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

The key characterizing red algal species found in this biotope have broad geographic distributions and are found in warmer waters than those around the UK. As this biotope is subtidal it is protected from exposure to air so that the thermal regime is more stable and desiccation is not a factor. Examples of distribution and thermal tolerances tested in laboratory experiments are provided as evidence to support assessments. Populations can acclimate to prevailing conditions which can alter tolerance thresholds and care should therefore be used when interpreting reported tolerances.

The key characterizing species Chondrus crispus has a wide distribution, it is found extensively throughout Europe and North America records also recorded under a number of synonyms from Africa and Asia (Guiry & Guiry, 2015).  Spore germination in Chondrus crispus appears to be temperature dependent with spores discharged at temperatures of 5^oC failing to germinate although in laboratory culture at 10^oC spores were viable all year round (Bhattacharya, 1985). In New Hampshire, USA, Chondrus crispus grows abundantly in waters with an annual variation in surface temperature from -1 to +19°C (Mathieson & Burns, 1975). The optimum temperature for growth has been reported as 10-15°C (Fortes & Lüning, 1980), 15°C (Bird et al., 1979), 15-17°C (Tasende & Fraga, 1999) and 20°C (Simpson & Shacklock, 1979). Above the optimum temperature, growth rate is reported to decline (Bird et al., 1979; Simpson & Shacklock, 1979). Compared to Chondrus crispus plants grown at 5°C, plants grown at 20°C had higher growth rates in terms of length, biomass, surface area, dichotomy and branch production. The differences resulted in growth of morphologically more complex thalli at higher temperatures with more efficient nutrient exchange and light harvesting (Kuebler & Dudgeon, 1996). Chondrus crispus plants acclimated to growth at 20°C (vs. 5°C) had higher levels of chlorophyll a and phycobilins, resulting in higher rates of light limited photosynthesis for a given photon flux density (Kuebler & Davison, 1995). Plants grown at 20°C were able to maintain constant rates of light saturated photosynthesis at 30°C for 9 hours. In contrast, in plants acclimated to 5°C, light saturated photosynthetic rates declined rapidly following exposure to 30°C (Kuebler & Davison, 1993). Prince & Kingsbury (1973) reported cessation of growth in Chondrus crispus cultures at 26°C, first mortality of spores at 21.1°C and total mortality of spores at 35-40°C, even if exposed for just 1 minute.

The key characterizing species Ahnfeltia plicata,  has a very wide geographic range, occurring from northern Russia to Portugal. The species is therefore likely to be tolerant of higher temperatures than it experiences in Britain and Ireland. Lüning & Freshwater (1988) incubated Ahnfeltia plicata from British Columbia at a range of temperatures for 1 week and tested their survivability by ability to photosynthesize at the end of the incubation period. The species survived from the coldest temperature tested (-1.5°C) to 28 °C. Total mortality occurred at 30 °C. Lüning & Freshwater (1988) suggested that Ahnfeltia plicata was therefore amongst the group of most eurythermal heat tolerant algae. Haglund et al. (1987) incubated Ahnfeltia plicata from the subtidal in Sweden at a range of temperatures and measured photosynthetic rate. There were no significant results, but photosynthetic rate appeared to be optimal at 15°C and decreased either side of this temperature.The key characterizing species Polyides rotunda, is found throughout the North Atlantic Ocean and related populations occur in the North Pacific. Growth and survival was tested over a temperature range of -5 to 30 ^oC. Polyides rotunda tolerated temperatures from -5 to 27 ^oC, grew well from 5 to 25 ^oC, and had a broad optimal range of 10-25 ^oC. This species tolerated 3 months in darkness at 0 ^oC (Novaczek & Breeman, 1990).

The associated species Furcellaria lumbricalis has a wide geographic range, occurring in Europe from northern Norway to the Bay of Biscay. Novaczek & Breeman (1990) recorded that specimens of Furcellaria lumbricalis grew well in the laboratory from 0-25°C with optimal growth between 10 and 15°C. Growth ceased at 25°C and 100% mortality resulted after 3 months exposure to 27°C. Similarly, Bird et al. (1979) recorded optimum growth at 15°C and cessation of growth at 25°C with associated necrosis of apical segments. Samples of Phyllophora pseudoceranoides from Nova Scotia, Iceland, Roscoff and Helgoland grew from 3 ^oC to 25 ^oC and survived from -2 ^oC to 27 ^oC but not 30 ^oC. Luning (1984) found that Phyllophora pseudoceranoides collected from Helgoland died after 1 week exposure to 33 ^oC (Molenaar & Breeman,1994). Edyvean & Ford (1984b) suggest that populations of Lithophyllum incrustans are affected by temperature changes and salinity and that temperature and salinity ‘shocks’ induce spawning but no information on thresholds was provided (Edyvean & Ford, 1984b). Populations of Lithophyllum incrustans were less stable in tide pools with a smaller volume of water that were more exposed to temperature and salinity changes due to lower buffering capacity. Sexual plants (or the spores that give rise to them) were suggested to be more susceptible than asexual plants to extremes of local environmental variables (temperature, salinity etc.) as they occur with greater frequency at sites where temperature and salinity were more stable (Edyvean & Forde, 1984b). Lithophyllum incrustans in the UK is close to the northern edge of its range and is likely to tolerate increased temperatures.

Sensitivity assessment. The geographic distribution and laboratory experiments indicate that the key characterizing species and many of the associated red algal turf species would tolerate either an acute or chronic increase in temperature at the pressure benchmark, although some sub-lethal decreases in photosynthesis may occur where temperatures exceed the optimal. Gamete release may also depend on lower winter temperatures and therefore non-lethal effects on reproduction may occur where optimal temperatures are exceeded. As these effects do not result in mortality, resistance is  assessed as ‘High’ and recovery as ‘High’ (by default) so that the biotope is considered to be ‘Not sensitive’ to short-term (not grater than a year) changes at the pressure benchmark..

Temperature decrease (local)

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

Evidence

The key characterizing red algal species found in this biotope have broad geographic distributions and are found in colder waters than those around the UK. As this biotope is subtidal it is protected from exposure to air so that the thermal regime is more stable. Examples of distribution and thermal tolerances tested in laboratory experiments are provided as evidence to support assessments. Populations can acclimate to prevailing conditions which can alter tolerance thresholds and care should therefore be used when interpreting reported tolerances.

