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

Intertidal species are exposed to extremes of high and low air temperatures during periods of emersion. They must also be able to cope with sharp temperature fluctuations over a short period of time during the tidal cycle. In winter air temperatures are colder than the sea, conversely in summer air temperatures are much warmer than the sea. Species that occur in this intertidal biotope are therefore generally adapted to tolerate a range of temperatures.

Palmaria palmata does well in low temperatures, with an optimum between 6 and 15°C (Bak, 2014), consistent with a distribution in northern temperate and arctic waters. The species is also found in warmer temperate waters as far south as Portugal in Europe and with localized large populations in northern Spain (Garbary et al., 2012 and references therein). In the laboratory, plants only became fertile if left at temperatures between 5-7 °C with a short light period (Van der Meer, 1979). Temperatures at or above 15 ^oC may induce physiological stress (Werner & Dring, 2011; Morgan et al., 1980). In tank cultures of Palmaria palmata maintained at 20°C and above, all plants were dead within a week (Morgan et al., 1980). Kain & Norton (1990) suggest, however, that a widely distributed species like Palmaria palmata reacts less strongly to temperature differences than some other red algae.

The associated Ulva spp. are distributed globally and occur in warmer waters than those surrounding the UK suggesting that they can withstand increases in temperature at the pressure benchmark.  Ulva spp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days. Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA. Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30 °C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976). 

Barnacles (Semibalanus balanoides) and Patella vulgata occur in this biotope. Laboratory studies suggest that adults of these species can tolerate temperature increases.   The median upper lethal temperature limit in laboratory tests on Semibalanus balanoides was approximately 35 ^oC (Davenport & Davenport, 2005).  Patella vulgata can also tolerate high temperatures. The body temperature of Patella vulgata can exceed 36 ^oC in the field, (Davies, 1970); adults become non-responsive at 37-38 ^oC and die at temperatures of 42 ^oC (Evans, 1948). Although adults may be able to withstand acute and chronic increases in temperature at the pressure benchmark, increased temperatures may have sub-lethal effects on the population by impacting the success of reproduction phases. Semibalanus balanoides and Patella vulgata are 'northern' with their range extending from Portugal or Northern Spain to the Arctic circle. Populations in the southern part of England are therefore relatively close to the southern edge of their geographic range.  Reproductive and recruitment success in both species is linked to temperature and long-term changes in temperature (exceeding the duration of the pressure benchmark) may to lead to replacement by the warm water species Chthamalus montagui and Chthamalus stellatus (Southward et al., 1995). In Northern Portugal warming seas appear to be linked to a shortening of the reproductive period and the lack of multiple spawning events in Patella vulgata and other northern species (Ribeiro et al., 2009).

Sensitivity assessment. As maxium sea surface temperatures around the British Isles exceed 20 °C (Hiscock, 1998) and that Palmaria palmata occurs in warmer waters in Spain and Portugal, it is considered unlikely that Palmaria palmata would suffer mortality due to the chronic benchmark increase in temperature of seawater. An acute increase at the pressure benchmark may, however, lead to mortalities or inhibit reproduction (depending on timing).  Adults of the associated species, Patella vulgata and Semibalanus balanoides are considered likely to be able to tolerate an acute or chronic increase in temperature at the pressure benchmark, although the timing of acute and chronic increases would alter the degree of impact and hence sensitivity.  An acute change occurring during warm, summer periods that exceeds thermal tolerances could lead to mortality. Sensitivity of Patella vulgata and Semibalanus balanoides  to longer-term, broad-scale perturbations would potentially be greater due to effects on reproduction. Ulva spp., are considered to tolerate increases in temperature at the pressure benchmark. This biotope is considered to be 'Not senstive' to chronic increases but to have 'Low' resistance to an acute increase in temperature. Biotope resilience is assessed as 'Medium' (as no evidence was found to suggest that holdfasts have great resistance) and biotope sensitivity is assessed as 'Medium'. Where resilience is Medium, it is based on expert judgement (Quality Low, applicability and concordance = NR (not relevant).

Temperature decrease (local)

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

Evidence

Many intertidal species are tolerant of freezing conditions as they are exposed to extremes of low air temperatures during periods of emersion. They must also be able to cope with sharp temperature fluctuations over a short period of time during the tidal cycle. In winter air temperatures are colder than the sea, conversely in summer air temperatures are much warmer than the sea. Species that occur in the intertidal are therefore generally adapted to tolerate a range of temperatures, with the width of the thermal niche positively correlated with the height of the shore (Davenport & Davenport, 2005).

Palmaria palmata does well in low temperatures, with an optimum between 6 and 15°C, consistent with a distribution in northern temperate and arctic waters. This species is also found in warmer temperate waters as far south as Portugal in Europe and with localized large populations in northern Spain (Garbary et al., 2012 and references therein). In the laboratory, plants only became fertile if left at temperatures between 5-7°C with a short light period (Meer van der, 1979). Acute or chronic changes in temperature below 5 °C may therefore reduce reproductive success although reproduction and vegetative growth in warmer months should compensate for any reduction in output. Temperatures at or above 15°C may induce physiological stresss (Werner & Dring, 2011; Morgan et al., 1980) In tank cultures of the species at 20°C and above, all plants were dead within a week (Morgan et al., 1980). Such high temperatures, however, are unlikely in most parts of Britain and Ireland. The growth of Palmaria palmata is reduced below 6^oC but the plant can survive lower temperatures as long as the tissue does not freeze (Werner & Dring, 2011).

