The Marine Life Information Network

Temperature increase (local)

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

Evidence

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

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

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

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

Sensitivity assessment. Considering that maximum sea surface temperatures around the British Isles rarely exceed 20°C (Hiscock, 1998), it is unlikely that Chondrus crispus would suffer mortality due to the acute or chronic  benchmark increase in temperature. Mastocarpus stellatus may be found higher on the shore and its distribution suggests that it has a higher  tolerance to increased temperatures and desiccation than Chondrus crispus. Adults of the associated species Patella vulgata are considered likely to be able to tolerate an acute or chronic increase in temperature at the pressure benchmark, although the timing of acute and chronic increases would alter the degree of impact and hence sensitivity.  An acute change occurring on the hottest day of the year and exceeding thermal tolerances could lead to mortality. Sensitivity of Patella vulgata and Semibalanus balanoides to longer-term, broad-scale perturbations would potentially be greater due to effects on reproduction . Ulva spp., are considered to tolerate increases in temperature at the pressure benchmark. Biotope resistance is therefore assessed as ‘High’ and recovery as ‘High’ (by default) so that the biotope is assessed as ‘Not sensitive’. 

Temperature decrease (local)

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

Evidence

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

The key characterizing species, Chondrus crispus and Mastocarpus stellatus 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).  In New Hampshire, USA, Chondrus crispus grows abundantly in waters with an annual variation in surface temperature from -1 to +19°C (Mathieson & Burns, 1975). Both the key characterizing species are able to tolerate freezing although the thermal tolerances vary between these two species and are linked to the upper shore limits of these species (see changes in emergence). The photosynthetic rate of Chondrus crispus recovered after 3hrs at -20 °C but not after 6 hrs whereas 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 more quickly after experimental freezing (Dudgeon et al., 1989, 1995). Frond bleaching and declines in photosynthesis and growth also occur in long-term experimental exposure to periodic freezing in Chondrus crispus (Dudgeon et al., 1990). Plants from Maine, USA, were frozen at -5°C for 3 hours a day for 30 days. Photosynthesis was reduced to 55% of control values, growth rates were reduced and fronds were eventually bleached and fragmented resulting in biomass losses. Additionally, fronds of Chondrus crispus which were frozen daily had higher photosynthetic rates following subsequent freezing events than unfrozen controls, indicating that the species is able to acclimate to freezing conditions (Dudgeon et al., 1990). Mastocarpus stellatus were also subjected to a similar periodic freezing regime (3 hours/day at -5^oC for 36 days) with no effect on photosynthesis or growth.

Spore germination in Chondrus crispus appears to be temperature dependent with spores discharged at temperatures of 5^oC failing to germinate although in laboratory culture at 10^oC spores were viable all year round (Bhattacharya, 1985).  Acute or chronic changes in temperature below 5^oC may therefore reduce reproductive success although reproduction and vegetative growth in warmer months should compensate for any reduction in output.

Other species associated with the biotope are able to tolerate decreases in temperature. Lüning (1990) reported that Corallina officinalis from Helgoland survived 0 °C when exposed for one week. New Zealand specimens were found to tolerate -4 °C (Frazer et al., 1988). Ulva spp. are eurytopic, found in a wide temperature range and in areas which frequently experience freezing conditions and are vulnerable to ice scour (Seed & Suchanek 1992). 

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

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

Sensitivity assessment.  Both the key characterizing species, Chondrus crispus and Mastocarpus stellatus, occur over a wide geographical range and as intertidal species are predicted to have high tolerances for decreased temperature at the acute and chronic pressure benchmarks. Laboratory experiments indicate that both species are able to tolerate periodic freezing (Dudgeon et al., 1995). However, reduced temperatures would probably result in suboptimal growth and may affect reproduction. Biotope resistance is assessed as ‘High’ as these effects do not result in mortality and resilience is assessed as ‘High’, so that the biotope is not considered to be sensitive to this pressure. 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

This biotope occurs in full salinity (30-35 ppt). Connor et al., (2004).  Biotopes found in the intertidal will naturally experience fluctuations in salinity where evaporation increases salinity and inputs of rainwater expose individuals to freshwater. Species found in the intertidal are therefore likely to have some form of behavioural or physiological adaptations to changes in salinity. 

