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

Schonbeck & Norton (1979) demonstrated that fucoids can increase tolerance in response to gradual change in temperature through a process known as 'drought hardening'.  However, acute changes in temperatures may cause damage to macroalgae and other species.  Temperature ranges of species may not accurately describe their ability to withstand localized changes in temperature.  Yet they will display the limits of the species genetic ability to acclimatize to temperatures.  Juvenile life stages of organisms can be less tolerant to environmental conditions than more mature stages.

Most fucoids are cold-temperate species (Lüning, 1984), and temperatures above 20 °C are generally considered unsuitable for these algae (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).

In the north east Atlantic, Fucus vesiculosus occurs from Northern Russia to Morocco (Powell, 1963).  Fucus vesiculosus is able to tolerate temperatures as high as 30 °C (Lüning,1990) and did not show any sign of damage during the extremely hot UK summer of 1983, when average temperatures were 8 °C hotter than normal (Hawkins & Hartnoll, 1985). Fucus vesiculosus also tolerates extended periods of freezing in the northern part of its range.

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.  Nielsen et al. (2014b) found no negative effects on growth rates of adult Fucus serratus to water temperatures of 22 °C (based on a laboratory experiment with specimen collected from Firth of Forth, Scotland).  Arrontes (1993) observed that Fucus serratus survived in laboratory experiments for 1 week at 25 °C.  Nielsen et al. (2014b) did, however, report that germlings were negatively affected by increased temperature indicating that early life stages are more vulnerable than mature algae to this pressure.

Several studies have observed adverse effects of Fucus serratus as a result of 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) determined that these negative impacts can be explained by restricted within-population genetic diversity.  South west Ireland and Brittany are hot-spots of genetic diversity with Fucus serratus (Coyer et al., 2003; Hoarau et al., 2007) and may thus be more resilient to changes in temperature.  Phenotypic plasticity therefore plays an important role in determining the sensitivity of individual populations to changes in temperature.

Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA.  Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30 °C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976).  Ulva spp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days and replace the brown algae where temperatures are increased for longer periods (exceeding the pressure benchmark).

In an exceptionally hot summer (1983, with an increase of between 4.8 and 8.5 °C), Hawkins & Hartnoll (1985) recorded that understorey red algae showed more signs of damage than canopy forming species, with bleached Corallina officinalis observed around the edges of pools due to desiccation.  Occasional damaged specimens of Palmaria palmata, Osmundea pinnatifida and Mastocarpus stellatus were also observed.  The median upper lethal temperature limit in laboratory tests on Littorina littorea and Littorina saxatilis was approximately 35 ^oC (Davenport & Davenport, 2005). 

Sensitivity assessment.  An increase in temperature at the pressure benchmark is not likely to have a detrimental effect on this biotope and its associated community, based on global distribution.  Phenotypic plasticity will influence the tolerance of individual population.  Some of the understorey of red algae may be lost during acute temperature increases if these occur in the summer when plants are already close to the limit of thermal tolerances.  Biotope resistance is assessed as 'High' and resilience as 'High' and the biotope is considered to be 'Not sensitive'. It should be noted that the timing of acute and chronic increases would alter the degree of impact and hence sensitivity.  An acute change occurring on the hottest days of the year and exceeding thermal tolerances may lead to mortality.

Temperature decrease (local)

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

Evidence

Schonbeck & Norton (1979) demonstrated that fucoids can increase tolerance in response to gradual change in temperature through a process known as 'drought hardening'.  However, acute changes in temperatures may cause damage to macroalgaes and other species. Temperature ranges of species may not accurately describe their ability to withstand localized changes in temperature.  Yet they will display the limits of the species genetic ability to acclimatize to temperatures. Juvenile life stages of organisms can be less tolerant to environmental conditions than more mature stages.

Lüning (1990) suggested that most littoral algal species were tolerant of cold and freezing.  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 and is therefore within its thermal range in the British Isles.

In the North-East Atlantic, Fucus vesiculosus occurs from Northern Russia to Morocco (Powell, 1963).  This distribution suggests that Fucus vesiculosus tolerates extended periods of freezing during winter in the norther part of its range.

Mastocarpus stellatus and Chondrus crispus have 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).  The photosynthetic rate of Mastocarpus stellatus higher on the shore fully recovered from 24 hrs at -20 °C (Dudgeon et al. (1989).  Photosynthesis in Mastocarpus stellatus also recovered quickly after experimental freezing (Dudgeon et al., 1989, 1995).  Davenport & Davenport (2005) found that the median lower lethal temperature tolerances for Littorina saxatilis and Littorina littorea were -16.4 and -13^oC respectively.

Sensitivity assessment.  A decrease in acute or chronic temperature above average British and Irish temperatures is not likely to have a detrimental effect on Fucus vesiculosus or Fucus serratus and associated communities, based on global distribution.  However, it should be noted that phenotypic plasticity and acclimation will influence the tolerance of individual population.  Based on the characterizing and associated species, this biotope is considered to have ‘High’ resistance and ‘High resilience (by default) to this pressure and is therefore considered to be ‘Not sensitive’.  The timing of changes and seasonal weather could result in greater impacts on species. An acute decrease in temperature coinciding with unusually low winter temperatures may exceed thermal tolerances and lead to mortalities of the associated species although this would not alter the character of the biotope.

