Kelp in variable or reduced salinity


UK and Ireland classification


Very wave-sheltered bedrock, boulders and cobbles subject to only weak tidal streams in the sublittoral fringe and infralittoral zone, in areas of variable/reduced salinity. This biotope complex is characterized by the kelp Saccharina latissima and coralline crusts such as Lithothamnion glaciale. Grazers such as the urchins Psammechinus miliaris and Echinus esculentus, and the gastropods Gibbula cineraria and Buccinum undatum may be present. The tube-dwelling polychaete Spirobranchus triqueter, the ascidians Ciona intestinalis, Corella parallelogramma and Ascidiella scabra, the barnacle Balanus crenatus, the starfish Asterias rubens and the brittlestar Ophiothrix fragilis may also be present. Red algal communities are composed primarily of Phycodrys rubens. The crabs Carcinus maenas and Pagurus bernhardus, and the bivalve Modiolus modiolus may also be observed. (Information from Connor et al., 2004; JNCC, 2015)

Depth range

0-5 m, 5-10 m

Additional information

The biotope SIR.SlatRS occurs as SIR.SlatRS.FIR with filamentous algae and sponges particularly characteristic in southwest Britain and as SIR.SlatRS.Phy, with Phyllophora crispa and SIR.SlatRS.Psa with Psammechinus miliaris especially characteristic in western Scotland.

Habitat review


Ecological and functional relationships

The sub-biotopes of SIR.LsacRS illustrate the importance of ecological relationships in determining the presence of different species assemblages in apparently similar situations with regard to physical and chemical conditions. In some examples of low water movement and reduced salinity, rocks are dominated by algae (SIR.LsacRS.FiR and SIR.LsacRS.Phy) but in others, the sea urchin Psammechinus miliaris grazes algae so that few foliose seaweeds are present (SIR.LsacRS.Psa). In the absence of grazing, algae dominate this biotope most likely providing a habitat for a community of small worms, crustaceans and molluscs but making movement difficult for larger species that require attachment to the surface. For instance, brittle stars, Ophiocomina nigra, occur extensively in the grazed sub-biotope but not in those dominated by foliose algae. Some other species may have difficulty settling onto bare rock in areas dominated by algae although the richness of communities in the LsacRS.FiR sub-biotope in south-west Britain suggests that algal growth may not be a great impedance to settlement. A significant fauna may also be associated with sponges (Peattie & Hoare, 1981).

Seasonal and longer term change

No specific information has been found in relation to this biotope.Saccharina latissima is a short-lived perennial. Sporophytes typically have a lifespan of 2 to 4 years although plants may occur as annuals suggesting the possibility of some seasonal fluctuation in abundance. Where surfaces have been cleared, Kain (1975) recorded that Saccharina latissima (studied as Laminaria saccharina) was abundant six months after substratum was cleared. Foliose algae are likely to show a seasonal change in condition of the fronds and in abundance (see Hiscock, 1986c). Also, solitary ascidians are short lived and may fluctuate in numbers through the year and from year to year. For instance, Svane (1988) describes Ascidiella scabra as "an annual ascidian".

Habitat structure and complexity

There are a wide range of microhabitats within this biotope. They include sediments, sometimes maerl, where infauna will occur, underboulder habitats, the sides and tops of boulder which often have different dominant species, the interstices of massive sponge growths, the holdfasts of kelp plants and the fronds of kelps and other algae.


No specific information found has been found but the communities in this biotope are likely to be highly productive. The biotope occurs in shallow depths where high light intensity will result in high primary productivity. Secondary productivity is also be high although due mainly to active suspension feeding by such species as ascidians, barnacles and mussels largely unassisted by external water movement.

Recruitment processes

The characterizing species in this biotope all have planktonic spores or larvae and are fairly short-lived. There is therefore high recruitment and high turnover. In sub-biotopes with significant algal presence (especially SIR.LsacRS.Phy), algae might attract a high abundance of solitary ascidians (see Schmidt, 1983) relative to the erect tubes of the hydroid Tubularia indivisa).

Time for community to reach maturity

The community would probably reach maturity within 2-3 years although recruitment of additional species to the biotope would continue for some further time.

Additional information

Examples of this biotope are notably rich for areas subject to low or variable salinity. It might be that, in areas not subject to grazing, the stability of physical conditions allows for settlement and survival of progressively more species with time.