The associated red algae Porphyra umbilicalis occurs in both temperate and arctic regions and freezing has been demonstrated to have little physiological effect (Green & Neefus, 2014). Other species associated with the biotope are able to tolerate decreases in temperature. Lüning (1990) reported that Corallina officinalis from Helgoland survived 0 °C when exposed for one week. New Zealand specimens were found to tolerate -4 °C (Frazer et al., 1988). Ulva spp. are eurytopic, found in a wide temperature range and in areas which frequently experience freezing conditions and are vulnerable to ice scour (Seed & Suchanek 1992). 

The limpet Patella vulgata and the barnacle Semibalanus balanoides are both northern species and relatively close to their southern range limit in the UK, suggesting these are tolerant of colder temperatures than those typically experienced in UK habitats. The tolerance of Semibalanus balanoides, collected in the winter (and thus acclimated to lower temperatures), to low temperatures was tested in the laboratory. The median lower lethal temperature tolerance was -14.6 ^oC (Davenport & Davenport, 2005). A decrease in temperature at the pressure benchmark is therefore unlikely to negatively affect this species. Adults of Patella vulgata are also largely unaffected by short periods of extreme cold. Ekaratne & Crisp (1984) found adult limpets continuing to grow over winter when temperatures fell to -6 °C, and stopped only by still more severe weather. Loss of adhesion after exposure to -13 °C has been observed with limpets falling off rocks and therefore becoming easy prey to crabs or birds (Fretter & Graham, 1994). However, in the very cold winter of 1962-3 when temperatures repeatedly fell below 0 °C over a period of 2 months large numbers of Patella vulgata were found dead (Crisp, 1964a).  Periods of frost may also kill juvenile Patella vulgata, resulting in recruitment failures in some years (Bowman & Lewis, 1977).

In colder conditions an active migration by mobile species found within the turf may occur down the shore to a zone where exposure time to the air (and hence time in freezing temperatures) is less.

Sensitivity assessment.  The key characterizing species, Palmaria palmata occurs over a wide geographical range and as an intertidal species is predicted to have high tolerances for decreased temperature at the acute and chronic pressure benchmarks. Biotope resistance is assessed as ‘High’ as these effects do not result in mortality and resilience is assessed as ‘High’, so that the biotope is not considered to be sensitive to this pressure. The timing of acute changes and seasonal weather could result in greater impacts on species. An acute decrease in temperature coinciding with unusually low winter temperatures may exceed thermal tolerances and lead to mortalities of the associated species although this would not alter the character of the biotope.

(Where resilience is assessed as high, confidence in the quality of evidence is assessed as ‘High (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as ‘Low’, concordance as High.)

Salinity increase (local)

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

Evidence

Biotopes found in the intertidal will naturally experience fluctuations in salinity where evaporation increases salinity and inputs of rainwater expose individuals to freshwater. Species found in the intertidal are therefore likely to have some form of behavioural or physiological adaptations to changes in salinity.   

Laboratory experiments have defined the upper and lethal lower limits for Palmaria palmata as 15 psu and 50 psu (Karsten et al., 2003), with optimal salinity defined as 23-34 psu (Robbins, 1978). It is not clear whether a sustained increase in salinity would be tolerated, or whether different life stages have different tolerances as this species is under studied, in comparison to some other species of commercial importance (Bak, 2014).

The associated Ulva species can survive hypersaline conditions in supralittoral rockpools subjected to evaporation and are considered to be a very euryhaline, tolerant of extreme salinities ranging from 0 psu to 136 psu (Reed & Russell, 1979).  Some variations in salinity tolerance between populations of Ulva intestinalis have been found, however, suggesting that plants have some adaptation to the local salinity regime (Alströem-Rapaport et al., 2010; Reed & Russell (1979). Increased salinity is most likely to occur in the region of the littoral fringe and supralittoral zone and specimens from these areas were able to tolerate very high salinities, a significant decrease in regeneration only being recorded after exposure to concentrated seawater (102 psu and 136 psu) for > 7 days (Reed & Russell, 1979). In laboratory experiments, Semibalanus balanoides was found to tolerate salinities between 12 and 50 psu (Foster, 1970).  

Sensitivity assessment. Based on the laboratory studies by Karsten et al., (2003) Palmaria palmata is considered likely to tolerate some increases in salinity although the level will be sub-optimal for growth, so that over a year the biomass of Palmaria palmata is likely to decrease and mortalities are likely.  An increase at the pressure benchmark may also lead to an increase in abundance of the very euryhaline Ulva spp.   As an increase in salinity at the pressure benchmark may lead to changes in the composition of the algal turf, altering it from the biotope description and biotope resistance is assessed as ‘Low’. Biotope resilience (following a return to normal habitat conditions) is assessed as ‘Medium’ as it is unclear whether holdfasts would survive. Biotope sensitivity is therefore assessed as ‘Medium’.

Salinity decrease (local)

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

Evidence

Biotopes found in the intertidal will naturally experience fluctuations in salinity where evaporation increases salinity and inputs of rainwater expose individuals to freshwater. Species found in the intertidal are therefore likely to have some form of behavioural or physiological adaptations to changes in salinity. As this biotope is present in full salinity, the assessed change at the pressure benchmark is a reduction in salinity to a variable regime (18-35 ppt) or reduced regime (18-30 ppt). 

Laboratory experiments have defined the upper and lethal lower limits for Palmaria palmata as 15 psu and 50 psu, (Karsten et al., 2003) with optimal salinity defined as 23-34 psu (Robbins, 1978). High growth rates of Palmaria palmata were observed in cultivation experiments at 21 psu in the  In-situ Palmaria palmata from the Arctic Kongsfjord (Spitsbergen) exposed for four days to salinities of 15 psu, following freshwater run-off suffered high levels of mortality (Karsten et al., 2003).