Salinity increase (local)

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

Evidence

Variation in salinity within saline lagoons is a characteristic of lagoonal habitats.  In larger lagoons is it also possible to get different salinity regimes within different areas of the lagoon.  Therefore, all species found within saline lagoon communities must be able to tolerate salinity fluctuations.  All lagoons are affected by short, medium and long-term changes in salinity (Bamber et al., 2001).  Semi-diurnal tides cause differences in salinity over short periods, changes in rainfall can cause the medium term changes and seasonal rainfall and drought can cause longer term salinity trends (Bamber et al., 2001).  Intertidal macroalga, such as those found within this biotope, often experience large but short-term changes in salinities (Lobban & Harrison, 1997).  However, the tolerance of intertidal macroalgae tolerances to longer term changes in salinities can be minimal and can quickly reduce photosynthetic abilities and cause mortality.  This biotope is only found in variable salinity conditions (18 – 40 psu) (Connor et al., 2004), an increase in the salinity would create fully marine conditions (30 – 40 psu).

A number of biotopes dominated by the same characterizing species and with many of the associated species occur in fully marine habitats.  Within these fully marine biotopes, species abundances are greater and species richness is higher, as the habitat conditions are closer to optimal for a wider range of species.  The assessed biotope could be considered an impoverished example of these biotopes, as the stress induced by variable salinity leads to reduced growth and lower species richness and diversity.

Investigations into the salinity tolerances of Fucus vesiculosus in laboratory controlled conditions found that the photosynthetic capabilities of both species decreased with reduced salinities (Connan & Stengel, 2011).  Fucus vesiculosusis well adapted to cope with varying salinities and can grow in full saline to brackish conditions.  Indeed Fucus vesiculosus is the dominant large perennial seaweed in the Baltic Sea growing in salinities down to 4 psu (Kautsky, 1992).  Bäck et al. (1991) compared Fucus vesiculosus individuals from Atlantic and the Baltic populations.  Both populations were able to withstand wide range of salinities in laboratory cultures, yet some differences were recorded.  The Atlantic population showed better growth in higher salinities and virtually no growth at 5 ppt.  Those individuals kept at 5 ppt mortality occurred after 7 weeks.  In contrast the Baltic wracks grew better in conditions with lower salinities.  Growth was negligible at the highest tested salinity (45 ppt).  Bäck et al. (1991) demonstrate that sensitivity of Fucus vesiculosus to changes in salinity differ between populations.

Serrao et al. (1996a) found that lower salinities can negatively affect both the fertilization rates and recruitment success of Fucus vesiculosus.  Serrao et al. (1996a) also concluded that the osmotic tolerances of Fucus vesiculosus gametes limit the species distribution in the Baltic Sea. These studies show that low salinities limit the recruitment and fertilization success of fucoids. There is also evidence suggesting that reduced salinities can influence the rate of receptacle maturation in fucoids (Munda, 1964). Rate of fructification in Fucus vesiculosus has been measured to increase in diluted seawater (Munda, 1964).

Sensitivity assessment.  The characterizing and associated species occur in fully marine habitats.  The biotope, however, is specifically described as occurring in variable salinity and to be structured by this factor.  A change in conditions would be likely to lead to increased abundance of characterizing species, particularly Fucus vesiculosus and Fucus serratus, coupled with increased species richness.  The biotope character would therefore be likely to change: biotope resistance is therefore assessed as ‘Low’ and resilience as ‘High’, following a return to a variable salinity regime (as the characterizing and associated species would be present). Biotope sensitivity is, therefore, assessed as ‘Low'.

Salinity decrease (local)

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

Evidence

Variation in salinity within saline lagoons is a characteristic of the habitat that they create.  In larger lagoons is it also possible to get different salinities within different areas of the lagoon itself.  Therefore, all species found within saline lagoon communities must be able to tolerate salinity fluctuations.  All lagoons are affected by short, medium and long-term changes in salinity (Bamber et al., 2001).  Semi-diurnal tides cause differences in salinity over short periods, response to changes in rainfall can cause the medium term changes, and seasonal rainfall and drought can cause longer term salinity trends (Bamber et al., 2001).  Intertidal macroalga, such as those found within this biotope, often experience large but short-term changes in salinities (Lobban & Harrison, 1997).  However, intertidal macroalgae tolerances to longer term changes in salinities can be minimal and can quickly reduce photosynthetic abilities and cause mortality.  This biotope is only found in variable salinity conditions (18 – 40 psu) (Connor et al., 2004).  Local populations may be acclimated to the prevailing salinity regime and may exhibit different tolerances to other populations subject to different salinity conditions.  Consequently, caution should be used when inferring tolerances from populations in different regions.  The plant and animal assemblage within this biotope is relatively impoverished compared with similar biotopes present in full salinity (Connor et al., 2004). At the pressure benchmark a decrease refers to a change in salinity regime to low ( <18 ppt).

Fucoids 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, 1992a; 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 fertilisation success was 87% at 9 psu but declined to 5% at 6 psu (Malm et al., 2001).  Reduced salinity does also affect dispersal by decreasing swimming performance of fucoid sperm (Serrão et al., 1996).

Laboratory controlled conditions found that the photosynthetic capabilities of Fucus vesiculous decreased with reduced salinities (Connan & Stengel, 2011).  Fucus vesiculosus is well adapted to cope with varying salinities and can grow in full saline to brackish conditions. Indeed Fucus vesiculosus is the dominant large perennial seaweed in the Baltic Sea growing in salinities down to 4 psu (Kautsky, 1992). Bäck et al. (1991) compared Fucus vesiculosus individuals from Atlantic and the Baltic populations. Both populations were able to withstand wide range of salinities in laboratory cultures, yet some differences were recorded. The Atlantic population showed better growth in higher salinities and virtually no growth at 5 ppt. Those individuals kept at 5 ppt mortality occurred after 7 weeks. In contrast the Baltic wracks grew better in conditions with lower salinities.  Back et al. (1991) demonstrate that sensitivity of Fucus vesiculosus to changes in salinity differ between populations.

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 & Ford, 1984b).

