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

Friedmann (1959, 1969 cited in Rindi et al., 1999) noted that Prasiola stipitata was seasonal from its southern limit to about 55° N (latitude) and disappeared in summer but that is was perennial further north. It is recorded throughout the North  Atlantic, from the Massachusetts to south west Greenland on the eastern seaboard and from north Spain to Iceland in the west and into the Baltic (Russell, 1991). The littoral fringe and supralittoral experiences the extremes of hot summers and cold frosty winters, so that Prasiola stipitata is probably adapted to extreme variation in temperature. However, an increase in temperature is likely to affect desiccation experienced by the biotope, in combination with wave splash, spray, rainfall and wind. An increase in temperature may affect the seasonality so that perennial populations in northern waters may become seasonal while die back in southern waters may be more prolonged.  Therefore, a resistance of Medium is suggested with Low confidence. Resilience is probably High so that sensitivity is assessed as Low.

Temperature decrease (local)

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

Evidence

Friedmann (1959, 1969 cited in Rindi et al., 1999) noted that Prasiola stipitata was seasonal from its southern limit to about 55° N (latitude) and disappeared in summer but that is was perennial further north. It is recorded throughout the North  Atlantic, from the Massachusetts to south west Greenland on the eastern seaboard and from north Spain to Iceland in the west and into the Baltic (Russell, 1991). The littoral fringe and supralittoral experiences the extremes of hot summers and cold frosty winters, so that Prasiola stipitata is probably adapted to extreme variation in temperature. However, a decrease in temperature is likely to affect desiccation experienced by the biotope, in combination with wave splash, spray, rainfall and wind. A decrease in temperature may affect the seasonality so that seasonal populations in southern waters may become perennial.  In addition, winter is the main growth period for Prasiola stipitata. Therefore, a resistance of High is suggested with Low confidence. Resilience is, therefore, High (by default) so that the biotope is assessed as 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

The littoral fringe is likely to experience localised evaporation and resultant increased surface salinity during neap and low tides in hot summers and/or warm windy conditions, together with reduced salinity due to rainfall or runoff. Russell (1991) reported that salinity tolerance in Prasiola stipitata showed local adaptation, depending on origin. Specimens from Norway, where summers were cool and wet, were less exposed to hypersaline events that more southern specimens (from north west England) that died back in summer while specimens from the Baltic were more exposed to hyposaline events. Specimens from Norway and NW England had the highest density of plantlets at 34‰ and markedly reduced density at 6‰ while Baltic specimens had a maximum density at 34‰ but a smaller reduction in density at 6‰, after three weeks.  All specimens had lower densities after three weeks at 68‰ and greatly reduced densities at 102‰.  Nevertheless, all specimens were very halotolerant (Russell, 1991).  Prasiola stipitata is probably adapted to extremes of salinity greater than expressed by the benchmark. Therefore, a resistance of High is suggested. Resilience is, therefore, High and the biotope has been 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

The littoral fringe is likely to experience localised evaporation and resultant increased surface salinity during neap and low tides in hot summers and/or warm windy conditions, together with reduced salinity due to rainfall or runoff. Russell (1991) reported that salinity tolerance in Prasiola stipitata showed local adaptation, depending on origin. Specimens from Norway, where summers were cool and wet, were less exposed to hypersaline events that more southern specimens (from north west England) that died back in summer while specimens from the Baltic were more exposed to hyposaline events. Specimens from Norway and NW England had the highest density of plantlets at 34‰ and markedly reduced density at 6‰ while Baltic specimens had a maximum density at 34‰ but a smaller reduction in density at 6‰, after three weeks.  All specimens had lower densities after three weeks at 68‰ and greatly reduced densities at 102‰.  Nevertheless, all specimens were very halotolerant (Russell, 1991).  Prasiola stipitata is probably adapted to extremes of salinity greater than expressed by the benchmark. Therefore, a resistance of High is suggested. Resilience is, therefore, High and the biotope has been 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

The littoral fringe and supralittoral are unlikely to be affected by changes in water flow as described in the pressure benchmark. 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

This biotope is characteristic of littoral fringe and supralittoral habitats that are rarely inundated and depend on wave action to provide splash or spray, or rainfall to moisten the habitat. Wooton (1991) noted that Prasiola stipitata grew over the Verrucaria belt in the presence of bird guano, only where wave action was sufficient to wet the habitat. In a tidal simulator experiment, Hruby & Norton (1979; Fig 2) reported that 60-100% of Prasiola stipitata propagules survived one to three weeks in culture at >7 hrs of immersion per tidal cycle, but 20-59% survived 4-6 hrs, and only 1-19% survived 0-4 hrs immersion per tidal cycle. Kang et al. (2013) examined photosynthesis in Prasiola stipitata under desiccation stress. They noted that photosynthesis recovered totally within one hour of immersion after two days of desiccation but after 15 days of desiccation recovery took 24 hrs. However, after 30 days the photosynthetic apparatus shows signs of damage and only partial recovery occurred. They noted that complete desiccation for 15 of more days in the field was unlikely and that the dense crowding of individual thalli within the algal mat, granted some protection from desiccation (Kang et al., 2013). 

