Rhodothamniella floridula on sand-scoured lower eulittoral rock

20-11-2002
Researched byKaren Riley Refereed byThis information is not refereed.
EUNIS CodeA1.215 EUNIS NameRhodothamniella floridula on sand-scoured lower eulittoral rock

Summary

UK and Ireland classification

EUNIS 2008A1.215Rhodothamniella floridula on sand-scoured lower eulittoral rock
EUNIS 2006A1.215Rhodothamniella floridula on sand-scoured lower eulittoral rock
JNCC 2004LR.MLR.BF.RhoRhodothamniella floridula on sand-scoured lower eulittoral rock
1997 BiotopeLR.MLR.Eph.RhoRhodothamniella floridula on sand-scoured lower eulittoral rock

Description

Lower eulittoral and sublittoral fringe sand-scoured bedrock and boulders are often characterized by canopy algae (usually Fucus serratus), beneath which a mat of the sand-binding red alga Rhodothamniella floridula occurs. These mats can also form distinct areas without Fucus serratus. The small hummocks of Rhodothamniella floridula also contain other small red and brown algae and species of worm and amphipod may burrow into the Rhodothamniella floridula mat. Other sand-tolerant algae, such as Polyides rotundus, Furcellaria lumbricalis, Gracilaria verrucosa and Cladostephus spongiosus, may be present. Ephemeral algae such as Ulva spp., Ulva spp. and Porphyra spp. may occur. Where sand scour is more severe, fucoids and Rhodothamniella floridula may be rare or absent and these ephemeral algae dominate the substratum (MLR.EntPor - Porphyra purpurea or Ulva spp. on sand-scoured mid or lower eulittoral rock). (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

Recorded in locations all around the British Isles, particularly along the Northumbrian and south coasts.

Depth range

Lower shore

Additional information

As the dominance of species varies from one to another so the colour of these populations may range from bright or dark green to various sandy, brownish-red shades, the whole contrasting sharply with adjacent areas of Fucus spp. (Lewis, 1964).

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Habitat review

Ecology

Ecological and functional relationships

This biotope is predominantly of algae which dominate the rock surface and canopy. Macroalgae provide habitats for many species of invertebrates and fish and also provide shade under their canopy.

Rock type and sand scour effects are of critical importance to the development of this biotope. Sand-binding algal species are able to colonize soft or crumbly rock more successfully than fucoids (Lewis, 1964). Where sand scour is severe, fucoids and Rhodothamniella floridula tend to be absent while ephemeral green algae dominate the substratum and a different biotope will be present (Connor et al., 1997b).

Seasonal and longer term change

No information was found specifically on this biotope. However, some general observations from rocky shore communities are relevant.
  • Ephemeral green algae may show a peak in abundance during the spring.
  • Winter storms will reduce or damage fucoids and macroalgal cover.
  • Crab and fish tend to move to deeper water in the winter months, so that predation is probably reduced.
  • Corallina officinalis may be overgrown by epiphytes, especially during summer. This overgrowth regularly leads to high mortality of fronds due to light reduction (Wiedemann pers comm. to Tyler-Walters, 2000).
  • At least in northern Britain, Littorina littorea migrates down shore as temperatures fall in autumn (to reduce exposure to sub-zero temperatures) and up shore as temperatures rise in spring; migration depends on local winter temperatures.
  • The upper limit of distribution of Patella vulgata on a shore is increased by shade and exposure. In some situations seasonal variations in sunshine causes a downward migration in spring/summer and an upward migration in autumn/winter (Lewis, 1954).

Habitat structure and complexity

Bedrock and boulders form the substratum in this biotope; the pits, crevices and inclination of which create microhabitats exploitable by both mobile and sessile epilithic species. In addition, the macroalgal species of the community add considerable structural complexity to the biotope in the form of additional substratum for settlement by epiphytic species. The sand scour tolerant species, Rhodothamniella floridula, enhances the structural complexity by binding sand within a mat over the rocky substratum into which polychaetes and amphipods can burrow. There is likely to be considerable structural heterogeneity over a small scale within the biotope. For instance, although barnacles may form a dense layer over the substratum that largely excludes other species, the gaps created by dead barnacles may be exploited by small invertebrates.

