low frequency continuous sounds are of greatest concern for effects on marine mammals and fish. Some species may be responsive to the associated particle motion rather than the usual concept of noise. Noise propagation can be over large distances (tens of kilometres) but transmission losses can be attributable to factors such as water depth and sea bed topography. Noise levels associated with construction activities, such as pile-driving, are typically significantly greater than operational phases (i.e. shipping, the operation of a wind farm).

Comments. Any loud noise made onshore or offshore by construction, vehicles, vessels, tourism, mining etc. may disturb birds and reduce time spent in feeding or breeding areas. Only relevant to birds and sea mammals that spend time on land for breeding purposes (haul-outs). It is unlikely to be relevant to marine habitat sensitivity assessments. The MSFD indicator (2010) states “the proportion of days within a calendar year, over areas of 15’N x 15’E/W in which anthropogenic sound sources exceed either of two levels, 183 dB re 1μPa2.s (i.e. measured as Sound Exposure Level, SEL) or 224 dB re 1μPa peak (i.e. measured as peak sound pressure level) when extrapolated to one metre, measured over the frequency band 10 Hz to 10 kHz”.

Introduction of light or shading

Change in incident light via anthropogenic means.

Direct inputs of light from anthropogenic activities, i.e. lighting on structures during construction or operation to allow 24-hour working; new tourist facilities, e.g. promenade or pier lighting, lighting on oil & gas facilities etc. Ecological effects may be the diversion of bird species from migration routes if they are disorientated by or attracted to the lights. It is also possible that continuous lighting may lead to increased algal growth.

Comments. The introduction of light is unlikely to be relevant for most benthic invertebrates, except where it is possible to interfere with spawning cues. But we are not aware of evidence to that effect. The introduction of light could potentially be beneficial for immersed plants, but again, we are not aware of any relevant evidence. Alternatively, shading (e.g. due to overgrowth, construction of jetties or other artificial structures) could adversely affect shallow sublittoral macroalgae, seagrass, and pondweeds.

Barrier to species movement

Benthic species

Permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion

The physical obstruction of species movements and including local movements (within & between roosting, breeding, feeding areas) and regional/global migrations (e.g. birds, eels, salmon, and whales). Both include up-river movements (where tidal barrages & devices or dams could obstruct movements) or movements across open waters (offshore wind farm, wave or tidal device arrays, mariculture infrastructure or fixed fishing gears). Species affected are mostly highly mobile birds, fish, and mammals.

Comments. The pressure is clearly relevant to mobile species such as fish, birds, reptiles and mammals. However, it should also be considered relevant to species or macrofauna such as crabs that undertake migrations to over-winter or to breed, and where populations are dependent on larval or other propagule supply from outside the site.

Death or injury by collision

Benthic species

Injury or mortality from collisions of biota with both static &/or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure

Injury or mortality from collisions of biota with both static &/or moving structures. Examples include collisions with rigs (e.g. birds) or screens in intake pipes (e.g. fish at power stations) (static) or collisions with wind turbine blades, fish & mammal collisions with tidal devices and shipping (moving). Activities increasing the number of vessels transiting areas, e.g. new port development or construction works will influence the scale and intensity of this pressure.

Comments. The benthic species benchmark is only relevant to larvae. Collision with benthic habitats due to grounding by vessels is addressed under ‘abrasion’.

Visual disturbance

Benthic species/Fish/Birds

Daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature

The disturbance of biota by anthropogenic activities, e.g. increased vessel movements, such as during construction phases for new infrastructure (bridges, cranes, port buildings etc.), increased personnel movements, increased tourism, increased vehicular movements on shore etc. disturbing bird roosting areas, seal haul-out areas etc.

Comments. Visual disturbance is only relevant to species that respond to visual cues, for hunting, behavioural responses or predator avoidance, and that have the visual range to perceive cues at a distance. It is particularly relevant to fish, birds, reptiles and mammals that depend on sight but less relevant to benthic invertebrates. The cephalopods are an exception but they are only likely to respond to a visual disturbance at close range (e.g. from divers). Sea horses are disturbed by photographic flash units but again at close range. It is unlikely to be relevant to habitat sensitivity assessments.

