The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

This biotope is characterized by a sparse assemblage (JNCC, 2015), rather than the presence of typical species: changes in temperature will therefore not alter the biotope (based on the abiotic habitat). Resistance to an increase in temperature is therefore assessed as 'High' and resilience as ‘High’ (by default) and this biotope is considered to be 'Not sensitive'.

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

This biotope is characterized by a sparse assemblage (JNCC, 2015) and is defined by environmental factors rather than the presence of typical species: changes in temperature will therefore not alter the biotope (based on the abiotic habitat). Resistance to a decrease in temperature is therefore assessed as 'High' and resilience as ‘High’ (by default) and this biotope is considered to be 'Not sensitive'.

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

This biotope is characterized by the absence of species resulting from sediment mobility and abrasion (JNCC, 2015), rather than the presence of typical species. The reduced and variable salinity is a key environmental factor characterizing the habitat. A change in salinity to full would alter the habitat conditions leading to reclassification to SS.SCS.ICS.SSh or similar, and may result in colonization by species more typical of coastal and marine habitats such as Balanus crenatus, Spirobranchus triqueter and encrusting bryozoand and sponges. Species such as amphipods and mysids that are present within estuaries may be lost.

Sensitivity assessment. As the change in salinity represents a change in habitat type.  Resistance to an increase in salinity is therefore assessed as 'None' and resilience is assesed as ‘High’  following restoration of habitat conditions (as the abiotic habitat will have recovered). Where species have low connectivity with other populations and have been lost from an estuarine system recolonization and recvoery of abundance may, however, be prolonged. 

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

This biotope is characterized by a sparse assemblage (JNCC, 2015), rather than the presence of typical species, present in variable or reduced salinity. A change at the pressure benchmark therefore refers to a change to reduced (for previously variable salinity examples) or a change to 'Low' salinity (<18ppt). A change in salinity would have little effect on the abiotic habitat but would result in a change in a key defining and structuring environmental factor. A change to reduced salinity could reduce species richness and the abundance of species typical of the habitat, although some species such as mysids may be able to tolerate very low salinities. 

Sensitivity assessment. Resistance to a decrease in salinity to Low (<18ppt)  is  assessed as 'Medium' as the character of some examples of the habitat would be altered and some changes in species richness and abundance may occur. Resilience is assessed as ‘High’ following restoration of habitat conditions based on the immediate recovery of the character of the abiotic habitat and recovery within two years of most species that occur in the biotope. Biotope sensitivity is therefore assessed as 'Low'.

Water flow (tidal current) changes (local)

Benchmark. 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. Further detail

Evidence

Changes in water flow at the pressure benchmark are considered unlikely to lead to alterations in the biotope as the biotope occurs in a range of tidal flows (JNCC, 2015) and wave action maystill result in sediment mobility, preventing the establishment of a more species rich biotope.  Resistance is therefore assessed as ‘High’ and resilience as ‘High’ (by default) so that the biotope is considered to be ‘Not sensitive’. If wave action and water flows were both reduced (at levels greater than the pressure benchmark) finer terrestrial sediments carried by riverine inputs may be deposited, depending on local sediment supply. Where deposition alters the sediment type these would allow the development of biological assemblages typical of the new habitat type, significantly altering the character of the habitat and leading to reclassification. The habitat would be considered sensitive to these changes.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

This pressure is 'Not relevant' to sublittoral biotopes.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

This biotope is found on shores that are judged to be moderately exposed sheltered or very sheltered (JNCC, 2015). The presence of this biotope across these three categories is considered to indicate (by proxy) that increases or decreases in wave exposure at the pressure benchmark are unlikely to lead to alterations to the biotope.  Resistance is therefore assessed as ‘High’ and resilience as ‘High’ (by default) so that the biotope is considered to be ‘Not sensitive’. If wave action and water flows were both reduced (at levels greater than the pressure benchmark) finer terrestrial sediments carried by riverine inputs may be deposited, depending on local sediment supply. Where deposition alters the sediment type these would allow the development of biological assemblages typical of the new habitat type, significantly altering the character of the habitat and leading to reclassification. The habitat would be considered sensitive to these changes.