A decrease in salinity may lead to replacement of more sensitive red algal turf forming species by those more tolerant of the changed conditions.  Chondrus crispus occurs in areas of 'low' salinity.  For example, the species occurs in estuaries in New Hampshire, USA, where surface water salinity varies from 16-32 psu (Mathieson & Burns, 1975).  Mathieson & Burns (1971) recorded maximum photosynthesis of Chondrus crispus in culture at 24 psu, but rates were comparable at 8, 16 and 32 psu.  Tasende & Fraga (1999) cultured Chondrus crispus spores from north west Spain and concluded that growth was correlated with salinity between 23 and 33 psu.  Littorina littorea is found in waters of full, variable and reduced salinities (Connor et al., 2004).

Ulva species are considered to be a very euryhaline, tolerant of extreme salinities ranging from 0 psu to 136 psu (Reed & Russell, 1979).  Some variations in salinity tolerance between populations of Ulva intestinalis have been found, however, suggesting that plants have some adaptation to the local salinity regime (Alströem-Rapaport et al., 2010; Reed & Russell 1979).  A salinity decrease at the pressure benchmark may lead to a shift to a biotope dominated by Ulva spp.

Sensitivity assessment.  The change in salinity at the pressure benchmark is interpreted as a change to a more stable salinity regime with salinity constantly lowered below 18 ppt.  Most of the literature found on this topic considered short-term (days to weeks) impacts of changes to salinity whilst the benchmark refers to a change for one year.  Prolonged reduction in salinity at the pressure benchmark is likely to reduce growth rates, species abundance and species richness as less tolerant species and individuals are lost. Some species replacements are likely as Ulva spp. may colonize the biotope, while Fucus vesiculosus, Fucus serratus and red seaweeds are likely to decrease in abundance or be out-competed.  Biotope resistance is assessed as 'Low' as changes in species composition and abundances are expected. Resilience is assessed as 'High’ (following a return to reduced salinity), as some of the characterizing species may survive, so that biotope sensitivity is assessed as ‘Low’.

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 has weak to very weak water flow conditions.  An increase in water flow may cause an increase in the level of erosion of the sea barrier.  This could consequently lead to the loss collapse of a lagoon wall and completely change the physical environment of the biotope, and lead to the loss of the lagoon biotope altogether.

Water motion is a key determinant of marine macroalgal ecology, influencing physiological rates and community structure (Hurd, 2000). Higher water flow rates increase mechanical stress on macroalgae by increasing drag. Fucoids are highly flexible but not physically robust and an increase in water flow could cause mechanical damage, breaking fronds or even dislodging whole algae from the substratum. Fucoids are however, highly flexible and are able to re-orientate their position in the water column to become more streamlined. This ability allows fucoids to reduce the relative velocity between algae and the surrounding water, thereby reducing drag and lift (Denny et al., 1998).Fucoids are permanently attached to the substratum and would not be 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. Wave exposure has been shown to limit size of fucoids (Blanchette, 1997) as smaller individuals create less resistance to water movement.

The presence of this biotope within conditions with minimal tidal flow suggests that there is unlikely to be a negative impact of a decrease in the mean spring bed flow velocity of 0.2m/s.  Yet some water flow is required to supply vital nutrients and gases and to remove waste products. If the reduction meant that water flow stopped all together then the biotope may suffer negative impacts, due to stagnant conditions.

An increase in this pressure at the bench mark rate within a biotope which is already found at the top of the tolerance for water flows may be negatively affected. The highest water flow that would be created within this biotope taking into consideration the level of the benchmark is 0.7 m/s. This flow rate is not high enough to remove the two characterizing species.

Fucus vesiculosus individuals of 10 cm or larger have been recorded to be completely removed at 7-8 m/s (Jonsson et al., 2006).  A much greater flow rate than what is experienced at the extreme end of this benchmark within this biotope.  Thomson & Wernberg (2005) provide strong evidence that with an increase in thallus size there is an increase in the break force required to remove algae.  This evidence suggests that the characterizing macroalgae populations are unlikely to be torn from the substratum at the level of this bench mark.  The risk of dislodgement would only be greater where algae are attached to pebbles instead of bedrock.  Indeed if sediment type is small and the substratum is less stable, individuals may eventually reach a critical size when the drag force exceeds gravity and the plant will be moved together with its substratum (Malm, 1999). This risk is increased during the late phase of reproduction for Fucus vesiculosus when its receptacles become swollen and gas-filled increasing the uplifting force of water flow (Isaeus, 2004).

Littorina littorea is found in areas with water flow rates from negligible to strong, although populations exposed to different levels of flow may have adapted to local conditions.  Increases in water flow rates above 6 knots may cause snails in less protected locations (e.g. not in crevices etc.) to be continually displaced into unsuitable habitat so that feeding may become sub-optimal.  Shell morphology within littorinids varies according to environmental conditions, in sheltered areas, where Carcinus maenas is more prevalent, shell apertures are small to inhibit predation.  In exposed areas the foot surface is larger to allow greater attachment and the shell spire is lower to reduce drag (Raffaelli 1982, Crothers, 1992).

Sensitivity assessment.  This biotope is only found in very weak water flow conditions.  An increase in water flow at the benchmark is unlikely to have a significant negative effect on the biological composition of the biotope.  Based on the available evidence, the characterizing species and associated macroalgae and animals are able to adapt to high flow rates.  Both the resilience and resistance have been assessed as ‘High’ resulting in a 'Not sensitive' sensitivity assessment.  A change in the water flow at the pressure benchmark is unlikely to cause the loss of the lagoon biotope.  However, an increase in this pressure above the given benchmark (e.g. storms or floods) has the possibility of removing the lagoon completely. 