Transitional elements & organometal (e.g. TBT) contamination

Includes those priority substances listed in Annex II of Directive 2008/105/EC

Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills

The increase in transition elements levels compared with background concentrations due to their input from land/riverine sources, by air or directly at sea.  For marine sediments, the main elements of concern are:

• Arsenic,
• Cadmium,
• Chromium,
• Copper,
• Mercury and organic mercury compounds,
• Nickel and its compounds,
• Lead and organic lead compounds, and
• Zinc.

However, the following may also be released into the marine environment:

• Aluminium
• Barium
• Cobalt
• Iron
• Molybdenum
• Selenium
• Tin
• Tungsten, and
• Vanadium.

Organometallic compounds such as butyl tins (tributyltin and its derivatives) can be highly persistent and chronic exposure to low levels has adverse biological effects, e.g. Imposex in molluscs.  The use of other organo-metalloids, such as organo-copper and organo-zinc compounds, has increased due to the ban on organo-tins.

Nanoparticulate metals such as Zinc oxide (ZnO), Iron oxide (FeO), Copper oxide (CuO), Titanium (n-TiO₂), Gold, and Silver nanoparticulate metals are included. 

Comments. Although the organometallics are synthetic, they are included here on the presumption that the metal ion is the active toxic component of the compound.  Note, that mercury and lead form organic compounds naturally in the environment.

Engineered Nanomaterials (ENMs) include nanoparticulate metals (e.g. ZnO, FeO, CuO, n-TiO₂, Ag, and Au), other inorganic nanomaterials (e.g. Quantum Dots, SiO₂), and organic nanomaterials such as fullerenes and carbon nanotubes (Rocha et al., 2015).  Nanoparticulate metals are included here while non-metallic nanomaterials may be considered under the ‘Introduction of other substances’ pressure below.

Hydrocarbon & PAH contamination

Includes those priority substances listed in Annex II of Directive 2008/105/EC

Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills

Increases in the levels of these compounds compared with background concentrations.  Naturally occurring compounds or complex mixtures of two basic molecular structures:

• straight-chained aliphatic hydrocarbons (relatively low toxicity and susceptible to degradation), and
• multiple ringed aromatic hydrocarbons (higher toxicity and more resistant to degradation).

These fall into three categories based on source (including both aliphatic and polyaromatic hydrocarbons):

• biogenic hydrocarbons (from plants & animals);
• petroleum hydrocarbons (from natural seeps, oil spills and surface water run-off); and
• pyrogenic hydrocarbons (from the combustion of coal, woods, and petroleum).

Ecological ‘chemical’ consequences include taint, acute toxicity, carcinomas, and/or growth defects. In addition, hydrocarbons may have ‘physical’ as well as ‘chemical’ (toxic) effects on marine species. Physical effects include smothering, suffocation, and clogging of feathers, breathing apparatus, or the digestive tracts of species at the air/water boundary, on rocks or in the sediment, they inhabit. 

Dispersants are included here as they are designed to break up oil spills.  Dispersants (used to disperse oils spills) are ‘synthetic mixtures’ often mixtures of distillates, surfactants, and other ingredients but their effects are linked to the oil spills or other oily waters (e.g. bilge water) they are designed to disperse.

Comments. Petroleum-based and vegetable-based (e.g. sunflower, palm) oils and other ‘persistent floaters’ can spread out over the surface of the water, smother, suffocate and clog feathers, breathing apparatus or the digestive tracts of species (e.g. mobile species) that cross or inhabit the air/water boundary. In addition, petroleum-based and vegetable-based oils may smother rock surfaces and/or bind and smother sediment, including the resident species, if they come ashore. Petroleum-based and vegetable-based oils may also release potentially toxic chemicals (Cunha et al., 2015). Therefore, we assess and score the physical effects separately from the chemical or toxicological effects, with an emphasis on ‘persistent floaters’ such as petroleum-based and vegetable-based oils.

Synthetic compound contamination

Includes pesticides, antifoulants, pharmaceuticals). Includes those priority substances listed in Annex II of Directive 2008/105/EC.

Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills

Increases in the levels of these compounds compared with background concentrations.  Synthetic compounds are manufactured for a variety of industrial processes and commercial applications. 

Chlorinated compounds and other organohalogens are often persistent and often toxic; including:

• Polychlorinated biphenols (PCBs);
• Brominated flame-retardants; and
• Chemical precursors and solvents.

Pesticides vary greatly in structure, composition, environmental persistence, and toxicity to non-target organisms, many of which are also organohalogens or organophosphates; including:

• Insecticides;
• Herbicides;
• Rodenticides;
• Fungicides;
• Parasiticides; and
• Antifoulants.

Pharmaceuticals and ‘Personal Care Products’ (PCPs) originate from veterinary and human applications and include a variety of products and over-the-counter medications:

• Analgesics (inc. NSAIDs)
• Adrenergic agonists and beta-blockers
• Antihyperlipidemic agents
• Antidepressants;
• Fungicides;
• Chemotherapy drugs and animal (e.g. fin-fish) therapeutics;
• Growth hormones and oestrogens; and
• UV-filters e.g. from sun screens.

Due to their biologically active nature, high levels of consumption, known combined effects, and their detection in most aquatic environments pharmaceuticals have become an emerging concern.  Ecological consequences include physiological changes (e.g. growth defects, carcinomas). This category also includes:

• other synthetic and organic esters;
• phthalate esters, and
• synthetic musks (which may also be PBTs).

Comments. At present, this category includes a number of alcohols such as ethanol and methanol that are transported in bulk as well as some such as 1-Dodecanol and Isononanol that are PBTs (Persistent, Bioaccumulative, or Toxic substances).  A number of synthetic chemicals that do not fit into other categories are also included as ‘synthetic (others’). Exposure to most of these synthetic compounds will probably be via the water column or adsorbed onto particulates. Some may be ‘floaters’ but further research is required to determine if we need to identify ‘physical’ and ‘chemical’ effects separately.

Radionuclide contamination

An increase in 10µGy/h above background levels

Introduction of radionuclide material, raising levels above background concentrations. Such materials can come from nuclear installation discharges, and from land or sea-based operations (e.g. oil platforms, medical sources). The disposal of radioactive material at sea is prohibited unless it fulfils exemption criteria developed by the International Atomic Energy Agency (IAEA), namely that both the following radiological criteria are satisfied: (i) the effective dose expected to be incurred by any member of the public or ship’s crew is 10 μSv or less in a year; (ii) the collective effective dose to the public or ship’s crew is not more than 1 man Sv per annum, then the material is deemed to contain de minimis levels of radioactivity and may be disposed at sea pursuant to it fulfilling all the other provisions under the Convention. The individual dose criteria are placed in perspective (i.e. very low), given that the average background dose to the UK population is ~2700 μSv/a. Ports and coastal sediments can be affected by the authorised discharge of both current and historical low-level radioactive wastes from coastal nuclear establishments.

Introduction of other substances (solid, liquid or gas)

Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills

The 'systematic or intentional release of solids, liquids, or gases …' (from MSFD Annex III Table 2) is considered e.g. in relation to produced water from the oil industry.  It should therefore be considered in parallel with the other contaminants’ pressures (P1, P2, and P3). This pressure includes compounds released as operational discharges, produced waters or spills from maritime (offshore/ inshore) installations (e.g. oil & gas, renewables), mariculture, shipping and harbours etc. that are not assessed elsewhere.  This pressure includes:

• Chemicals transported in bulk that may be spilt e.g. acetic acid, phosphoric acid, sulphuric acid, sodium hydroxide;
• Chemicals in drilling waste or produced waters e.g. barite, calcium carbonate, potash, zinc oxide;
• Natural products with varied uses, e.g. molasses (transported in bulk) but also glycerins, formalin etc.;
• Fin-fish food supplements – e.g. carotenoids, copper sulphate; and
• Releases from munitions dumps e.g. chemical warfare agents, explosives, or propellants

Comments. This pressure can include a large list of chemicals with mixed ecological effects or none.  At present, chemical warfare agents and explosives are included, based on legacy munitions dumps.  However, their effects are varied and localized to the vicinity of the dump and may not be a significant concern.