Transition elements & organo-metal contamination

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

Evidence

This pressure is Not assessed but evidence is presented where available. As this biotope is characterized by the lack of species, exposure to contaminants will not result in significant impacts.

Hydrocarbon & PAH contamination

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

Evidence

This pressure is Not assessed but evidence is presented where available. As this biotope is characterized by the lack of species, exposure to contaminants will not result in significant impacts.

Synthetic compound contamination

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

Evidence

This pressure is Not assessed but evidence is presented where available. As this biotope is characterized by the lack of species, exposure to contaminants will not result in significant impacts.

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

No evidence was found.

Introduction of other substances

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

Evidence

This pressure is Not assessed.

De-oxygenation

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

Evidence

As this biotope is characterized by the lack of species, de-oxygenation will not result in significant impacts. Biotope resistance is therefore assessed as 'High', and resilience as 'High' (by default) and the biotope is considered to be 'Not sensitive'.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

As this biotope is characterized by the lack of species present due to sediment mobility, nutrient enrichment will not result in significant impacts. Biotope resistance is therefore assessed as 'High', and resilience as 'High' (by default) and the biotope is considered to be 'Not sensitive'.

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

As this biotope is characterized by the lack of species, organic enrichment will not result in significant impacts. Organic deposits are likely to be removed rapidly by wave action although in periods of calm an organic deposit may be rapidly colonized by oligochaetes or amphipods. Biotope resistance is assessed as 'High' as enrichment is likely to be very short-lived, and resilience is assessed as 'High' (by default), the biotope is considered to be 'Not sensitive'.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’).  Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’.  Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

This biotope is characterized by pebbles, gravel and sand (JNCC, 2015). A change to a hard or artificial substratum would significantly alter the character of the biotope. The biotope is therefore considered to have 'No' resistance to this pressure (based on a change to a sediment habitat), recovery is assessed as 'Very low', as the change at the pressure benchmark is permanent. Biotope sensitivity is therefore assessed as 'High'.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

The benchmark for this pressure refers to a change in one Folk class.  The pressure benchmark originally developed by Tillin et al., (2010) used the modified Folk triangle developed by Long (2006) which simplified sediment types into four categories: mud and sandy mud, sand and muddy sand, mixed sediments and coarse sediments.  The change referred to is therefore a change in sediment classification rather than a change in the finer-scale original Folk categories (Folk, 1954).  The change in one Folk class is considered to relate to a change in classification to adjacent categories in the modified Folk triangle.  For coarse gravel and pebble habitats a change in one folk class may refer to a change to gravels, mixed sediments or muddy sands, sandy muds and muds. A change in sediment type would result in reclassification of the biotope (JNCC, 2015) and a change to mixed or fine sediments would likely result in the establishment of a species rich and more diverse community (depending on other habitat factors). Biotope resistance is therefore assessed as ‘None’ and resilience as ‘Very low’ as the change at the pressure benchmark is permanent. Sensitivity is therefore ‘High’.

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

The process of extraction will remove the abiotic habitat; therefore a resistance of ‘None’ is recorded. As the sediments characterizing this biotope are non-cohesive, where small areas are impacted infilling is likely to be rapid following sediment redistribution by wave action or water action. As a result, resilience is assessed as ‘High’, and sensitivity as ‘Medium’.  Recovery where large volumes of shingle are removed over wide areas may lead to slower recovery if sediments are not available and/or water transport is limited. 

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

This biotope is characterized by a species-poor assemblage of robust species and the abiotope habitat (JNCC, 2015). The highly mobile or robust species present occasionally in this biotope are not specifically dependent on this biotope and most can avoid abrasion by swimming e.g. shrimp, mysids and fish. Resistance to this pressure is therefore assessed as 'High' and resilience as ‘High’ (by default) and this biotope is considered to be 'Not sensitive'.

