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

Most fucoids are cold-temperate species (Lüning, 1984), and temperatures above 20°C are generally considered unsuitable (Zou et al., 2012). The effect of high temperature stress on photosynthesis in brown algae is related to inactivation of enzymes and the induction of reactive oxygen species (ROS), leading to photoinhibition (Suzuki & Mittler, 2006). Growth rates of adult brown macroalgae may be affected by temperature through the increase in metabolic rates (Nygard & Dring, 2008). However, Fucus serratus is found along the Atlantic coast of Europe from Svalbard to Portugal and on the shores of north-east America. The seaweed is thus well within its thermal range in the British Isles.

Increased temperature (>15°C) can enhance biotic stress on Fucus plants by increasing mico- and macrofouling rates (Wahl et al., 2010). Several studies observed adverse effects of Fucus serratus as a result to warm thermal stress in terms of growth, physiological performance and reproductive output in Spain and Portugal (Pearson et al., 2009; Viejo et al., 2011; Martínez et al., 2012). Jueterbock et al. (2014) however determined that these negative impacts can be explained by within-population genetic diversity. Southwest-Ireland and Brittany are hot-spots of genetic diversity (Coyer et al., 2003; Hoarau et al., 2007) and may thus be more resilient to changes in temperature. Indeed, Nielsen et al. (2014) found no negative effects on growth rates of adult Fucus serratus to water temperatures of 22°C (laboratory experiment with specimen collected from Firth of Forth, Scotland). Phenotypic plasticity plays therefore an important role in determining the sensitivity of individual populations to changes in temperature.

The geographical ranges of a variety of associated species such as Halichondria panicea, Chondrus crispus and Ascidiella scabra suggest that these organisms will be tolerant to a change in temperature at the pressure benchmark. It is however possible that acute changes in temperature will have adverse effects resulting in mortalities. 

Sensitivity assessment. An increase in 5°C above average British and Irish temperatures is not likely to have a detrimental effect of Fucus serratus and associated communities, however, phenotypic plasticity will influence the tolerance of individual population. Resistance and resilience are therefore both assessed as ‘High’ (no impacts to recover from). The biotope group is ‘Not Sensitive’ to a change in temperature 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

Lüning (1984) reported that Fucus serratus survived in the laboratory for a week a range temperature between 0°C and 25°C.  Fucus serratus is found along the Atlantic coast of Europe from Svalbard to Portugal and on the shores of north-east America. The seaweed is thus well within its thermal range in the British Isles. Lüning (1984) placed this species in his 'Cold temperature North Altantic group'.

Sensitivity assessment. A decrease in acute or chronic temperature above average British and Irish temperatures is not likely to have a detrimental effect of Fucus serratus and associated communities, based on global distribution. However, it should be noted that phenotypic plasticity will influence the tolerance of individual population. Resistance and resilience are therefore both assessed as ‘High’ (no impacts to recover from). The biotope group is ‘Not Sensitive’ to a change in temperature at the pressure benchmark. 

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 group is found in the intertidal and is therefore likely to experience cyclical periods of hypo- and hyper-salinity. Seaweeds are able to compensate for changes in salinity by adjusting internal ion concentrations. However this will occur at a cost, reducing photosynthetic rate and hence affecting the growth rate of the seaweed. Growth rates for Fucus serratus are maximal at a salinity of 20 psu with the critical limit for recruitment set at 7 psu (Malm et al., 2001).

Sensitivity assessment. Fucus serratus, commonly inhabit narrow fjords where salinity can vary widely along a spatial (kms) and/or temporal (hours to daily) scale. Species associated with this biotope are therefore likely to be tolerant to an increase in salinity from 35 to 40 units for one year.  No direct evidence was found on the effects of hypersaline (>40 units) conditions. However, hypersaline conditions may result in damage to the fucoid but loss of associated community (e.g. ascidians and sponges).  Therefore a tentative resistance of 'Medium' is recorded, at low confidence. Resilience is probably 'High', so that the biotope is probably of 'Low' sensitivity at the pressure benchmark.

Salinity decrease (local)

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

Evidence

This biotope group is found in the intertidal and is therefore likely to experience cyclical periods of hypo- and hyper-salinity. Seaweeds are able to compensate for changes in salinity by adjusting internal ion concentrations. However this will occur at a cost, reducing photosynthetic rate and hence affecting the growth rate of the seaweed. Growth rates for Fucus serratus are maximal at a salinity of 20 psu with the critical limit for recruitment set at 7 psu (Malm et al., 2001).

Sufficient salinity is essential for successful fertilization and germination in Fucus (e.g., Brawley, 1992; Serrão et al., 1999). Malm et al. (2001) found that fertilization success in Fucus serratus decreased substantially with strongly reduced salinity. Indeed the study found that fertilization success was 87% at 9 psu but declined to 5% at 6 psu. Reduced salinity also affects dispersal by decreasing swimming performance of fucoid sperm (Serrão et al., 1996).