The key characterizing species, Chondrus crispus has a broad geographical distribution (Guiry & Guiry, 2015) and throughout the range experience wide variation in temperatures (although local populations may be acclimated to the prevailing thermal regime).  In New Hampshire, USA, Chondrus crispus grows abundantly in waters with an annual variation in surface temperature from -1 to +19 °C (Mathieson & Burns, 1975). The photosynthetic rate of Chondrus crispus recovered after 3hrs at -20 °C but not after 6 hrs (Dudgeon et al. (1989). Frond bleaching and declines in photosynthesis and growth also occur in long-term experimental exposure to periodic freezing in Chondrus crispus (Dudgeon et al., 1990). Plants from Maine, USA, were frozen at -5 °C for 3 hours a day for 30 days. Photosynthesis was reduced to 55 % of control values, growth rates were reduced and fronds were eventually bleached and fragmented resulting in biomass losses. Additionally, fronds of Chondrus crispus which were frozen daily had higher photosynthetic rates following subsequent freezing events than unfrozen controls, indicating that the species is able to acclimate to freezing conditions (Dudgeon et al., 1990). Spore germination in Chondrus crispus appears to be temperature dependent with spores discharged at temperatures of 5 ^oC failing to germinate although in laboratory culture at 10 ^oC spores were viable all year round (Bhattacharya, 1985).  Acute or chronic changes in temperature below 5 ^oC may therefore reduce reproductive success although reproduction and vegetative growth in warmer months should compensate for any reduction in output.

Ahnfeltia plicata has a very wide geographic range, occurring from northern Russia to Portugal. The species is therefore likely to be tolerant of lower temperatures than it experiences in Britain and Ireland. Lüning & Freshwater (1988) incubated Ahnfeltia plicata from British Columbia at a range of temperatures for 1 week and tested their survivability by ability to photosynthesize at the end of the incubation period. The species survived from the coldest temperature tested (-1.5 °C) to 28 °C. Haglund et al. (1987) incubated Ahnfeltia plicata from the subtidal in Sweden at a range of temperatures and measured photosynthetic rate. There were no significant results, but photosynthetic rate appeared to be optimal at 15 °C and decreased either side of this temperature.

Growth and survival of the key characterizing species, Polyides rotunda was tested over a temperature range of -5 to 30 ^oC. Polyides rotunda tolerated temperatures from -5 to 27 ^oC, grew well from 5 to 25 ^oC, and had a broad optimal range of 10-25 ^oC (Novaczek & Breeman, 1990). This species tolerated 3 months in darkness at 0 ^oC (Novaczek & Breeman, 1990).

Edyvean & Forde (1984b) suggest that populations of Lithophyllum incrustans are affected by temperature changes and salinity and that temperature and salinity ‘shocks’ induce spawning but no information on thresholds was provided (Edyean & Ford, 1984b). 

Furcellaria lumbricalis has a wide geographic range, occurring in Europe from northern Norway to the Bay of Biscay. Novaczek & Breeman (1990) recorded that specimens of Furcellaria lumbricalis grew well in the laboratory from 0-25 °C with optimal growth between 10 and 15 °C. Growth ceased at 25 °C and 100 % mortality resulted after 3 months exposure to 27 °C. Similarly, Bird (1979) recorded optimum growth at 15 °C.

Sensitivity assessment.  The key characterizing species occur over a wide geographical range and can tolerate temperatures below 0 ^oC. Reduced temperatures may result in suboptimal growth and may affect reproduction. 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.

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 occurs in full salinity (Connor et al., 2004) a change above the pressure benchmark is assessed as a change to above 40 ppt. Species within this biotope such as Chondrus crispus that are also found in intertidal biotopes including rock pools are likely to have some form of physiological adaptations to increases in salinity as these habitats encounter more variation in salinity. However, local populations are likely to be acclimated to the prevailing conditions even over small spatial distances and gradients and caution should be used in extrapolating sensitivities.

More evidence was found to assess Chondrus crispus than the other turf forming red algae. Chondrus crispus is found in a range of salinities across its range and has been reported from sites with yearly salinity range 0-10 psu and 10-35 psu (Lindgren & Åberg 1996) and sites from an average of 26-32  psu. However, at different salinities the ratio between the abundance of the tetrasporophyte phase and the gametophyte alters (Guidone & Grace, 2010).  Mathieson & Burns (1971) recorded maximum photosynthesis of Chondrus crispus in culture at 24 psu, but rates were comparable at 8, 16 and 32 psu. Photosynthesis continued up to 60 psu. Bird et al. (1979) recorded growth of Canadian Chondrus crispus in culture between 10 and 50 psu, with a maximum at 30 psu. Chondrus crispus would therefore appear to be euryhaline and tolerant of a range of salinities.

Haglund et al. (1987) studied photosynthetic rate of Ahnfeltia plicata from the subtidal in Sweden and found that, at constant temperature, rate increased up to the maximum salinity tested (33 psu).

Furcellaria lumbricalis is a euryhaline species which occurs in a wide range of salinity conditions down to 6-8 psu (Bird et al., 1991). In the Kattegat and the Gulf of St Lawrence, it is reported to compete well with other species at salinities ranging from 25-32 psu (see review by Bird et al., 1991). Growth experiments in the laboratory revealed that optimum growth occurred at 20 psu, the species grew well at 10 psu and 30 psu, but that growth declined above 30 psu to negligible levels at 50 psu (Bird et al., 1979). It is expected that an increase in salinity may cause reduced growth and fecundity, but that mortality is unlikely.

Edyvean & Ford (1984b) suggest that populations of the crustose coralline Lithophyllum incrustans are affected by temperature changes and salinity and that temperature and salinity ‘shocks’ induce spawning but no information on thresholds was provided (Edyvean & Ford, 1984b).  Populations of Lithophyllum incrustans were less stable in rockpools with a smaller volume of water that were more exposed to temperature and salinity changes due to lower buffering capacity. Sexual plants (or the spores that give rise to them) were suggested to be more susceptible than asexual plants to extremes of local environmental variables (temperature, salinity etc.) as they occur with greater frequency at sites where temperature and salinity were more stable (Edyvean & Ford, 1984b).