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 can lead to greater exposure to desiccation, temperature and salinity, and reduced levels of time for filter feeding, nutrient uptake, and photosynthesis. Changes in emergence can also alter competitive interactions and trophic interactions such as grazing and predation.  Environmental factors partly set upper and lower limits of algal distribution on shores.  Spores and developing germlings are particularly susceptible to desiccation as they have very large surface-to-volume ratios, although they benefit from the film of water that persists in concavities on the substratum (Kain & Norton, 1990).  At higher shore levels red algae tend to occur only under canopy forming species, as these limit exposure to desiccation (Hawkins and Hartnoll, 1983). 

Fucus serratus is more susceptible to desiccation than other Fucus species that are located further up the shore and subjected more frequently to aerial exposure (Schonbeck & Norton, 1978).  In experiments Fucus serratus did not survive transplantation further up the shore, e.g. in the Fucus spiralis belt (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.  The upper shore extent of Fucus serratus populations may be replaced by species more tolerant of desiccation and more characteristic of the mid-eulittoral such as Fucus vesiculosus or Ascophyllum nodosum.

Fucus vesiculosus can tolerate desiccation until the water content is reduced to ~ 30%. If desiccation occurs beyond this level, irreversible damage occurs. Individuals at the top of the shore probably live at the upper limit of their physiological tolerance and therefore are likely to be unable to tolerate increased desiccation and would be displaced by more physiologically tolerant species. Tolerance to this pressure is likely to vary on a geographical scale. Gylle et al. (2009) found that Fucus vesiculosus populations naturally occurring in fully saline conditions had a higher emersion stress tolerance compared to brackish populations.

Early life history stages are more susceptible to this pressure compared to 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.

Occurrence of encrusting coralline algae seems to be critically determined by exposure to air and sunlight.  Colonies survive in damp conditions under algal canopies or in pools but not on open rock where desiccation effects are important.  Increased emergence leading to drying out of shallow pools would reduce habitat suitability for this group.  Spore release by the crusting coralline Lithophyllum incrustans is triggered by small changes in salinity and temperature and, therefore, changes in emergence may alter patterns in reproduction and recruitment (see relevant pressures for further information).  However, this species can occur both high and low in the intertidal (Edyvean & Ford, 1986) and presumably such impacts are limited.  In this impoverished biotope, however, the canopy cover may be too sparse to support encrusting corallines higher on the shore.

Sensitivity assessment:  This biotope is somewhat unusual because it is permanently submerged (Conner et al., 2004), yet the species within it are characteristic of intertidal habitats.  As all of the characterizing and associated species within this biotope can be found in intertidal biotopes, an increase in emergence would not create environmental conditions intolerable to these species.  However, the conditions required for this biotope would no longer present.  The resistance has been assessed as low, and resilience as ‘High’.  This results in an overall sensitivity of ‘Low’. 

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

This biotope is found in extremely wave sheltered conditions.  An increase in wave exposure at the benchmark is unlikely to have a significant negative effect on the biological composition of the biotope.  However, it must be assumed that if there is an increase in the water flow within the biotope there will also be an increase in the water flow around the lagoon.  An increase in water flow at the benchmark is unlikely could have a detrimental effect on the structure of the lagoon through erosion.  However, if water flow were to increase above the given benchmark then it is possible that water flow cause an increase in the level of erosion of the sea barrier.  This could consequently lead to the loss collapse of a lagoon wall and completely change the physical environment of the biotope, and lead to the loss of the lagoon biotope altogether.

Water motion is a key determinant of marine macroalgal ecology, influencing physiological rates and community structure (Hurd, 2000). Higher water flow rates increase mechanical stress on macroalgae by increasing drag. Fucoids are highly flexible but not physically robust and an increase in water flow could cause mechanical damage, breaking fronds or even dislodging whole algae from the substratum. Fucoids are however, highly flexible and are able to re-orientate their position in the water column to become more streamlined. This ability allows fucoids to reduce the relative velocity between algae and the surrounding water, thereby reducing drag and lift (Denny et al., 1998).Fucoids are permanently attached to the substratum and would not be 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. Wave exposure has been shown to limit size of fucoids (Blanchette, 1997) as smaller individuals create less resistance to water movement, it is likely that water flow exerts a very similar pressure on fucoids.

The presence of this biotope within conditions with minimal tidal flow suggests that there is unlikely to be a negative impact of a decrease in the mean spring bed flow velocity of 0.2m/s in flow rate.  Yet some water flow is required to supply vital nutrients and gases and to remove waste products. If the reduction meant that water flow stopped all together then the biotope may suffer negative impacts, due to stagnant conditions.

An increase in this pressure at the bench mark rate within a biotope which is already found at the top of the tolerance for water flows may be negatively affected. The highest water flow that would be created within this biotope taking into consideration the level of the benchmark is 0.7 m/s. This flow rate is not high enough to remove the two characterizing species.

Fucus vesiculosus individuals of 10cm or larger have been recorded to be completely removed at 7-8m/s (Jonsson et al., 2006).  A much greater flow rate than what is experienced at the extreme end of this benchmark within this biotope.  This evidence suggests that the characterizing macroalgae populations are unlikely to be torn from the substrate at the level of this bench mark. The risk of dislodgement would only be greater where algae are attached to pebbles instead of bedrock. Indeed if sediment type is small and the substratum is less stable, individuals may eventually reach a critical size when the drag force exceeds gravity and the plant will be moved together with its substratum (Malm, 1999). This risk is increased during the late phase of reproduction for Fucus vesiculosus when its receptacles become swollen and gas-filled increasing the uplifting force of water flow (Isaeus, 2004).

Propagule dispersal, fertilization, settlement, and recruitment are also influenced by water movement (Pearson & Brawley, 1996).  An increase in the mean water flow will reduce the time during which attachment is possible. In addition, greater water flow can increase scour through increased sediment movement. Small life stages of macroalgae are likely to be affected 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).