Preferences & Distribution

Habitat preferences

Depth Range 0-5 m, 5-10 m
Water clarity preferencesNo information
Limiting Nutrients No information
Salinity preferences Full (30-40 psu), Low (<18 psu), Reduced (18-30 psu), Variable (18-40 psu)
Physiographic preferences No information
Biological zone preferences Infralittoral, Sublittoral fringe
Substratum/habitat preferences Bedrock, Cobbles, Large to very large boulders, Small boulders
Tidal strength preferences Very weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave exposure preferences Extremely sheltered, Sheltered, Very sheltered
Other preferences None

Additional Information

The biotope occurs attached to bedrock and stable boulders and cobbles in wave and tidal stream sheltered areas.

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

    Additional information

    The nationally scarce mollusc Akera bullata has been recorded in two examples of SIR.LsacRS.Phy.

    Sensitivity review


    The biotope SIR.LsacRS occurs as SIR.LsacRS.FiR with filamentous algae and sponges particularly characteristic in southwest Britain and as SIR.LsacRS.Phy, with Phyllophora crispa especially characteristic and SIR.LsacRS.Psa with Psammechinus miliaris especially characteristic in western Scotland. The importance of Psammechinus miliaris in the biotope is, however, as a key functional species that affects the biotope through grazing. The range of species in the sub-biotopes is large but the species selected as indicative of sensitivity are or represent species that may be common in at least some examples of the biotope.

    Species indicative of sensitivity

    Community ImportanceSpecies nameCommon Name
    Important structuralAscidiella scabraA sea squirt
    Key structuralAsterias rubensCommon starfish
    Key structuralBalanus crenatusAn acorn barnacle
    Important otherCeramium virgatumA red seaweed
    Important otherClavelina lepadiformisLight bulb sea squirt
    Important otherHalichondria paniceaBreadcrumb sponge
    Important otherMytilus edulisCommon mussel
    Important otherPomatoceros triqueterKeel worm
    Key functionalPsammechinus miliarisGreen sea urchin
    Key structuralSaccharina latissimaSugar kelp
    Important otherUlva lactucaSea lettuce