Other characterizing species associated with this biotope are likely to be tolerant of a reduction in salinity. Halichondria panacea, Chondrus crispus  amd Ascidiella scabra can all be found in reduced salinity conditions. Patella vulgata can endure periods of low salinity and was found to die only when the salinity was reduced to 3-1 psu (Fretter & Graham, 1994). However, Little et al. (1991) observed reduced levels of activity in limpets after heavy rainfall and in the laboratory activity completely stopped at 12 psu.

Sensitivity assessment. At the level benchmark a reduction in salinity of from full to variable or reduced in one year could have beneficial effects on Fucus serratus as growth rates are maximal below full saline conditions. Other characterizing species associated with this biotope are also tolerant of reduced salinity at the level of the benchmark. Resistance and resilience are therefore both assessed as ‘High’ (no impacts to recover from). The biotope is therefore ‘Not Sensitive’.

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

The rich community of suspension feeders in this biotope is, in part, due to the strong tidal streams with which it is associated. Strong currents provide suspension feeder with a continual supply of food and removes sediment that would otherwise interfere with their feeding apparatus. A decrease in water flow rate could lead to siltation, to the detriment of filter feeders. Furthermore, grazers unable to cope with the strong flow rates normally associated with this biotope may be able to graze more efficiently, increasing herbivory pressure.  High water flow rates increases mechanical stress on macroalgae by increasing drag. This can result in individuals being torn off the substratum. Once removed, the attachment cannot be reformed causing the death of the algae. Any sessile organisms attached to the algae are also lost. Fucoids are however highly flexible and are able to reorientate their position in the water column to become more streamlined. By going with the flow, fucoids can reduce the relative velocity between algae and the surrounding water, thereby reducing drag and lift (Denny et al., 1998). Propagule dispersal, fertilization, settlement, and recruitment are also influenced by water movement (Pearson & Brawley, 1996). In addition, increased water flow will cause scours though increased sediment movement affecting in particular small life stages of macroalgae by removing new recruits from the substratum and hence reducing successful recruitment (Devinny & Volse, 1978) (see ‘siltation’ pressures).  Changes in water motion can thus strongly influence local distribution patterns of Fucus spp. (Ladah et al., 2008). Increases in drag can however be counterbalanced in the long-term by changes in morphology resulting in structurally more resistant thalli and holdfasts (Haring et al., 2002).

Sensitivity assessment.  Strong tidal flow, characteristic of this biotope, encourages communities of sponges and ascidians. Changes to the hydrological regime are therefore likely to directly influence the presence of these species. As the biotope occurs in very strong tidal flow (>3 m/s) an increase in water flow is unlikely.  A reduction in water flow is likely to result in a loss of the suspension feedeing species, an overall reduction in species richness, and result in loss of this biotope, as it is replaced by another Fucus serratus dominated biotope, e.g. LR.LLR.F.Fserr.FS.  However,  a change of 0.1-0.2 m/s(the benchmark)  is unlikely to adversely affect the biotope, although a reduction may decrease feeding and hence growth rates.  Therefore, a resistance of 'High' is recorded, with a resilience of 'High' and a sensitivity of 'Not sensitive' at the benchmark level. 

Emergence regime changes

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

Evidence

This biotope group is found in the intertidal and is therefore subjected to cyclical immersion and emersion. Fucus serratus and Chondrus crispus are both intertidal species adapted to a degree of periodic desiccation. Fucus serratus is more susceptible to desiccation than other Fucus species located further up the shore and subjected more frequently to aerial exposure (Schonbeck & Norton, 1978). The critical water content for Fucus serratus is estimated at 40% with water losses past this point causing irreversible damage. Beer et al. (2014) found that Fucus serratus could not regain any positive photosynthetic rates after rehydrating from 10% water content. In addition, early life history stages will be more susceptible than adults (Henry & Van Alstyne, 2004). Germlings are however protected from desiccation by the canopy of adults. A study by Brawley & Jonhnson (1991) showed that germling survival under adult canopy was close to 100% whereas survival on adjacent bare rock was close to 0% during exposure to aerial conditions. The Fucus canopy is also likely to protect other underlying species to a great extent. Mortalities of other component of the community will however occur if the canopy is removed (see ‘abrasion’ pressure). Mathieson & Burns (1971) measured the photosynthetic rate of Chondrus crispus at varying degrees of desiccation and found that after loss of 65% of its water content, the rate of photosynthesis dropped to 55% of the control rate. In Palmaria palmata, 50% of the plant's water content can be lost in less than 4 hours in dry air at 25°C (Kain & Norton, 1990). This scenario can reasonably be expected at low tide in summer in Britain, although the Fucus canopy is likely to protect the underlying red algae to some extent. The upper shore extent of Fucus serratus and Chondrus crispus may be replaced by species more tolerant of desiccation and more characteristic of the mid-eulittoral such as Fucus vesiculosus or Ascophyllum nodosum.