Sensitivity assessment. No specific evidence was found for the salinity tolerance of the key characterizing species Polyides rotunda. Based on the reported salinity tolerances of Chondrus crispus and other red algae species, it is considered that an increase at the pressure benchmark may lead to some changes in the composition of the red algal turf that characterizes this biotope and reduce species richness and abundance, although some more tolerant species may persist. Resistance (of the biotope) is therefore assessed as ‘Low’ and resilience as ‘Medium’ and biotope sensitivity is 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

As this biotope is present in full salinity (30-35 ppt, Connor et al., 2004), 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).  Populations can acclimate to local conditions and caution should be used in extrapolating observations from areas where populations are likely to he adapted to the prevailing conditons.A comparative study of salinity tolerances of macroalgae collected from North Zealand in the South Kattegat (Denmark) where salinity is 16 psu. Showed that species generally had a high tolerance (maintained more than half of photosynthetic capacity)  to short-term exposure (4 days) to salinities lower than 3.7. However, tolerances varied between species with Ahnfeltia plicata, Phyllophora pseudoceranoides and Chondrus crispus exhibiting greater tolerance than Rhodomela confervoides (Larsen & Sand-Jensen, 2006). The result illustrates that responses to this pressure will vary between species and that a change at the pressure benchmark is likely to alter the composition of the red algal turf that characterizes the biotope and may alter the biomass and density of more tolerant species.

Chondrus crispus is found in a range of salinities across its range and has been reported from sites with yearly salinity range 0-10 psu and 10-35 psu (Lindgren & Åberg 1996) and sites from an average of 26-32  psu. However, at different salinities the ratio between the abundance of the tetrasporophyte phase and the gametophyte alters (Guidone & Grace, 2010).  Mathieson & Burns (1971) recorded maximum photosynthesis of Chondrus crispus in culture at 24 psu, but rates were comparable at 8, 16 and 32 psu. Photosynthesis continued up to 60 psu. Bird et al. (1979) recorded growth of Canadian Chondrus crispus in culture between 10 and 50 psu, with a maximum at 30 psu. Chondrus crispus would therefore appear to be euryhaline and tolerant of a range of salinities.

Ahnfeltia plicata occurs over a very wide range of salinities. The species penetrates almost to the innermost part of Hardanger Fjord in Norway where it experiences very low salinity values and large salinity fluctuations due to the influence of snowmelt in spring (Jorde & Klavestad, 1963). Ahnfeltia plicata penetrates further than the euryhaline species, Polyides rotunda, and probably has a similar salinity tolerance to Furcellaria lumbricalis, which is limited only by the 4 psu isohaline (see review by Bird et al., 1991). Haglund et al. (1987) studied photosynthetic rate of Ahnfeltia plicata from the subtidal in Sweden and found that, at constant temperature, photosynthesis was positively correlated with salinity between 15 and 33 psu. It is likely therefore that the benchmark decrease in salinity would not result in mortality, but photosynthesis would not be optimal and so growth and reproduction may be compromised.

Furcellaria lumbricalis occurs in the lowest category on the salinity scale (Connor et al., 1997a) and therefore probably relatively tolerant of decreases in salinity. The species forms extensive populations in the main basin of the Baltic Sea where salinity is 6-8 psu in the upper 60-70 m and its extension into the Gulfs of Bothnia and Finland is limited by the 4 psu isohaline (see review by Bird et al., 1991).

Rhodomela confervoides shows local acclimation to prevailing salinity regimes in the brackish Baltic Sea, with populations surviving at 11 ppt or 2.5 ppt depending on the local salinity where collected (Rietema, 1995).

Edyvean & Ford (1984b) suggest that populations of the crustose coralline Lithophyllum incrustans are affected by temperature changes and salinity and that temperature and salinity ‘shocks’ induce spawning but no information on thresholds was provided (Edyvean & Ford, 1984b). Populations of Lithophyllum incrustans were less stable in tide pools with a smaller volume of water that were more exposed to temperature and salinity changes due to lower buffering capacity. Sexual plants (or the spores that give rise to them) were suggested to be more susceptible than asexual plants to extremes of local environmental variables (temperature, salinity etc.) as they occur with greater frequency at sites where temperature and salinity were more stable (Edyvean & Ford, 1984b).

The anemone Urticina felina occurs in estuaries e.g. the Thames estuary at Mucking  and the River Blackwater estuary (Davis, 1967).  Braber and Borghouts (1977) found that Urticina (as Tealia) felina penetrated to about the 11ppt Chlorinity isohaline (corresponding to about 20psu based on conversion rates) at mid tide during average water discharge in the Westerschelde estuary suggesting that it would be tolerant of reduced salinity conditions.  Intertidal and rock pool individuals will also be subject to variations in salinity because of precipitation on the shore; albeit for short periods on the lower shore.  Therefore, the species seems to have a high tolerance to reduction in salinity but may have to retract tentacles and suffer reduced opportunity to feed. 

Sensitivity assessment. Two of the key defining species,Chondrus crispus and Ahnfeltia plicata are euryhaline and occur over a range of salinities. Other species associated with the biotope such as the red algae Furcellaria lumbricalis and Urticina felina are likely to tolerate a reduction in alinity at the pressure benchmark.  Some changes in lgal composition may occur as a response to a decrease in salinity but may not significantly alter it from the biotope description. Resistance (of the biotope) is therefore assessed as ‘Medium’ and resilience as ‘Medium’ (as bases may not remain to enhance recovery), and biotope sensitivity is judged to be 'Medium'.

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

This biotope occurs across a range of flow speeds, from moderately strong (0.5-1.5 m/s) to areas where water flow is negligible (Connor et al., 2004).  As water velocity increases foliose macroalgae can flex and reconfigure to reduce the size of the alga when aligned with the direction of flow, this minimises drag and hence the risk of dislodgement (Boller & Carrington, 2007). These characteristics allow these species to persist in areas that experience a range of flow speeds. Biogenic habitat structures, including the fronds of algae, reduce the effects of water flows on individuals by slowing and disrupting flow. Boller and Carrington (2006) found that the canopy created by a turf of Chondrus crispus reduced drag forces on individual plants by 15-65%. The compact, turf forming growth of the algal species will therefore reduce water flow and the risk of displacement through turbulence and friction.

