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

Blidingia minima and B. marginata are both widely distributed around the coasts of Britain and Ireland (Burrows, 1991; Brodie et al., 2007). Blidingia minima is recorded from Spitzbergen, Svalbard to the Mediterranean and the Adriatic Sea in European coasts, the Atlantic and Pacific coasts of the Americas, South Africa, Japan, and South Island, New Zealand (Burrows, 1991; Tatewaki & Lima, 1984; OBIS 2016). Blidingia marginata is recorded from Norway to Portugal and the Mediterranean in the European Atlantic, and along the Atlantic coast of America from the Canadian Arctic to Connecticut and New Jersey, Bermuda, South America, South Africa, Japan and New Zealand (Burrows, 1991; OBIS, 2016).

Prange (1978) reported that the abundance of Blidingia minima var. subsalsa in the Squamish River estuary, British Columbia was correlated with brackish waters, high light intensity, high temperatures (20°C), moderate desiccation, and possibly favourable nutrient concentrations. The upper limit of its distribution was determined by either heavy rain or extreme desiccation.

Sensitivity assessment. This biotope is characteristic of the littoral fringe, where it is rarely inundated, but exposed to direct sunlight for prolonged periods, warm weather in summer and frost and ice in winter. Blidingia minima and B. marginata are widely distributed to the north and south of the British Isles and are unlikely to be affected by chronic (2°C for a year) increases in temperature.  A short-term 5°C increase in air temperature is likely to increase desiccation, especially in summer, and result in increased bleaching and dehydration of the thallus. However, the species probably exhibits adaptation and acclimation to local conditions and is unlikely to be affected adversely by an increase in temperature at the benchmark level.  Therefore, a resistance of High is suggested so that resilience is also High and the biotope is assessed as Not sensitive at the benchmark level.

Temperature decrease (local)

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

Evidence

Blidingia minima and B. marginata are both widely distributed around the coasts of Britain and Ireland (Burrows, 1991; Brodie et al., 2007). Blidingia minima is recorded from Spitzbergen, Svalbard to the Mediterranean and the Adriatic Sea in European coasts, the Atlantic and Pacific coasts of the Americas, South Africa, Japan, and South Island, New Zealand (Burrows, 1991; Tatewaki & Lima, 1984; OBIS 2016). Blidingia marginata is recorded from Norway to Portugal and the Mediterranean in the European Atlantic, and along the Atlantic coast of America from the Canadian Arctic to Connecticut and New Jersey, Bermuda, South America, South Africa, Japan and New Zealand (Burrows, 1991; OBIS, 2016).

Prange (1978) reported that the abundance of Blidingia minima var. subsalsa in the Squamish River estuary, British Columbia was correlated with brackish waters, high light intensity, high temperatures (20°C), moderate desiccation, and possibly favourable nutrient concentrations. Temperature, salinity, and nutrient levels interacted strongly. The lowest photosynthetic rates were recorded at 5°C and 0.25‰ irrespective of N and P concentrations.  Therefore, a reduction in temperature is likely to reduce photosynthesis and, hence, growth if salinity and nutrient levels were constant (Prange, 1978). But Blidingia minima was reported to persist through the winter months encased in ice in the Arctic Sea and to resume development when the ice melted (Burrows, 1991).

Sensitivity assessment. This biotope is characteristic of the littoral fringe, where it is rarely inundated, but exposed to direct sunlight for prolonged periods, warm weather in summer and frost and ice in winter. Blidingia minima and B. marginata are widely distributed to the north and south of the British Isles and are unlikely to be affected by chronic (2°C for a year) increases in temperature.  A short-term 5°C decrease in air temperature is likely to reduce growth in winter, and the fronds are probably subject to frost in the winter months. However, the species probably exhibits adaptation and acclimation to local conditions and is unlikely to be affected adversely by a decrease in temperature at the benchmark level.  Therefore, a resistance of High is suggested so that resilience is also High and the biotope is assessed as Not sensitive at the benchmark level.

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 (Lic.Bli) is recorded from ‘full’ and ‘variable’ salinity (Connor et al., 2004). Blidingia minima is recorded from the upper littoral and supralittoral, in harbours on  artificial structures and pontoons, and sea walls, in estuaries from brackish water to almost freshwater conditions (Fletcher, 1980b; Tittley & Shaw,1980; Burrows, 1991, Brodie et al., 2007). Blidingia marginata is recorded from steep rock faces, stones, artificial surfaces in harbours, on mud and in salt marshes and into estuaries (Burrows, 1991; Brodie et al., 2007). Brodie et al. (2007) suggested that Blidingia marginata tolerated a wide salinity range.