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

The associated Ulva species can survive hypersaline conditions in supralittoral rockpools subjected to evaporation and are considered to be a very euryhaline, tolerant of extreme salinities ranging from 0 psu to 136 psu (Reed & Russell, 1979).  Some variations in salinity tolerance between populations of Ulva intestinalis have been found, however, suggesting that plants have some adaptation to the local salinity regime (Alströem-Rapaport et al., 2010; Reed & Russell (1979). Increased salinity is most likely to occur in the region of the littoral fringe and supralittoral zone and specimens from these areas were able to tolerate very high salinities, a significant decrease in regeneration only being recorded after exposure to concentrated seawater (102 psu and 136 psu) for > 7 days (Reed & Russell, 1979). In the laboratory, Semibalanus balanoides was found to tolerate salinities between 12 and 50 psu (Foster, 1970). Young Littorina littorea inhabit rock pools where salinity may increase above 35psu. 

Sensitivity assessment. No specific evidence was found for the salinity tolerance of Mastocarpus stellatus. If Chondrus crispus has the greater tolerance for increased salinity a change at the pressure benchmark may lead to increased dominance of the turf by that species.  An increase at the pressure benchmark may also lead to an increase in abundance of the very euryhaline Ulva spp.  Based on the salinity tolerances of Chondrus crispus an increase at the pressure benchmark may lead to some changes in the composition of the algal turf but not alter it from the biotope description. Resistance (of the biotope) is therefore assessed as ‘High;’ and resilience as ‘High’ (by default), and the biotope is assessed as ‘Not sensitive’.

Salinity decrease (local)

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

Evidence

Biotopes found in the intertidal will naturally experience fluctuations in salinity where evaporation increases salinity and inputs of rainwater expose individuals to freshwater. Species found in the intertidal are therefore likely to have some form of behavioural or physiological adaptations to changes in salinity. As this biotope is present in full salinity (30-35 ppt, Connor et al., 2004), the assessed change at the pressure benchmark is a reduction in salinity to a variable regime (18-35 ppt) or reduced regime (18-30 ppt). 

Chondrus crispus does occur 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. A reduction in salinity, therefore, is unlikely to result in mortality of Chondrus crispus but may suppress growth.

Sensitivity assessment. No specific evidence was found for the salinity tolerance of Mastocarpus stellatus. If Chondrus crispus has the greater tolerance for reduced salinity a change at the pressure benchmark may lead to increased dominance of the turf by that species.  An increase at the pressure benchmark may also lead to an increase in abundance of the very euryhaline Ulva spp.  Based on the salinity tolerances of Chondrus crispus a decrease in salinity at the pressure benchmark may lead to some changes in the composition of the algal turf but not alter it from the biotope description. Resistance (of the biotope) is therefore assessed as ‘High;’ and resilience as ‘High’ (by default), and the biotope is assessed as ‘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

As water velocity increases Mastocarpus stellatus and Chondrus crispus can flex and reconfigure to reduce the size of the alga when aligned with the direction of flow, this minimises drag and hence the risk of dislodgement (Boller & Carrington, 2007). These characteristics allow these species to persist on shores that experience a range of flow speeds. For example, Chondrus crispus and Mastocarpus stellatus occur at sites in Maine, USA experiencing peak Autumn flow speeds as measured by current meters of 9.2 m/s and 5.8 m/s. At the more exposed sites with higher flow speeds some Chondrus crispus were dislodged during the winter.  Biogenic habitat structures reduce the effects of water flows on individuals by slowing and disrupting flow. Boller and Carrington (2006) found that the canopy created by a turf of Chondrus cripsus reduced drag forces on individual plants by 15-65%.

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

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

Emergence regime is a key factor structuring this (and other) intertidal biotopes. This biotope generally occurs in the lower eulittoral above the main kelp zone, stands of Alaria esculenta or the mussel, Mytilus edulis (Connor et al., 2004). In general red algae can tolerate low levels and can extend into the subtidal. However, decreased emergence would be likely to lead to the establishment of kelps and Alaria esculenta and would alter the character of the biotope from the description.