Penetration or disturbance of the substratum subsurface

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

Evidence

This biotope is characterized by the absence of species through sediment mobility (JNCC, 2015), rather than the presence of typical species: abrasion will therefore not alter biotope character. The highly mobile or robust species present occasionally in this biotope may only be found in  low abundance and are not specifically dependent on this biotope. Resistance to this pressure is therefore assessed as 'High' and resilience as ‘High’ (by default) and this biotope is considered to be 'Not sensitive'.

Changes in suspended solids (water clarity)

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

Evidence

This biotope occurs in scoured habitats and it is likely, depending on local sediment supply, that the biotope is exposed to chronic or intermittent episodes of high-levels of suspended solids as rivers transporty fine silts and clays from terrestrial habitats. This biotope is characterized by a species-poor assemblage (JNCC, 2015) many of which such as shrimps and mysids can occur in highly turbid systems such as the Severn Estuary (Bamber & Henderson, 1994) , An increase or decrease  in suspended solids is not considered to significantly alter this biotope as it is struvtured by physical factors such as reduced and variable salinity and the presence of clean sediments. Resistance to an increase or decrease in suspended solids is therefore assessed as 'High' and resilience as ‘High’ (by default) and this biotope is considered to be 'Not sensitive'. If an increase in suspended solids was accompanied by reductions in water flow and wave action then some deposition could occur, this is assessed through the physical change and siltation pressures.

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

This biotope is characterized by a species-poor assemblage structured by the reduced and variable salinity and the coarse sediments (JNCC, 2015). In some estuaries such as the Severn, sediment re-suspension and mobilisation occurs at spring tides with resulting deposition during neap tides. Some deposition may therefore be part of the tidal cycle and the abiotic habitat that defines this biotope is not significantly affected.

Sensitivity assessment. The addition of a single deposit of fine sediments which will be removed by wave action or currents will therefore not alter the biotope. Resistance to this pressure is therefore assessed as 'High' and resilience as ‘High’ (by default) and this biotope is considered to be 'Not sensitive'.

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

This biotope is characterized by a species-poor assemblage structured by the reduced and variable salinity and the coarse sediments (JNCC, 2015). In some estuaries such as the Severn, sediment re-suspension and mobilisation occurs at spring tides with resulting deposition during neap tides. Some deposition may, therefore, be part of the tidal cycle and the abiotic habitat that defines this biotope may not be significantly affected as fine deposits are remobilised and transported in the water column.

Sensitivity assessment. The addition of a single deposit of fine sediments is likely to be rapidly removed by wave action or currents will therefore not alter the biotope. Resistance to this pressure is therefore assessed as 'High' and resilience as ‘High’ (by default) and this biotope is considered to be 'Not sensitive'. Sensitivity will be greater where deposition is accompanied by reductions in wave action or water flows that reduce sediment transport.

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

Not relevant.

Underwater noise changes

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

Evidence

Not relevant.

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

Not relevant. This biotope is characterized by species-poor mobile coarse sediments. A change in light-levels is unlikely to direct alter the biotope.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Not relevant.

Death or injury by collision

Benchmark. 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. Further detail

Evidence

Not relevant’ to seabed habitats.  NB. Collision by grounding vessels is addressed under surface abrasion.

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

Not relevant.

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the 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. Further detail

Evidence

None of the typical species associated with this bitope such as mysids, amphipods crabs or fish are  translocated and this pressure is therefore considered 'Not relevant'. Salmon and trout may use estuaries as migration routes and could be exposed to farmed escappes allowing genetic mixing. However, this would not alter the character of this biotope.