In Danish waters where salinities are lowered by freshwater inputs, cultivation experiments found that Palmaria palmata growth over a seven month period was greatest at a site where mean salinity was 21±3 psu, while no growth occurred at a site where mean salinity was 17±5 psu (Bak, 2014).

Sensitivity assessment. The sensitivity of Palmaria palmata appears to be greater than some other turf-forming species such as Chondrus crispus. A change in salinity at the pressure benchmark is considered to lead to some mortality of Palmaria palmata, although the tolerance threshold reported in laboratory studies and the cultivation experiments found mortality and growth cessation occurred at slightly lower salinities than the assessed benchmark. Long-term changes may lead to replacement by more resistant species such as Chondrus crispus may occur altering the character of the biotope. Biotope resistance is assessed as ‘Low’ and resilience as ‘Medium’ following a return to full salinity conditions. Biotope sensitivity is therefore assessed as ‘Medium'.

NB. Where resilience is Medium, it is based on expert judgement  (Quality Low, applicability and concordance = NR (not relevant).

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

Palmaria palmata is found in a range of water flow regimes from moderately strong to weak. In increasing water flow rate the downstream deflection of the thallus caused by flowing water increases the plants rate of growth by presenting the thallus perpendicular to the incident light. As a result Palmaria palmata can achieve high growth rates in steady tidal streams, growing up to a meter long (Jorde, 1966). However, an increase to very strong flows may inhibit settlement of spores and may remove adults or germlings although flow rates experienced within dense populations will be reduced through friction. Experiments have shown that the flexibility of the very morphologically similar Grateloupia turuturu allows the species to show high reconfiguration rates (reduction in size when aligned with flow) to reduce drag and hence the risk of damage and dislodgement (Boller & Carrington, 2007).

Sensitivity assessment. As the key characterizing species Palmaria palmata can occur in a range of flow speeds and flex to reduce drag, resistance of the biotope was assessed as ‘High’, resilience was assessed as ‘High’ (by default), so that the biotope is classed as ‘Not sensitive’.

(Where resilience is assessed as 'High', confidence in the quality of evidence is assessed as 'High' (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as 'Low' and concordance as 'High')

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

The emergence regime is a key factor structuring this (and other) intertidal biotopes. This biotope generally occurs in the lower eulittoral above the main kelp zone, stands of Alaria esculenta or the mussel, Mytilus edulis and below biotopes dominated by Patella vulgata, Semibalanus balanoides and the wrack Fucus distichus (Connor et al., 2004).

Environmental factors partly set upper and lower limits of algal distribution on shores. Spores and developing germlings are particularly susceptible to desiccation as they have very large surface-to-volume ratios, although they benefit from the film of water that persists in concavities on the substratum (Kain & Norton, 1990). An increase in desiccation resulting from increased emergence is likely to result in the death of the upper portion of the Palmaria palmata population depressing the upper limit of the species. At higher shore levels red algae tend to occur only under canopy forming species, as these limit exposure to desiccation (Hawkins and Hartnoll, 1983).

Experimental grazer removal allowed algae including Palmaria palmata, Ceramium spp. and Osmundea (as Laurencia) pinnatifida to grow higher on the shore (during winter and damp summers) than usual (Hawkins & Hartnoll, 1985). Palmaria palmata also grew more abundantly higher up the shore following the massive mortality of molluscan grazers after the Torrey Canyon oil spill (Hawkins & Hartnoll, 1983). These observations and further grazer removal experiments by Boaventura et al. (2003), indicate that grazing, in combination with physiological tolerances, limits the upper shore extent of biotopes characterized by red algal turfs on moderately and more exposed shores, where grazing is greater than on sheltered shores (Hawkins & Hartnoll, 1983; Boaventura et al., 2003).  These results concord with other studies that show grazing and emersion stress limit the height to which red algal turfs can extend (Underwood, 1980; Boaventura, 2000).

The associated ephemeral green algae, Patella vulgata, Semibalanus balanoides and littorinids are found at a range of shore levels and are found in abundance at higher shore levels than this biotope typically occurs at. These species are therefore considered unaffected by increased emergence experienced by this low-shore biotope.  

Decreased emergence may increase predation on grazers by crabs, starfish and other predators, reducing grazing pressure and allowing the growth of algae more suited to the emergence regime (typically fucoids kelps and Alaria esculenta, depending on the shore height in relation to tidal changes). Competition may, however, be reduced by the level of wave exposure experienced by this biotope which will reduce habitat suitability for canopy forming macroalgae (Hawkins & Hartnoll, 1985).

Sensitivity assessment. Significant long-term increases or decreases in emergence are likely to alter environmental factors and grazing pressures which may result in increased competition or grazing from species better adapted to the changed conditions. Biotope resistance to this pressure is assessed as ‘Low’ based on Palmaria palmata. Resilience is assessed as ‘Medium’ (based on the loss of a large proportion of the population and the loss of holdfasts) and biotope sensitivity to this pressure is assessed as ‘Medium’.

(Where resilience is Medium, it is based on expert judgement  (Quality Low, applicability and concordance = NR (not relevant))

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 from locations that are judged to range from very exposed, moderately exposed or exposed (Connor et al., 2004). The degree of wave exposure influences wave height, as in more exposed areas with a longer fetch waves would be predicted to be higher. As this biotope occurs across a range of exposures, this was therefore considered to indicate, by proxy, that biotopes in the middle of the wave exposure range would tolerate either an increase or decrease in significant wave height at the pressure benchmark.

Sensitivity assessment. The biotope is found across a range of wave exposures, mid-range populations are considered to have 'High' resistance to a change in significant wave height at the pressure benchmark. Resilience is assessed as ‘High’, by default, and the biotope is considered ‘Not sensitive’.