The characterizing red algal turf is unlikely to be affected by changes in water flow alone as these can endure high current speeds. For example, Chondrus crispus occurs at intertidal sites in Maine, USA experiencing peak Autumn flow speeds as measured by current meters of 9.2 m/s and 5.8 m/s.  

The anemone Urticina felina favours areas with strong tidal currents (Holme & Wilson, 1985; Migné & Davoult, 1997a) although it is also found in calmer and sheltered areas as well as deep water. Records from the MNCR database were used as a proxy indicator of the resistance to water flow changes by this species by Tillin & Tyler-Walters (2014).  The records indicate the water flow categories for biotopes characterized by Urticina felina range from very strong to very weak (negligible) (negligible to >3m/s) suggesting that a change in the maximum water flow experienced by mid-range populations for the periods of peak spring tide flow would not have negative effects (Tillin & Tyler-Walters, 2014).

Scour is a key factor structuring this biotope, changes in the flow may increase or decrease sediment transport and associated scour. Reductions in flow may lead to increased deposition of silts and alter the sediment character. An increase in water flow at the pressure benchmark may re-suspend and remove sand particles which are less cohesive than mud particles. The level of impact will depend on site specific hydrodynamic and sediment conditions. Some periodic movement of sediments and changes in coverage is part of the natural temporal variation and periodic disturbances from storms may be more important than water flow in maintaining the character of the biotope, particularly in sheltered areas.

Sensitivity assessment. As the biotope can occur in a range of flow speeds, resistance of the biotope to changes in water flow that do not alter the substrata is assessed as ‘High’ and resilience as ‘High’ (by default) so that the biotope is assessed as ‘Not sensitive’.

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

Changes in emergence are not relevant to this biotope (group) which is restricted to fully subtidal habitats. Many of the species found in this biotope such as Ahnfeltia plicata, Chondrus crispus, Rhodomela confervoides occur intertidally but a change in emergence would alter the character of the habitat and lead to biotope reclassification.

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 extremely 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. As water movement increases foliose macroalgae can flex and reconfigure to reduce the size of the alga when aligned with the direction of flow, this minimises drag and hence the risk of dislodgement (Boller & Carrington, 2007). These characteristics allow these species to persist in areas that experience a range of flow speeds resulting from wave action. The crustose corallines associated with this biotope have a flat growth form and are unlikely to be dislodged by increased wave action.

Records from the MNCR database were used as a proxy indicator of the resistance to wave height changes by Urticina felina. The latest version of the JNCC National Biodiversity Database was used as the source of the MNCR data.  The records indicate the wave exposure categories for biotopes characterized by members of this ecological group as extremely sheltered; very sheltered; sheltered; moderately exposed; exposed; very exposed (Tillin & Tyler-Walters, 2014).

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.

Contamination at levels greater than the pressure benchmark may adversely impact the biotope. Little information was found concerning the intolerance of Chondrus crispus to heavy metals. Burdin & Bird (1994) reported that both gametophyte and tetrasporophyte forms accumulated Cu, Cd, Ni, Zn, Mn and Pb when immersed in 0.5 mg/l solutions for 24 hours. No effects were reported however, and no relationship was detected between hydrocolloid characteristics and heavy metal accumulation. 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 an intertidal red algae, Plumaria elegans, were reported by Boney (1971), 100 % growth inhibition was caused by 1 ppm Hg.

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

Contamination at levels greater than the pressure benchmark may adversely impact the biotope. The long-term effects on Chondrus crispus of continuous doses of the water accommodated fraction (WAF) of diesel oil were determined in experimental mesocosms (Bokn et al., 1993). Mean hydrocarbon concentrations tested were 30.1 µg/l and 129.4 µg/l. After 2 years, there were no demonstrable differences in the abundance patterns of Chondrus crispus. Kaas (1980) (cited in Holt et al., 1995) reported that the reproduction of adult Chondrus crispus plants on the French coast was normal following the Amoco Cadiz oil spill. However, it was suggested that the development of young stages to adult plants was slow, with biomass still reduced 2 years after the event. O'Brien & Dixon (1976) and Grandy (1984) (cited in Holt et al., 1995) comment on the high intolerance of red algae to oil/dispersant mixtures, but it is unclear which factor is responsible for the intolerance.

Crump et al. (1999) described "dramatic and extensive bleaching" of 'Lithothamnia' following the Sea Empress oil spill. Observations following the Don Marika oil spill (K. Hiscock, pers. comm.) were of rockpools with completely bleached coralline algae. However, Chamberlain (1996) observed that although Lithophyllum incrustans was affected in a short period of time by oil during the Sea Empress spill, recovery occurred within about a year. The oil was found to have destroyed about one third of the thallus thickness but regeneration occurred from thallus filaments below the damaged area.

The examples stated refer to intertidal areas, where the contaminants consist of lighter fractions and float on water subtidal habitats will be less exposed.

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.

Contamination at levels greater than the pressure benchmark may adversely impact the biotope. No evidence was found specifically relating to the intolerance of Chondrus crispus to synthetic chemicals. However, inferences may be drawn from the sensitivities of red algal species generally. 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. They also report that red algae are effective indicators of detergent damage since they undergo colour changes when exposed to relatively low concentration of detergent. Smith (1968) reported that 10 ppm of the detergent BP 1002 killed the majority of specimens in 24hrs in toxicity tests, although Chondrus crispus was amongst the algal species least affected by the detergent used to clean up the Torrey Canyon oil spill. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984, cited in Holt et al., 1995). Cole et al. (1999) suggested that herbicides, such as simazine and atrazine, were very toxic to macrophytes. The evidence suggests that in general red algae are very sensitive to synthetic chemicals. Intolerance of Chondrus crispus is therefore recorded as high.

Cole et al. (1999) suggested that herbicides were (not surprisingly) very toxic to algae and macrophytes. Hoare & Hiscock (1974) noted that with the exception of Phyllophora species, all red algae including encrusting coralline forms, were excluded from the vicinity of an acidified halogenated effluent discharge in Amlwch Bay, Anglesey and that intertidal populations of Corallina officinalis occurred in significant amounts only 600m east of the effluent. Chamberlain (1996) observed that although Lithophyllum incrustans was quickly affected by oil during the Sea Empress spill, recovery occurred within about a year. The oil was found to have destroyed about one third of the thallus thickness but regeneration occurred from thallus filaments below the damaged area.