Studies have demonstrated that Chondrus crispus is more sensitivie to freezing and desiccation than Mastocarpus stellatus (Mathieson & Burns, 1971; Dudgeon et al., 1989) which probably limits the height on which it grows on the shore. Chondrus crispus is therefore more likely to be sensitive than Mastocarpus stellatus to increased emergence although desiccation rather than temperature may exert a greater control where winter temperatures are higher. A study by Lubchenco (1980) on the coast of New England suggested that desiccation is an important factor determining the upper limit of Chondrus crispus. The species was found to extend into the mid-intertidal where it was found underneath a fucoid canopy. Removal of this canopy lead to bleached, dried out and dead plants within two to three weeks (Lubchenco, 1980). Hawkins & Hartnoll (1985) also observed bleaching of red algae species including Chondus crispus and Mastocarpus (as Gigartina) stellata, during an unusually hot summer. The loss of canopy forming alae exacerbated the impact. 

An increase in emergence will also increase the exposure of Chondrus crispus to solar radiation. Chondrus crispus is growth saturated at light levels of 60-70 µE/m²/s and is not photoinhibited at 250 µE/m²/s (Bird et al., 1979; Fortes & Lüning, 1980). However, Bischoff et al. (2000) reported that the photochemistry of Chondrus crispus is negatively affected by UV-B radiation, while Aguirre-von-Wobeser et al. (2000) concluded that photosynthetically active radiation (PAR) is responsible for most of the photoinhibition in the species. Bischof et al. (2000) suggested that intolerance to UV-B may be a factor restricting Chondrus crispus to the subtidal and lower intertidal, whereas Mastocarpus stellatus, which is better adapted to UV radiation, competes better at higher shore levels.

Increased emergence may reduce habitat suitability for the associated species, although ephemeral green algae, Patella vulgata, Semibalanus balanoides and littorinids are found at a range of shore levels and are found in abundance at higher shore levels than this biotope typically occurs at. These species are therefore considered not to be affected by increased emergence.   Experimental grazer removal has allowed algae including Palmaria palmata, Ceramium sp. and Osmundea (as Laurencia) pinnatifida  to grow higher on the shore (during winter and damp summers) than usual suggesting that grazing also limits the upper shore extent of this biotope. An increase in grazers and grazing within this biotope associated with reduced predation level by crabs and predators following increased emergence may removal algae but grazing on the characterizing, mature red algae turf is probably limited and may serve to check the growth of green algae. A significant, long-term, increase in emergence is therefore likely to lead to replacement of this biotope with one more typical of the changed conditions dominated by limpets, barnacles and fucoids for example.

Sensitivity assessment. Significant long-term changes in emergence would result in changes in environmental factors and grazing pressures and lead to increased competition from species better adapted to the changed conditions. Resistance to this pressure is therefore assessed as ‘Low’. Resilience is assessed as ‘Medium’ (where bases are removed) and sensitivity to this pressure is assessed as ‘Medium’. 

Wave exposure changes (local)

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

Evidence

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

Chondrus crispus typically occurs in 'sheltered' and 'moderately exposed areas' (Dixon & Irvine, 1977). Strong wave action is likely to cause some damage to fronds of both the key characterizing species resulting in reduced photosynthesis and compromised growth. Furthermore, individuals may be damaged or dislodged by scouring from sand and gravel mobilized by increased wave action (Hiscock, 1983). Dudgeon & Johnson (1992) noted wave induced disturbance of intertidal Chondrus crispus on shores of the Gulf of Maine during winter where 25-30% of cover of large Chondrus crispus thalli was lost in one winter. Chondrus crispus suffers greater losses than Mastocarpus stellatus in areas of increased wave action as the drag forces on the thallus are greater for the larger and bushier plants (Dudgeon & Johnson, 1992; Pratt & Johnson, 2002). Greater dislodgement of the faster growing Chondrus crispus by wave action during winter storms is a factor mediating competition between the two key characterizing species (Pratt & Johnson, 2002).