While Prasiola stipitata is desiccation tolerant, it is only abundant in the littoral fringe or supralittoral in areas that received some wetting, and dies back in the summer months (presumably due to reduced wetting, and increased desiccation) except in areas of consistent rainfall runoff or low temperatures (Rindi et al., 1999).  Therefore, a change in emergence regime will alter the degree of wetting. An increase in emergence could reduce the height of the Prasiola stipitata band on the shore or shift it from a perennial to a seasonal biotope. A decrease in emergence may allow it to colonize further up the shore where suitable substratum exists or cause it to be out-competed by upper shore algae.  Therefore, a resistance of Low is suggested. Resilience is probably High so that 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

This biotope is recorded on wave exposed to moderately wave exposed shores. Although the littoral fringe or supralittoral are rarely inundated, wave action (via splash and spray) are an important source of wetting within the biotope. A change in wave action could alter the degree of wetting received by the Prasiola stipitata algal mat and alter its abundance and height on the shore, especially in summer months.  However, a change of 3-5% of significant wave height is probably not significant on moderately to wave exposed shores. Therefore, the biotope is 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 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

The littoral fringe is is rarely inundated and is often exposed to the air.  For example, Fletcher (1980) noted that Lichina confinis, a species that occurs at the top of the littoral fringe, spent a maximum of 1% of time submerged each year while Verrucaria striatula, a species that occurs in the lower littoral fringe below the Verrucaria maura, spent a maximum of 44% of time submerged each year.  Therefore, this biotope (LR.FLR.Lic.Pra) is 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

The abundance of Prasiola stipitata that characterizes this biotope is associated with nutrient enrichment and the biotope occurs in areas affected by bird dropping and guano, eg. near bird colonies or roosts, or with sewage seeps and agricultural runoff.   Lewin (1955) demonstrated that organic nitrogen increased the growth of Prasiola stipitata in culture. Wooton (1991) demonstrated that Prasiola meridionalis became the dominant alga in the presence of guano and wave action, and out-competed Verrucaria maura in the splash zone.  Therefore, an increase in nutrients may benefit the biotope. Nevertheless, 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

Organic-rich runoff would probably promote Prasiola growth where wave exposure allowed.  However, no direct evidence on the effects of organic enrichment in the littoral fringe was found and not sensitivity assessment was made.

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 only found on hard substrata and dominates rocks in the littoral fringe. 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

Not Relevant on hard rock biotopes.

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

Not Relevant on hard rock biotopes.

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

The mat of Prasiola stipitata is composed of numerous individual thalli, each of which is loosely attached to the substratum. It can easily be removed by hand. It is, therefore, likely to be affected by trampling or vehicular access, although no direct evidence was found.  Therefore, a resistance of Low is suggested but with Low confidence. Resilience is probably High so that 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 is unlikely to be relevant to hard rock substrata. Therefore, the pressure is Not relevant. 

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 mid to littoral fringe and supralittoral and rarely inundated. Therefore, an increase in turbidity due to suspended solids (at the benchmark) is unlikely to adversely affect the biotope and Not relevant is recorded.

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

No information on siltation in the littoral fringe or supralittoral was found. 

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

No information on siltation in the littoral fringe or supralittoral was found. 

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

Introduction of light or shading

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

Evidence

The littoral fringe habitat is likely to be exposed to high levels of irradiance, direct sunlight when compared to the littoral or sublittoral that are emersed. However, Kang et al. (2013) noted that high irradiance (up to 1800 µmol photons/m²/s) had no negative impact on photosynthesis in Prasiola stipitata. In addition, a largely shaded and moist population of Prasiola stipitata showed no changes in photosynthetic parameters from one hour after sunrise to sunset. Although the evidence is limited, it suggests that Prasiola stipitata is probably resistant of a range of light and shade conditions.  Therefore, resistance is probably High, so that resilience is High and the biotope is assessed as Not sensitive.

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

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

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 in Prasiola stipitata 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 evidence was found.

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 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

Prasiola stipitata 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

Accidental physical disturbance due to access (e.g. trampling) or grounding is examined under abrasion above.  Where present, mobile invertebrate fauna are probably not entirely dependent on the algal mat for food or habitat and would forage elsewhere.  However, this biotope is unlikely to be targetted by any commercial or recreational fishery or harvest.