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

The high levels of abrasion resulting from the movement of gravels and sands and the subsequent sediment instability will limit the establishment of all but the most highly scour-resistant invasive non-indigenous species (INIS) and no direct evidence was found for the effects of INIS on this biotope.  The low levels of organic matter retained by this biotope, are considered to additionally inhibit permanent colonization by invasive species. Crepidula fornicata was reported from 'rough sediments' subject to strong tidal streams in the English Channel (Hinz et al., 2011). However, this biotope is characterized by unstable, mobile, cobbles and pebbles whose scour due to wave action and in winter storms removes most of the resident fauna on a seasonal basis, so Crepidula is unlikely to become established. 

Sensitivity assessment. Overall, there is no evidence of this biotope being adversely affected by non-native species. As scouring of this biotope by mobile coarse sediments limits the establishment of all but robust species, resistance to INIS is assessed as ‘High’ and resilience as ‘High’ (by default) so that the biotope is assessed as ‘Not sensitive’.

Introduction of microbial pathogens

Benchmark. 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). Further detail

Evidence

As this biotope is characterized by a species poor biological assemblage apart from crabs and fish and estuarine invertebrates (JNCC, 2015), this pressure is considered to be 'Not relevant'. Species within the biotope may be infected and pathogens and parasites of Carcinus maenas are described below. However, the presence of these pathogens and parasites is unlikely to alter biotope classification and this pressure is considered to be 'Not reelvant'. 

The most well known parasite of Carcinus maenas is the rhizocephalan barnacle Sacculina carcinini. This parasite infects by larval settlement on the exoskeleton and subsequent infection into the haemocoel by injection through a chitin 'needle' at the base of a hair on one of the legs of the host. Any larvae that do not settle adjacent a hair base do not survive (Smith, 1907). Sacculina carcini castrates male and female Carcinus maenas and prevents moulting for the rest of the crabs life (Naylor, 2000; Thresher et al., 2000 and references therein). Infected crabs with sexually mature parasites carry a reproductive externae in the same way as females carry an egg-mass when they are berried. The externae is distinguishable from an egg-mass because it is smooth rather than granular (Naylor, 2000).

Carcinus maenas is the 1st host of the acanthocephalan helminth Profilicollis botulus which infects eider ducks (Somateria mollissima) by ingestion of infected crabs. Juvenile eider ducks suffer some mortality from heavy infections and crabs are infected by eggs of the parasite from duck faeces(Thompson, 1985).

Small Carcinus maenas (3-11 mm CW) can be attacked by the parasitoid platyhelminth Fecampia erythrocephala. This parasitoid is 8-12 mm long and replaces much of the digestive gland in the haemocoel. Infection is usually 1 worm per crab but may be as many as 4. Once the worm is mature it exits the crab, killing it in the process. Prevalence in natural populations is about 7% and Kuris et al., (2002) suggested Fecampia erythrocephala may be a useful biocontrol where introduced Carcinus maenas are a pest because it kills crabs before they can mature and breed. 

Removal of target species

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

Evidence

As this biotope is characterized by a species poor biological assemblage abnd defined on the basis of abiotic factors this pressure is considered to be 'Not relevant' as removal of species will not alter the biotope classification. Within the habitat species are unlikely to be targeted. Fish that move through the estuary may be targeted as estuaries provide nursery grounds and migration routes for a number of species and some, such as eel, salmon and sea trout may be targeted both commercially and recreationally. Carcinus maenas may also be targeted by commercial and recreational harvesters as 'peelers', the soft shelled crabs that have recently moulted and that are used as bait. This collecting takes place in intertidal habitats rather than subtidal.

Removal of non-target species

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

Evidence

As this biotope is characterized by a species-poor biological assemblage and defined on the basis of the salinity regime and sediments (JNCC, 2015), this pressure is considered to be 'Not relevant'. A removal of species would not alter the biotope classification. it should be noted however, that some estuaries, while species poor, may contain large numbers of individuals and these contribute to ecosystem services such as secondary production that support higher trophic levels such as fish and birds. The Severn Estuary, for example, contains large numbers of shring, Crangon crangon and mysids such as Neomysis integer, that move within the estuary in response to environmental factros such as turbidity, tides, salinity and temperature (Bamber & Henderson, 1994).