    Physical Pressures

     IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence / Confidence
    High High Moderate Major decline High
    Most of the species characteristic of this biotope are permanently or firmly attached to the substratum so would be removed upon substratum loss. Intolerance is therefore high. Recovery would be likely within a few years and by five years the biotope is likely to appear as before the impact (see additional information below).
    Intermediate High Low Decline Moderate
    Some species, especially Saccharina latissima, are likely to protrude above smothering material. Others such as the active suspension feeders and foliose algae are likely to be killed by smothering. An intolerance of intermediate is suggested as some individuals might die but the biotope will persist and recoverability will be high (see additional information below). However, if smothering is in the form of impermeable material, intolerance will be high.
    Low Very high Very Low No change Moderate
    Increased suspended sediment levels will reduce the amount of light reaching the seabed and may therefore inhibit photosynthesis of the algal component of the biotope (see increase in turbidity below). However, the biotope occurs in very shallow depths and algae are likely to survive. Suspended silt may clog respiratory and feeding organs (especially of sea squirts). However, since many of the species in this biotope live in areas of high silt content (turbid water) it is expected that they would survive increased levels of silt in the water. Both algae and animals would suffer some decrease in viability. On return to lower suspended sediment levels it is expected that recovery of condition will be rapid. Therefore an intolerance of low and recoverability of very high is indicated.
    Low High Moderate Major decline High
    Decreased suspended sediment levels will increase the amount of light reaching the seabed and may therefore increase competitiveness of the algal component of the biotope (see decrease in turbidity below). Suspended sediment may include organic matter and a decrease may reduce the amount of food available to suspension feeding animals. Both algae and animals would suffer some decrease in viability. On return to higher suspended sediment levels it is expected that recovery of condition will be rapid. Therefore an intolerance of low and recoverability of very high is indicated.
    Low High Low Minor decline Moderate
    The biotope is predominantly sublittoral but does extend onto the shore and therefore has some ability to resist desiccation. On a sunny day at low water of spring tides, damage (bleaching) is likely to occur to the Saccharina latissima plants and other foliose algae but not destroy them completely. Species living below the kelp fronds will be protected by them from the worst effects of desiccation. Sponges, such as Halichondria panicea, are likely to withstand some desiccation as they hold water. An intolerance of low is suggested as although some individuals of species might die, the biotope will persist. Recoverability will be high or possibly very high (see additional information below).
    High High Moderate Major decline Moderate
    The biotope is predominantly sublittoral and the dominant species (Saccharina latissima) and many of the subordinate species, especially foliose algae and solitary sea squirts, are unlikely to survive an increased emergence regime. Several mobile species are likely to move away. However, providing that suitable substrata are present, the biotope is likely to re-establish further down the shore within a similar emergence regime to that which existed previously (see additional information below). An intolerance of high and a recoverability of high is therefore indicated.
    Tolerant* Not sensitive No change High
    The biotope is subtidal and thrives in fully submerged conditions.
    Intermediate High Low No change Moderate
    Increase in tidal flow rates may dislodge substrata (especially where large plants of Saccharina latissima subject to drag are attached to cobbles). Also, increased water flow rate may result in certain species being unable to feed when water flow is likely to damage feeding organs (see Hiscock 1983). However, it is unlikely that species attached to non-mobile substrata in the biotope will be killed by an increase in flow rate. Therefore a decline in the abundance of some species that are swept away is suggested with some reduction in viability of others depending on whether the current velocity reaches a high enough level to inhibit feeding. An intolerance of intermediate has been recorded with a recoverability of high (see additional information below).
    Not sensitive* No change High
    The biotope occurs in areas of weak or very weak tidal flow and a further decrease may adversely affect the biotope through the onset of stagnation and consequent deoxygenation as well as siltation and smothering. However, some species in the biotope are active suspension feeders (sponges, solitary ascidians) that are known to thrive in extremely sheltered locations (see, for instance, Hiscock & Hoare, 1973) or at least survive in such situations (barnacles). Therefore, there may be some localized mortality but all-in-all, the biotope is likely to survive. An intolerance of low is therefore indicated and a recovery of very high.
    Low Very high Very Low No change Low
    The biotope occurs as different sub-biotopes in warmer and colder parts of Britain and Ireland and it might be that northern elements would be adversely affected and, in the long-term, northern version of the biotope may be lost. However, exposure to high temperatures for several days may produce stress in some component species but not mortality and recovery would be expected to be rapid. An intolerance of low is therefore indicated and a recoverability of very high.
    Low Very high Moderate No change Low
    The biotope occurs in warmer and colder parts of Britain and Ireland as different sub-biotopes. Similar assemblages of species are known to occur in Scandinavia so that long-term decrease in temperature is unlikely to cause a significant impact on the northern sub-biotopes but may adversely affect the southern form. However, exposure to low temperatures for several days may produce stress in some component species but recovery would be expected to be rapid. An intolerance of low is therefore indicated and a recoverability of very high.
    Intermediate High Low No change Moderate
    Several of the characteristic species are algae that rely on light for photosynthesis. Reduction in light penetration as a result of higher turbidity is unlikely to be fatal to algae in the short term but in the long term will result in a reduction in downward extent and therefore overall extent of the biotope. Species richness may decline in the long-term as algae are unable to survive high turbidity and low light but reduced extent of the biotope (depth limits) is the most significant likely decline. An intolerance of intermediate will apply and recoverability will be high (see additional information below).
    Tolerant* Not sensitive No change High
    Decreased turbidity and the subsequent increase in light levels is likely to result in an extension of the downward extent of the biotope. Not sensitive* is therefore indicated.
    High High Moderate Major decline Moderate
    This is a fundamentally sheltered coast biotope with species that does not appear to occur in wave exposed situations. Increased wave action is likely to dislodge Saccharina latissima plants and interfere with feeding in solitary tunicates. Massive growths of Halichondria panicea are likely to be displaced. Although 'major decline' is indicated with regard to species richness, the results of increased wave exposure would be replacement of biotope-characteristic species with others and the development of a different biotope. A change of biotope means high intolerance. On return to previous conditions, the 'new' biotope would have to degrade before A3.32 developed. Nevertheless, such a change should occur within five years and a recoverability of high is indicated (see additional information below).
    Not sensitive* No change High
    This biotope occurs in locations not subject to any significant wave exposure so that decrease in wave exposure is considered not relevant.
    Tolerant Not relevant Not relevant Not relevant High
    The macroalgae characterizing the biotope have no known sound or vibration sensors and animals such as the sponges, urchins and solitary sea squirts are not known to respond to noise. Therefore 'not sensitive' is indicated.
    Tolerant Not relevant Not relevant Not relevant High
    None of the animals that characterize the biotope respond significantly to visual presence although barnacles, whose cirri are consumed by blennies and probably other fish, are likely to cease feeding briefly as a response to shadowing. Overall, an intolerance of not relevant is suggested.
    High High Moderate Major decline High
    Saccharina latissima, other algae, sponges and the large solitary tunicates are likely to be removed from the substratum by physical disturbance and sea urchins may be crushed. Physical disturbance will also overturn boulders and cobbles so that the epibiota becomes buried. Mortality of species is therefore likely to be high although many, particularly mobile species, will survive. An intolerance of high is therefore indicated. Recoverability is expected to he high (see additional information below).
    Intermediate High Low Decline High
    Although many of the species in the biotope are sessile and would therefore be killed if removed from their substratum, displacement will often be of the boulders or cobbles on which the community occurs in which case survival will be high. The 'Intermediate' ranking given here supposes that some individual sessile organisms will be removed and die. Mobile organisms such as the prosobranchs and sea urchins in the biotope are likely to survive displacement. Recovery is likely to be high (see additional information below).