Prange (1978) suggested that the distribution of Blidingia minima var. subsalsa in the Squamish River estuary, British Columbia was limited by ‘high salinity on the marine side’ and the ‘absence of seawater on the freshwater side’. Temperature, salinity, and nutrient levels interacted strongly. The highest photosynthetic rates occurred at 20°C, 20‰, and high nutrient levels, which were associated in the Squamish River estuary with low runoff and emersion in summer in areas of nutrient enrichment or tide pools. The lowest photosynthetic rates were recorded at 5°C and 0.25‰ irrespective of N and P concentrations, which were associated with high runoff and rainfall while emersed in winter (Prange, 1978).

Sensitivity assessment. An increase in salinity at the benchmark level could expose the biotope to hypersaline conditions. No direct evidence of the effects of hyposaline conditions was found. However, the littoral fringe is probably exposed to a wide range of salinities due to the evaporation of seawater from splash and spray, and direct rainfall or freshwater runoff. Therefore, the biotope is likely to be resistant of changes in salinity. The occurrence of the characteristic species in supralittoral pools and salt marshes also suggests they could resist hypersaline conditions. Therefore, a resistance of High is suggested so that resilience is also High and the biotope is assessed as Not sensitive at the benchmark level.

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 (Lic.Bli) is recorded from ‘full’ and ‘variable’ salinity (Connor et al., 2004). Blidingia minima is recorded from the upper littoral and supralittoral, in harbours on  artificial structures and pontoons, and sea walls, in estuaries from brackish water to almost freshwater conditions (Fletcher, 1980b; Tittley & Shaw,1980; Burrows, 1991, Brodie et al., 2007). Blidingia marginata is recorded from steep rock faces, stones, artificial surfaces in harbours, on mud and in salt marshes and into estuaries (Burrows, 1991; Brodie et al., 2007). Brodie et al. (2007) suggested that Blidingia marginata tolerated a wide salinity range.

Prange (1978) suggested that the distribution of Blidingia minima var. subsalsa in the Squamish River estuary, British Columbia was limited by ‘high salinity on the marine side’ and the ‘absence of seawater on the freshwater side’. Temperature, salinity, and nutrient levels interacted strongly. The highest photosynthetic rates occurred at 20°C, 20‰, and high nutrient levels, which were associated in the Squamish River estuary with low runoff and emersion in summer in areas of nutrient enrichment or tide pools. The lowest photosynthetic rates were recorded at 5°C and 0.25‰ irrespective of N and P concentrations, which were associated with high runoff and rainfall while emersed in winter (Prange, 1978).

Sensitivity assessment. A decrease in salinity at the benchmark level could expose the biotope to ‘reduced (18-30) conditions. The characterizing species are recorded from estuarine, brackish and nearly freshwater conditions so the biotope is likely to be resistant of changes in salinity. The species probably exhibit adaptation and acclimation to local conditions, and local strains that prefer marine conditions may be replaced by strains that prefer reduced salinity, and the relative abundance of Blidingia minima and B. marginata may change but the biotope remain. Therefore, a resistance of High is suggested so that resilience is also High and the biotope is assessed as Not sensitive at the benchmark level.

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

Mathieson et al. (1983) recorded Blidingia minima on bridge piers in ca 1.6 - 2 knots (ca 0.8 - 1 m/s) in an estuarine tidal rapid. However, the littoral fringe is unlikely to be affected by changes in water flow as described in the pressure benchmark as it is rarely inundated. Runoff due to heavy rainfall is possible but is outside the scope of the pressure. Therefore, the pressure is Not relevant.