A decrease in submergence is likely to adversely affect the suspension feeder population by reducing feeding opportunities as immersion is a prerequisite of feeding. This can prove fatal for short lived species such as bryozoans and ascidians. The tissue of Halichondria panicea holds some water and can tolerate a certain degree of desiccation. On the other hand, the soft bodied sea squirt Ascidiella scabra has a greater vulnerability to this pressure. The sea squirt is commonly found in damp crevices or under the canopy of macroalgae offering protection from desiccation but individuals at the highest point on the shore may dry out and die at the benchmark level.

On the other hand, an increase in submergence is likely to benefit this biotope. Feeding opportunity for suspension feeders will increase; desiccation and temperature stresses for all flora and fauna will decrease as will predation from birds. The biotope may extend further up the shore but this extension is likely to be counteracted by a reduction in the lower shore extent of the biotope likely to be taken over by seaweeds more characteristic of the sublittoral fringe. Furthermore, predation by the common shore crab Carcinus maenas is likely to increase.

Sensitivity assessment.  Severe desiccation and associated osmotic stress can increase mortality in Fucus serratus (Pearson et al., 2009). Other species better able to tolerate desiccation will competitively displace Fucus serratus following changes in emergence regime. The characterizing species of this biotope are largely protected from extreme levels of desiccation by the macroalgal canopy. However, the increase in emergence will result in loss of the extent of the biotope up the shore.  Therefore, resistance is thus assessed as ‘Low’, resilience assessed as ‘Medium’, and the biotope assessed as ‘Medium’ sensitivity to changes in emersion regime at the level of the benchmark.

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

Fucus serratus is highly flexible but not physically robust and an increase in wave exposure will cause mechanical damage, breaking fronds or even dislodging algae from the substratum. Fucoids are permanently attached to the substratum and are not able to re-attach if removed. Organisms living on the fronds and holdfasts will be washed away with the algae whereas free-living community components could find new habitat in surrounding areas. The biotope is found in wave sheltered to extremely sheltered habitats. In these locations, the breadcrumb sponge Halichondria panicea grows in massive forms. Poorly attached massive forms may be ripped off by an increase in water flow rate leading to the death of large colonies. A reduction in wave action would have little effect as the species is naturally found in wave sheltered conditions.

Sensitivity assessment. Fucus serratus and associated communities are sensitive to an increase in wave action as increased exposure would result in important losses both in biomass and species richness. The biotope may be preplaced by another Fucus serratus dominated biotope e.g. LR.MLR.BF.Fser. Resistance is thus assessed as ‘Medium’. Recovery will depend on the extent of Fucus serratus loss but will be rapid once conditions return to normal if some of population remain, resulting in ‘High’ resilience. Overall this biotope group scores a ‘Low’ sensitivity to this pressure at the pressure benchmark. 

Transition elements & organo-metal contamination

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

Evidence

This pressure is Not assessed but evidence is presented where available.

Hydrocarbon & PAH contamination

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

Evidence

This pressure is Not assessed but evidence is presented where available.

Synthetic compound contamination

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

Evidence

This pressure is Not assessed but evidence is presented where available.

Radionuclide contamination

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

Evidence

No evidence

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

Sustained reduction of dissolved oxygen can lead to hypoxic (reduced dissolved oxygen) and anoxic (extremely low or no dissolved oxygen) conditions. Sustained or repeated episodes of reduced dissolved oxygen have the potential to severely degrade an ecosystem (Cole et al., 1999). Josefson & Widbom (1988) investigated the response of benthic macro and meiofauna to reduced dissolved oxygen levels in the bottom waters of a fjord in Sweden. At dissolved oxygen concentrations of 0.21 mg/l, the macrofaunal community was eradicated and was not fully re-established 18 months after the hypoxic event. Meiofauna seemed, however, unaffected by de-oxygenation.

Sensitivity assessment. Macroalgae are negatively impacted by reduced dissolved oxygen level at the level of the benchmark (2 mg/l for 1 week) resulting in direct mortalities. However, the strong water movement in tide-swept tidal currents combined with turbulent flow over rocks would aerate the water column, and emersion at low tide would mean that any oxygen depletion was transient. Therefore, resistance is assessed as ‘High’. Hence, resilience is assessed as ‘High’, and the biotope as 'Not sensitive'.