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.

However, exposure to contaminants at levels greater than the benchmark may lead to impacts. Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. The sub-lethal effects of Hg (organic and inorganic) on the sporelings of another intertidal red algae, Plumaria elegans, were reported by Boney (1971), where 100% growth inhibition was caused by 1 ppm Hg in his study. However, no information concerning the effects of heavy metals on Palmaria palmata was found. Heavy metals have the potential to accumulate in plant tissue, therefore it may take some time for tissue levels to fall before recovery can begin.

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.

However, exposure to contaminanats at levels greater than the benchmark may lead to impacts. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction, but that the filamentous forms were the most sensitive. Laboratory studies of the effects of oil and dispersants on several red algae species, including Palmaria palmata (Grandy, 1984 cited in Holt et al. 1995) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages.

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.

However, exposure to synthetic chemical at levels greater than the benchmark may lead to impacts. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil contamination, although the filamentous forms were the most sensitive. Laboratory studies of the effects of oil and dispersants on several red algae species, including Palmaria palmata (Grandy, 1984 cited in Holt et al., 1995) concluded that they were all intolerant of oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. Cole et al. (1999) suggested that herbicides, such as simazina and atrazine were very toxic to macrophytes. Hoare & Hiscock (1974) noted that all red algae was excluded from Amlwch Bay, Anglesey by acidified halogenated effluent discharge. Such evidence suggests Palmaria palmata has high intolerance to synthetic chemicals at levels greater than the benchmark.

Radionuclide contamination

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

Evidence

No evidence was found to assess this pressure at the benchmark. Algae bioaccumulate radionuclides (with extent depending on the radionuclide and the algae species). Adverse effects have not been reported at low levels.

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. However, exposure to contaminants at levels greater than the benchmark may lead to impacts.

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

This biotope would only be exposed to low oxygen in the water column intermittently during periods of tidal immersion. In addition, in areas of wave exposure and moderately strong current flow, low oxygen levels in the water are unlikely to persist for very long as oxygen levels will be recharged by the incorporation of oxygen in the air into the water column or flushing with oxygenated waters.  

Little information on the effects of oxygen depletion on macroalgae was found although Kinne (1972) reports that reduced oxygen concentrations inhibit both photosynthesis and respiration which may affect growth and reproduction. The effects of decreased oxygen concentration equivalent of the benchmark would be greatest during the dark when the macroalgae are dependent on respiration. However, this biotope occurs in the intertidal and Palmaria palmata will be able to respire during periods of emersion.

The associated species are unlikely to be impacted by this pressure, at the benchmark. Experiments have shown that thallus discs of Ulva lactuca plants can survive prolonged exposure to anoxia and hypoxia (Vermaat & Sand-Jensen, 1987; Corradi et al., 2006). Following resumption of normal oxygen conditions gametes were produced. The associated invertebrate species also show high tolerances for reduced oxygen at levels that exceed the pressure benchmark. Semibalanus balanoides can respire anaerobically, so they can tolerate some reduction in oxygen concentration (Newell, 1979). When placed in wet nitrogen, where oxygen stress is maximal and desiccation stress is low, Semibalanus balanoides have a mean survival time of 5 days (Barnes et al., 1963). Limpets can also survive for a short time in anoxic seawater; Grenon & Walker, (1981) found that in oxygen free water limpets could survive up to 36 hours, although Marshall & McQuaid (1989) found a lower tolerance for Patella granularis, which survived up to 11 hours in anoxic water. Patella vulgata are able to respire in air, mitigating the effects of this pressure during the tidal cycle.

Sensitivity assessment. As the biotope will only be exposed to this pressure when emersed and respiration of characterizing and associated will occur in air, biotope resistance was assessed as ‘High’ and resilience as ‘High’ (no effect to recover from), resulting in a sensitivity of 'Not sensitive'.

Nutrient enrichment

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

Evidence

This pressure relates to increased levels of nitrogen, phosphorus and silicon in the marine environment compared to background concentrations.  The pressure benchmark is set at compliance with Water Framework Directive (WFD) criteria for good status, based on nitrogen concentration (UKTAG, 2014).  

Marine algae are often nutrient limited, by nitrogen in particular, so an increase in nutrient levels usually results in increase growth and fecundity. In the Bay of Fundy, for example, where there is a tidal flux of nutrients from the marshes there is luxurious growth of Palmaria palmata. However, very high levels of nutrients can be toxic to macroalgae. Plants placed in tanks with continuous immersion in high nutrients over several weeks stopped growing (Morgan et al., 1980). In general, the great majority of reports refer to an increase in the number of green algae associated with eutrophicated waters, usually at the expense of red and brown algae. In Palmaria palmata nitrogen accumulates in the blades when growth does not keep up with uptake (Morgan et al., 1980). Such storage can be particularly important at high latitudes where nutrient availability and light are limited at certain times of the year.

Atalah & Crowe (2010) added nutrients to rockpools. The experimental treatments do not directly relate to the pressure benchmark but indicate some general trends in sensitivity. The rockpools were occupied by a range of algae including encrusting corallines, turfs of Mastocarpus stellatus, Chondrus crispus and Corallina officinalis and green and red filamentous algae. Nitrogen and phosphorous enhancement was via the addition of fertilisers, as either 40 g/litre or 20 g/litre. The treatments were applied for seven months and experimental conditions were maintained every two weeks. Nutrients had no significant effect on the cover of crustose coralline algae or the cover of red turfing algae (Atalah & Crowe, 2010). However, the cover of green filamentous algae increased where grazers were removed (Atalah & Crowe, 2010).  The study suggests that, although red algal turfs may be tolerant of eutrophication and may even benefit, biotope composition may alter due to the proliferation of fast growing ephemeral algae.

