MarLIN

information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Fucoids and kelp in deep eulittoral rockpools

03-04-2018

Summary

UK and Ireland classification

Description

Deep rockpools in the mid to lower eulittoral zone often contain a community characterized by Fucus serratus and Laminaria digitata. Other large brown algae, including Saccharina latissima, Himanthalia elongata and Halidrys siliquosa, may also occur. The rock surface is usually covered by encrusting coralline algae. A wide variety of filamentous and foliose algae, which are typical of lower shore and shallow sublittoral zones (e.g. Palmaria palmata, Chondrus crispus, Ceramium spp., Membranoptera alata and Gastroclonium ovatum) occur beneath the brown algal canopy. Algal-free vertical and overhanging faces often support the sponge Halichondria panicea and anemones Actinia equina. The abundance of grazing molluscs varies considerably. In some, large numbers of littorinids and limpets are probably responsible for the limited variety of red seaweeds present. In other pools, fewer grazers may result in an abundance of these algae. Where boulders occur in these pools they provide a greater variety of micro-habitats which support a variety of fauna. Mobile crustaceans (Pagurus bernhardus and Carcinus maenas), brittlestars (Ophiothrix fragilis and Amphipholis squamata), encrusting bryozoans and ascidians are typically found beneath and between boulders. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Depth range

Mid shore, Lower shore

Additional information

Factors such as pool depth, surface area, volume, orientation to sunlight, shading, internal topography, sediment content and type, together with wave exposure, shore height, and hence flushing rate, and the presence of absence of freshwater runoff, results in large spatial variation in community structure, even between adjacent pools at the same shore height (Ganning, 1971; Metaxas & Scheibling, 1993). Individual rockpools and the communities that occupy them are highly variable.

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Habitat review

Ecology

Ecological and functional relationships

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Seasonal and longer term change

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Habitat structure and complexity

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Productivity

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Recruitment processes

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Time for community to reach maturity

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Additional information

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Preferences & Distribution

Habitat preferences

Depth Range Mid shore, Lower shore
Water clarity preferences
Limiting Nutrients No information found
Salinity preferences Full (30-40 psu)
Physiographic preferences Enclosed coast / Embayment, Open coast
Biological zone preferences Lower eulittoral, Eulittoral
Substratum/habitat preferences Bedrock
Tidal strength preferences
Wave exposure preferences Exposed, Moderately exposed, Sheltered
Other preferences Deep rockpools

Additional Information

This biotope is characterized by macroalgal dominated, deep rockpools. The physical characteristics of the rockpool environment are described under 'Seasonal and longer term change' on the 'Ecology' page. Pyefinch (1943) and Goss-Custard et al. (1979) provide detailed species lists for the rockpools they studied in British and Irish waters.

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

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    Additional information

    The MNCR database lists 667 species in 213 records of this biotope (JNCC, 1999), although not all species occur in all records of the biotope. Lewis (1964) noted that deep pools in the lower shore, especially in the southwest, are rich areas for collecting the rarer species of algae.

    Sensitivity review

    Explanation

    Laminaria digitata, Saccharina latissima, Fucus serratus and Halidrys siliquosa have been selected as important characterizing species since they are faithful fucoids and kelps within the biotope (see Connor et al., 1997b). However, loss of any one of these species would not in itself result in loss of a recognizable biotope. Therefore, for the sake of sensitivity assessment the fucoids and kelps have been treated as a functional group.

    Palmaria palmata and Ceramium virgatum have been chosen to represent the sensitivity of characteristic foliose and filamentous red algae, and Corallina officinalis to represent corallines. Littorinids, limpets and amphipods have been shown to be important grazers in rockpool environments (see 'ecological relationships') that affect community structure and development. Their sensitivities are represented by Littorina littorea and Patella vulgata. The sensitivity of amphipods is treated as a functional group, although reference has been made to relevant species reviews e.g. Hyale prevostii.

    Species indicative of sensitivity

    Community ImportanceSpecies nameCommon Name
    Important functionalAmphipodaAmphipods
    Important structuralCeramium virgatumA red seaweed
    Important structuralChondrus crispusCarrageen
    Important structuralCorallina officinalisCoral weed
    Important characterizingFucus serratusToothed wrack
    Important characterizingHalidrys siliquosaSea oak
    Important characterizingLaminaria digitataOarweed
    Important functionalLittorina littoreaCommon periwinkle
    Important structuralPalmaria palmataDulse
    Important functionalPatella vulgataCommon limpet
    Important characterizingSaccharina latissimaSugar kelp