Productivity

Rocky shore communities are highly productive and are an important source of food and nutrients for members of neighbouring terrestrial and marine ecosystems (Hill et al., 1998). Macroalgae exude considerable amounts of dissolved organic carbon which is taken up readily by bacteria and may even be taken up directly by some larger invertebrates. Dissolved organic carbon, algal fragments and microbial film organisms are continually removed by the sea. This may enter the food chain of local, subtidal ecosystems, or be exported further offshore. Rocky shores make a contribution to the food of many marine species through the production of planktonic larvae and propagules which contribute to pelagic food chains.

Recruitment processes

Many rocky shore species, plant and animal, possess a planktonic stage: gamete, spore or larva which float in the plankton before settling and metamorphosing into adult form. This strategy allows species to rapidly colonize new areas that become available such as in the gaps often created by storms. For these organisms it has long been evident that recruitment from the pelagic phase is important in governing the density of populations on the shore (Little & Kitching, 1996). Both the demographic structure of populations and the composition of assemblages may be profoundly affected by variation in recruitment rates.

  • Community structure and dynamics are strongly influenced by larval supply. Annual variation in recruitment success, of algae, limpets and barnacles can have a significant impact on the patchiness of the shore.

  • The propagules of most macroalgae tend to settle near the parent plant (Schiel & Foster, 1986; Norton, 1992; Holt et al., 1997). For example, red algal spores and gametes are immotile and the propagules of Fucales are large and sink readily. Norton (1992) noted that algal spore dispersal is probably determined by currents and turbulent deposition (zygotes or spores being thrown against the substratum). For example, spores of Ulva spp. have been reported to travel 35km. The reach of the furthest propagule and useful dispersal range are not the same thing and recruitment usually occurs on a local scale, typically within 10m of the parent plant (Norton, 1992). Vadas et al. (1992) noted that post-settlement mortality of algal propagules and early germlings was high, primarily due to grazing, canopy and turf effects, water movement and desiccation (in the intertidal) and concluded that algal recruitment was highly variable and sporadic. However, macroalgae are highly fecund and widespread in the coastal zone so that recruitment may be still be rapid, especially in the rapid growing ephemeral species such as Ulva spp. and Ulva lactuca, which reproduce throughout the year with a peak in summer. Similarly, Ceramium species produce reproductive propagules throughout the year (Dixon & Irvine, 1977; Burrows, 1991; Maggs & Hommersand, 1993).
  • Gastropods exhibit a variety of reproductive life cycles. The common limpet Patella vulgata and the periwinkle Littorina littorea have pelagic larvae with a high dispersal potential, although recruitment and settlement is probably variable.
  • Barnacles such as Semibalanus balanoides have a planktonic nauplius larva, which spends about 2 months in the plankton, with high dispersal potential. Peak settlement in Semibalanus balanoides occurs in April-May in the west and May-June in the east and north of the British Isles, However, settlement intensity is variable, subsequent recruitment is inhibited by the sweeping action of macroalgal canopies (e.g. fucoids) or the bulldozing of limpets and other gastropods (see MarLIN review for details).
  • Many species of mobile epifauna, such as polychaetes that may be associated with patches of mussels or rock crevices, have long lived pelagic larvae and/or are highly motile as adults.

Time for community to reach maturity

The MLR.Rho biotope consists mainly of algal species, with high spore production and dispersal potential, enabling rapid colonization and recolonization. The development of the community from bare or denuded rock is likely to be similar to that occurring after an oil spill. Recovery of rocky shore populations was intensively studied after the Torrey Canyon oil spill in March 1967. Areas affected by oil alone recovered rapidly, within 3 years. If rocks or boulders are present with sand in suspension, it is likely that recovery of the MLR.Rho biotope would take approximately the same amount of time.

Additional information

No text entered

Preferences & Distribution

Recorded distribution in Britain and IrelandRecorded in locations all around the British Isles, particularly along the Northumbrian and south coasts.

Habitat preferences

Depth Range Lower shore
Water clarity preferencesOceanic water
Limiting Nutrients Nitrogen (nitrates)
Salinity Full (30-40 psu)
Physiographic Open coast
Biological Zone Lower eulittoral
Substratum Bedrock, Large to very large boulders, Small boulders
Tidal Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.), Weak < 1 knot (<0.5 m/sec.)
Wave Moderately exposed, Sheltered, Very sheltered
Other preferences

Additional Information

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Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

    -

    Additional information

    No text entered

    Sensitivity reviewHow is sensitivity assessed?