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). A study in France found that Chondrus crispus was capable of absorbing a large number of artificial radioactive elements and that this had consequences considering the exploitation of this species as a harvestable resource (Cosson et al., 1984). However, no information was found concerning the actual effects of radionuclide on Chondrus crispus.

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 effects of reduced oxygenation on algae are not well studied. Plants require oxygen for respiration, but this may be provided by production of oxygen during periods of photosynthesis. Lack of oxygen may impair both respiration and photosynthesis (see review by Vidaver, 1972). A study of the effects of anoxia on a red algae found within this biotope, Delesseria sanguinea, revealed that specimens died after 24 hours at 15°C but that some survived at 5°C (Hammer, 1972). No evidence is available to make an intolerance assessment for the key characterizing species.

Nutrient enrichment

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

Evidence

Although Chondrus crispus and Polyides rotunda and other characterizing species may be out-competed by faster growing or ephemeral green and red algal species where nutrient enrichment is extensive or prolonged (Johansson et al., 1998) , the levels of scour and sand abrasion are likely to limit the growth of competing species as these tend to be thin and less robust.

Short-term experiments with low levels of nutrient enrichment showed little impacts on red algal turfs. Atalah & Crowe (2010) added nutrients to rockpoolsoccupied 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. The experimental treatments do not directly relate to the pressure benchmark or biotope type but indicate some general trends in sensitivity. Nutrients had no significant effect on the cover of crustose coralline algae or the cover of red turfing algae. However, the cover of green filamentous algae increased only where grazers were removed (Atalah & Crowe, 2010). 

Over geological timescales periods of increased nutrient availability have experienced increases in the distribution of crustose coralline species at the expense of corals (Littler & Littler, 2013), suggesting that this group have some tolerance for enhanced nutrient levels. Overall. Littler & Littler (2013) suggest that corallines as a group can tolerate both low and elevated levels of nutrients.   The crusting coralline Lithophyllum incrustans were present at sites dominated by Ulva spp. in the Mediterranean exposed to high levels of nutrient enrichment from domestic sewage (Arévalo et al., 2007). 

Sensitivity assessment. The pressure benchmark is relatively protective and may represent a reduced level of nutrient enrichment in previously polluted areas. Due to the tolerance of high levels of nutrient input demonstrated generally by red algal turfs, resistance to this pressure is assessed as ‘High’ and resilience as ‘High’ so that the biotope is assessed as ‘Not sensitive’. 

Organic enrichment

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

Evidence

Where the biotope occurs in tide swept or wave exposed areas (Connor et al., 2004) water movements will disperse organic matter reducing the level of exposure. the crusting coralline Lithophyllum incrustans were present at sites dominated by Ulva spp. in the Mediterranean exposed to high levels of organic pollution from domestic sewage (Arévalo et al., 2007). As turf forming algae, including the red algal turf trap large amounts of sediment the turf itself is not considered sensitive to sedimentation. The turfs probably host a variety of associated species and deposit feeders amongst these would be able to consume inputs of organic matter.

In a recent review, assigning species to groups based on tolerances to organic pollution, the anemone Urticina felina was assigned to AMBI Group II described as 'species indifferent to enrichment, always present in low densities with non-significant variations with time, from initial state, to slight unbalance'  (Gittenberger & van Loon, 2011).

Sensitivity assessment. Based on resistance to sedimentation, exposure to wave action, and the  dominance of red algal turfs in areas subject to sewage inputs, resistance is assessed as ‘High’ and resilience as ‘High’ (by default). The biotope is therefore considered to be ‘Not sensitive’ to this pressure at the benchmark.  

Physical loss (to land or freshwater habitat)

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

Evidence

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

Physical change (to another seabed type)

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

Evidence

This biotope is characterized by a hard rock substratum that is overlain or periodically exposed to, a layer of coarse sand. Removal of the bedrock would remove the attachment surface for the red algal turf that characterizes this biotope and the absence of sand may allow colonisation ofless scour-tolerant species, significantly altering the character of the biotope.

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., 2014) or the presence of non-native species (Bulleri & Airoldi, 2005). The key characterizing species, Chondrus crispus readily colonised artificial settlement plates and by the end of the experiment was the dominant species on plates (Harlin & Lindbergh, 1977). Chondrus crispus were however significantly more abundant on the substratum with the largest particles (1-2 mm) and only a few individuals were found on the smooth surface, demonstrating that artificial smooth surfaces may not provide an optimal habitat.

In the absence of hard substratum crustose corralines can propagate as free-living rhodolith nodules and can form extensive subtidal habitats (Littler & Little, 2013). However, these biogenic reefs are not analogous to this habitat type.

Sensitivity assessment. Based on the loss of suitable habitat, biotope resistance is assessed as ‘None’ and recovery is assessed as ‘Very Low’ as the change at the pressure benchmark is permanent. 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

Generally this pressure is considered to be 'Not relevant' to biotopes occurring on bedrock. However, as this biotope is often overlain by sands or exposed to shifting sands this pressure is assessed. The sand covering and scour is an important factor supporting development and maintenance of this biotope. Removal of sands may allow species with less scour tolerance to colonize altering the character of the biotope. Siltation by finer sediments may have less impact but may lead to subtle changes and changes such as anoxia at the bedrock/sediment interface may lead to removal or damage of holdfasts and bases. A change to coarser gravels, pebbles and cobbles would increase the degree of abrasion where these are mobile and this may also remove the red algal turf.

Sensitivity assessment. A change in the character of the overlying sediment may alter the character of the biotope. Resistance is, therefore, assessed as 'Low' and resilience is Very low (the pressure is a permanent change), so that the biotope is considered to have 'High' sensitivity to this pressure.

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 epifauna or epiflora 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

The red algal turf that characterizes this biotope has some resistance to abrasion as these species persist where scour rates are high from resuspension and transport of sand particles. Little empirical evidence was found to support this asessment.