    Chemical Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence / Confidence
    Intermediate High Low Decline Moderate
    Several of the species characteristic of the biotope are reported as having high intolerance to synthetic chemicals. For instance, Cole et al. (1999) suggested that herbicides such as Simazine and Atrazine were very toxic to macrophytic algae. Hiscock & Hoare (1974) noted that almost all red algal species and many animal species were absent from Amlwch Bay in North Wales adjacent to an acidified halogenated effluent. Red algae have also been found to be sensitive to oil spill dispersants (O'Brien & Dixon 1976; Grundy quoted in Holt et al. 1995). However, this biotope typically occurs in enclosed areas including harbours and so some tolerance of contaminants must occur and an intolerance of intermediate is suggested. Recovery is likely to occur fairly rapidly. For recoverability, see additional information below.
    Heavy metal contamination
    Low Very high Very Low Minor decline Moderate
    Sporophytes of Saccharina latissima have a low intolerance to heavy metals, but the early life stages are more intolerant. The effects of copper, zinc and mercury on Saccharina latissima (studied as Laminaria saccharina) have been investigated by Thompson & Burrows (1984). They observed that the 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. The effects of contaminants on Mytilus sp. were extensively reviewed by Widdows & Donkin, (1992) and Livingstone & Pipe (1992). Widdows & Donkin (1992) list tolerances of Mytilus edulis adults and larvae but note that lethal responses give a false impression of high tolerance, since the adults can close their valves and isolate themselves from the environment for days. They suggested that sublethal effects e.g. shell growth and 'scope for growth' (SFG), are more sensitive indicators of the effects of contaminants. Overall, Mytilus edulis is probably relatively tolerant of heavy metal contamination. (For more information see the MarLIN review of Mytilus edulis. Barnacles accumulate heavy metals and store them as insoluble granules (Rainbow, 1987). Pyefinch & Mott (1948) recorded a median lethal concentration of 0.19 mg/l copper and 1.35 mg/l mercury, for Balanus crenatus over 24 hours. Barnacles may tolerate fairly high level of heavy metals in nature, for example they are found in Dulas Bay, Anglesey, where copper reaches concentrations of 24.5 µg/l, due to acid mine waste (Foster et al., 1978). Overall, the biotope is unlikely to be lost although there may be some species mortality so that an intolerance of low is indicated. Recoverability is expected to be very high.
    Hydrocarbon contamination
    Intermediate High Low Decline Low
    Red algae have been found to be sensitive to oil and oil spill dispersants (O'Brien & Dixon 1976; Grundy quoted in Holt et al. 1995). Foliose red algae in the biotope may therefore be subject to bleaching and death. Holt et al. (1995) reported that Saccharina latissima (studied as Laminaria saccharina) had been observed to show no discernible effects from oil spills. Echinoderms seem especially intolerant of the toxic effects of oil, likely because of the large amount of exposed epidermis (Suchanek, 1993). Following the Torrey Canyon incident, large numbers of dead Psammechinus miliaris were found in the vicinity of Sennen, presumably due to exposure to the oil spill and the heavy spraying of hydrocarbon based dispersants in that area (Smith 1968). However, elements of the biotope, especially sponges and solitary ascidians were abundant on jetty piles adjacent to an oily refinery effluent in Milford Haven (Hiscock et al. 1980-83). The shallow nature of this biotope suggests that oil might diffuse in significant quantities to the biota. Overall, because of the equivocal nature of evidence, an intolerance of intermediate is suggested.
    Radionuclide contamination
    No information No information No information Insufficient
    Changes in nutrient levels
    Low Very high Very Low No change Low
    Evidence is equivocal. For Saccharina latissima (studied as Laminaria saccharina), Conolly & Drew (1985) found that plants at the most eutrophic site in a study on the east coast of Scotland where nutrient levels were 25% higher than average exhibited a higher growth rate. However, Read et al. (1983) reported that, after removal of a major sewage outfall in the Firth of Forth, Saccharina latissima (studied as Laminaria saccharina) became abundant where previously it had been absent. Increased nutrients may increase the abundance of ephemeral algae and result in smothering or changing the character of the biotope. For a review of potential impacts on algae, see Fletcher (1996) and for impacts of eutrophication on the Swedish west coast, see Lundälv (1990). In relation to the level of nutrient increase in the benchmark, an intolerance of low has been reported. Any recovery is likely to be very high as species are unlikely to be lost and anyway have planktonic propagules and high growth rates. See also additional information below.
    High High Moderate Rise Moderate
    The biotope is typically found in areas subject to reduced or low salinity. It is most likely that, with an increase in salinity, the biotope will change to another one, possibly A3.3133 or A3.321 and Saccharina latissima might be joined by Laminaria digitata so that the biotope becomes A3.3131. Change to another biotope means that SIR.LsacRS is lost and so intolerance is high. Species richness might increase as low salinity ceases to be an adverse factor. Species that replace those characteristic of SIR.LsacRS may persist for some time and delay recovery of the original biotope but recoverability is still considered likely to be high (see additional information below).
    High High Intermediate Major decline High
    The biotope is described as occurring in low salinity suggesting that it survives in salinities of less than 18 psu (Connor et al., 1997a). However, the richness of the communities described in examples of the sub-biotopes and the presence of species not generally associated with low salinity (many red algae, echinoderms and crustaceans especially) suggests that at most it occurs in reduced salinity conditions. However, Saccharina latissima (studied as Laminaria saccharina) can survive in salinities of 8 psu although growth is retarded below 16 psu (Kain 1979). Delesseria sanguinea is also tolerant of salinities as low as 11 psu in the North Sea Rietema (1993) whilst Halichondria panicea occurs in the reduced salinity of the western Baltic probably as low as 14 psu. Most of the species in the biotope are unlikely to survive further reduction in salinity and an intolerance of high is reported. Recovery is expected to be high (see additional information below).
    Intermediate High Low Decline Very low
    The still water conditions that characterize this biotope suggest that some tolerance of reduced oxygen conditions is likely. Sponges and ascidians produce their own feeding currents and may be important in circulating water. Also, the algae in the biotope produce oxygen. However, any dead material is likely to rot and cause local pockets of de-oxygenation. If the water becomes very still, de-oxygenation might occur and the sort of situation that develops in Abereiddy Quarry (Hiscock & Hoare, 1973) may develop with organisms below a thermocline dying. Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2mg/l. Whilst there is some tolerance of deoxygenation, some of the species in the biotope may die and so an intolerance of intermediate is suggested. However, on return to oxygenated conditions, rapid recovery of surviving organisms is likely and others will settle readily (see additional information below).