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

Water retention and wetting are probably vital to the survival of this biotope where wave action supplies the water to the littoral fringe in the form of wave splash and spray. The vertical extent of the biotope is probably determined by wave action (via spray and splash) and in turn the emergence regime. Prange (1978) noted that the upper limit of the distribution of Blidingia minima was determined by either heavy rain or extreme desiccation and Burrows (1991) noted that Blidingia marginata was able to remain dry for long periods under ‘unfavourable moisture conditions’. Hruby & Norton (1979) reported that 60-100% of propagules of Blidingia minima survived ca 8 to 12 hours of submersion per tidal cycle after 1-3 weeks in a tidal simulator but only 20-59% survived ca 5.5- 8 hours and 1-19% survived 4.5-5 hours of submersion. Survival was increased if the propagules were cultured for 14 days before being placed in the simulator. For example, after 10 weeks in culture, Blidingia minima disappeared from plates submerged for less than 4.7 hr per cycle but sporelings (cultured for 14 days beforehand) grew on plates 2 mm above the level of total emersion (Hruby & Norton, 1979; Figure 2).  Therefore, the species resistance to emergence increases with age.

Sensitivity assessment.  This biotope is recorded below the Lic.UloUro and LIc.Ver bands and above the Ulva (syn. Enteromorpha) band in the littoral fringe.  The upper limit of the biotope is probably determined by desiccation and, hence, emergence regime, depending on wave splash and season.  A change in emergence will result in a reduction in the upper limit or increased competition at its lower limit. Therefore, a proportion of the biotope will be lost but recover quickly so that biotope moves up or down the shore. Therefore, a resistance of Low is recorded. As resilience is probably High, sensitivity is assessed as Low.

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

Water retention and wetting are probably vital to the survival of this biotope where wave action supplies the water to the littoral fringe in the form of wave splash and spray. The vertical extent of the biotope is probably determined by wave action (via spray and splash), especially on steep or vertical faces.  For example, Fletcher (1980b) noted that the vertical height of the green algal band on artificial substrata (pontoons) in Langstone harbour was greater in areas subject to wave exposure when compared to the sheltered inner reaches of the harbour.  Therefore, a decrease in wave exposure is likely to reduce the vertical extent of the biotope, while an increase in wave exposure may increase its extent, depending on competition from other green algae. However, a 3-5% change in significant wave height is unlikely to be significant in wave exposed conditions. Therefore, the biotope is probably Not sensitive (resistance and resilience are High) at the benchmark level.

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.

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.

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.

Radionuclide contamination

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

Evidence

No evidence 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

The littoral fringe is rarely inundated and this biotope is probably exposed to the air for the majority of the time. Even if the water lapping over the littoral fringe was deoxygenated, wave action and turbulent flow over the rock surface would probably aerate the water column. Hence, the biotope is unlikely to be exposed to deoxygenated conditions. 

Nutrient enrichment

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

Evidence

Fletcher (1996) listed Blidingia minima as a species characteristic of eutrophic waters.  Therefore, the biotope might benefit from eutrophication. However, this biotope is considered to be Not sensitive at the pressure benchmark that assumes compliance with good status as defined by the WFD.

Organic enrichment

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

Evidence

Opportunistic green algae are reported to flourish in nutrient enriched conditions (Fletcher, 1996). Organic enrichment will result in the release of nutrients due to bacterial decomposition and, so, may lead to an increase in green algal cover.  Organic enrichment may occur on cliffs due to runoff from agricultural land and may benefit the biotope.  Therefore, the biotope is considered to be Not sensitive (resistance and resilience are High).

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

Blidingia minima and B. marginata can occur on saltmarsh plants, on mud and on artificial substrata (Brodie et al., 2007). However, this biotope is characteristic of hard rock or soft rock (chalk) substrata. A change to a sedimentary substratum, however unlikely, would result in the permanent loss of the biotope. Therefore, the biotope has a resistance of None, with a Very low resilience (as the effect is permanent) and, therefore, a sensitivity of 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 sediment type)

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

Evidence

Blidingia minima and B. marginata can occur on saltmarsh plants, on mud and on artificial substrata (Brodie et al., 2007). However, this biotope is characteristic of hard rock or soft rock (chalk) substrata. Therefore, a change in sediment type is Not relevant.

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

This biotope is characteristic of hard rock or soft rock (chalk) substrata. Removal of the substratum is not relevant where the biotope occurs on hard bedrock. However, chalk habitats can be subject to landslides but also direct extraction as a result of tunnelling or other construction activities. Removal of the substrata would remove the biotope from the affected area. Therefore, a resistance of None is recorded. However, where suitable habitat remains (e.g chalk or hard rock surface) or where artificial hard substrata are introduced, the characteristic species could colonize the habitat quickly, and resilience is probably High. Therefore, sensitivity is assessed as Medium.