Nutrient enrichment

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

Evidence

Nutrient enrichment generally stimulates ephemeral macroalgae growth (Duarte, 1995). This stimulation of annual ephemerals may accentuate the competition for light and space and hinder perennial species development or harm their recruitment (Kraufvelin et al., 2007). Krauflin et al. (2006) found only minor effects on the fucoid community structure as a response to high nutrient levels during the first 3 years of the experiment. During the 4th year of exposure, however, Fucus serratus started to decline and population consequently crashed in the 5th year. The study observed full recovery of the algal canopy and animal community in less than two years after conditions returned to normal. The results indicate that established rocky shore communities of perennial algae with associated fauna are able to persist for several years, even at very high nutrient levels, but that community shifts may suddenly occur if eutrophication continues. They also indicate that rocky shore communities have the ability to return rapidly to natural undisturbed conditions after the termination of nutrient enhancement.

An influx of nutrients is also likely to stimulate phytoplankton production, depending on other environmental conditions. This means that the amount of food potentially available to the suspension feeders could increase but in the long-term, a sustained increase in nutrients could lead to algal blooms. Algal blooms have the potential to block light from underlying plants, thereby reducing their photosynthetic capacity. In addition, the eventual biodegradation of the blooms will result in the reduction of available oxygen causing reduced growth in macroalgae species such as Fucus serratus. Johansson et al. (1998) investigated the changes in the algal vegetation of the Swedish Skagerrak coast, an area heavily affected by eutrophication, between 1960 and 1997. Slow growing species, including Chondrus crispus, declined in abundance, probably due to competition from faster growing red algal species such as Phycodrys rubens and Delesseria sanguinea. However, this biotope occurs in areas with moderately strong to very strong tidal currents rapidly renewing depleted oxygen levels (‘see ‘de-oxygenation’ pressure).  

Sensitivity assessment. The benchmark of this pressure (compliance with WFD ‘good’ status) allows for a slightly less diverse community of red, green and brown seaweeds with cover variable depending on local physical conditions. Therefore, at the level of the benchmark both resistance and resilience are assessed as ‘High’. The biotope group is, therefore ‘Not Sensitive’ to this pressure at the pressure benchmark.

Organic enrichment

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

Evidence

Organic enrichment can stimulate the production of primary consumers and may lead to eutrophication (see ‘nutrient enrichment’ pressure). Husa et al. (2014) found that the macroalgal communities beyond the immediate proximity of fish farms in Hardangerfjord, Norway, seemed to be little affected by the deposition of organic matter from the salmon farming industry. Bellgrove et al. (2010) however determined that coralline turfs out-competed fucoids at a site associated with organic enrichment caused by an ocean sewage outfall.

Sensitivity assessment. At the level of the benchmark, resistance is assessed as ‘Medium’ as some mortalities are likely to occur. Recovery will be rapid resulting in ‘High’ resilience score. The biotope has thus a ‘Low’ sensitivity to organic enrichment at the level of 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 group occurs on hard substratum (bedrock, boulders, pebbles and cobbles). A change towards a sedimentary or soft rock substratum would lead to the direct loss of suitable attachment areas resulting in the loss of Fucus serratus, Chondrus crispus and other red seaweeds. The loss of macroalgae will result in the loss of habitat for associated sponge and ascidian communities. Resistance is assessed as ‘Low’. As this pressure represents a permanent change, recovery is impossible as the suitable substratum for fucoids is lacking. Consequently, resilience is assessed as ‘Very low’ (the pressure is a permanent change).  The habitat, therefore, scores a ‘High’ sensitivity. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.  

Physical change (to another sediment type)

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

Evidence

Not relevant to biotopes found on hard rock substratum.

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

Extraction of 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 biotope group is found in the lower intertidal, an area easily accessible by humans, especially at low tide. Most macroalgae are very flexible but not physically robust. The trampling of shores by humans will result in increased breakage of algal thalli, decreased thallus height and a net reduction in biomass (see Tyler-Walters & Arnold, 2005 for review).  

In the UK, Boalch et al. (1974) and Boalch & Jephson (1981) noted a reduction in the cover of fucoids at Wembury, south Devon, when compared to surveys conducted by Colman (1933). The size ranges of Ascophyllum nodosum, Fucus vesiculosus and Fucus serratus were skewed to a smaller length, and the abundance of Ascophyllum nodosum, in particular, was reduced (Boalch & Jephson, 1981). It was suggested that visitor pressure, especially after the construction of a car park, was responsible for the reduced cover of fucoids (Boalch et al., 1974). They suggested that the raised edges of the slatey rock severed fronds when the rocks were walked over. However, no quantitative data was provided.