    Biological Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence / Confidence
    Low Very high Very Low No change Low
    There is little information on microbial pathogen effects on the characterizing species in this biotope. However, Saccharina latissima may be infected by the microscopic 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). Infection can reduce growth rates of host algae. It is likely that microbial pathogens will have only a minor possible impact on this biotope and an intolerance of low has been reported
    High High Moderate Decline Very low
    The sub-biotope A3.225 which occurs in south-west Britain is colonized by the slipper limpet Crepidula fornicataand by the solitary ascidian Styela clava at a few locations. Crepidula fornicata may be common in some examples of the biotope and is known to smother areas of seabed both by itself and through the pseudofaeces it produces. Styela clava occurs in small numbers and occupies little space. Crepidula could extend its distribution northwards and may have a significant impact. Another non-native species that might colonize this biotope is Sargassum muticum which is generally considered to be a 'gap-filler'. However, it may displace some native species. The biotope does seem to be threatened to some degree by non-native species and an intolerance of high is proposed by with a very low confidence. Recovery would be high (see additional information below).
    High High Moderate Rise Low
    Psammechinus miliaris is important as both a characterizing and a key functional species. Extraction of Psammechinus miliaris is becoming increasingly more likely to be a factor. An alternative source of the continental delicacy of urchin gonads is sought as other urchin species are declining due to over extraction (e.g. Paracentrotus lividus). The aquaculture potential of this smaller species is being investigated (Kelly et al., 1998). Collecting of Echinus esculentus for the curio trade was studied by Nichols (1984). He concluded that the majority of divers collected only large specimens that are seen quickly and often missed individuals covered by seaweed or under rocks, especially if small. As a result, a significant proportion of the population remains. He suggested that exploited populations should not be allowed to fall below 0.2 individuals per square metre. Similar principles should apply to Psammechinus miliaris. Recruitment to the remaining population will occur by larval settlement from the plankton. Although Psammechinus miliaris is quite long lived (up to 12 years) (Allain, 1978), it has immature gonads within a year of settling (Jensen, 1969) and probably breeds the following year. Breeding occurs in spring/early summer each year (Mortensen, 1927; Sukarno et al., 1979) and fecundity is likely to be high (MacBride, 1903) and the larvae are long lived (30-40 days) (Jensen, 1969; Massin, 1999b. Dispersal potential is therefore large. For the sub-biotope A3.322, intolerance to extraction is therefore high as it would be likely to change to a different sub-biotope (probably SIR.Lsac.Phy). However, because intense urchin grazing reduces diversity, extraction may allow for increased species richness. Recoverability is likely to be high (see additional information below).
    Not relevant Not relevant Not relevant Not relevant High