    Physical Pressures

     IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
    High Moderate Moderate Major decline Low
    Loss of the substratum would involve loss of all the species within the rockpool and hence loss of the biotope. Break up of the rocky substratum (e.g. by a grounded vessel) and or infill of the rockpool would constitute loss of available substratum and hence the habitat. Infilling of the rockpool by permanent material (e.g. by cement) or occlusion by revetment material would constitute a permanent loss of the rockpool and biotope. However, in other instances the species could recolonize the remaining pool and recoverability is likely to be high (see additional information below).
    High Moderate Moderate Decline Low
    Seapy & Littler (1982) reported a decrease in macroalgal cover from 47.3 to 37.5% on a Californian rocky shore due to sediment deposition on the mid to lower shore following rain and flooding. Corallina sp. and Pelvetia sp. were the most affected macroalgal species, while associated red algae were only slightly affected by the resultant scour. Macroinvertebrates declined in cover from 15.8% to 6.5% particularly barnacle species. Daly & Mathieson (1977) examined intertidal zonation on a shore affected by sand scour, and noted that fucoids were reduced to small or young plants, while sand tolerant species such as Ahnfeltia plicata dominated on areas affected by sediment. Smothering by 5 cm of sediment (see benchmark) is likely to increase scour and be detrimental to macroalgae, especially Corallina officinalis and fucoids, and the more fleshy red algae. While laminarians and red algae such as Chondrus crispus and Ceramium spp. are large enough not to be smothered completely by 5 cm of sediment, the resultant scour is likely to damage fronds but, in particular, remove juveniles, sporelings and other propagules. In addition, the rockpool environment is likely to be more vulnerable to smothering as sediment is likely to accumulate in, and be retained by the rockpool itself, effectively increasing the depth of the sediment layer in the pool. In wave exposed conditions the sediment may be removed but in sheltered areas it is likely to be retained for longer than indicated by the benchmark. In deep pools, the macroalgae and associated invertebrates are likely to reduce in depth penetration into the pool while sediment tolerant algae increase. Overall, smothering is likely to reduce the macroalgal diversity of the pool, exclude grazing littorinids, and smother small epifaunal species such as sponges, bryozoans, small anemones and ascidians, although large anemones may survive (e.g. Urticina felina). Where sediment is retained the sediment tolerant algae may come to dominate and the biotope will resemble A1.413. Therefore, an intolerance of high has been recorded. Recoverability is likely to be moderate (see additional information below). However, in extremely high suspended sediment loads, as found in estuaries, rockpools may become completely filled with fine sediment, so that only infaunal species survive.
    Intermediate High Low Decline Low
    An increase in suspended sediment could potentially result in increased turbidity (see below), smothering, especially on sheltered shores (see above), and increased scour. Fucoids, kelps and other macroalgae, and the community they support, are likely to be adversely affected, as shown above (Daly & Mathieson, 1977; Seapy & Littler, 1982). On wave sheltered shores, sediment may accumulate in low to mid shore pools, which will favour sand tolerant species and infauna. Overall, macroalgae are likely to be damaged but the biotope is likely to remain but the species diversity decrease (for example see Daly & Mathieson, 1977). Therefore, an intolerance of intermediate has been recorded, although recovery is potentially high (see additional information below). However, in extreme situations deposition of fine sediments may result in smothering of the rockpool (see above).
    Tolerant Not relevant No change Low
    A decrease in suspended sediment could reduce the turbidity (see below) and potentially reduce the food availability for suspension feeders, due to a reduction in organic particulates. However, suspension feeders will continue to feed on available plankton and detritus and be little affected. Similarly, the resident macroalgae are unlikely to be adversely affected by reduced sediment loads, except that scour is reduced. Therefore, tolerant has been recorded.
    Intermediate High Low Decline Low
    Rockpools are natural refuges from desiccation but may be drained due to slow seepage or due to 'bucketing' by shore users, resulting in a decrease in the water level and hence desiccation exposure. Many members of the biotope are common on the emergent rock surface (e.g. fucoids, red algae, littorinids) and therefore, exhibit relative tolerance of desiccation. However, the presence of the rockpool allows species to occur in niches higher on the shore than they would otherwise. Low shore, sublittoral fringe or sublittoral species within the pool would be particularly intolerant of desiccation, e.g. Furcellaria lumbricalis and low shore algae. However, such drainage is likely to be short-lived, and the water level return to normal levels after the next high tide. Therefore, an increase in desiccation at the benchmark level, an increase equivalent to a rise in shore height, is likely to result in a decrease in species richness, although the biotope itself is likely to remain and an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information).
    High Moderate Moderate Decline Low
    An increase in emergence is likely to significantly affect physico-chemical environment of the rockpool and its resident community. An increase in emergence will increase the time that the pool is exposed to fluctuating air temperatures, wind, rain and sunlight, all of which will affect the temperature and salinity regime within the pool. Lower shore pools will come to resemble mid shore pool communities, with a reduction in sublittoral species and species sensitive to extremes of temperature, for example the laminarians (see individual reviews). For example, the upper limit of Bifurcaria bifurcaria within rockpools in Roscoff, France was shown to be limited by the summer temperatures where the surface pool water temperatures exceeded 20 °C (Kooistra et al., 1989). Mid shore examples of LR.FK are likely to be worst affected. High shore pools tend to support communities of temperature tolerant or opportunistic algae, especially green algae such as Ulva spp., and temperature and salinity tolerant species such as harpacticoid copepods, ostracods, and small gastropods (for example see A1.421). This biotope would be lost from mid shore areas as a result of an increase in emergence at the benchmark level. Therefore, an intolerance of high has be recorded and recoverability is probably moderate (see additional information below).
    Low Very high Moderate Rise Low
    A decrease in emergence will reduce the time the pool spends exposed to the air and cut off from the sea. Therefore, the range of temperatures and oxygen levels characteristic of rockpool environments is likely to decrease. Hence the mid shore pool communities will come to resemble low shore pools. Low shore pools are characterized by higher abundance of large macroalgae, such as Halidrys siliquosa, Cystoseira sp. and laminarians and a larger diversity of red algae and macrofauna. Low shore pools will probably be colonized by an increasing number of sublittoral species. Therefore, although the community is likely to increase in diversity the biotope is likely to remain. Therefore, an intolerance of low has been recorded to reflect changes in community structure.
    Not relevant Not relevant Not relevant Not relevant Moderate
    Water flow rate in this biotope is typically only that of the ebb and flood tide speed, which hardly affects intertidal habitats and is far exceeded by the strength of wave action. A change in water flow rate is therefore considered not relevant.
    High Moderate Intermediate Major decline Low
    Water flow rate in this biotope is typically only that of the ebb and flood tide speed, which hardly affects intertidal habitats and is far exceeded by the strength of wave action. A change in water flow rate is therefore considered not relevant.
    Low Very high Very Low Minor decline Low
    Rockpools experience variation in temperature on a daily and seasonal basis. The range and extremes of temperature change increasing with shore height but also dependent on shading, aspect, topography and depth of the pool (Pyefinch, 1943; Ganning, 1971; Daniel & Boyden, 1975; Goss-Custard et al., 1979; Morris & Taylor, 1983; Huggett & Griffiths, 1986; Metaxas & Scheibling, 1993). For example, reported temperature ranges for mid to low shore pools include annual maxima and minima of 1-25 °C and 2-22°C (Morris & Taylor, 1983), a diurnal range of 24°C (day) and 13°C (night) for a mid shore pool (Daniel & Boyden, 1975), and surface water temperature ranges of 14-19.25°C and 15.5-20.75°C in mid shore pools (Pyefinch, 1943). Temperature stratification within pools may result in higher surface temperatures and lower deep water temperatures in sunlight (Daniel & Boyden, 1977) or be reversed due to wind cooling, night or in winter (Naylor & Slinn, 1958; Ganning, 1971; Morris & Taylor, 1983). The temperature range will limit the distribution of sensitive species within the pools, especially normally sublittoral species, e.g. laminarians (see individual reviews). For example, the upper limit of Bifurcaria bifurcaria within rockpools in Roscoff, France was shown to be limited by the summer temperatures where the surface pool water temperatures exceeded 20 °C (Kooistra et al., 1989). Therefore, an increase in ambient temperatures is likely to reduce the abundance or vertical extent of sensitive species within the biotope, especially in shallower examples of the biotope. However, the range and extremes of temperature routinely experienced by the biotope are greater than the benchmark level and an intolerance of low has been recorded to represent a potential decrease in species diversity.
    Intermediate High Low Minor decline Low
    Rockpools experience variation in temperature on a daily and seasonal basis. The range and extremes of temperature change increasing with shore height but also dependent on shading, aspect, topography and depth of the pool (Pyefinch, 1943; Ganning, 1971; Daniel & Boyden, 1975; Goss-Custard et al., 1979; Morris & Taylor, 1983; Huggett & Griffiths, 1986; Metaxas & Scheibling, 1993). For example, reported temperature ranges for mid to low shore pools include annual maxima and minima of 1-25 °C and 2-22°C (Morris & Taylor, 1983), a diurnal range of 24°C (day) and 13°C (night) for a mid shore pool (Daniel & Boyden, 1975), and surface water temperature ranges of 14-19.25°C and 15.5-20.75°C in mid shore pools (Pyefinch, 1943). Temperature stratification within pools may result in higher surface temperatures and lower deep water temperatures in sunlight (Daniel & Boyden, 1977) or be reversed due to wind cooling, or in winter (Naylor & Slinn, 1958; Ganning, 1971; Morris & Taylor, 1983). Morris & Taylor (1983) reported that the surface of an upper shore was seen to freeze one winter night, although that this was a rare event. Freezing is likely to be rare in mid or low shore pools. Nevertheless the severe winter of 1962/63 resulted in a wide variety of mortalities in the intertidal and shallow subtidal (Crisp, 1964a). For example, few macroalgae were damaged but specimens of Cystoseira spp. in the south and south west were smaller than usual. However, the anemone Anemonia viridis was missing from shallow pools and that only a single specimen of Cereus pedunculatus was found in an area of usual abundance, while many dead specimens of both species were found in south Wales. Similarly, many dead porcelain crabs (Porcellana spp.) were found. Patella vulgata exhibited increasing mortality with shore height and hence emersion (Crisp, 1964a), and several species of gastropod exhibited mortality. Although southern, lusitanian, species were worst affected, mortalities of individual species varied with location. However, rockpools, especially deep pools and low shore pools are likely to represent a buffer from the extreme cold and frosts experienced by fauna and flora on the emergent rock surface. Overall, the range of temperatures routinely experienced by mid to low shore rock pools is greater than the benchmark level. However, the severe winter of 1962/63 suggests that some sensitive species, particularly limpets and gastropods, and anemones near the surface of deep pools may be affected. The loss of grazers may benefit the macroalgal community, resulting in increased growth of fucoids and green algae. Therefore, an intolerance of intermediate has been recorded to represent the loss of species diversity and changes in community structure, especially in mid shore examples of the biotope. Recoverability is probably high (see additional information below).
    Intermediate High Low Minor decline Low
    An increase in turbidity due to suspended sediment, dissolved organics or phytoplankton blooms will reduce the depth that light can penetrate the pool and hence the depth within the pool that different groups of algae can grow, particularly kelps. For example, in the silt-laden waters around Helgoland, Germany the depth limit for Laminaria digitata growth may be reduced to between 0 m and 1.5 m (Birkett et al., 1998b). Increased turbidity around a sewage treatment plant was thought to be responsible for the absence of Laminaria digitata plants in the Firth of Forth (Read et al., 1983). In Narragansett Bay, Rhode Island growth rates of Laminaria digitata fell during a summer bloom of microalgae that dramatically reduced down welling irradiance. Quality of light is also important with blue light necessary for gametogenesis and development of gametophytes in laminarians. Dissolved organic materials (yellow substance or gelbstoff) absorbs blue light strongly, therefore changes in riverine input or other land based runoff are likely to influence kelp density and distribution. Light levels often determine the maximum depth for survival of Saccharina latissima (studied as Laminaria saccharina) at a particular site (Lüning & Dring, 1975; Gerard, 1988) therefore an increase in turbidity may lead to the mortality of some plants towards the deeper end of their depth range, although Gerard (1988) reported that Saccharina latissima populations may adapt to low or variable light conditions. Moss & Sheader (1973) demonstrated that the growth of Halidrys siliquosa germlings was dependent on light intensity but that germlings could survive total darkness for 120 days (see general biology). Fucus serratus can normally photosynthesize when emersed so that increased turbidity on emergent rocks is unlikely to be detrimental although growth rates are likely to be reduced. Overall, an increase in turbidity of the water will reduce the depth within the pool that macroalgae can grow, so that kelps and to a lesser extent the fucoids are likely to be limited to the upper margin of the pool. However, shade tolerant red algae may benefit and dominate the deeper parts of the pool. An increase in turbidity at the benchmark level may result in loss of laminarians from deep pools, especially Laminaria digitata, but fucoids and hence the biotope will probably remain at the surface. Therefore, an intolerance of intermediate has been recorded to represent the potential loss of kelp species, although recoverability is likely to be high.
    Low Very high Moderate No change Low
    A decrease in turbidity will increase light penetration, and hence the growth of all macroalgae, especially kelps species, and increase the depth at which red algae or fucoids may grow, possibly increasing competition for space between the algae themselves and other space occupiers such as sponges and ascidians. However, the effects are likely to depend on the size of the pool. In smaller pools, increased growth of kelps and fucoids is likely to result in self-shading, so that the net effect is likely to be minimal. Therefore, an intolerance of low has been recorded.
    High Moderate Moderate Minor decline Low
    This rockpool biotope occurs in wave sheltered to wave exposed habitats. The rockpool provides a degree of shelter from wave action, especially deep pools, allowing more fragile sublittoral algae to survive. However, an increase in wave exposure from, for example moderately exposed to very exposed is likely change the community. Fucoid abundance in characteristic of wave sheltered conditions, and on more wave exposed shores shallow rockpools are dominated by Corallina officinalis (see A1.411). Therefore, an increase in wave exposure at the benchmark level is likely to reduce the abundance or remove fucoids from the margin of the pool, in favour of corallines. Laminaria digitata is likely to be replaced by Alaria esculenta, which tolerates strong water movement. Lewis (1964) noted that Halidrys siliquosa, and Cystoseira spp. were restricted to deep mid shore pools with increasing wave exposure. Similarly, the increased turbulence within the pool itself will favour species that prefer strong water movement, such as the passive suspension feeders e.g. hydroids (e.g. Tubularia larynx) and anemones (e.g. Metridium dianthus) and other epifauna, together with more wave exposure tolerant red algae, e.g. Porphyra sp., Plocamium sp. and Gigartina sp.. However, with increasing wave exposure the biotope is likely to change, and may come to resemble Corallina officinalis rockpool biotopes, depending on the relative abundance of Bifurcaria bifurcata (in the south west) and Cystoseira spp (see LR.Cor). Therefore, the biotope is likely to be lost, and although replaced by another healthy community, an intolerance of high has been recorded. Recoverability is likely to be moderate (see additional information below).
    High Moderate Intermediate Major decline Low
    This rockpool biotope occurs in wave sheltered to wave exposed habitats. A decrease in wave exposure from e.g. sheltered to very sheltered, or extremely sheltered is likely to adversely affect the biotope. The resultant lack of water movement is likely to result in increased suspended sediment and siltation of the rockpool, smothering and filing the rockpool. Fucoids will survive on the margins of the pool and emergent rock, however laminarians, and epifauna are likely to be lost and only sediment tolerant red algae survive within the pool. The biotope may come to resemble LR.SwSed, or in worst case situations become silted up, so that only infauna survive. Therefore, an intolerance of high has been recorded, with moderate recoverability (see additional information below).
    Tolerant Not relevant Not sensitive No change High
    Few organisms within the biotope are likely to respond to noise or vibration at the benchmark level. Fish may attempt to leave the biotope at high tide but would otherwise be trapped at low tide. Overall, little if any effect on the biotope is expected.
    Tolerant Not relevant Not sensitive No change High
    Mobile invertebrates and fish are able to react to shading, usually darting to cover in order to avoid a potential predator. However, their visual acuity is low, and they are unlikely to be adversely affected by visual presence.
    Intermediate High Low Minor decline Low
    Abrasion by an anchor or mooring may remove some fronds of the large macroalgae, foliose red algae and coralline turf, although most species would grow back from their remaining holdfasts. However, trampling may be more damaging. Deep pools are protected by their depth but shallower pools or the shallower margins of larger pools are probably more vulnerable.