    Explanation

    Rhodothamniella floridula is considered to be the main characterizing species in the MLR.Rho biotope and dominates the rock surface. It is a sand scour tolerant species, which enhances stability and habitat diversity by binding sand together as a mat on the rocky substratum. In its absence the biotope would not necessarily be recognised. The dominant grazer in the biotope, Patella vulgata, is considered to be important as its grazing activity contributes to the regulation of algal patches and maintains diversity. Fucus serratus is usually abundant and provides habitat. Although the MLR.Rho biotope occurs patchily amongst fucoids, it is an important primary producer and enhances species diversity and patchiness.

    Species indicative of sensitivity

    Community ImportanceSpecies nameCommon Name
    Important otherFucus serratusToothed wrack
    Important functionalPatella vulgataCommon limpet
    Important characterizingRhodothamniella floridulaA red seaweed

    Physical Pressures

     IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
    High High Moderate Major decline High
    The community would be highly intolerant of substratum loss as it is dominated by sessile epilithic species. Removal of the substratum would remove these species and slow moving species associated with them. Intolerance has been assessed to be high. Recoverability is likely to be high (see additional information below).
    High High Moderate Major decline High
    Whilst the community is characterized by the binding of sand which, no doubt, would smother underlying species such as barnacles, smothering is a part of the characteristic of the community. However, a 5cm covering of sediment will most likely completely cover the algal understorey and unless the tide removes the smothering material, photosynthesis will be inhibited and the algae may begin to rot or at least suffer cell damage on fronds. Respiration, feeding and locomotion of other faunal species would probably also be inhibited or prevented. Over a period of one month it is likely to affect the species viability, if not cause death. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. An intolerance of high is recorded. A recoverability of high is recorded (see additional information below).
    High High Moderate Major decline High

    Although Rhodothamniella floridula needs a certain amount of sand in suspension to bind with, Connor et al. (1997b) noted that in areas where sand scour is more severe, fucoids and Rhodothamniella floridula may be rare or absent and ephemeral algae such as Enteromorpha spp., Ulva spp. and Porphyra spp. dominate the substratum. If this occurs, the biotope may change and not be recognised as MLR.Rho.

    The respiration and feeding of suspension feeders, such as barnacles and mussels may be limited, due to blockages. Fucus serratus and Patella vulgata are unlikely to be affected by an increase in suspended sediment, as they occur naturally in areas where there is a high suspended sediment concentration. Therefore, assuming that suspended sediment causes scour and loss of the dominant characterizing species intolerance has been assessed to be high. Recoverability is likely to be high (see additional information below).

    Low High Low Decline Moderate
    Rhodothamniella floridula needs sediment to bind to and will therefore need enough available to do so. In situations where suspended sediment (sand) is reduced or not present for a significant period of time (> 1 year) barnacles, limpets, mussels and algae will probably thrive and become dominant and the biotope will no longer be recognised as MLR.Rho. Intolerance has been assessed to be low. Recoverability is likely to be high (see additional information below).
    Intermediate High Low No change Moderate

    Seaweeds have a critical water content, desiccation past this point causes irreversible damage. The critical point for Fucus serratus is 40% water content. A reduction in water content to 40% can occur after 2 hours exposure to sunshine. Fucus spiralis, a similar species to Fucus serratus, transplanted further up the shore to the Pelvetia canaliculata zone (greater desiccation) died within 4-8 weeks (Schonbeck & Norton, 1978). Rhodothamniella floridula may be protected from desiccation by the water held in the sand it binds with. However, drying is likely to cause mortality of a proportion of the population. Patella vulgata is able to tolerate desiccation very well as it can clamp down to the rock. In the absence of grazers and competition for space between barnacles and Fucus serratus, Rhodothamniella floridula may increase in abundance. However, little information is known about its desiccation tolerance. Intolerance to desiccation has been assessed to be intermediate. Recoverability is likely to be high (see additional information below).