Pinn & Rodgers (2005) compared a heavily visited ledge with a less visited ledge at Kimmeridge Bay, Dorset. Although the mean species richness was similar at both sites, the total number of species was greater at the less utilized site.  Comparatively, the heavily utilized ledge displayed a reduction in larger, branching algal species (e.g. Fucus serratus) and increased abundances of ephemeral and crustose species (e.g. Ulva linza and Lithothamnia spp. respectively). Fletcher and Frid (1996a; 1996b) examined the effects of persistent trampling on two sites on the north-east coast of England. The trampling treatments used were 0, 20, 80, and 160 steps per m² per spring tide for 8 months between March and November. Using multivariate analysis, they noted that changes in the community dominated by fucoids (Fucus vesiculosus, Fucus spiralis and Fucus serratus) could be detected within 1 to 4 months of trampling, depending on intensity. Intensive trampling (160 steps/m² /spring tide) resulted in a decrease in species richness at one site. The area of bare substratum also increased within the first two months of trampling but declined afterwards, although bare space was consistently most abundant in plots subject to the greatest trampling (Fletcher & Frid, 1996a, 1996b). The abundance of fucoids was consistently lower in trampled plots than in untrampled plots. Fletcher and Frid (1996a) noted that the species composition of the algal community was changed by as little as 20 steps per m² per spring tide of continuous trampling since recolonization could not occur. A trampling intensity of 20 steps per m² per spring tide could be exceeded by only five visitors taking the same route out and back again across the rocky shore in each spring tide. Both of the sites studied receive hundreds of visitors per year and damage is generally visible as existing pathways, which are sustained by continuous use (Fletcher & Frid, 1996a, 1996b). However, the impact was greatest at the site with the lower original abundance of fucoids.

Brosnan & Crumrine (1994) noted that trampling significantly reduced algal cover within 1 month of trampling. Foliose algae were particularly affected and decreased in cover from 75% to 9.1% in trampled plots. Mastocarpus papillatus decreased in abundance from 9% to 1% in trampled plots but increased in control plots. Fucus distichus decreased in the summer months only to recover in winter but in trampled plots remained in low abundance (between 1 and 3% cover). Trampling resulted in a decrease in the cover of Pelvetiopsis limitata from 16% to 1.5%. Iridaea cornucopiae decreased from 38 to 14% cover within a month and continued to decline to 4-8% cover. However, after trampling ceased, recovery of algal cover including Iridaea cornucopiae and Mastocarpus papillatus was rapid (ca 12 months) (Brosnan & Crumrine, 1994). Fletcher & Frid (1996a; 1996b) reported a decrease in the understorey algal community of encrusting coralline algae and red algae, which was probably an indirect effect due to increased desiccation after removal of the normally protective fucoid canopy (see Hawkins & Harkin, 1985) by trampling. They also noted that opportunistic algae (e.g. Ulva sp.) increased in abundance. Schiel & Taylor (1999) also observed a decrease in understorey algae (erect and encrusting corallines) after 25 or more tramples, probably due to an indirect effect of increased desiccation as above. However, Schiel & Taylor (1999) did not detect any variation in other algal species due to trampling effects. Similarly, Keough & Quinn (1998) did not detect any effect of trampling on algal turf species.

Algal turfs seem to be relatively tolerant of the direct effects of trampling (based on the available evidence) and some species may benefit from the removal of canopy forming algae (Tyler-Walters, 2005). Their tolerance may result from their growth form as has been shown for vascular plants and corals (Liddle, 1997). Brosnan (1993) suggested that algal turf dominated areas (on shores usually dominated by fucoids) were indicative of trampling on the rocky shores of Oregon. However, tolerance is likely to vary with species and their growth form and little species specific data was found. Furthermore, algal turfs may suffer negative indirect effects where they form an understorey below canopy forming species.

Conversely, fucoid algae are particularly intolerant of trampling, depending on intensity. Fucoid algae demonstrate a rapid (days to months) detrimental response to the effects of trampling, depending on species, which has been attributed to either the breakage of their fronds across rock surfaces (Boalch et al., 1974) or their possession of small discoid holdfasts that offer little resistance to repeated impacts (Brosnan & Crumrine, 1992; Fletcher & Frid, 1996b). Foliose species such as Mastocarpus papillatus, Pelvetiopsis limitata and Iridaea cornucopiae are also likely to be intolerant of trampling (Brosnan & Crumrine, 1994). Brosnan (1993) suggested that the presence or absence of foliose algae (e.g. fucoids) could be used to indicate the level of trampling on the rocky shores of Oregon.