Chondrus crispus is flexible (Dixon & Irvine, 1977) and would be expected to be relatively resistant to physical abrasion. Indeed, Worm & Chapman (1998) suggested that Chondrus crispus was highly resistant to intense physical and herbivore induced disturbance, ensuring competitive dominance on the lower shore. Chondrus crispus is capable of regenerating from its holdfasts (e.g. Dudgeon & Johnson, 1992) and so no mortality is expected.

Taylor (1970) (cited in Sharp et al., 1993) stated that clumps of fronds of Furcellaria lumbricalis were easily removed from the substratum by drag-raking, but only where the plant had a sufficient number of dichotomies (usually more than 3) to snag in the rake.

Dethier (1994) experimentally manipulated surface abrasion on a range of encrusting algae including Lithophyllum impressum. Crusts were brushed with either a nylon or steel brush for 1 minute a month for 24 months. Unbrushed controls grew by approximately 50% where the cover of nylon brushed crusts and steel brushed crusts decreased by approximately 25% and 40% respectively (interpreted from figures in Dethier, 1994). In laboratory tests on chips of Lithophyllum impressum brushing with a steel brush for 1 minute once a week for 3 weeks, resulted in no cover loss of two samples while a third ‘thinned and declined’ (Dethier, 1994).   Mechanical abrasion from scuba divers was also reported to impact encrusting corallines, with cover of Lithophyllum stictaeforme greater in areas where diving was forbidden than visited areas (abundance, 6.36 vs 1.4; it is presumed this refers to proportion of cover, although this is not clear from the text, Guarinieri et al., 2012).

Sensitivity assessment. The impact of surface abrasion will depend on the footprint, duration and magnitude of the pressure. Based on evidence from the step experiments and the relative robustness of the red algal turf and encrusting corallines, resistance, to a single abrasion event is assessed as ‘Medium’ (loss of <25% cover/abundance) and recovery as ‘High’ (as bases are likely to remain), so that 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.

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 epifauna or epiflora 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

As this biotope occurs where sands cover the rock and scour is a significant factor this biotope is potentially sensitive to changes in suspended solids. Siltation and abrasion, which may be associated with changes in suspended solids are assessed separately.

The red algal species that characterize this biotope are scour tolerant and occur in turbid waters and in general algal turfs replace fucoids and kelps in areas where turbidity and sedimentation increase (Airoldi, 2003). Many of the red algal species, including the key characterizing Chondrus crispus, occur beneath canopies of larger macroalgae and are tolerant of low light levels (Gantt, 1990). Ahnfeltia plicata is not likely to be affected directly by an increase in suspended sediment. In general, subtidal red algae are able to exist at relatively low light levels (Ahnfeltia plicata typically occurs as an understorey alga beneath Laminaria sp. (Lüning, 1990) and so is presumably well adapted to growth in low light conditions. Furcellaria lumbricalis often occurs in relatively turbid waters. Laboratory experiments by Bird et al. (1979) revealed that Furcellaria lumbricalis was growth saturated at very low light levels (ca 20µE/m²/s) compared to other algae such as Chondrus crispus (50-60µE/m²/s). They suggest that this may be an explanation why Furcellaria lumbricalis is able to proliferate in relatively deep and turbid waters. Similarly, in their review, Bird et al. (1979) comment that in all studies, saturation and inhibition radiances were low for Furcellaria lumbricalis compared to other macroalgae indicating good competitive ability in the attenuated light of deeper or more turbid waters. Increases in turbidity may provide the species with a competitive advantage over other macroalgae.

Crustose coralline alga are thought to be fairly resistant of sediment scour (Littler & Kauker, 1984) and are tolerant of very low light levels. Encrusting corallines can occur in deeper water than other algae where light penetration is limited. Samples of Lithophyllum impressum suspended from a raft and shaded (50-75% light reduction) continued to grow over two years (Dethier, 1994).

A decrease in suspended solids and a reduction in scour may favour species more typical of areas of lower turbidity and lower levels of scour. This may result in an increase in kelp or Alaria esculenta (where the sand layer characterizing this biotope is removed).

Sensitivity assessment.  Changes in suspended solids at the pressure benchmark may lead to changes in the biotope assemblage, however, no empirical evidence was found to assess this pressure. Increases in suspended solids may lead to greater scour damaging plants and reduce light availability impacting growth. Decreased suspended solids may increase the suitability of the biotope for species less tolerant of scour and turbidity that can out-compete the characterizing species. The assessment is based on the characteristic sands remaining in the biotope covering the rocks and limiting the establishment of other competing species, In this scenario the biotope will still be subject to episodes of re-suspension and water transport.  As the species present are tolerant of scour and turbidity, biotope resistance is assessed as ‘Medium’ and resilience as ‘High’ (as crustose bases are expected to remain to support recovery) sensitivity is therefore assessed as ‘Low’.

Smothering and siltation rate changes (light)

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

Evidence

This biotope is characterized by a turf of red algae occurring on rock that is overlain with coarse sediments. These sediments are likely to move and therefore the turf and associated species will be subject to periodic burial. In areas exposed to wave action or strong water flows deposited sediments ar e likely to be moved rapidly mitigating the impact. The key characterizing species Chondrus crispus, Polyides rotunda and Ahnfeltia plicata are erect and grow to over 20 cm, therefore mature plants are unlikely to be affected by smothering with 5 cm of sediment. However, recently settled propagules, regenerating holdfasts and small developing plants would be buried by 5 cm of sediment and be unable to photosynthesize.

In a review of the effects of sedimentation on rocky coast assemblages, Airoldi (2003) outlined the evidence for the sensitivity of coralline algae to sedimentation. The reported results are contradictory with some authors suggesting that coralline algae are negatively affected by sediments while others report that encrusting corallines are often abundant or even dominant in a variety of sediment impacted habitats (Airoldi, 2003 and references therein). Crustose corallines have been reported to survive under a turf of filamentous algae and sediment for 58 days (the duration of experiment) in the Galapagos (species not identified, Kendrick, 1991). The crustose coralline Hydrolithon reinboldii, has also been reported to survive deposition of silty sediments on subtidal reefs off Hawaii (Littler, 1973).