On the other hand, a reduction in water flow can cause a thicker boundary layer resulting in lower absorption of nutrients and CO₂ by the macroalgae. Slower water movement can also cause oxygen deficiency directly impacting the fitness of algae (Olsenz, 2011).

Sensitivity assessment.  A change in the water flow at the pressure benchmark is unlikely to cause the loss of the lagoon biotope.  However, an increase in this pressure above the given benchmark has the possibility of removing the lagoon completely.  A decrease in water flow could reduce the removal of waste products and the return of nutrients and gases. For this reason biotopes which experience the lowest levels of water flow naturally may be more affected than those found in areas with more water movement.  However, this is unlikely to cause any mass mortality, more a decrease in the health of the biotope. An increase in the level of water flow would be more likely to affect the reproductive and recruitment success of the species. Again this would not cause a mass mortality, but more a decrease in the health of the biotope. The resistance and resilience have been assessed as ‘High’. This gives the biotope an overall sensitivity of ‘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.

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

Reduced oxygen concentrations have been shown to inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977).  Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012).  Reduced oxygen levels are likely to inhibit respiration whilst immersed, but it is unlikely to cause a loss of the macroalgae population directly.

Although the macroalgae species within this biotope may not be negatively affected some of the associated fauna may be lost, causing a reduction in species richness.  Josefson & Widbom (1988) investigated the response of benthic macro and meiofauna to reduced dissolved oxygen levels in the bottom waters of a fjord.  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.  Mobile species will be able to relocate to more optimal conditions, whereas immobile species such as barnacles are likely to be put under more stress by de-oxygenation. 

The extremely wave sheltered conditions and the weak to very weak water flows which are characteristic of this biotope mean that water mixing is not very strong.  Water retention rates within lagoons are also known to be high, with very low flushing times.  Therefore water movement within this area will not reverse any oxygen depletion quickly, possibly exacerbating any negative effects.

Sensitivity assessment.  The characterizing species Fucus vesiculosus and Fucus serratus would suffer significant mortalities by a decrease in oxygen within the water column for at the benchmark level of this pressure.  However, it is possible that some of the associated fauna may be negatively affected by the decrease in oxygen.  Mobile species such the Littorinids would relocate to conditions that were less physiologically taxing, and would be able to return when the pressure abated.  The very low levels of water movement within the biotope habitat slow down the re-oxygenation of this biotope after the pressure event.  Resistance is assessed as ‘High’, as it the resilience.  The biotope sensitivity is ‘Not sensitive’.

Nutrient enrichment

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

Evidence

The nutrient enrichment of a marine environment leads to organisms no longer being limited by the availability of certain nutrients.  The consequent changes in ecosystem functions can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).

Johnston & Roberts (2009) undertook a review and meta analysis of the effect of contaminants on species richness and evenness in the marine environment. Of the 47 papers reviewed relating to nutrients as a contaminants, over 75% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect. Of the 47 papers none considered the impact of nutrients on lagoons.  Yet this finding is still relevant to this biotope as the meta analysis revealed that the effect of marine pollutants on species diversity were ‘remarkably consistent’ between habitats (Johnston & Roberts, 2009). It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009).  Throughout their investigation there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant. These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls. However, research into the impacts of nutrient enrichment from these sources on intertidal rocky shores often lead to shores lacking species diversity and the domination by algae with fast growth rates (Abou-Aisha et al., 1995, Archambault et al., 2001, Arévalo et al., 2007, Diez et al., 2003, Littler & Murray, 1975).  The lagoon habitat within which this biotope is found is not studied within this paper.  However, the characterizing species are most commonly found on intertidal rocky shores and therefore this statement has been considered to be relevant to this assessment.

Major declines of Fucus vesiculosus have been reported from all over the Baltic Sea. These declines have been associated to eutrophication from nutrient enrichment (Kautsky et al., 1986). Nutrient enrichment alters the selective environment by favouring fast growing, ephemeral species such as Ulva lactuca and Ulva intestinalis (Berger et al., 2004, Kraufvelin, 2007). Rohde et al., (2008) found that both free growing filamentous algae and epiphytic microalgae can increase in abundance with nutrient enrichment. This stimulation of annual ephemerals may accentuate the competition for light and space and hinder perennial species development or harm their recruitment (Berger et al., 2003; Kraufvelin et al., 2007). Nutrient enrichment can also enhance fouling of Fucus fronds by biofilms (Olsenz, 2011). Nutrient enriched environments can not only increase algae abundance, but the abundance of grazing species (Kraufvelin, 2007). High nutrient levels may directly inhibit spore settlement and hinder the initial development of Fucus vesiculosus (Bergström et al., 2003).

Kraufvelin 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 an enrichment experiment. During the 4^th year of exposure however, Fucus serratus started to decline and population consequently crashed in the 5^th year. The study observed full recovery of algal canopy and animal community in less than 2 year after conditions returned to normal.

Changes in infralittoral community composition can happen rapidly, and fast growing ephemeral species can become established quickly in the presence of higher concentrations of nutrients. The establishment and growth of these species are not controlled by wave exposure (Kraufvelin, 2007). However, even though these fast growing ephemeral species can become well established quickly, healthy infralittoral communities can survive long periods of time, and maintain ecological function after these species have become established (Bokn et al., 2002, 2003, Karez et al.,2004, Kraufvelin, 2007, Kraufvelin et al., 2006).

Sensitivity assessment. A slight increase in nutrients may enhance growth rates but high nutrient concentrations could lead to the overgrowth of the algae by ephemeral green algae and an increase in the number of grazers. If the biotope is well established and in a healthy state the biotope could persist.  The extremely wave sheltered conditions and the weak to very weak water flows which are characteristic of this biotope mean that water mixing is not very strong.  Lagoons are also known to have high levels of water retention rates which could exacerbate the negative impacts of this pressure.  However, the biotope is ‘Not Sensitive’ at the pressure benchmark as the benchmark complies with all relevant environmental protection standards.