Once Fucus serratus has been removed, understorey algae will become exposed. Macroalgae canopies buffer the effects of high temperatures and water loss on organisms below their fronds in particular when exposed to air. For instance Bertness et al. (1999) determined that substratum temperatures were on average 8-10°C lower under the canopy than on bare rock. Desiccation of understorey algae will create bare patches (see ‘changes in emergence regime’ pressure). These bare patches can lead to invasions by grazing limpets which in turn can promote even greater changes in community composition (Little et al., 2009). The removal of macroalgae canopy due to abrasion will thus have a direct impact on the entire community. However, cracks and crevices are ideal places for germlings to develop and sessile species to settle as these sites may be protected from abrasion.  Stagnol et al. (2013) found that opportunistic ephemeral green algae such as Ulva sp. responded positively to disturbance. These green ephemeral algae are major competitors of Fucus serratus for space colonization and nutrient uptake. Blooms of ephemeral algae facilitated by disturbance may then slow the development of longer-lived perennial algae, especially fucoids. Disturbance is a structuring factor in intertidal habitats. Perturbation events often remove organisms, increase mortality, and release resources such as space, nutrients and light that may enhance the appearance of new colonists (Connell et al., 1997). As a result of these contrasting effects, post-disturbance communities are frequently different from initial communities in terms of composition and dominance of species. Overall, disturbance causes a shift towards a disturbance tolerant seaweed community (Little et al., 2009).

Epifaunal species have been found to be particularly adversely affected by physical disturbance, either due to direct damage or modification of the habitat (Jennings & Kaiser, 1998). Similarly, Dayton (1971) observed greatly reduced the abundance of species living on, under, and among fucoids following large disturbance events. Hydroids, bryozoans and encrusting fauna are easily ripped from the substratum and are unlikely to re-attach and will die. The shells of limpets, tubeworms and periwinkles may be crushed by the weight and force of the abrasion. However, some epifaunal species have been reported to exhibit increased abundances on high fishing effort areas, probably due to their ability to colonize and grow rapidly (Bradshaw et al., 2000). For instance, Ascidiella species had increased in abundance in an area subject to scallop dredging (Bradshaw et al., 2002). The breadcrumb sponge Halichondria panicea is attached to the substratum and will not survive abrasion and physical disturbance. Hiscock (1983) noted that a community, under conditions of scour and abrasion from stones and boulders moved by storms, developed into a community consisting of fast growing species such as Spirobranchus triqueter due to decreased competition. A shift in community composition is thus expected immediately after the disturbance event.  

The effects of trampling are dependent on intensity, expressed as frequency and force per unit area of the impacting 'foot print' (see Liddle, 1997, Tyler-Walters & Arnold, 2008). Clearly, mechanical abrasion due to vehicles, jack-up-barges, or grounding vessels will exceed the abrasive 'intensity' of trampling by humans or livestock.

Sensitivity assessment. Physical disturbance resulting from activities such as trampling (by humans and livestock) or abrasive activities (e.g. vehicles, jack-up-barges, or grounding vessels) could cause a significant loss of fucoid cover and an important reduction in species abundance and diversity. Resistance is thus assessed as ‘Low’. If some Fucus serratus population remain recovery will be fair. However, recruitment mortality, grazing by limpets and the presence of turfs and encrusting algae can slow down and limit recovery. Resilience is thus assessed as ‘Medium’. The biotope, therefore, scores a ‘Medium’ sensitivity to abrasion pressure. If the entire population of Fucus serratus is removed, other species may come to dominate and the recovery will take considerably longer. Re-establishment of the seaweed may depend on the ability to out-compete other species and this may be dependent on suitable environmental conditions.

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.  Therefore, ‘penetration’ is 'Not relevant'. The assessment for abrasion at the surface only is, therefore, considered to equally represent sensitivity to this pressure’. Please refer to ‘abrasion’ above.

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

Light is an essential resource for all photoautotrophic organisms. Changes in suspended solids affecting water clarity will have a direct impact on the photosynthesising capabilities of Fucus serratus. Irradiance below light compensation point of photosynthetic species can compromise carbon accumulation (Middelboe et al., 2006). However, water clarity is only relevant when the biotope is covered with water. Seaweed photosynthesis declines on emersion and recommences when recovered with water. In addition, increased siltation may cover the frond surface of Fucus serratus with a layer of sediment further reducing photosynthesis and growth rate. Sediment deposition can also interfere with attachment of microscopic stages of seaweeds reducing recruitment (see ‘siltation’ pressures). Red algae can tolerate a wider range of light levels than any other group of photosynthetic plants (Kain & Norton, 1990) and will, therefore, be less affected by a reduction in water clarity. 

In turbid waters, the feeding apparatus of suspension feeders may become clogged with particles interfering with their feeding and respiratory currents resulting in net losses. For instance, the hydroid Dynamena pumila experienced marked decline in areas with increased silt content in Strangford Lough, Northern Ireland (Seed et al., 1983). Some filter feeders have the ability to cope with siltation and excess suspended material. For example, the sea squirt  Ascidiella scabra can extend its siphons to a small extent and can maintain a passage through the silt to the siphons. However, Robbins (1985b) found that increased inorganic particulate concentrations reduced growth rates of Ascidiella scabra with mortalities occurring in a high level of suspended sediments. The breadcrumb sponge Halichondria panicea has a cleaning mechanism sloughing off its complete outer tissue layer together with any debris (Barthel & Wolfrath, 1989). There is, however, an energetic cost in cleaning resulting in reduced growth. For short-lived species, such as the star ascidian Botryllus schlosseri, reduced growth could prove fatal.