Communities dominated by Urticina felina were described on tide swept seabed, exposed to high levels of suspended sediment, sediment scour and to periodic smothering by thin layers of sand, up to ca 5cm in the central English Channel (Home & Wilson, 1985). Urticina felina is abundant in the sediment-scoured, silty rock communities CR.HCR.XFa.FluCoAs and CR.MCR.EcCr.UrtScr (Connor et al. 2004). Laboratory experiments have shown that another anemone Cylista lacerata (studied as Sagartiogeton laceratus) is able to survive under sediments for 16 days and to be capable of re-emerging under shallow (2cm) burial (Last et al., 2011).  The percentage mortality increased with both depth and increasingly finer sediment fraction.  Bijkerk (1988, results cited from Essink (1999) indicated that the maximal overburden through which the anemone Cylista elegans could migrate was <10cm in sand.  No further information was available on the rates of survivorship or the time taken to reach the surface.

Sensitivity assessment. Based on the growth form of the characterizing red algae and the presence of these algae and Urticina felina in biotopes subject to sand covering (including the assessed biotope one), resistance to this pressure, at the benchmark, is assessed as 'High', resilience is assessed as 'High' (by default) and the biotope is considered to be 'Not sensitive'.

Smothering and siltation rate changes (heavy)

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

Evidence

The available evidence for siltation pressures is outlined for the ‘light’ deposition pressure.  At the pressure benchmark ‘heavy deposition’ represents a considerable thickness of deposit. Complete burial of algal turf and encrusting corallines and associated animals would occur. Removal of the sediments by wave action and tidal currents would result in considerable scour. The effect of this pressure will be mediated by the length of exposure to the deposit.

Sensitivity assessment.  Resistance is assessed as ‘Low’ as the impact on the characterizing and associated species could be significant but may be mitigated by rapid removal. Resilience is assessed as ‘High’ based on vegetative re-growth from the scour-tolerant surviving bases of the characterizing species. Sensitivity is therefore assessed as 'Low'. 

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

Coralline crusts are shade tolerant algae, often occurring under a macralgal canopy that reduces light penetration. These species can acclimate to different levels of light intensity and quality and encrusting corallines can occur in deeper water than other algae where light penetration is limited. Samples of Lithophyllum impressum suspended from a raft and shaded (50-75% light reduction) continued to grow over two years (Dethier, 1994). In areas of higher light levels, the fronds and bases may be lighter in colour due to bleaching (Colhart & Johansen, 1973). Other red algae in the biotope are flexible with regard to light levels and can also acclimate to different light levels.  Canopy removal experiments in a rocky sub tidal habitat in Nova Scotia, Canada by Schmidt & Scheibling (2007) did not find a shift in understorey macraoalgal turfs (dominated by Corallina officinalis, Chondrus crispus and Mastocarpus stellatus) to more light-adapted species over 18 months. 

Ahnfeltia plicata is not likely to be affected directly by an increase in suspended sediment. In general, subtidal red algae are able to exist at relatively low light levels (Gantt, 1990). Ahnfeltia plicata typically occurs as an understorey alga beneath Laminaria sp. (Lüning, 1990) and so is presumably well adapted to growth in low light conditions. An increase in turbidity would reduce the amount of light reaching the understorey. Over the course of a year, this may result in mortality of the Ahnfeltia plicata individuals at the limit of their depth range. 

A decrease in turbidity would result in greater light availability for Ahnfeltia plicata. Haglund et al. (1987) reported no inhibition of photosynthesis up to 500 µE/m²/s and suggested that Ahnfeltia plicata had a high potential for growth provided no other factors were limiting. Ahnfeltia plicata is therefore assessed as being tolerant to decrease in turbidity, with the potential to benefit from the factor.

Two species of cold-temperate algae from the North Atlantic Ocean, Polyides rotunda and Furcellaria lumbricalis, were tested for growth and survival over a temperature range of -5 to 30-degrees-C. In comparisons of eastern and western isolates, both Furcellaria lumbricalis, a North Atlantic endemic, and Polyides rotunda, a species having related populations in the North Pacific, were quite homogeneous. Furcellaria lumbricalis tolerated -5 to 25-degrees-C and grew well from 0 to 25-degrees-C, with optimal growth at 10-15-degrees-C. P. rotundus tolerated -5 to 27-degrees-C, grew well from 5 to 25-degrees-C, and had a broad optimal range of 10-25-degrees-C. Both species tolerated 3 months in darkness at 0-degrees-C (Novaczek & Breeman, 1990).

Some populations of Plocamium cartilagineum were found to be light-limited in the Isle of Man and removal of the Laminaria canopy enhanced growth (Kain, 1987). However, in shallow water in summer, light levels are high enough to inhibit growth and it can only inhabit shallow waters where shaded by Laminarians (Kain, 1987 and references therein).  A maximum irradiance of 0.5 mmol/m2/s was inhibitory for Plocamium cartilagineum (Kain, 1987)

The responses of the red algae to shading Plocamium cartilagineum and exposure to light vary, some such as are found in the deeper subtidal and are more tolerant of shade than species such as Chondrus crispus that are found in the intertidal .

Furcellaria lumbricalis often occurs in relatively turbid waters. Laboratory experiments by Bird et al. (1979) revealed that Furcellaria lumbricalis was growth saturated at very low light levels (ca 20µE/m²/s) compared to other algae such as Chondrus crispus (50-60µE/m²/s) and Fucus serratus (100µE/m²/s). They suggest that this may be an explanation why Furcellaria lumbricalis is able to proliferate in relatively deep and turbid waters. Similarly, in their review, Bird et al. (1999) comment that in all studies, saturation and inhibition radiances were low for Furcellaria lumbricalis compared to other macroalgae indicating good competitive ability in the attenuated light of deeper or more turbid waters. In light of its tolerance of turbid conditions it is expected that the majority of the Furcellaria lumbricalis population would be unaffected by increases in turbidity, indeed, such changes may even provide the species with a competitive advantage over other macroalgae.

 Sensitivity assessment. As  the key structuring and characterizing species colonize a broad range of light environments from intertidal to deeper sub tidal and shaded understorey habitats the biotope is considered to have ‘High’ resistance and, by default, ‘High’ resilience and therefore is ‘Not sensitive’ to this pressure.