    Additional information

    The main characterizing species, Saccharina latissima, rapidly colonizes cleared areas of the substratum and Kain (1975) recorded that Saccharina latissima (studied as Laminaria saccharina) was abundant six months after the substratum was cleared. Foliose algae would probably settle and grow rapidly. For instance, Hawkins & Harkin (1985) observed a rapid increase in the number of red algae, Palmaria palmata, sporelings and the species came to dominate cleared plots within five months. Rhodophyceae have non flagellate, and non-motile spores that stick on contact with the substratum. Norton (1992) noted that algal spore dispersal is probably determined by currents and turbulent deposition. However, red algae produce large numbers of spores that may settle close to the adult especially where currents are reduced by an algal turf or in kelp forests. It is likely that species in this biotope could recolonize an area from adjacent populations within a short period of time in ideal conditions. However, recolonization from distant populations would probably take much longer. The main species covering rock, Lithophyllum incrustans, grows at a rate of only <7mm a year (Irvine & Chamberlain 1994) and will take much longer to colonize than foliose algae. In £SIR.LsacRS.Psa£, Psammechinus miliaris are likely to produce larvae every year and settlement from long-lived plankton would recolonize locations within a year. However, growth rate is unclear although Elmhirst (1922; cited in Gage, 1991) noted that maturity was reached in the first year after settlement. Bull, (1939) estimated longevity to be up to 6 years, Jensen, (1969) up to 8 years and Allain, (1978) up to 10 or 12 years. Ascidiella scabra has a high fecundity and settles readily, probably for an extended period from spring to autumn. Svane (1988) describes it as "an annual ascidian" and demonstrated recruitment onto artificial and scraped natural substrata. Eggs and larvae are free-living for only a few hours and so recolonization would have to be from existing individuals no more than a few km away. It is also likely that Ascidiella scabra larvae are attracted by existing populations and settle near to adults (Svane et al., 1987) . Fast growth means that a dense cover could be established within about 2 months. Most other characterizing species have a planktonic larva and/or are mobile and so can migrate into the affected area. Many or most of the species in the biotope grow rapidly. For instance, Halichondria panicea increases in size by about 5% per week (Barthel, 1988). Some species present in the biotope may not colonize for several years after a catastrophic event but the appearance of the biotope, whether dominated by algae or grazed by urchins will be much as before the impact within two or three years. A recoverability of high is suggested even after a catastrophic event.


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    This review can be cited as:

    Hiscock, K. 2002. Kelp in variable or reduced salinity. 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 21-05-2024]. Available from:

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    Last Updated: 21/11/2002