Sensitivity assessment. The pressure benchmark is set at a level that is relatively protective and based on the evidence and considerations outlined above the biological assemblage is considered to be 'Not sensitive' at the pressure benchmark. Resistance and resilience are therefore assessed as 'High'.

Organic enrichment

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

Evidence

As this biotopes occurs in wave exposed areas it is considered unlikely to be exposed to the build-up of organic matter (at the pressure benchmark), as wave action will remove organic deposits. The effects of sedimentation of organic matter are therefore not considered relevant to this biotope. Organic enrichment and nutrient enrichment commonly co-occur, for example sewage deposits or outputs from fish farms may enhance nitrogen and phosphorous and organic matter. The effect of inorganic nutrients has more effects on algal communities than inorganic matter which is not assimilated. Deposit and filter feeders within the biotope may benefit from increased organic matter where this can be used as food. 

Cabral-Oliveira et al., (2014), found higher abundances of juvenile Patella sp. and lower abundances of adults closer to sewage inputs, Cabral-Oliveira et al., (2014) suggested the structure of these populations was due to increased competition closer to the sewage outfalls. 

Sensitivity assessment. Based on resistance to sedimentation, it is judged that this biotope has ’High’ resistance to increased organic matter at the pressure benchmark (which represents enrichment rather than gross pollution).  Resilience is therefore assessed as ‘High’ (no effect to recover from) and the biotope is considered to be 'Not sensitive'.

(Where resilience is assessed as ‘High’, confidence in the quality of evidence is assessed as ‘High' (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as ‘Low’ and concordance as '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

The loss of hard substratum would remove the rock habitat; sediments would be unsuitable for Palmaria palmata and other attached algae that characterize this biotope. Other associated species such as barnacles and limpets would also be lost as these are associated with rock habitats.

Artificial hard substratum may also differ in character from natural hard substratum, so that replacement of natural surfaces with artificial may lead to changes in the biotope through changes in species composition, richness and diversity (Green et al., 2012; Firth et al., 2013) or the presence of non-native species (Bulleri & Airoldi, 2005).  Rock types may also have indirect effects on distribution. On the Isle of Cumbrae, porous sandstone retains water and probably allows some red algae to grow further up the shore than is typical (Hawkins & Hartnoll, 1985).

Sensitivity assessment. Based on the loss of suitable habitat, biotope resistance is assessed as ‘None’, resilience is assessed as ‘Very Low’, as the change at the pressure benchmark is permanent. Biotope sensitivity is therefore ‘High’.

Physical change (to another sediment type)

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

Evidence

Not relevant to biotopes occurring on bedrock.

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 species characterizing this biotope are epiflora and epifauna occurring on rock and would be sensitive to the removal of the habitat. However, extraction of rock substratum is considered unlikely and this pressure is considered to be ‘Not relevant’ to hard substratum habitats.

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

Little information is available on the effects of abrasion on intertidal red algae. Although no reports of the effects of trampling (a source of abrasion) were found for Palmaria palmata, Brosnan & Crumrine (1994) found that the foliose red algae Mastocarpus papillatus was intolerant of moderate levels of trampling.

Sensitivity assessment. The impact of surface abrasion will depend on the footprint, duration and magnitude of the pressure. Biotope resistance, to a single abrasion event is assessed as ‘Medium’ (<25% of population damaged or removed), as some damage may occur and some fronds may be removed although the bases may remain. Resilience is assessed as ‘High’, (through regrowth of fronds), so that biotope sensitivity is assessed as ‘Low’.  Resistance and resilience will be lower (and hence sensitivity greater) to abrasion events that exert a greater crushing force and remove the bases, or that occur at greater intensities and duration.

(Where resilience is assessed as high, confidence in the quality of evidence is assessed as ‘High (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as ‘Low’ concordance as High. Where resilience is Medium, it is based on expert judgement  (Quality L, applicability and concordance = NR (not relevant)

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

The species characterizing this biotope group are epiflora and epifauna occurring on rock which is resistant to subsurface penetration.  The assessment for abrasion at the surface only is therefore considered to equally represent sensitivity to this pressure

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

Intertidal biotopes will only be exposed to this pressure when submerged during the tidal cycle and thus have limited exposure. Siltation, which may be associated with increased suspended solids and the subsequent deposition of these is assessed separately (see siltation pressures). In general, increased suspended particles reduce light penetration and increase scour and deposition. They may enhance food supply to filter or deposit feeders (where the particles are organic in origin) or decrease feeding efficiency (where the particles are inorganic and require greater filtration efforts).  

Increases in the cover of robust, sediment trapping, turf forming algae at the expense of canopy forming species has been observed worldwide in temperate systems and has been linked to increased suspended solids linked to human activities worldwide (Airoldi, 2003l. Increased suspended sediment may also result in increased scour, which may adversely affect foliose red algae, and interfere with settling spores and recruitment if the factor is coincident with their major reproductive period. However, coralline algae, especially the crustose forms and most likely the crustose holdfasts of other algal turf forming species, including Palmaria palmata are considered likely to be resistant of sediment scour (Littler & Kauker, 1984) and regeneration will not be dependent on settlement.

This community is unlikely to be dependent on suspended sediment. Although accumulated sediment within turf habitats is likely to increase the species diversity of the epiphytic fauna, in wave exposed locations, accumulated sediment in the habitat is likely to be minimal. A reduction in suspended sediment will probably reduce the risk of scour, and reduce food availability for the few suspension feeding species in the biotope (e.g. barnacles and spirorbids present), although effects are not likely to be lethal.