    Intermediate High Low No change Low
    The upper limits of Rhodothamniella floridula may be depressed by a greater risk of desiccation and larger fluctuations in temperature and salinity, as a result of an increase in emergence. Replacement may occur by other flora and fauna more tolerant of desiccation. Barnacles, Mytilus edulis and other seaweeds occur higher up the shore, therefore an increase in emergence at the benchmark level would probably not affect these species. Similarly, Patella vulgata typically moves about when submerged or when conditions are very damp so a change in emergence may alter grazing time, but will probably have little other effect. Some mortality of key species is likely, so an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).
    Intermediate High Low Decline Low
    Decreases in emergence may put the algal species in competition with species that typically remain submerged (e.g. laminarians). A decrease in the time exposed to air would reduce the likelihood of desiccation and the upper limit of the biotope may extend up the shore. However, algal species may not benefit as grazing species would probably be more active and epiphytic species that were kept in check by periodic exposure to air may increase in abundance and smother the species they are attached to. Also, species from the zone/community below may become more dominant which could result in a depression in the lower limit of the MLR.Rho biotope. An intermediate intolerance has been recorded. Recoverability has been assessed to be high (see additional information below).
    Tolerant Not relevant Not relevant Decline High
    Moderate water movement is beneficial to seaweeds as it carries a supply of nutrients and gases to the plants and removes waste products. The MLR.Rho biotope occurs in areas where the water flow rate is either 'moderately strong' or 'weak' (Connor et al., 1997b). However, this biotope occurs in wave exposed situations where the forces of wave surge are likely to be much more damaging than an increase in tidal flow. It is unlikely therefore that the benchmark increase in water flow rate would result in any adverse effect or mortality. Therefore, not sensitive has been recorded.
    High High Intermediate No change Moderate
    The MLR.Rho biotope occurs in areas where the water flow rate is either 'moderately strong' or 'weak' (Connor et al., 1997b). However, the most important water movement in this biotope is wave action. The biotope occurs in wave exposed situations so that supply of suspended sediment will continue even if tidal flow reduces. Therefore intolerance has been assessed as not sensitive.
    Low Very high Very Low No change High

    Maximum sea surface temperatures around the British Isles rarely exceed 20 °C (Hiscock, 1998) and, as Rhodothamniella floridula and Fucus serratus occur south of the British Isles, an increase in temperature is not likely to cause mortality. An acute change in temperature may cause photosynthesis and growth to be impaired, compensating for increased spore production. For instance, spore production of Rhodothamniella floridula is higher at higher temperatures (Stegenga, 1978).

    No mortality of key species is likely to occur, although physiological compensation may take place. Therefore, intolerance is assessed as low. When temperatures return to normal, respiration, reproduction and growth will quickly recover. Recoverability is assessed as very high.

    Intermediate High Low Decline Moderate

    Minimum surface sea water temperatures rarely fall below 5 °C around the British Isles (Hiscock, 1998). Fucus serratus, barnacles and limpets are all found to the north of the British Isles and will therefore probably be tolerant of a chronic 2°C decrease in temperature. However, the distribution of Rhodothamniella floridula has not been recorded north of the British Isles and may not be able to survive a chronic decrease in temperature.

    Dixon & Irvine (1977) observed that Rhodothamniella floridula (as Audouinella floridula) grows much faster in winter, but low temperatures may delay or slow reproduction (Stegenga, 1978). A long-term decrease in temperature is likely to increase the survival and abundance of Semibalanus balanoides in south west England (Southward et al., 1995).

    As mortality of characterizing species may occur if chronic changes in temperature occur, intolerance has been assessed to be intermediate. When temperature returns to normal, respiration, reproduction and growth will quickly recover in surviving species. Recoverability has been assessed to be high (see additional information below).
    Intermediate High Low Decline Moderate
    Changes in turbidity will probably have little direct effect on the key species within this biotope. An increase in turbidity for one month is likely to cause a reduction in the photosynthetic capability and growth of algae, but will probably not result in any mortality. However, a long term increase in turbidity, for one year, may result in mortality of a proportion of the population. Reduced food availability may reduce limpet growth rates and reproductive capacity.

    In the short term, the viability of the population would probably decrease, but in the long term some mortality of Rhodothamniella floridula may occur. Intolerance has been assessed to be intermediate. Recoverability is likely to be high (see additional information below).