Organic enrichment

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

Evidence

The organic enrichment of a marine environment at this pressure benchmark leads to organisms no longer being limited by the availability of organic carbon. The consequent changes in ecosystem functions can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) and decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).

Johnston & Roberts (2009) undertook a review and meta analysis of the effect of contaminants on species richness and evenness in the marine environment. Of the 49 papers reviewed relating to sewage as a contaminant, over 70% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect.  None of the 49 papers considered the impact of sewage on lagoons.  However, intertidal rocky shores were considered and are thought relevant to the characterizing species and to some of the features of the biotope.  The findings are also still relevant as the meta analysis revealed that the effect of marine pollutants on species diversity were ‘remarkably consistent’ between habitats (Johnston & Roberts, 2009). It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009). Throughout their investigation there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant. These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls. However, research into the impacts of organic enrichment from these sources on intertidal rocky shores often lead to shores lacking species diversity and the domination by algae with fast growth rates (Abou-Aisha et al., 1995, Archambault et al., 2001, Arévalo et al., 2007, Diez et al., 2003, Littler & Murray, 1975).

Major declines of Fucus vesiculosus have been reported from all over the Baltic Sea. These declines have been associated to eutrophication from nutrient enrichment (Kautsky et al., 1986). Nutrient enrichment alters the selective environment by favouring fast growing, ephemeral species such as Ulva lactuca and Ulva intestinalis (Berger et al., 2004, Kraufvelin, 2007). Rohde et al., (2008) found that both free growing filamentous algae and epiphytic microalgae can increase in abundance with nutrient enrichment. This stimulation of annual ephemerals may accentuate the competition for light and space and hinder perennial species development or harm their recruitment (Berger et al., 2003; Kraufvelin et al., 2007). Nutrient enrichment can also enhance fouling of fucoid fronds by biofilms (Olsenz, 2011). Nutrient enriched environments can not only increase algae abundance, but the abundance of grazing species (Kraufvelin, 2007). High nutrient levels may directly inhibit spore settlement and hinder the initial development of Fucus vesiculosus (Bergström et al., 2003). Bellgrove et al. (2010) found that coralline turfs out-competed fucoids at a site associated with organic enrichment caused by an ocean sewage outfall.

Changes in community composition on infralittoral shores can happen rapidly, and fast growing ephemeral species can become established quickly in the presence of higher concentrations of nutrients. The establishment and growth of these species are not controlled by wave exposure (Kraufvelin, 2007). However, even though these fast growing ephemeral species can become well established quickly, healthy infralittoral communities can survive long periods of time, and maintain ecological function after these species have become established (Bokn et al., 2002, 2003, Karez et al.,2004, Kraufvelin, 2007, Kraufvelin et al., 2006b).

Sensitivity assessment. Little empirical evidence was found to support an assessment of this biotope at this benchmark. Due to the negative impacts that can be experienced with the introduction of excess organic carbon both resistance and resilience have been assessed as ‘Medium’. This gives an overall sensitivity score of ‘Medium’.

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 lagoon formed from bedrock, boulders and cobbles.  Removal of this substratum would remove the attachment surface for the macroalgae that characterize this biotope, 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).

Sensitivity assessment. A change to a sedimentary habitat would reduce habitat suitability for this biotope, resistance is assessed as ‘None’ and resilience as ‘Very Low’ as the change is considered to be permanent. Sensitivity is assessed as 'High'.

Physical change (to another sediment type)

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

Evidence

Not Relevant for bedrock biotopes.

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

The species characterizing this biotope occur 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

No studies of the effects of trampling or netting on lagoons were found but studies of the effects on emergent algal communities are probably indicative.  Trampling on the rocky shore has been observed to reduce fucoid cover which decreased the microhabitat available for epiphytic species, increased bare space and increased cover of opportunistic species such as Ulva (Fletcher & Frid, 1996a).  The location of this biotope within a saline lagoon means that the area is easily accessible by humans especially at low tide.  Individual microalgae are flexible but not physically robust. Fucoids are intolerant of abrasion from human trampling, which has been shown to reduce the cover of seaweeds on a shore (Holt et al., 1997).

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.  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.  Conversely, 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.

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 & Frid (1996a,b) also 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.  Fletcher and Frid (1996a) report 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).  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.  In general, studies show that turf-forming algae appear to be relatively resistant to single events and low levels of trampling.  Brosnan & Crumrine (1994), for example, found that in experimentally trampled plots the cover of foliose and canopy forming species declined while turf-forming algae were relatively resistant.

Schiel & Taylor (1999) reported the death of encrusting corallines one month after trampling, due to the removal of their protective canopy of fucoids by trampling (10 -200 tramples where one trample equals one transect walked by one person).  A higher proportion of corallines died back in spring treatments, presumably due to the higher levels of desiccation stress expected at this time of year.  However, encrusting corallines increased within the following year and cover returned to control levels within 21 months (Schiel & Taylor, 1999).  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).

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).

Sensitivity assessment.  The impact of surface abrasion will depend on the footprint, duration and magnitude of the pressure.  Lagoons form natural shallow water mesocosms and can attract considerable attention from the general public, educational events and scientists alike.  All of whom can cause abrasion damage to the species within the biotope.  Abrasion of the substratum will cause a reduction in the abundances of both characterizing species, as well as other species found in the associated community.  The resistance to this pressure at the benchmark level is ‘Low’.  The resilience is ‘High’ due to the fast recolonization abilities of the characterizing and associated species, giving a sensitivity of ‘Low’.