Red algae in general are shade tolerant and are common components of the understorey on seaweed dominated shores. Palmaria palmata is often found under partially shaded conditions as an epiphyte on the stems of Laminaria spp. (Morgan et al. 1980) in the sublittoral zone (Lüning 1990). Research on light tolerance of Palmaria palmata is limited (Bak, 2014), however, red algae are well adapted to low light conditions and so may be tolerant of increased turbidity. In the Bay of Fundy where the tidal flux of nutrients from the marshes includes a high level of suspended sediment, Palmaria palmata grows well despite high turbidity. Irvine (1983), observed morphological adaptation of the plant in fairly sheltered, silty conditions; sometimes the blade divisions are wedge-shaped and finely dissected above or the blade has numerous linear divisions throughout. It is likely that this form reduces possible smothering that may result from increased siltation resulting from increased levels of suspended sediments. In the absence of nutrients short-term increase in turbidity may affect growth and reproduction, however, as a perennial, the adults will probably survive.

 Although not sensitive to light attenuation, Palmaria palmata has relatively thin fronds and may be damaged through scour where levels of suspended sediments are high. On sites affected by high levels of resuspended colliery waste particles, Hyslop et al. (1997) found that Palmaria palmata and Ulva spp. were reduced or absent, although the more tough fucoids were less affected. It is not clear how the levels of suspended solids experienced by these sites relate to the pressure benchmark.

 Experiments have shown that the associated green algae, Ulva spp.  is a shade tolerant genus and can compensate for reduced irradiance by increasing chlorophyll concentration and light absorption at low light levels.  Ulva spp. was able to survive over two months in darkness and to begin photosynthesising immediately when returned to the light (Vermaat & Sand-Jensen, 1987).  Limited shading from suspended sediments is therefore not considered to negatively affect this genus. Therefore, a decrease in light intensity is unlikely to adversely affect the biotope. An increase in light intensity is unlikely to adversely affect the biotope as plants can acclimate to different light levels.

Sensitivity assessment. The exposure of biotope to suspended sediments in the water column will be limited to immersion periods, and wave action will reduce accumulation.  The biotope is considered to be ‘Not sensitive’ to a reduction in suspended solids, although this may reduce food supply to the barnacles and other filter and deposit feeders that occur in this biotope. An increase in suspended solids may lead to some abrasion of fronds of Palmaria palmata and Ulva spp., and biotope resistance is therefore assessed as ‘Medium’, resilience is assessed as ‘High’, based on survival of holdfasts.  Evidence globally indicates that increases in suspended solids favour robust turf-forming algae such as Corallina officinalis (Airoldi, 2003). An increase in suspended solids for longer periods than a year, may result in a change in species composition with an increase in species seen in very turbid, silty environments e.g. Ahnfeltia plicata, Rhodothamniella floridula, Polyides rotunda and Furcellaria lumbricalis.

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

Sedimentation can directly affect assemblages inhabiting rocky shores through burial/smothering and scour/abrasion of organisms. This biotope occurs low on the shore, in very exposed to moderately exposed conditions. In areas experiencing wave action, excess sediments are likely to be removed from the rock surface within a few tidal cycles, reducing the time of exposure to this pressure.

The state of the tide may mediate the degree of impact on macroalgae. If smothering occurs at low tide when the algae is lying flat on the substratum, then most of the organism as well as the associated community will be covered by the deposition of fine material at the level of the benchmark. Smothering will prevent photosynthesis resulting in reduced growth and eventually death. If however smothering occurs whilst the alga is submerged standing upright some of the fronds may be left uncovered. The resistance of this biotope to the given pressure could therefore vary with time of day.

No empirical evidence was found to assess the sensitivity of the key characterizing species, Palmaria palmata, to this pressure. Irvine (1983), observed morphological adaptation of the plant in fairly sheltered, silty conditions; sometimes the blade divisions are wedge-shaped and finely dissected above, or the blade has numerous linear divisions throughout. It is likely that this form reduces possible smothering that may result from increased siltation. However, this adaptation occurs in areas with chronic, relatively low levels of siltation and the blade form is unlikely to confer different levels of resistance to a single deposition event at the pressure benchmark.  The perennial holdfasts may survive short periods of siltation, even though fronds may be damaged or removed aiding recovery.

In general, propagules, early post-settlement stages and juveniles suffer severe stress and mortality from sediments (Devinny & Volse, 1978; Eriksson & Johansson, 2003; Berger et al. 2003; Vadas et al., 1992; Airoldi, 2003). Moss et al., (1973), for example, found that growth of zygotes of Himanthalia elongata was inhibited by a layer of silt 1-2 mm thick and that attachment on silt was insecure.

Other species within the biotope, particularly limpets are sensitive to sedimentation. Field observations and laboratory experiments have highlighted the sensitivity of limpets to sediment deposition. Airoldi & Hawkins (2007) tested the effects of different grain sizes and deposit thickness in laboratory experiments using Patella vulgata. At 1 and 2 mm thicknesses, fine sediments decreased grazing by 40 and 77 % respectively. The addition of approximately 4 mm of fine sediment completely inhibited grazing. Limpets tried to escape the sediment but lost attachment and died after a few days (Airoldi & Hawkins, 2007) Observations on exposed and sheltered shores with patches of sediment around Plymouth in the south west of England confirmed that Patella vulgata abundances were higher where deposits were absent. The limpets were locally absent in plots with 50-65 % sediment cover (Airoldi & Hawkins, 2007).