    Tolerant* Not sensitive No change Moderate
    Decreased turbidity would probably lead to more light available for algal photosynthesis. Photosynthesis will probably be more efficient and growth rates may therefore increase, but a decrease in turbidity is not likely to affect faunal species within the biotope and an assessment of not sensitive* has been made.
    High High Moderate Major decline High
    Fucus serratus and Rhodothamniella floridula only occur on coasts with moderate wave exposure or less. On more exposed coasts, adult Fucus serratus are fewer. Increased wave action above this level may cause damage to individual plants, breaking fronds and removing entire plants from the substratum. As Fucus serratus is taller than Rhodothamniella floridula it will probably be more susceptible to wave damage. Growths of Rhodothamniella floridula may become dislodged, leading to susceptible patchiness.

    Semibalanus balanoides can tolerate all levels of wave exposure. However, as wave exposure increases on rocky shores, barnacles and fucoids are replaced by mussel dominated communities, meaning that the MLR.Rho biotope may be reduced or destroyed. Therefore, intolerance has been assessed to be high. Recoverability is likely to be high (see additional information below).

    High High Intermediate No change Moderate
    A decrease in the level of wave exposure could cause a shift in the community towards fucoid algae, which may prevent barnacle larvae from settling and provide more substratum for Rhodothamniella floridula to occupy. However, Rhodothamniella floridula is characterizing of situations where there is sand in suspension and, since decreased wave exposure may lead to absence of sand in suspension, Rhodothamniella floridula may be adversely affected and may decline. The biotope may have a high intolerance to decrease in wave exposure. Recoverability is likely to be high.
    Tolerant Not relevant Not relevant No change High
    Seaweeds have no known mechanism for detection of noise vibrations and species of barnacles and mussels are also unlikely to be affected by noise. Although limpets are not likely to be affected by atmospheric noise levels, vibrations near to the animal will cause the shell muscles to contract vigorously, clamping the limpet to the rock (Fretter & Graham, 1994). This may briefly affect the animals grazing ability. However, the biotope is unlikely to be sensitive.
    Tolerant Not relevant Not relevant No change High
    Algae have no known visual perception, and most macroinvertebrates have poor or short range visual perception and are unlikely to be affected by visual disturbance at the benchmark level. The biotope has therefore, been assessed as not sensitive.
    Intermediate High Low Decline Moderate
    Although algal species are highly flexible, abrasion is likely to cause damage to and removal of fronds and may even remove entire plants from the substratum. The cushion-like base of turf forming algae (such as Rhodothamniella floridula) may offer some protection against abrasion but if a portion is removed, the sharp edges may be subject to lifting by wave action. Limpets, Mytilus edulis and barnacle populations have also been reported to be dislodged by abrasion or physical disturbance. Intolerance has been assessed to be intermediate. Recoverability is likely to be high (see additional information below).
    High High Moderate Major decline High
    Rhodothamniella floridula, Fucus serratus and barnacles are permanently attached to the substratum. If removed, the attachment cannot be reformed. Limpets are intolerant of being knocked off the rock by trampling on the shore and if the foot is damaged do not re-attach easily (Professor Steve Hawkins, pers. comm. to Hill, 2000). Therefore, intolerance has been assessed to be high. Recoverability is likely to be high (see additional information below).

    Chemical Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    High High Moderate Major decline Moderate

    Rhodothamniella floridula, Patella vulgata and Fucus serratus (particularly juvenile stages) are all highly intolerant of synthetic chemical contamination.

    Scalan & Wilkinson (1987) found that spermatozoa and newly fertilised eggs of Fucus serratus were the most intolerant of biocides, while adult plants were only just significantly affected at 5 ml/l of the biocides Dodigen v181-1, Dodgen v 2861-1 and ML-910.

    O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination. 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 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.

    Therefore, a high intolerance has been recorded. Recovery is likely to be high (see additional information below).

    Heavy metal contamination
    Intermediate High Low Decline Moderate

    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. Fucoid algae readily accumulate heavy metals within their tissues. Copper significantly reduces the growth rate of vegetative apices at 25 µg/l over 10 days (Strömgren, 1979b). Zinc, lead, cadmium and mercury significantly reduced growth rate at 1400 µg/l , 810µg/l, 450µg/l and 5µg/l respectively (Strömgren, 1980a & b).