De-oxygenation

Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for 1 week (a change from WFD poor status to bad status).

Any deoxygenation that is not directly associated with nutrient or organic enrichment. The lowering, temporarily or more permanently, of oxygen levels in the water or substrate due to anthropogenic causes (some areas may naturally be deoxygenated due to stagnation of water masses, e.g. inner basins of fjords). This is typically associated with nutrient and organic enrichment, but it can also derive from the release of ballast water or other stagnant waters (where organic or nutrient enrichment may be absent). Ballast waters may be deliberately deoxygenated via treatment with inert gases to kill non-indigenous species.

Comments. There is considerable evidence on the effects of de-oxygenation in the marine environment due to ongoing work and reviews by Diaz & Rosenberg among others. Therefore, we suggest a return to the MarLIN benchmark of a reduction in oxygen to ≤2mg/l for one week. The proposed benchmark would be based on the WFD status of ‘poor’ to ‘bad’ in marine waters and the ‘action levels’ for transitional waters (UKTAG, 2014).

Organic enrichment

A deposit of 100gC/m²/yr

Resulting from the degraded remains of dead biota & microbiota (land & sea); faecal matter from marine animals; flocculated colloidal organic matter and the degraded remains of: sewage material, domestic wastes, industrial wastes etc. Organic matter can enter marine waters from sewage discharges, aquaculture or terrestrial/agricultural runoff. Black carbon comes from the products of incomplete combustion (PIC) of fossil fuels and vegetation. Organic enrichment may lead to eutrophication (see also nutrient enrichment). Adverse environmental effects include deoxygenation, algal blooms, and changes in the community structure of benthos and macrophytes.

Comments. Direct evidence on the effect of organic enrichment was used to make sensitivity assessments by Tillin & Tyler-Walters (2014). In the absence of direct evidence, reference was made to the AMBI index, supplemented by any other relevant evidence on the effects of organic enrichment on habitats.

Nutrient enrichment

Compliance with WFD criteria for good status

Increased levels of the elements nitrogen, phosphorus, silicon, and iron in the marine environment compared to background concentrations. Nutrients can enter marine waters by natural processes (e.g. decomposition of detritus, riverine, direct and atmospheric inputs) or anthropogenic sources (e.g. wastewater runoff, terrestrial/agricultural runoff, sewage discharges, aquaculture, atmospheric deposition). Nutrients can also enter marine regions from ‘upstream’ locations, e.g. via tidal currents to induce enrichment in the receiving area. Nutrient enrichment may lead to eutrophication (see also organic enrichment). Adverse environmental effects include deoxygenation, algal blooms, and changes in the community structure of benthos and macrophytes.

Genetic modification & translocation of indigenous species

Benthic species, habitats, or fish

Translocation of indigenous species or introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure.

Genetic modification (GM) can be either deliberate (e.g. introduction of farmed individuals to the wild, GM food production) or a by-product of other activities (e.g. mutations associated with radionuclide contamination). Former related to escapees or deliberate releases e.g. cultivated species such as farmed salmon, oysters, and scallops if GM practices are employed. The scale of pressure is compounded if GM species were "captured" and translocated in ballast water. Mutated organisms from the latter could be transferred on ships' hulls, in ballast water, with imports for aquaculture, aquaria, live bait, species traded as live seafood or 'natural' migration.

This pressure also relates to the translocation of indigenous species that may compete with local populations of species, alter the community of the receiving habitat, or provide the opportunity for hybridization between similar species (e.g. Spartina spp. and Mytilus spp.).

Introduction of microbial pathogens

Benthic species, habitats, fish, birds, or mammals

The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus).

Untreated or insufficiently treated effluent discharges & run-off from terrestrial sources & vessels. It may also be a consequence of ballast water releases. In mussel or shellfisheries where seed stock is imported, 'infected' seed could be introduced, or it could be from accidental releases of effluvia. Escapees e.g. farmed salmon could be infected and spread pathogens in the indigenous populations. Aquaculture could release contaminated faecal matter, from which pathogens could enter the food chain.