Sensitivity assessment. Changes in suspended solids reducing water clarity will have adverse effects on the biotope group reducing species richness. Resistance is thus assessed as ‘Medium’. Once conditions return to 'normal' Fucus serratus is likely to rapidly regain photosynthesising capabilities as well as growth rate. Associated communities will also rapidly recover as most of the intolerant species produce planktonic larvae and are therefore likely to be able to recolonize quickly from surrounding areas. Resilience is thus assessed as ‘High’. Overall this biotope group scores a ‘Low’ sensitivity to this pressure.

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

Macroalgae are attached to the substratum by a holdfast and are thus not able to relocate in response to increased sedimentation. Sedimentation of bedrock can impede attachment of Fucus embryos as well as decrease survival and growth of juvenile through both scour and burial (Schiel et al., 2006). An increase in the vertical sediment overburden can also reduce growth whilst hindering the regeneration abilities of adults (Umar et al., 1998).

Some filter feeders have the ability to cope with siltation and excess suspended material. For example, Ascidiella scabra can extend its siphons, to a small extent, above silt whilst maintaining a passage through the silt to the siphons. It also attaches to other erect biota and may thereby escape smothering effects. The breadcrumb sponge Halichondria panicea has a mechanism for sloughing off its complete outer tissue layer together with any debris (Barthel & Wolfrath, 1989). However, there is an energetic cost in cleaning, and this species, together with other filter feeders, would probably experience reduced. For annual species, including the star ascidian Botryllus schlosseri, reduced growth could prove fatal. The hydroid Dynamena pumila experienced marked decline in areas with increased silt content in Strangford Lough, Northern Ireland (Seed et al., 1983).

Sensitivity assessment. Smothering by a 5 cm layer of sediment is unlikely to adversely affect this biotope given that it is associated with areas of moderately strong to very strong tidal flow. The sediment layer will be washed away and 'normal' conditions will resume rapidly. The suspension feeders may experience some short-lived interference with feeding but, at the level of the benchmark, this is not likely to adversely affect their viability. Resistance and resilience are therefore both assessed as ‘High’ (no impacts to recover from). The biotope group is ‘Not Sensitive’ to a decrease in salinity at the pressure benchmark.

Smothering and siltation rate changes (heavy)

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

Evidence

Several studies found that increasing the vertical sediment burden negatively impact species characterizing this biotope. At the level of the benchmark (30 cm of fine material added to the seabed in a single event), smothering will result in important mortalities. Resistance is assessed as ‘Low’ as all individuals exposed to siltation at the benchmark level are predicted to die. However, the biotope is associated with areas of moderately strong to very strong tidal flow. The sediment layer will be washed away and 'normal' conditions will resume rapidly. Resilience is thus assessed as ‘Low’ and resistance as ‘Medium.  Therefore, sensitivity is assessed as ‘Medium’.

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

Not relevant

Underwater noise changes

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

Evidence

Species characterizing this biotope do not have hearing perception but vibrations may cause an impact, however no studies exist to support an assessment.

Introduction of light or shading

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

Evidence

Fucoids are dependent on light so that changes in light intensity are likely to affect photosynthesis, growth, competition and survival. Chapman (1995) noted that too little or too much light are likely to be stresses.  There is considerable literature on the light compensation point of marine algae (see Luning, 1990) but it is difficult to correlate such evidence with 'shading', as light saturation and compensation points depend on light availability, light quality, season and turbidity.  As fucoids are out-competed in sublittoral conditions, it is likely that permanent shading would affect their growth and allow them to be out-competed by other, more shade tolerant species, within the affected area. Therefore a resistance of ' Medium' is suggested albeit at low confidence. Resilience is likely to be 'High' so that sensitivity is 'Low.  

Barrier to species movement

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

Evidence

Not relevant – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit propagule dispersal.  But propagule dispersal is not considered under the pressure definition and benchmark.

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

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

Key characterizing species within this biotope are not cultivated or translocated. 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

Thompson & Schiel (2012) found that native fucoids showed high resistance to invasions by the Japanese kelp Undaria pinnatifida. However cover of Fucus serratus was inversely correlated with the cover of Sargassum muticum indicating competitive interaction between the two species (Stæhr et al., 2000). Stæhr et al. (2000) determined that the invasion of Sargassum muticum could affect local algal communities through competition mainly for light and space.  The Portuguese oyster Magallana gigas was introduced in England in 1926 for cultivation purposes and is now found in the wild. The species can form dense beds e.g. in the Netherlands, and, together with Crepidula fornicata, have the potential to cover large patches on the shore. In areas where the biotope coincides with the distribution of Magallana gigas, i.e. the south coast of Devon and coast of Essex, the oyster may become dominant.