    In the Fal estuary Patella vulgata occurs at, or just outside, Restronguet Point at the end of the creek where metal concentrations are in the order: Zinc (Zn) 100-2000µg/l, copper (Cu) 10-100µg/l and cadmium (Cd) 0.25-5µg/l (Bryan & Gibbs, 1983). However, in the laboratory Patella vulgata was found to be intolerant of small changes in environmental concentrations of Cd and Zn by Davies (1992). At concentrations of 10µg/l pedal mucus production and levels of activity were both reduced, indicating a physiological response to metal concentrations. Exposure to Cu at a concentration of 100µg/l for one week resulted in progressive brachycardia (slowing of the heart beat) and the death of limpets. Zn at a concentration of 5500µg/l produced the same effect (Marchan et al.,1999).

    Barnacles and mussels have all been reported to be fairly tolerant of heavy metals (Foster et al., 1978).

    intolerance has been assessed to be intermediate. Recoverability is likely to be high (assuming deterioration of contaminants) (see additional information below).

    Hydrocarbon contamination
    High High Moderate Major decline Moderate

    No evidence was found specifically relating to the intolerance of Rhodothamniella floridula to hydrocarbon contamination. 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. 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).

    Adult Fucus serratus plants are tolerant of exposure to spills of crude oil although very young germlings are intolerant of relatively low concentrations of 'water soluble' extractions of crude oils. Exposure of eggs to these extractions (at 1.5 micrograms/ml for 96 hours) interferes with adhesion during settling) and (at 0.1micrograms/ml) prevents further development (Johnston, 1977).

    Limpets, mussels and barnacles can survive moderate levels of contamination, but mortality may occur at high levels of contamination (Smith, 1968; Glegg et al., 1999; Holt et al., 1995 & Highsmith, et al., 1996). Therefore intolerance has been assessed to be high. Recoverability has been assessed to be high (see additional information below).

    Radionuclide contamination
    No information Not relevant No information Insufficient
    information
    Not relevant
    Mytilus edulis has been shown to be able to accumulate radionuclides (Widdows & Donkin, 1992, Cole et al., 1999), but no information concerning the effects of radionuclides on any other species within the biotope was found and insufficient information has been recorded.
    Changes in nutrient levels
    Intermediate High Low Decline High
    Nutrient availability is the most important factor controlling algal germling growth. Plants under low nutrient regimes achieve smaller sizes and may be out competed. A moderate increase in nutrient levels may enhance their growth. This would increase the food available to Patella vulgata. However, if nutrient loading is excessive this can have a detrimental effect on algal productivity and hence limpet growth. Mytilus edulis and Semibalanus balanoides would also benefit from a moderate increase in nutrients, as food would be more readily available. However, Holt et al. (1995) predict that smothering of barnacles by ephemeral green algae is a possibility under eutrophic conditions. Some mortality of key species within the biotope may occur. Therefore, intolerance has been assessed to be intermediate. Recoverability is likely to be high ( see additional information below).
    Tolerant Not relevant Not relevant No change High
    Rhodothamniella floridula and Fucus serratus occur in full salinity. However, the maximal growth rate for Fucus serratus is at a salinity of 20 psu, above and below this level its growth rate declines. As most of the key species also occur in rockpools, where hypersaline conditions can occur, it is likely that they would tolerate an increase in salinity. Therefore not sensitive has been recorded.
    Intermediate High Low Decline Moderate
    Rhodothamniella floridula, occurs only in full salinity conditions and it is probable that a proportion of the population would die in lower salinities, or at least be out-competed by brackish water tolerant species. Although Fucus serratus will probably survive at lower salinities, its maximal growth rate is at a salinity of 20 psu. Above and below this level its growth rate declines. Little et al. (1991) found that growth and reproduction was impaired in Patella vulgata at lower salinity, although the species was found to die only when the salinity was reduced to <3psu (Fretter & Graham, 1994). As mortality of a proportion of the key species within the biotope may occur, an intermediate intolerance has been recorded. Recoverability is likely to be high (see additional information below).
    Intermediate High Low Decline High

    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 Delesseria sanguinea (a red algae), revealed that specimens died after 24 hours at 15°C but that some survived at 5°C (Hammer, 1972). Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2mg/l.