Sensitivity assessment. Deposition of 5 cm of fine material (see benchmark) in a single incident will lower survival and germination rates of spores and cause some mortality in early life stages of Palmaria palmata and other algae within the biotope. Adults are more resistant but will experience a decrease in growth and photosynthetic rates.  Mortality will be more limited, and possibly avoided, where the smothering sediment is removed due to wave action or tidal streams, depending on how long the sediment remains.  Biotope resistance is assessed as ‘Medium’ and resilience is assessed as ‘High’ (based on regrowth from holdfasts). So that biotope sensitivity is judged to be ‘Low’. It should be noted that the associated.

(Where resilience is assessed as high, confidence in the quality of evidence is assessed as ‘High' (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as ‘Low’ and concordance as 'High'. Where resilience is 'Medium', it is based on expert judgement (Quality 'Low', applicability and concordance is 'NR' (not relevant))

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 evidence was found to assess this pressure at the benchmark. Sensitivity to this pressure will be mediated by site-specific hydrodynamic conditions and the footprint of the impact. A deposit at the pressure benchmark would cover species with a thick layer of fine materials, however, as this biotope occurs in the lower intertidal on wave exposed shores it is subject to prolonged immersion and silts may be relatively rapidly re-suspended and removed. Where a large area is covered sediments may be shifted by wave and tides rather than removed. 

Mortality of red algae is likely to depend on the duration of smothering, where wave action rapidly mobilises and removes fine sediments, survival may be much greater.

Species associated with this biotope such as limpets would not be able to escape from deposits and would likely suffer mortality (see evidence for light siltation). Even the most tolerant of organisms would eventually suffer from inhibition and mortality following smothering although the thresholds for these effects have has not been identified (Airoldi, 2003).

The evidence for siltation effects on the associated species, Patella vulgata, are outlined above for ‘light’ deposition. In summary, experiments by Airoldi & Hawkins (2007), supported by field observations, indicate that this species would be unable to escape from sediment deposits of 30cm thickness and would rapidly die.

Sensitivity assessment. At the level of the benchmark (30 cm of fine material added to the seabed in a single event), smothering is likely to result in death and removal of red algal fronds, germlings and invertebrate grazers and biotope resistance is assessed as ‘Low’. Resilience is assessed as ‘High’ (based on survival of holdfasts). Overall the biotope has a ‘Low’ sensitivity to siltation at the pressure benchmark, based on recovery of Palmaria palmata via re-growth from holdfasts.

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.

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 key structuring and characterizing species, Palmaria palmata, can colonize a broad range of light environments from intertidal to subtidal and shaded understorey habitats.  Palmaria palmata appears to be light saturated between 75 and 210 µmol photons m²/s¹ (Bak, 2014 and references therein) and photoinhibition has been observed at 290 µmol photons m²/s¹ (Pang & Lüning, 2004). 

Sensitivity assessment. Based on occurrence beneath canopies, Palmaria palmata and other associated species are considered to have ‘High’ resistance and, by default, ‘High’ resilience to some shading, The biotope is, therefore, assessed as ‘Not sensitive’ to this pressure. A change in shading, which severely reduced light penetration would negatively impact Palmaria palmata and other algae within the biotope. Very high light levels can also negatively impact algae through photoinhibition.

(Where resilience is assessed as ‘High’, confidence in the quality of evidence is assessed as ‘High' (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as ‘Low’ and concordance as 'High'. 

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

Barriers that reduce the degree of tidal excursion may alter larval supply to suitable habitats from source populations. Conversely the presence of barriers may enhance local population supply by preventing the loss of larvae from enclosed habitats.  Barriers and changes in tidal excursion are not considered relevant to the characterizing red algal species, as dispersal is limited by the rapid rate of settlement and vegetative growth from bases rather than reliance on recruitment from outside of populations. Other species associated with the biotope are widely distributed and produce large numbers of larvae capable of long distance transport and survival, resistance to this pressure is assessed as 'High' and resilience as 'High' by default. This biotope is, therefore, considered to be 'Not sensitive'.

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

The key characterizing species Palmaria palmata may be cultivated for use as biofilters and/or food. No information was found on current production in the UK and no evidence was found for the effects of gene flow between cultivated species and wild populations. Experiments by Van der Meer (1987) found that the hybrids of Palmaria palmata crosses from Canada and Ireland had vigorous growth and normal morphology, however the tetraspores had lower viability and those that germinated produced abnormal sporelings.  It was concluded that populations from Ireland and Canada represent the same species that is in the process of splitting into sibling species. Populations around the UK express different haplotypes (Provan et al., 2005) indicating some genetic variation between populations. Although cultivation of different genotypes may lead to gene flow between wild and cultivated populations the limited dispersal may reduce exposure. Some negative effects may arise from hybridisation between very geographically separated populations but there is no evidence to suggest that gene flow between different UK haplotypes would lead to negative effects.

Sensitivity assessment. No direct evidence for genetic effects arising from cultivation and/or translocation of Palmaria palmata was found. Translocation of individuals between widely separated areas may lead to hybridisation and changes in genetic structure.  Cultivation of Palmaria palmata is understood to currently involve collecting spores from locally collected plants in hatcheries or from on-growing locally collected fronds. Where locally collected material is used, as seems usual, resistance is assessed as ‘High’ and resilience as ‘High’ so that the biotope is ‘Not sensitive’. This assessment may require updating if cultivation methods change and translocate material from geographically separate locations.

(Where resilience is assessed as ‘High’, confidence in the quality of evidence is assessed as ‘High' (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as ‘Low’ and concordance as 'High')

Introduction or spread of invasive non-indigenous species

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

Evidence

Invasive non-indigenous species (INIS) that can alter habitats (ecological engineers), or out-compete native macroalgae for space and other resources such as light and nutrients, are the most likely species to negatively affect this biotope. Space pre-emption by holdfasts may prevent settlement of INIS until disturbance events create gaps for invasion. However, in the Mediterranean crustose corallines and algal turfs facilitate attachment of Caulerpa racemosa by providing a more complex substratum than bare rock (Bulleri & Benedetti-Cecchi, 2008).