    No studies of the effects of trampling on rockpools were found but studies of the effects on emergent algal communities are probably indicative. For example, moderate (50 steps per 0.09 square metre) or more trampling on intertidal articulated coralline algal turf in New Zealand reduced turf height by up to 50%, and the weight of sand trapped within the turf to about one third of controls. This resulted in declines in densities of the meiofaunal community within two days of trampling. Although the community returned to normal levels within 3 months of trampling events, it was suggested that the turf would take longer to recover its previous cover (Brown & Taylor, 1999). Similarly, Schiel & Taylor (1999) noted that trampling had a direct detrimental effect on fucoid algae and coralline turf species on the New Zealand rocky shore. Low trampling intensity (10 tramples) reduced fucoid cover by 25%, while high intensity (200 tramples) reduced fucoid cover by over 90%, although over 97% cover returned within 21 months after spring trampling; autumn treatments took longer to recover due to the delay in recruitment. Coralline bases were seen to peel from the rocks (Schiel & Taylor, 1999) due to increased desiccation caused by loss of the algal canopy. Brosnan & Cumrie (1994) demonstrated that foliose species (e.g. fucoids and Mastocarpus papillatus) were the most susceptible to trampling disturbance, while turf forming species were more resistant. Barnacles were also crushed and removed. However, the algae and barnacles recovered in the year following the trampling (Brosnan & Cumrie, 1994). Similarly, Boalch et al. (1974) and Boalch & Jephson (1981) noted a reduction in fucoid cover (especially of Ascophyllum nodosum) at Wembury, Devon, when compared with the same transects surveyed 43 years previously. They suggested that the reduction in fucoid cover was due to the large number of visitors and school groups received by the site.