    In laboratory experiments a reduction in the oxygen tension of seawater from 148mm Hg (air saturated seawater) to 50mm Hg rapidly resulted in reduced heart rate in Patella spp. (Marshall & McQuaid, 1993). Heartbeat rate returned to normal in oxygenated water within two hours. However, Patella vulgata is an intertidal species, being able to respire in air, so would only be intolerant of low oxygen in the water column intermittently during periods of tidal immersion. However, long periods of deoxygenation may increase the mortality of the population.

    Mytilus edulis is regarded as euryoxic, tolerant of a wide range of oxygen concentrations including zero (Zwaan de & Mathieu, 1992). Diaz & Rosenberg (1995) suggest it is resistant to severe hypoxia, but incurs a metabolic cost.

    Semibalanus balanoides can respire anaerobically, so it can tolerate some reduction in oxygen concentration (Newell, 1979). As some important species within the biotope may die, an intermediate intolerance has been recorded. Recoverability is likely to be high (see additional information below).

    Biological Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    No information Not relevant No information Insufficient
    information
    Not relevant
    Patella vulgata, Mytilus edulis and Semibalanus balanoides have all been observed to have parasites. Heavy infestation of Hemioniscus balani can cause castration of barnacles. No other information relating to the effects of microbial pathogens on the key species within the biotope.
    No information Not relevant No information Insufficient
    information
    Not relevant
    No alien species are known to compete with species within the biotope. The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second world war. The species does well in estuaries and bays, where it can displace Semibalanus balanoides and Chthamalus montagui. However, as these species are not characteristic of the biotope, it is considered that insufficient information is available.
    Intermediate High Low Decline Low

    Extraction of the key or important characterizing species is not likely to occur at present. However, Fucus serratus is one algal species that might be harvested. Removal of some of the adult canopy will allow the understorey and algal turf to grow faster, due to greater light available for photosynthesis. Although the biotope is likely to remain, intermediate intolerance has been suggested to reflect the likely loss of some of this important species. Recovery is expected to be high providing some Fucus serratus remains.

    No information Not relevant No information Not relevant Not relevant

    Additional information

    Recoverability

    Following major loss of component species, there will be a colonization succession such as that observed following a severe oil spill. The loss of grazing species results in an initial proliferation of ephemeral green then fucoid algae, which then attracts mobile grazers, and encourages settlement of other grazers. Limpet grazing reduces the abundance of fucoids allowing barnacles to colonize the shore. Recovery rates were dependant on local variation in recruitment and mortality so that sites varied in recovery rates, for example maximum cover of fucoids occurred within 1-3 years, barnacle abundance increased in 1-7 years, limpet number were still reduced after 6-8 years and species richness was regained in 2 to >10 years. Overall, recovery took 5-8 years on many shores but was estimated to take about 15 years on the worst affected shores (Southward & Southward, 1978; Hawkins & Southward, 1992; Raffaelli & Hawkins, 1999).

    This biotope is characterized by mats of Rhodothamniella floridula. No information was found relating to colonization or recolonization rates of Rhodothamniella floridula, however, red algae are typically highly fecund, but their spores are non-motile (Norton, 1992) and therefore highly reliant on the hydrodynamic regime for dispersal. Kain (1975) reported that after displacement some Rhodophyceae were present after 11 weeks, and after 41 weeks, in June, Rhodophyceae species predominated. However, Stegenga (1978) noted that tetrasporangia of Rhodothamniella floridula (as Rhodochorton floridulum) germinated in 'rather low numbers'. Recoverability of the biotope has been assessed as high, although recovery of remote populations will be more protracted and dependent upon favourable currents bringing spores.

    Importance review

    Policy/Legislation

    Habitats Directive Annex 1Reefs
    UK Biodiversity Action Plan Priority

    Exploitation

    • Fucus serratus is one of several algal species that might be harvested. Removal of some of the adult canopy will allow the understorey and algal turf to grow faster.
    • Chondrus crispus, a small purplish-red seaweed, is harvested commercially as carragheen to be used in the pharmaceutical and food industries.
    • The harvesting of these species could affect the species distribution and diversity as a whole.

    Additional information

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    Citation

    This review can be cited as:

    Riley, K. 2002. Rhodothamniella floridula on sand-scoured lower eulittoral rock. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/12

    Last Updated: 20/11/2002