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 probably overlooked and included under 'green algae', therefore, little direct evidence on the effect of abrasion was found. The characteristic species are probably a component of the 'green algae' regularly cleaned from jetties, pontoons, and slipways. In experimental trampling studies, Fletcher & Frid (1996a&b) noted that the abundance of Ulva spp. (as Enteromorpha) was routinely greater in trampled rather than un-trampled areas. This suggested that opportunistic algae were able to colonize the bare space created by trampling, and benefited from the reduced abundance of other macroalgae. Overall, Blidingia minima and B. marginata are not physically robust and are probably removed easily from the rock surface, except in cracks and fissures protected from abrasion, so the resistance is probably Low.  Vertical surfaces are probably protected from trampling except in areas subject to climbing. However, resilience is probably High and sensitivity is assessed as Low.

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

Penetration of hard rock (as described by the pressure definition) is 'Not relevant'.  However, soft rock may be tunnelled into or removed by construction activities. Removal of the rock surface would result in loss of the biotope from the affected area (as above). Therefore, resistance is assessed as Low. As resilience is likely to be High sensitivity is assessed as Low.

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

The littoral fringe or supralittoral are rarely inundated. It is, therefore, unlikely to be exposed to changes in water clarity due to changes in suspended sediment.

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

Smothering could occur because of rainwater runoff of silt and soil from the tops of the cliffs. However, where the biotope occurs on vertical or steep cliffs the slope would preclude the build-up of significant deposits (except on crevices and pits) sufficient to block the algal communities access to sunlight. Therefore, the factor is probably Not relevant at the level of the benchmark.

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

Smothering could occur because of rainwater runoff of silt and soil from the tops of the cliffs. However, where the biotope occurs on vertical or steep cliffs the slope would preclude the build-up of significant deposits (except on crevices and pits) sufficient to block the algal communities access to sunlight. Therefore, the factor is probably Not relevant at the level of the benchmark.

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

No evidence was found.

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.  The biotope is rarely underwater and macroalgae are not known to respond to noise.

Introduction of light or shading

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

Evidence

The littoral fringe is rarely submerged. Therefore, the species that characterize this biotope are probably adapted to prolonged exposure to sunlight, and unlikely to be affected by introduced artificial light. Prange (1979) suggested that the lower limit of Blidingia minima was determined by low light intensities. However, its lower limit is probably also determined by grazing pressure from littorinids (Lein, 1980). Prolonged or permanent shading (e.g. from an artificial structure) is undoubtedly detrimental to macroalgal growth, and may result in the replacement of the biotope by a cave biotope. Norton et al. (1971) noted that Ulva sp. penetrated ca 5 m into a sea cave near Lough Ine. Anand (1937b) noted that his Enteromorhpa belt (that may have included Blidingia minima) penetrated into chalk sea caves but stopped abruptly at 8 m from the entrance. Anand (1937c) reported that Ulva (as Enteromorpha) in caves required about 5-6% of the external illumination. Therefore, only prolonged shading may be detrimental but the presence of Lic.Bli on exposed cliff faces suggests that it may be out-competed in shaded areas. Therefore, a resistance of Medium is suggested, with Low confidence. Resilience is likely to be High so that sensitivity is assessed a Low.

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. This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of spores. But spore dispersal is not considered under the pressure definition and benchmark.

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

The pressure definition is not directly applicable to the littoral fringe so Not relevant has been recorded.  Collision via ship groundings or terrestrial vehicles is possible but the effects are probably similar to those of abrasion above.

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. Macroalgae respond to light intensity but are unlikely to respond to 'visual' cues.

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

No evidence of the translocation, breeding or species hybridization was found.

Introduction or spread of invasive non-indigenous species

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

Evidence

No direct evidence on the effect of non-native species on this biotope was found. However, this assessment should be revisited in the light of new evidence.

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

No evidence on disease or pathogens mediated mortality was found.

Removal of target species

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

Evidence

The algal community characteristic of this biotope is unlikely to be targetted by any commercial or recreational fishery or harvest.

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

Incidental removal of the algal mat would probably remove the entire belt rather than specific characteristic species. Where present, mobile invertebrate fauna are probably not entirely dependent on the 'belt' for food or habitat and would forage elsewhere.  However, this algal community is unlikely to be targetted by any commercial or recreational fishery or harvest. Accidental physical disturbance due to access (e.g. trampling) or grounding is examined under abrasion above.