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 dispersal is limited by the rapid rate of settlement and vegetative growth from bases rather than reliance on recruitment from outside of populations. 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

No information was found on current production of Chondrus crispus or other turf forming red seaweeds in the UK and it is understood that wild harvesting rather than cultivation is the method of production for these. No evidence was found for the effects of gene flow between cultivated species and wild 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. This pressure is therefore considered ‘Not relevant’ to this biotope group.

Introduction or spread of invasive non-indigenous species

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

Evidence

The high levels of scour in this biotope will limit the establishment of all but scour resistant invasive non-indigenous species (INIS) from this biotope and no direct evidence was found for the effects of INIS on this biotope. A number of invasive red algae have been recorded in the UK, from reported habitat preferences Bonnemaisonia hamifera does not appear to be present in scoured environments although the harpoon weed, Asparagopsis armata is found in sandy pools (Guiry & Guiry, 2015). In North America Grateloupia turuturu is a major competitor of Chondrus crispus, although Grateloupia turuturu is present in the UK, this large foliose species may not be able to colonize this scoured biotope due to the effects of drag and abrasion. Undaria pinnatifida has the potential to out-compete Saccharina latissima in suitable habitats. However, it is unlikely to do so in this wave exposed and sand scoured biotope. 

Sensitivity assessment. As sand scouring of this biotope limits establishment of all but robust species, resistance to INIS is assessed as ‘High’ and resilience as ‘High’ (by default) so that the biotope is considered to be ‘Not sensitive’.

Introduction of microbial pathogens

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

Evidence

Extracts of some red algae show antimicrobial and antifungal activity limiting disease, Dilsea carnosa extracts, for example, limit colony extension in Microsporum canis and Trichophyton varrucosum (Tariq, 1991), providing some protection against pathogens. Some examples of infection by microbial pathogens have been found in the literature. Craigie & Correa (1996), for example, described 'green spot' disease in the key characterizing species Chondrus crispus, caused by the interaction of several biotic agents including fungi, bacteria, algal endophytes and grazers, and resulting in tissue necrosis. Correa & McLachlan (1992) infected Chondrus crispus with the green algal endophytes Acrochaete operculata and Acrochaete heteroclada. Infections resulted in detrimental effects, including slower growth, reduced carrageenan yield, reduced generation capacity and tissue damage. Stanley (1992) described the fungus Lautita danica being parasitic on cystocarpic Chondrus crispus and Molina (1986) was the first to report Petersenia pollagaster, a fungal invasive pathogen of cultivated Chondrus crispus. At usual levels of infestation in wild populations these are not considered to lead to high levels of mortality.  Barton (1901) noted that Furcellaria lumbricalis may become infested with nematode worms and reacts by gall formation.

Diseased encrusting corallines were first observed in the tropics in the early 1990’s when the bacterial pathogen Coralline Lethal Orange Disease (CLOD) was discovered (Littler & Littler, 1995). All species of articulated and crustose species tested to date are easily infected by CLOD and it has been increasing in occurrence at sites where first observed and spreading through the tropics. Another bacterial pathogen causing a similar CLOD disease has been observed with a greater distribution and a black fungal pathogen first discovered in American Samoa has been dispersing (Littler & Littler, 1998). An unknown pathogen has also been reported to lead to white ‘target-shaped’ marks on corallines, again in the tropics (Littler et al., 2007). No evidence was found that these are impacting temperate coralline habitats.

Sensitivity assessment. Based on the lack of evidence for major pathogens and significant mortalities of other turf-forming macroalgae 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.  Incidental removal of the key characterizing species and associated species would alter the character of the biotope.  Intertidal populations of Chondrus crispus are harvested commercially in Scotland and Ireland, the stipe is removed but the base is left intact to allow the algae to re-grow.  As a key characterizing and structuring species extensive removal of Chondrus crispus would alter the character of the biotope.  The effect of harvesting Chondrus crispus has been best studied in Canada. Prior to 1980, the seaweed beds of Prince Edward Island were dominated by Chondrus crispus and the species was heavily exploited, following this period a marked increase in abundance of the red seaweed, Furcellaria lumbricalis, which was avoided by the commercial harvest, and an associated decline in abundance of Chondrus crispus (Sharp et al., 1993). The authors suggested that harvesting has brought about the shift in community structure. Sharp et al. (1986) reported that the first drag rake harvest of the season, on a Nova Scotian Chondrus crispus bed, removed 11% of the fronds and 40% of the biomass. Efficiency declined as the harvesting season progressed. Chopin et al. (1988) noted that non-drag raked beds of Chondrus crispus in the Gulf of St Lawrence showed greater year round carposporangial reproductive capacity than a drag raked bed. In the short-term, therefore, harvesting of Chondrus crispus may remove biomass and impair reproductive capacity, while in the long-term, it has the potential to alter community structure and change the dominant species. The other key characterizing  red algal species are not commercially targeted but have been investigated as alternative sources of carrageenan and agar (Mathieson et al., 1984) and in the future may be subject to harvesting.

The removal of kelps or brown algae from this biotope would reduce shading and is not considered to negatively affect this biotope (for assessment of removal of the key characterizing species as by-catch, see the removal of non-target species pressure).

Sensitivity assessment.  The species that are harvested, or potentially harvested, in this biotope are all attached and relatively conspicuous. A single event of targeted harvesting could therefore efficiently remove individuals and resistance is assessed as ‘Low’. This assessment is supported by evidence from Sharp et al., (1993) on the proportion of biomass of Chondrus crispus removed commercially.  Resilience of the turf forming red seaweeds is assessed as ‘Medium’ (based on evidence for recovery from harvesting where some damage occurred to the bases although see caveats in the resilience section) and biotope sensitivity is assessed as ‘Medium'. This assessment refers to a single collection event, long-term harvesting over wide spatial scales will lead to greater impacts, with lower resistance and longer recovery times. 

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 key characterizing species and associated species would alter the character of the biotope. The biotope is characterized by the turf of red algae. The loss of this due to incidental removal as by-catch would therefore alter the character of the habitat and result in the loss of species richness. The ecological services such as primary production and the habitat structure provided by these species would also be lost.

Sensitivity assessment.  Removal of a large percentage of the characterising species resulting in bare rock would alter the character of the biotope, species richness and ecosystem function. Resistance is therefore assessed as ‘Low’ and recovery as ‘Medium’, so that sensitivity is assessed as 'Medium'.