Sensitivity assessment. Resistance is assessed as ‘Medium’ since invasive species have the potential to alter the recognizable biotope. Recovery would be rapid once conditions return to normal, resulting in a ‘High’ resilience. However, return to ‘normal’ conditions is highly unlikely if an invasive species would come to dominate the biotope. Indeed recovery would only be possible if the majority of the INIS were removed (through either natural or unnatural process) to allow the re-establishment of other species. Therefore actual resilience will be much lower (‘Low’ to ‘Very Low’) resulting in an overall ‘Medium’ sensitivity score. 

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

Very little is known about infections in Fucus (Wahl et al., 2012). Coles (1958) identified parasitic nematodes that caused galls on Fucus serratus in the Southwest of Britain. More recently, Zuccaro et al. (2008) detected a number of fungal species associated with Fucus serratus. So far no mortalities have been associated to the introduction of microbial pathogens however the potential for increased biotic interactions involving parasites or pathogens is on the rise in many marine systems (Torchin et al., 2002). Other characteristic species, for example Chondrus crispus and Mytilus edulis are known to be adversely affected by infestation by microbial pathogens (see relevant MarLIN reviews). However, even if microbial infestation resulted in the loss of these two species from the biotope, the recognizable biotope per se would not be affected.

Sensitivity assessment. Both resistance and resilience are assessed as ‘High’; the biotope is therefore ‘Not Sensitive’ to this pressure. However the assessment has a low confidence score as more research is needed into the effects of microbial pathogen on Fucus serratus and associated communities. 

Removal of target species

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

Evidence

Fucus serratus is one of several harvested and exploited algal species. Seaweeds were collected from the middle of the 16th century for the iodine industry. Nowadays seaweeds are harvested for their alginates, which are used in the cosmetic and pharmaceutical industries, for agricultural supply, water treatment, and for human food and health supplements (Bixler & Porse, 2010).

The commercial harvest removes seaweed canopies which will have important direct and indirect effects on the wider ecosystem. Stagnol et al.(2013) investigated the effects of commercial harvesting of intertidal Fucus serratus on ecosystem biodiversity and functioning. The study found that the the removal of macroalgae affected the metabolic flux of the area. Flows from primary production and community respiration were lower on the impacted area as the removal of the canopy caused changes in temperature and humidity conditions. Suspension feeders were the most affected by the canopy removal as canopy-forming algae are crucial habitats for these species, most of them being sessile organisms.

Other studies confirm that loss of canopy had both short and long-term consequences for benthic communities in terms of diversity resulting in shifts in community composition and a loss of ecosystem functioning such as primary productivity (Lilley & Schiel, 2006; Gollety et al., 2008). Removal of the canopy caused bleaching and death of understorey red turfing algae. Stagnol et al. (2013) observed Patella vulgata recruiting in bare patches of disturbed plots. Experimental studies have shown that limpets control the development of macroalgae by consuming microscopic phases (Jenkins et al., 2005) or the adult stages (Davies et al., 2007). The increase in Patella vulgata abundance could thus limit the recruitment and growth of Fucus serratus on the impact zone. Due to the high intolerance of macroalgae communities to human exploitation, the European Union put in place a framework to regulate the exploitation of algae establishing an organic label that implies that ‘harvest shall not cause any impact on ecosystems’ (no. 710/2009 and 834/2007).

Sensitivity assessment. Removal of the Fucus serratus canopy will have a negative impact on the diversity of animal community and the metabolism of the area. The harvesting impact on the animal community was amplified by the settlement of an ephemeral canopy of Ulva spp., a seasonal opportunistic green alga (Stagnol et al.,2013). Resistance is thus assessed as ‘Low’. If some Fucus serratus population remain recovery will be fairly rapid. However recruitment mortality, grazing by limpets and the presence of turfs and encrusting algae can slow down and limit recovery. A switch to a disturbance community will also slow the recovery of Fucus serratus and associated community. Resilience is thus assessed as ‘Medium’. The biotope therefore scores a ‘Medium’ sensitivity to this pressure.  If the entire population of Fucus serratus is removed, other species may come to dominate and the recovery will take considerably longer. Re-establishment of the seaweed may depend on the ability to out-compete other species and this may be dependent on suitable environmental conditions.

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

The harvest of algae, crabs snails, mussels, and some species of fish from the shore is a widespread practice. None of the components of this biotope have known obligate relationships and the removal of non-target species will therefore not have a significant impact.  Resistance to this pressure is deemed ‘High’.  Resilience is also ‘High’ as there are no ecological impacts to recover from, resulting in a ‘Not Sensitive’ score. The assessment is based on expert knowledge resulting in a 'Low' confidence score.

Components of this biotope may be directly removed or damaged by static or mobile gears that are targeting other species. These direct, physical impacts 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.