Gutierrez & Fernandez (1992) described morphological variability of Chondrus crispus according to wave exposure and emersion. They identified 2 well defined morphotypes; filiform and planiform. The filiform morphotype had fewer dichotomies per unit length, a circular cross section, narrow fronds and was abundant in the low intertidal and at more exposed sites. The planiform morphotype had more dichotomies, was smaller, with a flattened cross section, broader fronds and was abundant higher up the shore and in more sheltered areas. An increase or decrease in wave exposure greater than the pressure benchmark may therefore lead to shifts between the filiform and planiform morphyotypes.

A decrease in wave exposure at the pressure benchmark is unlikely to affect Chondrus crispus or Mastocarpus stellatus directly. Decreases greater than the pressure benchmark that lead to changes in suspended solids and subsequent deposition may lead to changes in the assemblage (see siltation and changes in suspended sediment pressures).

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

Transition elements & organo-metal contamination

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

Evidence

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

Contamination by non-synthetic chemicals, at levels greater than the pressure benchmark may adversely impact the biotope. Little information was found concerning the intolerance of Chondrus crispus to heavy metals. Burdin & Bird (1994) reported that both gametophyte and tetrasporophyte forms accumulated Cu, Cd, Ni, Zn, Mn and Pb when immersed in 0.5 mg/l solutions for 24 hours. No effects were reported however, and no relationship was detected between hydrocolloid characteristics and heavy metal accumulation. Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. The sub-lethal effects of Hg (organic and inorganic) on the sporelings of an intertidal red algae, Plumaria elegans, were reported by Boney (1971). 100% growth inhibition was caused by 1 ppm Hg. In light of the lack of information found, an intolerance assessment has not been attempted.

Hydrocarbon & PAH contamination

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

Evidence

This pressure is Not assessed but evidence is presented where available

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

Synthetic compound contamination

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

Evidence

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

Contamination at levels greater than the pressure benchmark may adversely impact the biotope. No evidence was found specifically relating to the intolerance of Chondrus crispus to synthetic chemicals. However, inferences may be drawn from the sensitivities of red algal species generally. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. They also report that red algae are effective indicators of detergent damage since they undergo colour changes when exposed to relatively low concentration of detergent. Smith (1968) reported that 10 ppm of the detergent BP 1002 killed the majority of specimens in 24hrs in toxicity tests, although Chondrus crispus was amongst the algal species least affected by the detergent used to clean up the Torrey Canyon oil spill. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984, cited in Holt et al., 1995). Cole et al. (1999) suggested that herbicides, such as simazine and atrazine, were very toxic to macrophytes. The evidence suggests that in general red algae are very sensitive to synthetic chemicals. Intolerance of Chondrus crispus is therefore recorded as high. Recoverability is recorded as high (see additional information below) although it may take up to 5 years as recovery will be largely dependent on recruitment of spores from distant unperturbed populations.

Radionuclide contamination

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

Evidence

No evidence was found to assess this pressure at the benchmark. Algae bioaccumulate radionuclides (with extent depending on the radionuclide and the algae species). A study in France found that Chondrus crispus was capable of absorbing a large number of artificial radioactive elements and that this had consequences considering the exploitation of this species as a harvestable resource (Cosson et al., 1984). However, no information was found concerning the actual effects of radionuclide on Chondrus crispus. Adverse effects have not been reported at low levels.

Introduction of other substances

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

Evidence

This pressure is Not assessed.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

The effects of reduced oxygenation on algae are not well studied. Plants require oxygen for respiration, but this may be provided by production of oxygen during periods of photosynthesis. Lack of oxygen may impair both respiration and photosynthesis (see review by Vidaver, 1972). A study of the effects of anoxia on another red alga, Delesseria sanguinea, revealed that specimens died after 24 hours at 15°C but that some survived at 5°C (Hammer, 1972). This biotope would only be exposed to low oxygen in the water column intermittently during periods of tidal immersion. In addition, in areas of wave exposure and moderately strong current flow low oxygen levels in the water are unlikely to persist for very long as oxygen levels will be recharged by the incorporation of oxygen in the air into the water column or flushing with oxygenated waters.  