    Rockpools form natural mesocosms and so attract considerable attention from the general public, educational events and scientists alike. In addition to trampling within shallower pools and the margins of deeper pools, turning of rocks within the pool is likely to disturb underboulder communities (e.g. see A1.2142). Overall, a proportion of the macroalgal community, and the invertebrates it supports are likely to be removed, depending on trampling intensity, and an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below) once trampling has stopped. However, it should be noted that ongoing trampling is likely to result in a long term reduction in the diversity of the margins of the affected pools.
    High Moderate Moderate Decline Low
    The majority of the epiphytic fauna, such as the isopods, amphipods and harpacticoid copepods are highly mobile are unlikely to be adversely affected by displacement. Similarly, gastropods are likely to survive and migrate back to suitable feeding areas. But the dominant macroalgae and sessile epifauna (e.g. barnacles and tubeworms) are permanently attached to the substratum and if removed will be lost. Loss of the fucoids and kelps especially will result in loss of the biotope overall. If macroalgal holdfasts and bases are also removed then recovery will be prolonged.

    Chemical Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    High Moderate Moderate Major decline Low
    The different groups of organisms within the biotope are likely to vary in their response to synthetic chemical pollution. Key examples are summarized below.
    • Cole et al. (1999) suggested that the following were very toxic to macrophytes: atrazine; simazine; diuron; and linuron (herbicides). Atrazine was lethal to young sporophytes of Laminaria hyperborea at 1 mg/l and caused growth suppression at 10 µg/l in short term experiments (Hopkin & Kain, 1978). Mixed detergents, herbicides (dalapon and 2,4-D) were not toxic at the levels tested (Hopkin & Kain, 1978). Although Laminaria hyperborea sporelings and gametophytes are intolerant of atrazine (and probably other herbicides) overall mature specimens may be relatively tolerant of synthetic chemicals probably due to the presence of alginates (Holt et al. 1995).
    • Laminaria hyperborea survived within >55m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater the 5 years of age, suggesting that spores and/or early stages were more intolerant (Hoare & Hiscock, 1974). However, Laminaria digitata was less tolerant, and although it was found within Amlwch Bay, it was excluded from >90 m of the effluent source (Hoare & Hiscock, 1974). Patella pellucida was excluded from Amlwch Bay by the pollution and the species richness of the holdfast fauna decreased with proximity to the effluent discharge; amphipods were particularly intolerant although polychaetes were the least affected (Hoare & Hiscock, 1974). The richness of epifauna/flora decreased near the source of the effluent and epiphytes were absent from Laminaria hyperborea stipes within Amlwch Bay.
    • Fucoids are generally quite robust in terms of chemical pollution (Holt et al., 1997). However, Fucus vesiculosus is extraordinarily highly intolerant of chlorate, such as from pulp mill effluents. In the Baltic, the species has disappeared in the vicinity of pulp mill discharge points and is affected even at immediate and remote distances (Kautsky, 1992). The different life stages of Fucus serratus differ in their intolerance to synthetic chemicals. Scalan & Wilkinson (1987) found that spermatozoa and newly fertilized 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, Dodigen 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, possibly due to the susceptibility of phycoerythrins to destruction. They also suggested that red algae were effective indicators of detergent damage since they undergo colour changes when exposed to relatively low concentration of detergent. Smith (1968) reported that red algae such as Ahnfeltia plicata, Chondrus crispus, Furcellaria fastigiata, Mastocarpus stellatus, Polyides rotundus and Osmundea pinnatifida were amongst the algae least affected by detergents, whereas other species, including Ceramium spp., Cryptopleura ramosa, Cladophora rupestris, Lomentaria articulata and Ulva lactuca were either killed or unhealthy, although the effects were worst higher on the shore, which had received the most detergents. Delesseria sanguinea was probably to most intolerant since it was damaged at depths of 6m (Smith, 1968). Holt et al. (1995) suggested that Delesseria sanguinea is probably generally sensitive of chemical 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). Hoare & Hiscock (1974) noted that all red algae except Phyllophora sp. were excluded from near to an acidified halogenated effluent discharge in Amlwch Bay, Anglesey and that intertidal populations of Corallina officinalis occurred in significant amounts only 600 m east of the effluent.
    • Smith (1968) reported that oil and detergent dispersants from the Torrey Canyon spill affected high water specimens of Corallina officinalis more than low shore specimens and some specimens were protected in deep pools. In areas of heavy detergent spraying, however, Corallina officinalis was killed, and was affected down to 6m depth at one site, presumably due to wave action and mixing (Smith, 1968). However, regrowth of fronds had begun within 2 months after spraying ceased (Smith, 1968).
    • Gastropods and amphipods were found to be amongst the most sensitive species to detergents and oils. For example, limpets are extremely intolerant of aromatic solvent based dispersants used in oil spill clean-up. During the clean-up response to the Torrey Canyon oil spill nearly all the limpets were killed in areas close to dispersant spraying. Viscous oil will not be readily drawn in under the edge of the shell by ciliary currents in the mantle cavity, whereas detergent, alone or diluted in sea water, would creep in much more readily and be liable to kill the limpet (Smith, 1968). A concentration of 5 ppm killed half the limpets tested in 24 hours (Southward & Southward, 1978; Hawkins & Southward, 1992). Toxicity experiments with gastropods demonstrated that 10 ppm of BP1002 was enough to cause the animals to close and stop climbing (Smith, 1968). Smith (1968) noted that over a 100 ppm of BP1002 was required to kill the majority of Nucella lapillus in experiments, while different concentrations of BP1002 killed the majority of the following: Littorina littorea (100 ppm); Calliostoma zizyphinum (10 ppm); Aplysia punctata (50 ppm), and Patella vulgata (5 ppm) (see individual reviews). Nucella lapillus and other muricid gastropods are noted for their sensitivity to tri-butyl tin contamination (see review).
    • Smith (1968) also noted that after detergent treatment, only beadlet anemone Actinia equina, and tufts of Bifurcaria sp., Corallina sp., and other algae were present in a rockpool. The pool had previously supported a community of anemones, gastropods, Corallina, Lithophyllum, Ulva, crabs, prawns and fish.
    • Most pesticides and herbicides were suggested to be very toxic for invertebrates, especially crustaceans (amphipods, isopods, mysids, shrimp and crabs) and fish (Cole et al., 1999). For example, lindane was shown to be very toxic to gobies (Gobius spp.; see Pomatoschistus minutus review) (Ebere & Akintonwa, 1992). The pesticide ivermectin is very toxic to crustaceans, and has been found to be toxic towards some benthic infauna such as Arenicola marina (Cole et al., 1999).
    Overall, the evidence suggests that, on balance, the characterizing red algae are probably very intolerant to synthetic chemicals, while resident gastropods, crustaceans and fish vary in their sensitivity. Loss of grazing invertebrates will affect community structure. Contamination with herbicides or other pesticides, e.g. from agricultural runoff, could adversely affect all components of the community. Therefore, biotope intolerance is assessed as high. Rockpools might be expected to accumulate chemical contaminants, depending on the rate of flushing, so that mid shore pools may be more vulnerable than low shore examples of the biotope. Recoverability is probably moderate (see additional information below).
    Heavy metal contamination
    Intermediate High Low Minor decline Low
    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. Burdin & Bird (1994) reported that both gametophyte and tetrasporophyte forms of Chondrus crispus 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.