Comments. Any significant pathogens or disease vectors relevant to species or the species that characterize biotopes/ habitats identified during the evidence review phase will be noted in the review text.

Introduction or spread of invasive non-indigenous species (INIS)

The introduction of one or more invasive non-indigenous species (INIS)

The direct or indirect introduction of invasive non-indigenous species, e.g. Chinese mitten crabs, slipper limpets, and Pacific oysters, and their subsequent spreading and out-competing of native species. Ballast water, hull fouling, and stepping stone effects (e.g. offshore wind farms) may facilitate the spread of such species. This pressure could be associated with aquaculture, mussel or shellfishery activities due to imported seed stock or accidental releases.

Comments. Sensitivity assessments are made against a prescribed list of INIS based on the GBNNSIP list of potentially invasive species.

Removal of non-target species

Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale.

By-catch is associated with all fishing, harvesting and extraction activities. Ecological consequences include food web dependencies, and the population dynamics of fish, marine mammals, turtles and sea birds (including survival threats in extreme cases, e.g. Harbour Porpoise in Central and Eastern Baltic). The physical effects of fishing gear on sea bed communities are addressed by the "abrasion" pressure type so the pressure addresses the direct removal of individuals associated with fishing/ harvesting.

Comments. This pressure addresses only the ecological effects of the removal of species and not the effects of the removal process on the species, community or habitat itself, which results in confusion. Food-web impacts are only relevant to higher trophic levels (birds, fish, mammals and turtles): for benthic habitats and associated species, the pressure has been interpreted as specifically referring to the risk of ecological effects arising from the removal of species that are not directly targeted by fisheries.

The assessment considers whether species present in the biotope are likely to be damaged or removed by relevant activities and whether this removal is likely to result in measurable effects on biotope classification, structure (in terms of both biological structure e.g. species richness and diversity and the physical structure, sometimes referred to as habitat complexity) and function. Examples of biotopes that are sensitive to this pressure are therefore i) biogenic habitats that are created by species which may be removed by fishing activities, e.g. maerl beds and hard substrata that are dominated by plant and animal assemblages, ii) biotopes characterized by ecosystem engineers or keystone species that strongly determine the rate of some ecological processes, e.g. beds of suspension feeders that cycle nutrients between the water column and substratum and iii) biotopes with key characterizing species, (e.g. those named in the biotope description or identified as important by the biotope description) that are likely to be removed or displaced as by-catch.

Removal of target species

Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale.

The commercial exploitation of fish & shellfish stocks, including smaller scale harvesting, angling and scientific sampling. The physical effects of fishing gear on sea bed communities are addressed by the "abrasion" pressures above. This pressure addresses the direct removal/harvesting of biota. Ecological consequences include the sustainability of stocks, impacting energy flows through food webs and the size and age composition within fish stocks.

Comments. This pressure addresses only the ecological effects of the removal of species and not the effects of the removal process on the species, community or habitat itself. Food-web impacts are only relevant to higher trophic levels (birds, fish, mammals and turtles): for benthic habitats and associated species, the pressure has been interpreted as specifically referring to the risk of ecological effects arising from the removal of species that are directly targeted.

The assessment considers whether species present in the biotope are likely to be directly targeted and whether this removal is likely to result in measurable effects on biotope classification, structure (in terms of both biological structure e.g. species richness and diversity and the physical structure, sometimes referred to as habitat complexity) and function. Examples of biotopes that are sensitive to this pressure are therefore i) biogenic habitats that are created by species which may be directly targeted, e.g. bivalve beds, kelp beds, Ostrea edulis reefs ii) biotopes characterized by ecosystem engineers or keystone species that strongly determine the rate of some ecological processes and that are directly targeted, e.g. Echinus esculentus as keystone grazers maintaining urchin barrens, and Arenicola marina which are key bioturbators that may be collected for bait, and iii) biotopes with key characterizing species, (e.g. those named in the biotope description or identified as important by the biotope description) that are likely to be removed as target species, e.g. collection of piddocks for bait or food from biotopes defined on the presence of piddocks.