No evidence was found to assess this pressure for the red algae turfs. However, the associated species are unlikely to be impacted by this pressure, at the benchmark. Experiments have shown that thallus discs of Ulva lactuca plants can survive prolonged exposure to anoxia and hypoxia (Vermaat & Sand-Jensen, 1987; Corradi et al., 2006). Following resumption of normal oxygen conditions gametes were produced. The associated invertebrate species also show high tolerances for reduced oxygen at levels that exceed the pressure benchmark. Littorina littorea can easily survive 3-6 days of anoxia (Storey et al., 2013). Semibalanus balanoides can respire anaerobically, so they can tolerate some reduction in oxygen concentration (Newell, 1979). When placed in wet nitrogen, where oxygen stress is maximal and desiccation stress is low, Semibalanus balanoides have a mean survival time of 5 days (Barnes et al., 1963). Limpets can also survive for a short time in anoxic seawater; Grenon & Walker, (1981) found that in oxygen free water limpets could survive up to 36 hours, although Marshall & McQuaid (1989) found a lower tolerance for Patella granularis, which survived up to 11 hours in anoxic water. Patella vulgata and Littorina littorea are able to respire in air, mitigating the effects of this pressure during the tidal cycle.

Sensitivity assessment. No direct evidence for the effects of hypoxia on red algal turfs was found. As the biotope will only be exposed to this pressure when emersed and respiration will occur in air, biotope resistance was assessed as ‘High’ and resilience as ‘High’ (no effect to recover from), resulting in a sensitivity of 'Not sensitive'.  

Nutrient enrichment

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

Evidence

In studies of Chondrus crispus from Prince Edward Island, Canada, Juanes & McLachlan (1992) concluded that primary production was limited by temperature during the autumn to spring period and by nitrogen availability when production was maximal in the summer. They suggested that growth of Chondrus crispus became nutrient limited at approximately 14°C. To a certain degree, therefore, an increase in the level of nutrients would be likely to enhance growth of Chondrus crispus.

However, if nutrient enrichment is extended or prolonged, Chondrus crispus may be out-competed by faster growing or ephemeral species. 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.

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

The study and Atalah & Crowe (2010) suggests that, although red algal turfs may be tolerant of eutrophication  and may even benefit biotope composition may alter due to the proliferation of fast growing ephemeral algae.

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

Organic enrichment

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

Evidence

No evidence was found to assess this pressure. The biotope is considered to be structured largely by wave exposure and the presence of algal turfs rather than food supply. Additional organic matter supplied to this biotope is likely to be removed by wave action or trapped and incorporated into the sediment mat associated with the algal turf. Within the mat it would enhance secondary production by the associated polychaetes and amphipods and would be likely to be rapidly consumed. Resistance to this pressure is therefore assessed as 'High' and resilience as 'High' and the biotope is considered to be 'Not sensitive'. 

Physical loss (to land or freshwater habitat)

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

Evidence

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

Physical change (to another seabed type)

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

Evidence

The loss of hard substratum would remove the rock habitat and sediments would be unsuitable for Mastocarpus stellatus and Chondrus crispus and other attached algae that characterize this biotope. Other associated species such as barnacles and limpets and spirorbid polychaetes would be lost as these are associated with hard surfaces rather than sedimentary habitats.

Artificial hard substratum may also differ in character from natural hard substratum, so that replacement of natural surfaces with artificial may lead to changes in the biotope through changes in species composition, richness and diversity (Green et al., 2012; Firth et al., 2013) or the presence of non-native species (Bulleri & Airoldi, 2005). Chondrus crispus readily colonised artificial settlement plates and by the end of the experiment was the dominant species on plates (Harlin & Lindbergh, 1977). Chondrus crispus were however significantly more abundant on the substratum with the largest particles (1-2 mm) and only a few individuals were found on the smooth surface, demonstrating that artificial smooth surfaces may not provide an optimal habitat.