    It is generally accepted that adult fucoids are relatively tolerant of heavy metal pollution (Holt et al., 1997). The effect of heavy metals on the growth rate of adult Fucus serratus plants has been studied by Strömgren (1979b;1980a, b). Copper significantly reduces the growth rate of vegetative apices at 25 µg/l over 10 days (Strömgren, 1979b). Zinc, lead, cadmium & mercury significantly reduce growth rate at 1400 µg/l, 810 µg/l, 450 µg/l and 5 µg/l respectively (Strömgren, 1980a, b).

    Zinc was found to inhibit growth in Laminaria digitata at a concentration of 100 µg/L and at 515 µg/L growth had almost completely ceased (Bryan, 1969). Axelsson & Axelsson (1987) investigated the effect of exposure to mercury (Hg), lead (Pb) and nickel (Ni) for 24 hours by measuring ion leakage to indicate plasma membrane damage. Inorganic and organic Hg concentrations of 1 mg/L resulted in the loss of ions equivalent to ion loss in seaweed that had been boiled for 5 minutes. Laminaria digitata was unaffected when subjected to Pb and Ni at concentrations up to 10 mg/L. Their results also indicated that the species is intolerant of the tin compounds butyl-Sn and phenyl-Sn. Sporophytes of Saccharina latissima (studied as Laminaria saccharina) have a low intolerance to heavy metals but the early life stages are more intolerant (Thompson & Burrows, 1984). Growth of sporophytes was significantly inhibited at 50 µg Cu /l, 1000 µg Zn/l and 50 µg Hg/l. Zoospores were found to be more intolerant and significant reductions in survival rates were observed at 25 µg Cu/l, 1000 µg Zn/l and 5 µg/l (Thompson & Burrows, 1984).

    Bryan (1984) suggested that adult gastropod molluscs were relatively tolerant of heavy metal pollution. Cole et al. (1999) suggested that Pb, Zn, Ni and As were very toxic to algae, while Cd was very toxic to Crustacea (amphipods, isopods, shrimp, mysids and crabs), and Hg, Cd, Pb, Cr, Zn, Cu, Ni, and As were very toxic to fish. Bryan (1984) reported sublethal effects of heavy metals in crustaceans at low (ppb) levels. In laboratory investigations Hong & Reish (1987) observed 96 hr LC50 of between 0.19 and 1.83 mg/l in the water column for several species of amphipod.

    Cd, Hg, Pb, Zn and Cu are highly persistent, have the potential to bioaccumulate significantly and are all considered to be very toxic to fish (Cole et al., 1999). Mueller (1979) found that in Pomatoschistus sp., very low concentrations of Cd, Cu and Pb (0.5 g/l Cd2+; 5 g/l Cu2+; 20 g/l Pb2+) brought about changes in activity and an obstruction to the gill epithelia by mucus. This may also be true for other goby species. Inorganic Hg concentrations as low as 30 µg/l (96-h LC5) are considered to be toxic to fish, whereas organic Hg concentrations are more toxic to marine organisms (WHO, 1989, 1991). Oertzen et al. (1988) found that the toxicity of the organic Hg complex exceeded that of HgCl2 by a factor of 30 for the goby Pomatoschistus microps.