Algal species which may have overlapping habitat requirements include the green seaweed Codium fragile subsp tormentosoides (now renamed as Codium fragile fragile) and the red seaweed Heterosiphonia japonica, neither of these have so far been recorded in nuisance densities (Sweet, 2011j). Wireweed, Sargassum muticum and Grateloupia turuturu gros best on sheltered shores and in rockpools (Sewell, 2011c, 2011g) and the wave exposed habitats where this biotope occurs may not be suitable for establishment. The red seaweeds Heterosiphonia japonica and Neosiphonia harveyi may also occur in this biotope but, again, no impacts have been reported.

The tunicates Didemnum vexillum and Asterocarpa humilis, the hydroid Schizoporella japonica and the bryozoan Watersipora subatra (Bishop, 2012c; Bishop, 2015a and b; Wood, 2015) are currently only recorded from artificial hard substratum in the UK and it is not clear what their established range and impacts in the UK would be. 

A significant potential INIS is the Pacific oyster Magallana gigas, as its distribution and environmental tolerances are considered to overlap with this biotope on moderately exposed shores where this reef forming species can alter habitat structure. This species may also affect the grazers present in the biotope.  In the Wadden Sea and North Sea, Magallana gigas overgrows mussel beds in the intertidal zone (Diederich, 2005, 2006; Kochmann et al., 2008).

The non-native crab Hemigrapsus sanguineus has recently been recorded in the UK (Sweet & Sewell, 2014) and has the potential to be a significant predator of intertidal invertebrates.  Significant reductions in common shore crab abundance and mussel density have been reported where the Asian shore crab has achieved high densities in mainland Europe (Sweet & Sewell, 2014). In Rye, New York, declines of approximately 80 % of Littorina littorea in the intertidal were reported to coincide with an expansion of the Hemigrapsus sanguineus population (Kraemer et al., 2007). This crab occurs on exposed shores and may therefore occur in this biotope when established.

Sensitivity assessment. Little evidence was found to assess the impact of INIS on this biotope and much of the evidence comes from intertidal habitats in other countries.  The conversion of this biotope to a Magallana gigas reef on moderately exposed shores would present a significantly negative impact. Colonization of red algal turfs by other similar species may lead to some subtle effects on local ecology but at low abundances the biotope would still be recognisable from the description. Based on Magallana gigas, biotope resistance to this pressure is assessed as ‘Low’.  The biotope will only recover if these species are removed, either through active management or natural processes. To recognise that recovery may be prolonged, resilience is assessed as ‘Very Low’ and sensitivity is therefore assessed as ‘High’. Where this biotope occurs on exposed or very exposed shores, the level of wave action may prevent colonization by Magallana gigas.

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 to assess this pressure. The fungal pathogen, Petersenia palmaria n. sp (Oomycetes) which infects Palmaria mollis, does not affect Palmaria palmata (Meer & Pueschel, 1985). Other species associated with this biotope such as, patellid limpets and other algae also experience low levels of infestation by pathogens but mass-mortalities have not been recorded.

Sensitivity assessment. Based on the lack of evidence for major pathogens or significant mortalities of the key characterizing species Palmaria palmata, this biotope is considered to have ‘High’ resistance and hence ‘High’ resilience and is classed as ‘Not sensitive’ at the pressure benchmark. 

Removal of target species

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

Evidence

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures. The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of target species on this biotope. Palmaria palmata (known as dulse) is harvested from the wild for human consumption both commercially and recreationally. As the key characterizing and structuring species, extensive removal of Palmaria palmata would alter the character of the biotope. Garbary et al., (2012) studied harvested and non-harvested shores in Nova Scotia, Canada containing stands of Palmaria palmata. They also conducted experimental removal of Palmaria palmata and assessed simulated removal of Palmaria palmata by an experienced commercial harvester. Simulated commercial harvesting reduced cover of Palmaria palmata from 70% to 40%, although experimental removal on shores not usually harvested reduced cover to 20% (Garbary et al., 2012).

Sensitivity assessment.  Based on evidence from Garbary et al., (2012), biotope resistance, based on the commercial removal of Palmaria palmata, is assessed as 'Low' (removal of 25-75% of cover). Resilience is assessed as ‘High’ (based on removal by cutting, leaving the holdfast to regenerate) and biotope sensitivity is assed as ‘Low'.

(Where resilience is assessed as ‘High’, confidence in the quality of evidence is assessed as ‘High' (based on Hawkins & Harkin, 1985 and Connor et al., 2004), applicability is assessed as ‘Low’ and concordance as 'High')

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

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures. The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of non-target species on this biotope.  The biotope is characterized by dense stands of Palmaria palmata. The loss of this species due to incidental removal as by-catch would alter the character of the habitat from the biotope description. The ecological services such as primary production and the habitat provided by this species would also be lost.

Sensitivity assessment.  Removal of a large percentage of the characterizing species, resulting in bare rock would alter the character of the biotope, species richness and ecosystem function. Resistance is, therefore, assessed as ‘Low’ and resilience as ‘Medium’, (based on the loss of fronds and holdfasts, but see resilience section for caveats) so that sensitivity is assessed as 'Medium'. If a high proportion of holdfasts remained, recovery would be assessed as ‘High’ and sensitivity would be assessed as ‘Low’. Where resilience is 'Medium', it is based on expert judgement (Quality 'Low', applicability and concordance is 'NR' (not relevant))