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

Physical change (to another sediment type)

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

Evidence

Not relevant to biotopes occurring on bedrock.

Habitat structure changes - removal of substratum (extraction)

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

Evidence

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

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

Little information is available on the effects of abrasion on intertidal red algae. 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.

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

Penetration or disturbance of the substratum subsurface

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

Evidence

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

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

No empirical evidence was found to assess this pressure. Intertidal biotopes will only be exposed to this pressure when submerged during the tidal cycle and thus have limited exposure. Siltation, which may be associated with increased suspended solids is assessed separately. As photoautotrophs, the key characterizing red algal turf species Mastocarpus stellatus and Chondrus crispus are likely to benefit from reduced turbidity, as the light attenuating effects of turbid water reduce photosynthesis. As these species can occur subtidally the limited shading from suspended solids during immersion is not considered to negatively affect the red algal turf. Suspended sediments may have abrading effects on the fronds. However as turfs of red algae trap sediments they clearly have some tolerance for abrasion and scour. Chondrus crispus occurs in areas of sand covered rock in the subtidal biotope IR.HIR.KSed.ProtAhn suggesting it is very resistant to high levels of turbidity and scour associated with high levels of resuspended particles. An increase in suspended solids above the pressure benchmark may result in a change in species composition with an increase in species seen in very turbid, silty environments e.g. Ahnfeltia plicata, Rhodothamniella floridula, Polyides rotunda and Furcellaria lumbricalis.

Sensitivity assessment. The exposure of this biotope to suspended solids in the water column will be limited to immersion periods.  The biotope is considered to be ‘Not sensitive’ to a reduction in suspended solids. An increase in suspended solids may lead to some sub-lethal abrasion of fronds but this will be compensated by the high growth rates exhibited by the characterizing species. Resistance is therefore assessed as ‘High’ and resilience as ‘High’ (by default) so that the biotope is considered to be ‘Not sensitive’. 

Smothering and siltation rate changes (light)

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

Evidence

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

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

Recently settled propagules, regenerating holdfasts and small developing plants would be buried by 5 cm of sediment and be unable to photosynthesize. For example, Vadas et al. (1992) stated that algal spores and propagules are adversely affected by a layer of sediment, which can exclude up to 98% of light.

Other species within the biotope, particularly limpets and littorinids are considered more sensitive to sedimentation. Chandrasekara & Frid (1998) specifically tested the siltation tolerance of Littorina littorea. Approximately half of the test individuals could not regain the surface from 1cm of burial except in the most favourable conditions (low temperatures, high water, high silt when a majority (10 out of 15) of the test cohort surfaced. Field observations support the findings that Littorina littorea are generally unable to survive smothering. Albrecht & Reise (1994) observed a population of Littorina littorea in a sandy bay near the Sylt island in the North Sea. They found that the accretion of mud within Fucus strands and subsequent covering of Littorina by the sediment resulted in them suffocating and a significant reduction in their abundance. Field observations and laboratory experiments have highlighted the sensitivity of limpets to sediment deposition Airoldi & Hawkins (2007) tested the effects of different grain sizes and deposit thickness in laboratory experiments using Patella vulgata. At 1 and 2 mm thicknesses, fine sediments decreased grazing by 40 and 77 %. The addition of approximately 4 mm of fine sediment completely inhibited grazing. Limpets tried to escape the sediment but lost attachment and died after a few days (Airoldi & Hawkins, 2007) Observations on exposed and sheltered shores with patches of sediment around Plymouth in the south west of England confirmed that Patella vulgata abundances were higher where deposits were absent. The limpets were locally absent in plots with 50-65% sediment cover (Airoldi & Hawkins, 2007).