    The intolerance of crustaceans to heavy metal contaminants suggests that amphipod and isopod grazers would be lost, allowing rapid growth of opportunistic algae such as Ulva spp. In addition, the characterizing laminarians and their propagules may be adversely affected, and the growth rates of fucoids reduced. Therefore, an intolerance of intermediate has been recorded to represent a decrease in species diversity, although a recognizable biotope is likely to remain. Recoverability is likely to be high (see additional information below).
    Hydrocarbon contamination
    Intermediate Moderate Moderate Major decline Low
    Hydrocarbon contamination, e.g. from spills of fresh crude oil or petroleum products, may cause significant loss of component species in the biotope, through impacts on individual species viability or mortality, and resultant effects on the structure of the community. Rockpools are potentially vulnerable habitats, depending on depth, flushing rate and tidal height. Rockpool organisms may be protected, since oil will float on the pool surface. However, rockpool organisms will be exposed to the water soluble fraction of fresh oils, and a surface film of oil will prevent gaseous exchange and may reduce or exclude light. If exposed to oil the resident sediment is likely to adsorb oil and release it slowly, causing chronic long-term contamination and potentially prolonged recovery. The effects of oil contamination on marine organisms were reviewed by Suchanek (1993) and are summarized below.
    • Laminaria digitata is less susceptible to coating with oil than some other seaweeds because of its preference for exposed locations where wave action will rapidly dissipate oil. The effects of oil accumulation on the thalli are mitigated by the perennial growth of kelps. No significant effects of the Amoco Cadiz spill were observed for Laminaria populations and the World Prodigy spill of 922 tons of oil in Narragansett Bay had no discernible effects on Laminaria digitata (Peckol et al., 1990). Mesocosm studies in Norwegian waters showed that chronic low level oil pollution (25 µg/L) reduced growth rates in Laminaria digitata but only in the second and third years of growth (Bokn, 1985).
    • Holt et al. 1995 reported that oil spills in the USA and from the 'Torrey Canyon' had little effect on kelp forest. Similarly, surveys of subtidal communities at a number sites between 1-22.5m below chart datum, including Laminaria hyperborea communities, showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997)
    • Fucus vesiculosus shows limited intolerance to oil. After the Amoco Cadiz oil spill Fucus vesiculosus suffered very little (Floc'h & Diouris, 1980). Indeed, Fucus vesiculosus may increase significantly in abundance on a shore where grazing gastropods have been killed by oil, although very heavy fouling could reduce light available for photosynthesis and in Norway a heavy oil spill reduced fucoid cover.
    • Littoral barnacles (e.g. Semibalanus balanoides) have a high resistance to oil (Holt et al., 1995) but may suffer some mortality due to the smothering effects of thick oil (Smith, 1968).
    • Gastropods (e.g. Littorina littorea and Patella vulgata) and especially amphipods have been shown to be particularly intolerant of hydrocarbon and oil contamination (see Suchanek, 1993).
    • The abundance of littorinids decreased after the Esso Bernica oil spill in Sullom Voe in December 1978 (Moore et al., 1995). The abundance of Patella sp., Littorina saxatilis, Littorina littorea and Littorina neglecta and Littorina obtusata were reduced but had returned to pre-spill levels by May 1979. In heavily impacted sites, subjected to clean-up, where communities were destroyed in the process, Littorina saxatilis recovered an abundance similar to pre-spill levels within ca 1 year, while Littorina littorea took ca 7 years to recover prior abundance (Moore et al., 1995).
    • Widdows et al. (1981) found Littorina littorea surviving in a rockpool, exposed to chronic hydrocarbon contamination due to the presence of oil from the Esso Bernica oil spill.
    • The anemones Actinia and Anthopleura were reported to survive in waters with severe oil pollution (Smith, 1968; Suchanek, 1993).
    • Echinoderms are thought to be especially sensitive to oil (Suchanek, 1993). In a survey of rock pool at West Angle Bay, Pembrokeshire, Crump & Emson (1997) noted that limpets, crustaceans (amphipods and Palaemon) and the echinoderms Amphipholis squamata and the rare Asterina phylactica were adversely affected. However, the majority of adult Asterina gibbosa survived. The macrofauna, except Asterina phylactica, had recovered its diversity and abundance within 12 weeks of the spill (Crump & Emson, 1997).
    • Laboratory studies of the effects of oil and dispersants on several red algae species (Grandy, 1984, cited in Holt et al., 1995) concluded that they were all intolerant of oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination. However, Smith (1968) noted that ed algae such as Ahnfeltia plicata, Chondrus crispus, Furcellaria fastigiata, Mastocarpus stellatus, Polyides rotundus and Osmundea pinnatifida were amongst the algae least affected by detergents, whereas other species, including Ceramium spp., Cryptopleura ramosa, Cladophora rupestris, Lomentaria articulata and Ulva lactuca were either killed or unhealthy, although the effects were worst higher on the shore, which had received the most detergents.
    • Cole et al. (1999) suggested a moderate to high toxicity of oils and petrochemicals for fish. Bowling et al. (1983) found that anthracene, a Polyaromatic hydrocarbon (PAH) had a photo-induced toxicity to the bluegill sunfish. They reported that when exposed to sunlight anthracene was at least 400 times more toxic than when no sunlight was present. According to Ankley et al. (1997) only a subset of PAH's are phototoxic (fluranthene, anthracene, pyrene etc.). Effects of these compounds are destruction of gill epithelia, erosion of skin layers, hypoxia and asphyxiation (Bowling et al., 1983). In PAH contaminated areas, fish have been observed to develop tumours (GESAMP, 1993). Oil spills were reported to have low acute toxicity to adult fish (GESAMP, 1993), probably since adults can avoid contaminated areas, but that fish kills may occur after exposure to emulsified oil in shallow waters, e.g. after the Braer oil spill (GESAMP, 1993). However, in the rockpool environment, fish are unlikely to be able to avoid the water soluble fractions, and may suffer chronic or acute toxicity depending on the oil type and fish species concerned.
    • Loss of grazing gastropods and mesoherbivores after oil spills results in marked increases in the abundance of ephemeral green algae (e.g. Ulva spp.) and fucoids (Southward & Southward, 1978; Hawkins & Southward, 1992; Raffaelli & Hawkins, 1999).
    Overall, red algae, gastropods, amphipods and other crustaceans, and echinoderms within the rockpool community are likely to be adversely affected. However, kelps, fucoids and some of the characterizing red algae (e.g. Chondrus crispus) are likely to survive and the biotope is likely to remain, although with a greatly reduced species richness. Therefore, an intolerance of intermediate has been recorded. The loss of grazers will allow increased growth of ephemeral greens and fucoids. However, the extent of damage may be exaggerated by the clean-up techniques employed e.g. detergents (see synthetic chemicals above) or high pressure water sprays. High water pressure sprays are likely to denude the rock surface of most life.

    On wave exposed rocky coasts oil will be removed relatively quickly. Recovery of rocky shore populations was intensively studied after the Torrey Canyon oil spill in March 1967. Loss of grazers results in an initial flush of ephemeral green then fucoid algae, followed by recruitment by grazers including limpet, which free space for barnacle colonization. On shores that were not subject to clean up procedures, the community recovered within ca 3 years, however, in shores treated with dispersants recovery took 5-8 years but was estimated to take up to 15 years on the worst affected shores (Southward & Southward, 1978; Hawkins & Southward, 1992; Raffaelli & Hawkins, 1999). Therefore, the community may take longer to recover, especially in oil is retained within pool bound sediments or as a coating of tar. Hence, a recoverability of moderate has been recorded (see additional information below).

    Radionuclide contamination
    No information Not relevant No information Not relevant Not relevant
    Insufficient
    information
    Changes in nutrient levels
    Intermediate High Low Decline Low
    Little information on the nutrient regime of rockpools was found. Rockpools are cut off from the sea for periods of time, depending on their shore height, and hence nutrients could potentially become limiting (e.g. nitrogen and phosphorous) within the period of emersion. Similarly, pools could also become eutrophic due to the presence of washed up seaweeds and bird droppings and in some cases sewage effluent. The effluent from rotting seaweeds on the strandline can severely impact upper shore pools (e.g. at Wembury, Devon) although lower shore pools are unlikely to be affected in LR.FK. However, eutrophication only likely to be a problem in high shore pools cut off from the sea for days at a time.

    Increased nutrient may increase growth in fast growing species (e.g. Ulva spp.) to the detriment of slower growing species of macroalgae. However, Fucus vesiculosus was observed to grow in the vicinity of a sewage outfall (Holt et al., 1997) and is probably not sensitive.