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

The species characterizing this biotope group are epifauna or epiflora occurring on hard 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.  A change in turbidity would affect light availability to photosynthesising organisms during immersion.  This could lower both the growth rate and the biomass of photosynthetic organisms.  Changes in the suspended sediment load could also change the levels of scour within the biotope.  Those species which are not tolerant to an increase in scour would consequently decrease in abundance.  Alternatively, if there was a decrease in the level of scour, competition may increase for the scour tolerant species as new species settle within the biotope.  Due to the weak to very weak water flows and extremely wave sheltered position of this biotope, scour is not considered to have an important effect.

The distribution of Fucus vesiculosus occurs along a depth gradient which strongly correlates with light penetration.  In areas with low sedimentation Fucus vesiculosus can survive down to 9-10 m depth (Eriksson & Bergstrom, 2005).  Changes in suspended solids affecting water clarity will have a direct impact on the photosynthesising capabilities of Fucus vesiculosus.  Irradiance below light compensation point of photosynthetic species can compromise carbon accumulation (Middelboe et al., 2006).  Kõuts et al. (2006) found decreases in light intensity in the vicinity of the dredging site resulted in the net decline of Fucus vesiculosus biomass. A decrease in light penetration in the Kiel Fjord caused by an increase in phytoplankton density and shading from filamentous algae has caused an upwards shift of the lower depth limit of Fucus vesiculosus (Rohde et al., 2008). 

Sensitivity assessment. The environmental conditions of this biotope mean that the biotope remains fully immersed throughout the tidal cycle.  Therefore, a change in the pressure benchmark will have more effect on the Fucus vesiculosus and Fucus serratus within this biotope compared the effect that the pressure might have on them within an intertidal biotope.  The lack of tidal effect will mean that the algae, especially those at the bottom limit of the biotope may become light limited.  This may affect their growth rates and could potentially cause mortality of characterizing species, causing a decrease in the width of the biotope.  The levels of water movement within this biotope, through water flow and wave exposure, are very unlikely to cause any significant damage through scour.  Consequently, the resistance has been assessed as ‘Medium’ and resilience of this biotope has been assessed as ‘High’. The sensitivity of this biotope to this pressure at the benchmark is ‘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

A discrete event where 5 cm of sediment is deposited into the lagoon will partially cover the stipe and holdfast of the characterizing species.  Leaving the fronds sediment free, and able to continue photosynthesising.  The low water flow and wave sheltered position on this biotope will mean that the sediment will not be removed from the shore quickly.  

Germlings are likely to be smothered and killed by this pressure.  Indeed early life stages are smaller in size than adults and are thus most vulnerable to this pressure as even a small load of added sediment will lead to the complete burial. Sediment deposition can reduce macroalgal recruitment by (1) reducing the amount of substratum available for attachment of propagules; (2) scour, removing attached juveniles and (3) burial, altering the light and/or the chemical microenvironment (Devinny & Volse, 1978, Eriksson & Johansson, 2003). Berger et al. (2003) demonstrated that both interference with sediment during settlement, and burial after attachment, were significant causes of mortality for Fucus vesiculosus germlings. Eriksson & Johansson (2003) found that sedimentation had a significant negative effect on the recruitment success of Fucus vesiculosus. Even fine sediment fractions can reduce the successful attachment of fucoids by as much as 90% (Schiel & Foster, 2006).

Another consideration for this biotope is the effect that sedimentation may have on the physical aspect of the lagoon.  If saline lagoons become silted up then the basin can be raised above percolation input, causing the lagoon to become a freshwater lake (Bamber et al., 2001).  Each lagoon will respond differently to 5 cm of sediment inundation and there is no evidence to suggest how different lagoons might respond.

Sensitivity assessment.  Fucus vesiculosus adults are relatively tolerant to sediment inundation and can regenerate from its holdfast.  Germlings of both Fucus vesiculosus and Fucus serratus are intolerant of even small levels of sediment.  Many of the smaller species found within the associated community will be totally smothered by 5 cm.  This biotope is found in extremely wave sheltered conditions.  Therefore, sediment is likely to be retained for long periods of time, allowing greater negative effects to occur.  Resistance has been assessed as ‘Low’ and resilience is assessed as ‘Medium’.  Overall the biotope probably has a ‘Medium’ sensitivity to smothering at the level of the benchmark.

Smothering and siltation rate changes (heavy)

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

Evidence

A deposit at the pressure benchmark would cover all species with a thick layer of fine materials.  Species associated with this biotope such as limpets and littorinids would not be able to escape and would likely suffer mortality (see evidence for light siltation).  The low water flow and wave sheltered position on this biotope will mean that the sediment will not be removed from the shore quickly.  Therefore, sediment is likely to be retained for long periods of time, allowing greater negative effects to occur.  Resistance has been assessed as ‘Low’ and resilience is assessed as ‘Medium’.  Overall the biotope probably has a ‘Medium’ sensitivity to smothering at the level of the benchmark.  The biotope could be more sensitive to this pressure however, there is insufficient evidence to create a more detailed assessment.

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

Species characterizing this habitat 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

Increased levels of diffuse irradiation correlate with increased growth in macroalgae (Aguilera et al., 1999).  Macroalgae require light to photosynthesize 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.  Levels of diffuse irradiation increase in summer, and with a decrease in latitude. As Fucus vesiculosus and Fucus serratus are found in the middle their natural range in the British Isles an increase in the level of diffuse irradiation will not cause a negative impact on the species or the biotope.  However, it is not clear how these findings may reflect changes in light levels from artificial sources, and whether observable changes would occur at the population level as a result.  There is, therefore, 'No evidence' on which to base an assessment.

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

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. Therefore this pressure is considered ‘Not Relevant’ for this biotope.

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.