Atalah & Crowe (2010) added sediment to rockpools. The rockpools were occupied by a range of algae including encrusting corallines and turfs of Mastocarpus stellatus, Chondrus crispus and Corallina officinalis and green and red filamentous algae. Sediment treatment involved the addition of a mixture of coarse and fine sand of either 300 mg/cm²/month or 600 mg/cm² every 15 days. The treatments were applied for seven months and experimental conditions were maintained every two weeks. The experimental treatments do not directly relate to the pressure benchmark but indicate some general trends in sensitivity. Sedimentation led to an increase in the mean cover of red turfing algae (Mastocarpus stellatus and Chondrus crispus and Corallina officinalis) from 11.7% (±1.0 S.E.) in controls to 26.1% (±4.7 S.E.) in sedimented assemblages, but there were no differences between the two levels of sedimentation (Atalah & Crowe, 2010).

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

Smothering and siltation rate changes (heavy)

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

Evidence

No evidence was found to assess this pressure at the benchmark. Sensitivity to this pressure will be mediated by site-specific hydrodynamic conditions and the footprint of the impact. A deposit at the pressure benchmark would cover species with a thick layer of fine materials, however, as this biotope occurs in the lower intertidal on wave exposed shores it is subject to prolonged immersion and silts may be relatively rapidly re-suspended and removed. Where a large area is covered sediments may be shifted by wave and tides rather than removed. 

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

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

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

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

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

No evidence.

Underwater noise changes

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

Evidence

Not relevant.

Introduction of light or shading

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

Evidence

Canopy removal experiments in a rocky sub tidal habitat in Nova Scotia, Canada by Schmidt & Scheibling (2007) did not find a shift in understorey macraoalgal turfs (dominated by Corallina officinalis, Chondrus crispus and Mastocarpus stellatus) to more light-adapted species over 18 months. 

Chondrus crispus is growth saturated at light levels of 60-70 µE/m²/s and is not photoinhibited at 250 µE/m²/s (Bird et al., 1979; Fortes & Lüning, 1980). However, Bischof et al. (2000) reported that the photochemistry of Chondrus crispus is negatively affected by UV-B radiation, while Aguirre-von-Wobeser et al. (2000) concluded that photosynthetically active radiation (PAR) is responsible for most of the photoinhibition in the species.

Sensitivity assessment. As the key structuring and characterizing species colonize a broad range of light environments from intertidal to deeper sub tidal and shaded understorey habitats the biotope is considered to have ‘High’ resistance and, by default, ‘High’ resilience and therefore is ‘Not sensitive’ to this pressure. A change in shading, greater than the pressure benchmark which severely reduced light penetration would negatively impact Palmaria palmata and other algae within the biotope. Very high light levels can also negatively impact algae through photoinhibition.

Barrier to species movement

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

Evidence

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

Death or injury by collision

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

Evidence

Not relevant’ to seabed habitats.  NB. Collision by grounding vessels is addressed under ‘surface abrasion.

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

Not relevant.

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

No information was found on current production of Mastocarpus stellatus, Chondrus crispus or other turf forming red seaweeds in the UK and it is understood that wild harvesting rather than cultivation is the method of production for these and littorinids. No evidence was found for the effects of gene flow between cultivated species and wild populations. Although cultivation of different genotypes may lead to gene flow between wild and cultivated populations the limited dispersal may reduce exposure. Some negative effects may arise from hybridisation between very geographically separated populations but there is no evidence to suggest that gene flow between different UK haplotypes would lead to negative effects. This pressure is therefore considered ‘Not relevant’ to this biotope group.

Introduction or spread of invasive non-indigenous species

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

Evidence

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

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

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

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

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

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

Introduction of microbial pathogens

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

Evidence

No evidence was found for pathogens of Mastocarpus stellatus, the key characterizing species. Craigie & Correa (1996) described 'green spot' disease in Chondrus crispus, caused by the interaction of several biotic agents including fungi, bacteria, algal endophytes and grazers, and resulting in tissue necrosis. Correa & McLachlan (1992) infected Chondrus crispus with the green algal endophytes Acrochaete operculata and Acrochaete heteroclada. Infections resulted in detrimental effects on host performance, including slower growth, reduced carrageenan yield, reduced generation capacity and tissue damage. Stanley (1992) described the fungus Lautita danica being parasitic on cystocarpic Chondrus crispus and Molina (1986) was the first to report Petersenia pollagaster, a fungal invasive pathogen of cultivated Chondrus crispus. At usual levels of infestation in wild populations  these are not considered to lead to high levels of mortality.  