    Eutrophication can potentially increase oxygen consumption leading to deoxygenation. However, the rockpool environment normally experience considerable variation in oxygen levels. Overall, an intolerance of intermediate has been recorded.
    Low Very high Very Low No change Low
    High air temperatures cause surface evaporation of water from pools, so that salinity steadily increases, especially in pools not flooded by the tide for several days. However, Daniel & Boyden (1975) and Morris & Taylor (1983) reported little variability in salinity over one tidal cycle, and Ganning (1971) suggested that changes in salinity were of limited importance. Morris & Taylor (1983) reported an annual maximum salinity of 36.5 ppt in the pools studied on the west coast of Scotland. Goss-Custard et al. (1979) recorded salinities of 34.8 and 35.05 ppt in mid-shore pools. Therefore, the biotope is probably tolerant of small increases in salinity and an intolerance of low has been recorded. High shore pools exhibit greater variation and higher extremes of salinity (Pyefinch, 1943; Ganning, 1971) and different communities but mid to low shore pools are unlikely to experience such extremes unless the emergence regime is increased (see above) or they are exposed to hypersaline effluents.
    Tolerant Not relevant No change Low
    During periods of emersion, high rainfall will reduce pool salinity or create a surface layer of brackish/nearly fresh water for a period. The extremes of salinity experienced will depend on the depth of the pool, shore height and flushing rate, and season. For example, Morris & Taylor (1983) stated that a low salinity layer of 2-10 mm was normal but after one storm the low salinity layer increased in depth, eventually resulting in a homogeneous pool of brackish water. Morris & Taylor (1983) reported an annual salinity range in mid to low shore pools of 26-36.5 ppt. Mid shore examples of this biotope may lack more sensitive species, such as Laminaria digitata and some sublittoral species. Nevertheless, decreases in salinity equivalent of a reduction from full to reduced (see benchmark) are likely to be a regular occurrence in rockpool communities, and the biotope is unlikely to be adversely affected. Hence, tolerant has been recorded.
    Tolerant Not relevant Not sensitive No change Low
    During emergence rockpools are closed systems and gaseous exchange occurs over the air/water interface. In shallow pools the volume to surface area ratio is likely to be high, whereas in deep pools the ratio is likely to be low. In addition, the oxygen concentration is dependant on the community present. During the day, photosynthesis uses up CO2 and produces O2, in excess of respiration. However, at night respiration by flora and fauna deplete oxygen levels. As a result rockpool environments exhibit marked variation in oxygen levels. In summer, rockpools are likely to be supersaturated with oxygen during the day (Pyefinch, 1943). For example, the greatest range of oxygen saturation of 101.7% occurred in a seaweed dominated, sediment floored pool, which reach over 190% saturation on some days (Pyefinch, 1943). Daniel & Boyden (1975) noted that a mid shore, seaweed dominated pool reached 194% saturation (ca 15 mg O2/l) but that oxygenation was also marked in shaded pools. A pool with dense fauna exhibited a maximum saturation of 210% (Pyefinch, 1943). During photosynthesis algae absorb carbon dioxide and as concentrations fall, the pH rises. Morris & Taylor (1983) recorded pH values >9 in rockpools on the Isle of Cumbrae. At night, oxygen levels may fall below 100% saturation and pH will decrease as CO2 levels increase. Morris & Taylor (1983) noted an annual maximum of oxygen concentration of 400-422 mm Hg (ca 23.4-24.7 mg/l) and an annual minimum of 18-38 mm Hg (ca 1-2.2 mg/l) in mid shore pools. Daniel & Boyden (1975) reported oxygen depletion at night, with mid to low shore pools reduced to 8-44% saturation. They noted that the crab Carcinus maenas leaves the pools at night, and that other species with the ability to air-breathe could also do so, e.g. limpets, littorinids, and the shanny Lipophrys pholis. They also observed that shrimps gathered at the edge of high shore pools at night, presumably to take advantage of the better oxygenated surface layer (Daniel & Boyden, 1975). Goss-Custard et al. (1979) noted that oxygen saturation levels decreased with depth in deep mid shore pools, while Morris & Taylor (1983) noted that oxygen saturation varied with depth and proximity to algae, especially green algae such as Cladophora spp.

    The range of extremes in oxygen concentration were greater in summer than in winter. On immersion, the rockpool community was exposed to potentially large, sudden fluctuations in oxygen concentrations depending on season and time of day (Morris & Taylor, 1983). Therefore, rockpools communities are probably exposed to variations equivalent to or greater than the benchmark level on a regular basis and tolerant has been recorded.

    Biological Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    Low Very high Very Low No change Low
    Laminarians are susceptible to brown spot disease, caused by the brown alga Streblonema aecidioides. Infected algae show symptoms of Streblonema disease, i.e. alterations of the blade and stipe ranging from dark spots to heavy deformations and completely crippled thalli (Peters & Scaffelke, 1996). The occurrence of hyperplasia or gall growths, seen as dark spots, on Laminaria digitata is well known and may be associated with the presence of endophytic brown filamentous algae. Ectocarpus deformans, for example, was considered the cause of galls in Laminaria digitata by Apt (1988). In Helgoland, Ellertsdottir and Peters (1997) found 86% of Laminaria digitata thalli infected with endophytic brown algae and all those that exhibited weak to moderate but visible thallus alterations such as dark spots on the lamina or small warts on the stipe were infected. Several coralline and non-coralline species are epiphytic on Corallina officinalis. Irvine & Chamberlain (1994) cite tissue destruction caused by Titanoderma corallinae. However, no information on pathogenic organisms in the British Isles was found. In Rhodophycota, viruses have been identified by means of electron microscopy (Lee, 1971) and they are probably widespread. However, nothing is known of their effects on growth or reproduction in red algae and experimental transfer from an infected to an uninfected specimen has not been achieved (Dixon & Irvine, 1977). Intertidal gastropods often act a secondary hosts for trematode parasites of sea birds. For example, Nucella lapillus may be infected by cercaria larvae of the trematode Parorchis acanthus. Infestation causes castration and continued growth (Feare, 1970b; Kinne, 1980; Crothers, 1985). Overall, a wide variety of pathogens may affect members of the community but no information on associated mortality was found. Therefore, an intolerance of low has been recorded.
    Intermediate None Very High Decline Moderate
    Sargassum muticum is a non-native macroalgae spreading around the coasts of Britain and Europe (see Eno et al., 1997) and is often found in low to mid shore rockpools in the intertidal in areas it has colonized. Although, no studies on its effects on rockpool species were found, studies of its effect on shallow sublittoral macroalgae suggest that it can out-compete fucoids and kelps. For example, Stæhr et al. (2000) reported that an increase in the abundance of Sargassum muticum in the Limfjorden (Denmark) from 1990 to 1997 was accompanied by a decrease in the abundance of thick, slow growing macroalgae such as Saccharina latissima (studied as Laminaria saccharina), Codium fragile, Halidrys siliquosa, Fucus vesiculosus, and Fucus serratus, together with other algae such as Ceramium nodulosum (as rubrum) and Dictyota dichotoma. In Sargassum muticum removal experiments on the coast of Washington State, Britton-Simmonds (2004) concluded that Sargassum muticum reduced the abundance of native canopy algae (especially kelps) by 75% and native understorey algae by 50% probably as a result of shading. However, Viejo (1999) noted that mobile epifauna (e.g. amphipods, isopods) successfully colonized Sargassum muticum which provided additional habitat. Overall, Sargassum muticum can successfully invade rockpools, and would probably out-compete resident fucoids and kelp species, and some red algae. In addition, mesoherbivores will probably adapt to the new substratum offered by Sargassum muticum since they feed primarily on epiphytes. Therefore, the biotope is likely to remain but with a reduced species richness due to the loss of some species of macroalgae and resemble the sub-biotope A1.4121. Therefore, an intolerance of intermediate has been recorded. Recovery is potentially high but assumes removal of Sargassum muticum which is unlikely. Hence, a recoverability of 'none' has been recorded since the biotope is likely to change, although a viable community will remain.
    Intermediate High Low Decline Low
    Several of the characterizing red algae species are subject to harvesting. Chondrus crispus is extracted commercially in Ireland, but the harvest has declined since its peak in the early 1960s (Pybus, 1977). Mathieson & Burns (1975) described the recovery of Chondrus crispus following experimental drag raking (see MarLIN review) and concluded that control levels of biomass and population structure are probably re-established after 18 months of regrowth. Palmaria palmata is used as a vegetable substitute or animal fodder although harvesting on a commercial scale only takes place in Ireland and France (Guiry & Blunden, 1991). Littorina littorea is also subject to harvesting in the UK and limpets in France. Hand collection may reduce the population of Littorina littorea within rockpools and hence reduce grazing pressure which may actually benefit the algal component of the biotope, especially opportunistic green algae and epiphytes.