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 show high resistance to invasions by the Japanese kelp Undaria pinnatifida. However, cover of Fucus vesiculosus was inversely correlated with the cover of the invasive 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.

Gracilaria vermiculophylla is suggested to be one of the most successful marine non-native species (Kim et al., 2010, Sfriso et al., 2010 taken from Thomsen et al., 2013). This species invades wave sheltered, shallow water areas, and have been found in biotopes naturally dominated by fucoid canopies (Weinberger et al., 2008).  Hammann et al. (2013) found that in the Baltic Sea Gracilaria vermiculophylla could impact Fucus vesiculosus through direct competition for resourses, decreasing the half-life of germlings, and increasing the level of grazing pressure. To date Gracilaria vermiculophylla has only been recorded in Northern Ireland.  The introduction of this species to infralittoral shores around the British Isles could have negative impacts on native fucoid biotopes, and could become relevant to this specific biotope.

Sensitivity assessment. Fucoid species have been negatively affected by both the direct and indirect consequences of INNS being present.  However, no evidence can be found on the impacts of INNS on Fucus vesiculosus and Fucus serratus within this biotope.  For this reason the effect of this pressure has been given as ‘No Evidence’. Literature for this pressure should be revisited.

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., 2011). Coles (1958) identified parasitic nematodes that caused galls on Fucus serratus in the Southwest of Britain. But to date no mortalities have been associated to the introduction of microbial pathogens. Torchin et al. (2002) suggests that there is potential for increased biotic interactions with parasites or pathogens in many marine systems. 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).  No evidence was found for pathogens of red algae which may be present in this biotope.  Other species associated with this biotope such as littorinids experience low levels of infestation by pathogens but mass-mortalities have not been recorded.  For example, parasitism by trematodes may cause sterility in Littorina littorea.  Littorina littorea are also parasitized by the boring polychaete, Polydora ciliate and Cliona sp, which weakens the shell and increases crab predation.  An assessment of ‘No Evidence’ has been given for this biotope due to the lack of direct evidence.

Removal of target species

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

Evidence

Seaweeds have been collected from the middle of the 16th century for the iodine industry. Modern day industrial uses for seaweed are extensive and include fertilizer, animal feed, alginate extracts (Phillipi et al., 2014), water treatment, and human food and health supplements (Bixler & Porse, 2010). The characteristic fucoid algae within this biotope are commercially collected. These commercial harvests remove seaweed canopies which have important effects on the wider ecosystem.

Stagnol et al. (2013) investigated the effects of commercial harvesting of intertidal fucoids on ecosystem biodiversity and functioning. The study found that the removal of the macroalgae canopy 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 (Stagnol et al., 2013).

Stagnol et al. (2013) found that suspension feeders were the most affected by the canopy removal as canopy-forming algae are crucial habitats for these species. Other studies confirm that loss of canopy had both short and long-term consequences for benthic community diversity resulting in shifts in community composition and a loss of ecosystem functioning such as primary productivity (Lilley & Schiel, 2006; Gollety et al., 2008).

Red algae within the biotope may also be subject to hand gathering. Mastocarpus stellatus is harvested commercially in Scotland and Ireland to produce carageen, the stipe is removed but the base is left intact to allow the algae to re-grow. Palmaria palmata and Osmundea pinnatifida are also collected by hand commercially and recreationally for consumption.

Littorinids are one of the most commonly harvested species of the rocky shore. Large scale removal of Littorina littorea may allow a proliferation of opportunistic green algae, such as Ulva, on which it preferentially feeds.  Experiments designed to test the effects of harvesting by removing individuals at Strangford Lough found that there was no effect of experimental treatments (either harvesting or simulated disturbance) on Littorina littorea abundance or body size over a 12 week period (Crossthwaite et al., 2012). This suggests that these animals are generally abundant and highly mobile; thus, animals that were removed were quickly replaced by dispersal from surrounding, un-harvested areas. However, long-term exploitation, as inferred by background levels of harvest intensity, did significantly influence population abundance and age structure (Crossthwaite et al., 2012).  A broadscale study of harvesting in Ireland using field studies and interviews with wholesalers and pickers did suggest that some areas were over harvested.  But the lack of background data and quantitative records make this assertion difficult to test (Cummins et al., 2002). Changes in grazer abundance can alter the character of the algal assemblage.  Grazer removal (manual removal of all gastropods in pool and a 1 m surrounding perimeter) caused strong and highly significant changes in assemblage structure in rockpools that contained red turf forming algae mainly due to an increase in the cover of green filamentous algae and a decrease in cover of live crustose coralline algae (25.40%) (Atalah & Crowe, 2010).

Sensitivity assessment.  The removal of Fucus vesiculosus and Fucus serratus canopy will significantly change the community composition of the biotope. The quantity of biomass removed from the shore and the regularity of removal will all affect how quickly the biotope will be able to recover. Fucus vesiculosus and Fucus serratus have a ‘Low’ resistance to removal as both of them are easy to locate and have no escape strategy. Resilience is ‘High’, however recovery will only be able to start when the pressure is removed from the shore i.e. harvesting is no longer occurring. A sensitivity of ‘Low’ is recorded.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures.  The characterizing species Fucus vesiculosus and Fucus serratus are the dominant species within this biotope.  The dominance of these characterizing species means it could easily be incidentally removed from this biotope as by-catch when other species are being targeted.  The loss of this species and other associated species would decrease species richness and negatively impact on the ecosystem function.

Sensitivity assessment. Removal of a large percentage of the characterizing species would alter the character of the biotope. The resistance to removal is ‘Low’ due to the easy accessibility of the biotopes location and the inability of these species to evade collection. The resilience is ‘Medium’, with recovery only being able to begin when the harvesting pressure is removed altogether. This gives an overall sensitivity score of ‘Medium’.