 Sensitivity assessment. Based on the lack of evidence for major pathogens and significant mortalities of Mastocarpus stellatus and other turf-forming macroalgae this biotope is considered to have ‘High’ resistance and hence ‘High’ resilience and is classed as ‘Not sensitive’ at the pressure benchmark.

Removal of target species

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

Evidence

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures. The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of target species on this biotope.  Incidental removal of the key characterizing species and associated species would alter the character of the biotope. Mastocarpus stellatus and Chondrus crispus are both harvested commercially in Scotland and Ireland , 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 for consumption. As the key characterizing and structuring species extensive removal of Mastocarpus stellatus and Chondrus crispus would alter the character of the biotope.  The effect of harvesting Chondrus crispus has been best studied in Canada. Prior to 1980, the seaweed beds of Prince Edward Island were dominated by Chondrus crispus and the species was heavily exploited. Recently, there has been a marked increase in abundance of anotherred seaweed, Furcellaria lumbricalis, which is avoided by the commercial harvest, and an associated decline in abundance of Chondrus crispus (Sharp et al., 1993). The authors suggested that harvesting has brought about the shift in community structure. Sharp et al. (1986) reported that the first drag rake harvest of the season, on a Nova Scotian Chondrus crispus bed, removed 11% of the fronds and 40% of the biomass. Efficiency declined as the harvesting season progressed. Chopin et al. (1988) noted that non-drag raked beds of Chondrus crispus in the Gulf of St Lawrence showed greater year round carposporangial reproductive capacity than a drag raked bed. In the short-term, therefore, harvesting of Chondrus crispus may remove biomass and impair reproductive capacity, while in the long-term, it has the potential to alter community structure and change the dominant species. Removal of other associated algae such as Palmaria palmata and Osmundea pinnatifida will reduce cover of turf forming red algae in this biotope.

The winkle Littorina littorea and the limpet Patella vulgata occur in low densities in this biotope and may be gathered by hand. Changes in grazer abundance can alter the character of the assemblage.  Grazer removal (manual removal of all gastropods in pool and a 1m 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).

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

Sensitivity assessment.  The species that are harvested in this biotope are all attached, sedentary or slow moving and relatively conspicuous. A single event of targeted harvesting could therefore efficiently remove individuals and resistance is assessed as ‘Low’. This assessment is supported by evidence from Sharp et al., (1993) on the proportion of biomass of Mastocarpus stellatus and Chondrus crispus removed commercially.  Resilience of the turf forming red seaweeds is assessed as ‘High’ (based on evidence for recovery from harvesting that did not damage the algal bases although see caveats in the resilience section) and biotope sensitivity is assessed as ‘Low'. This assessment refers to a single collection event, long-term harvesting over wide spatial scales will lead to greater impacts, with lower resistance and longer recovery times. Intense harvesting of littorinids, coupled with removal of limpets would be likely to result in enhance growth of ephemeral algae based on Atalah & Crowe (2010).

Removal of non-target species

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

Evidence

Incidental removal of the turf of the key characterizing species and associated species would alter the character of the biotope. The biotope is characterized by a turf of Mastocarpus stellatus and other turf-forming red algae. The loss of the biological assemblage due to incidental removal as by-catch would therefore alter the character of the habitat and result in the loss of species richness. The ecological services such as primary production and the habitat provided by these species would also be lost. Changes in abundance of grazers and the creation of large areas of bare rock through the removal of basal crusts could lead to significant long-term changes in community composition and result in a higher sensitivity.

Sensitivity assessment.  Removal of a large percentage of the characterizing species resulting in bare rock would alter the character of the biotope through removal of the turf, with consequent changes in species richness and ecosystem function. Resistance is therefore assessed as ‘Low’ and recovery as ‘High’ (where the basal crusts are not removed- see resilience section), so that sensitivity is assessed as 'Low'. If the basal crusts were removed sensitivity would be considered to be greater as recovery times would be longer.