    Overall, while rockpools in areas subject to commercial algal harvesting may be directly affected, most examples of the biotope are unlikely to be affected by commercial harvesting in the UK. In deep pools characterized by this biotope, only the margins of the pool are likely to be affected. However, due to the relative small size of the community, even small scale hand collecting may have a significant effect. Therefore, an intolerance of intermediate has been recorded to represent the loss of a proportion of the macroalgae and the invertebrate community it supports, and loss of some littorinids. However, recovery is likely to be rapid since holdfasts and sporelings are likely to remain and the littorinids will probably recover quickly by migration and recruitment.

    Low Very high Very Low No change Low

    Additional information

    Recoverability
    Kain (1975) examined recolonization of cleared concrete blocks in a subtidal kelp forest. Red algae colonized blocks within 26 weeks in the shallow subtidal (0.8m) and 33 weeks at 4.4m. After about 2.5 years, Laminaria hyperborea standing crop, together with an understorey of red algae, was similar to that of virgin forest. Red algae were present throughout the succession increasing from 0.04 to 1.5 percent of the biomass within the first 4 years. Colonizing species varied with time of year, for example blocks cleared in August 1969 were colonized by primarily Saccharina latissima (studied as Laminaria saccharina) and subsequent colonization by Laminaria hyperborea and other laminarians was faster than blocks colonized by Saccorhiza polyschides; within 1 year the block was occupied by laminarians and red algae only. Succession was similar at 4.4m, and Laminaria hyperborea dominated within about 3 years. Blocks cleared in August 1969 at 4.4m were not colonized by Saccorhiza polyschides but were dominated by red algae after 41 weeks, e.g. Cryptopleura ramosa. Kain (1975) cleared one group of blocks at two monthly intervals and noted that brown algae were dominant colonists in spring, green algae (solely %) in summer and red algae were most important in autumn and winter. Overall, red algae are likely to be able to recolonize and recover abundance with a year in some instances and probably within 5 years. Similarly, laminarians could potentially colonize low shore rockpools within 3-4 years, depending on grazing and competition for space. Red algae produce non motile spores, dependant on the hydrography and most recruitment is likely to occur within about 10 m of the parent plants (Norton, 1992). Therefore, within a rock pool or a pool surrounded by macroalgae, recruitment is likely to be good. However, recruitment from remote populations is likely to be more protracted and sporadic.

    Recovery of a population of Chondrus crispus following a perturbation is likely to be largely dependent on whether holdfasts remain, from which new thalli can regenerate (Holt et al., 1995). Following experimental harvesting by drag raking in New Hampshire, USA, populations recovered to 1/3 of their original biomass after 6 months and totally recovered after 12 months (Mathieson & Burns, 1975). Raking is designed to remove the large fronds but leave the small upright shoots and holdfasts. The authors suggested that control levels of biomass and reproductive capacity are probably re-established after 18 months of regrowth. It was noted however, that time to recovery was much extended if harvesting occurred in the winter, rather than the spring or summer (Mathieson & Burns, 1975). Minchinton et al. (1997) documented the recovery of Chondrus crispus after a rocky shore in Nova Scotia, Canada, was totally denuded by an ice scouring event. Initial recolonization was dominated by diatoms and ephemeral macroalgae, followed by fucoids and then perennial red seaweeds. After 2 years, Chondrus crispus had re-established approximately 50% cover on the lower shore and after 5 years it was the dominant macroalga at this height, with approximately 100% cover. The authors pointed out that although Chondrus crispus was a poor colonizer, it was the best competitor.

    Fucoids (e.g. Fucus serratus and Fucus vesiculosus) recruit readily to cleared areas, especially in the absence of grazers (Holt et al., 1997). However, fucoid propagules tend to settle near to the parent plants, due to turbulent deposition by water flow. Within monospecific stands recruitment of conspecifics is most likely, and community recovery is likely to be rapid. For example, after the Torrey Canyon oil spill, fucoids attained maximum cover within 1-3 years (Southward & Southward, 1978; Hawkins & Southward, 1992; Raffaelli & Hawkins, 1999). However, in cleared areas, recruitment is likely to be rapid but recovery of the original community structure is likely to take some years (Holt et al., 1997). For example, after the Torrey Canyon oil spill, although maximum cover of fucoids occurred within 1-3 years, the abundance of barnacles increased in 1-7 years, limpet number were still reduced after 6-8 years and species richness was regained in 2 to >10 years (Southward & Southward, 1978; Hawkins & Southward, 1992; Raffaelli & Hawkins, 1999).

    Sousa et al. (1981) reported that experimental removal of sea urchins significantly increased recruitment in long-lived brown algae. In experimental plots cleared of algae and sea urchins in December, Halidrys dioica colonized the plots, in small numbers, within 3-4 months. Plots cleared in August received few , if any recruits, suggesting that recolonization was dependant on zygote availability and therefore the season. Wernberg et al. (2001) suggested that the lack of long range dispersal success in Halidrys siliquosa was responsible for its regional distribution in the north east Atlantic

    Corallina officinalis probably has good recruitment and settled on artificial substrata within 1 week of their placement in the intertidal during summer in New England (Harlin & Lindbergh, 1977). New fronds of Corallina officinalis appeared on sterilized plots within six months and 10% cover was reached with 12 months (Littler & Kauker 1984). Bamber & Irving (1993) reported that new plants grew back in scraped transects within 12 months, although the resistant crustose bases were probably not removed. Similarly, in experimental plots, up to 15% cover of Corallina officinalis fronds returned within 3 months after removal of fronds and all other epiflora/fauna but not the crustose bases (Littler & Kauker, 1984). Although new crustose bases may recruit and develop quickly the formation of new fronds from these bases and recovery of original cover may take longer, and it is suggested that the population is likely to recover within a few years.

    Gastropods and other mobile grazers (e.g. amphipods, isopods) are likely to be attracted by developing microalgae and macroalgae and could return quickly by either migration or larval recruitment. Epifaunal species vary in their recruitment rates. Sebens (1985, 1986) reported that rapid colonizers such as encrusting corallines, encrusting bryozoans, amphipods and tubeworms recolonized cleared rock surfaces within 1-4 months. Ascidians such as Aplidium spp. achieved significant cover in less than a year, and, together with Halichondria panicea, reached pre-clearance levels of cover after 2 years. Anemones colonized within 4 years (Sebens, 1986) and would probably take longer to reach pre-clearance levels. The anemone Urticina felina has poor powers of recoverability due to poor dispersal (Sole-Cava et al., 1994 for the similar Tealia crassicornis) and slow growth (Chia & Spaulding, 1972), though populations should recover within 5 years.

    Overall, members of the rockpool community could potentially recolonize with a year and a recognizable biotope return within 5 years. However, rockpool recruitment is reported to be sporadic and variable (Metaxas & Scheibling, 1993). While a recognizable biotope will return the exact community may differ from that present prior to perturbation. In addition, although the biotope is likely to be recognizable within less than 5 years, if the community was completely destroyed by perturbation, it may take longer for a typically diverse community to become established, especially the biotopes supported anemones and the rarer red algal species.

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    Citation

    This review can be cited as:

    Tyler-Walters, H., 2015. Fucoids and kelp in deep eulittoral rockpools. 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. [cited 19-06-2018]. Available from: http://www.marlin.ac.uk/habitat/detail/282

    Last Updated: 16/12/2015