Biodiversity & Conservation

IR.EIR.KFaR.Ala

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The entire community will be removed with the substratum and macroalgae cannot re-attach. However, Alaria esculenta can recolonize within a year and grows rapidly. Although Corallina officinalis can colonize new substrata within a week it grows slowly. Hawkins & Harkin (1985) noted that, in one canopy clearance experiment, Alaria esculenta attained 80 percent cover within 8 months, although dormant gametophytes of Alaria esculenta may have been present. Therefore it is likely that the Alaria esculenta canopy would return within a year, however the encrusting and articulated coralline turf, and associated community would take less than 5 years to recover.
Smothering
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Smothering of the adult sporophyte of Alaria esculenta by up to 5 cm of sediment for 1 month is unlikely to cause damage, especially under wave exposed conditions where it would be rapidly removed. Juvenile sporophytes, germlings, gametophytes and spores may be more intolerant of. However, Laminarian gametophytes can survive in the dark for several months (Kain 1979). Coralline algae, especially encrusting forms, are thought to be resistant of sediment scour and Corallina spp. accumulate sediment (Littler & Kauker 1984; Moore & Seed 1985). Seapy & Littler (1982) noted a substantial decline in Corallina spp.. and macroinvertebrate (e.g. barnacles) cover as the result of smothering. However, loss of barnacles and Pelvetia spp. allowed Corallina spp. to expand further up shore in the following 6 months. Fronds can regrow from resistant crustose bases (Littler & Kauker 1984). It would appear macroinvertebrates such as barnacles, sponges, and hydroids would be worst affected by smothering and may take longer to recover than macrophytes, especially where available space is colonized by Corallina officinalis. Growth of macroalgae would be inhibited, but they would recover relatively quickly. However, smothering would inhibit recolonization and settlement while present, the severity of its effects depending on season.
Increase in suspended sediment
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Alaria esculenta is not found in areas of siltation and sediment scour (Birkett et al. 1998b). Increased siltation and sediment scour inhibits photosynthesis and algal growth, interfere with spore or larval recruitment and smother germlings and gametophytes (see above) (Fletcher 1996). Sediments are likely to inhibit gametophyte development and fewer new plants are found amongst older plants in the vicinity of sewage outfalls (Fletcher 1996). Seapy & Littler (1982) recorded a decline in macroinvertebrate and coralline turf cover as a result of sedimentation in Santa Cruz, California. Adult Alaria esculenta and the crustose bases of Corallina officinalis are likely to survive in the short term however if increased siltation continues and older plants are removed the biotope may be lost. Once siltation returns to its pre-effect level the biotope is likely to recover its canopy within a year and the rest of the community in no more than five years. Increased siltation will also increase turbidity (see below). Increased sediment my benefit Mytilus edulis and its abundance may increase in EIR.Ala.Myt although large individuals are likely to be removed by wave action.
Decrease in suspended sediment
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Desiccation
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Alaria esculenta may extend into the lower eulittoral in extremely wave exposed conditions. However, these marginal populations have reduced age range in comparison to subtidal populations due to loss of plants due to desiccation at low tide. An increase in desiccation is likely to remove Alaria esculenta plants. The resultant loss of canopy would expose Corallina officinalis turf and macrofaunal crust to desiccation and/or damage by high light intensity (bleaching). Hawkins & Harkin (1985) noted that encrusting corallines and Corallina officinalis often die when their protective algal canopy is removed. Severe damage was noted in Corallina officinalis as a result of unusually hot and sunny weather in the UK summer 1983 (Hawkins & Hartnoll 1985). Laminaria digitata is likely to be intolerant of desiccation and destruction of its meristem (base of blade) exposed at low tide will kill the plant. Therefore, both EIR.Ala.Myt and EIR.Ala.Ldig are likely to be highly intolerant of increases in desiccation and the upper limit of the population would be depressed. Desiccation is unlikely to be relevant in EIR.Ala.AnSC due to its depth.
Increase in emergence regime
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An increase in emergence will result in an increased risk of desiccation (see above). Decreases in emergence regime are likely to allow the upper limit of the population to increase. However, the lower limit of the Alaria esculenta forest will come under increased competition from the erect kelp, Laminaria hyperborea while its upper limit will be subject to competition from Laminaria digitata.
Decrease in emergence regime
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Increase in water flow rate
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Alaria esculenta is associated with strong wave action and moderately strong to weak water flow rates. It is likely to be intolerant of any reduction in wave exposure, which will subject it to competition from other laminarians. Increased water flow may remove fronds of Corallina officinalis however calcification is thought to be an adaptation to mechanical damage (Littler & Kauker 1984). Within the biotope, increases of water flow rate may favour EIR.Ala.Myt over EIR.Ala.Ldig which prefers weak tidal streams (Connor et al. 1997b). Similarly, reduced water flow may enable Laminaria digitata to invade EIR.Ala.Myt to form EIR.Ala.Ldig.
Decrease in water flow rate
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Increase in temperature
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Kelp are considered stenothermal and unlikely to tolerate 1-2 deg C above or below their normal temperature tolerances (Birkett et al. 1998b). Given the distribution of Alaria esculenta is the North Atlantic it is probably tolerant of low temperatures. However, Sundene (1962) noted that its distribution lies within the 16 deg C isotherm for August mean surface temperature and that growth is inhibited above 16 deg C. Corallina officinalis may tolerate between minus 4 to 28 °C (Lüning, 1990). Abrupt temperature changes (10 deg C in California, Seapy & Littler 1984; 4.8 to 8.5 deg C, Hawkins & Hartnoll 1985) result in dramatic declines. However in both cases recovery was rapid, suggesting that the crustose bases survived. Therefore, both species are probably intolerant of acute short term temperature change of 5 deg C for a month. Long term change of two deg C may reduce the southern limit of the population of Alaria esculenta.
Decrease in temperature
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Increase in turbidity
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Increased turbidity is likely to reduce the depth to which Alaria esculenta can grow. An increase of one level in the turbidity scale is unlikely to affect the population since its lower limit, in less wave exposed deeper areas, is generally determined by competition from other Laminarians rather than light penetration. An increase in two levels in the short term (1 month) will reduce photosynthesis and growth, but is unlikely to cause loss of adults in this time frame. Corallina officinalis is shade and silt tolerant and unlikely to be affected by increased turbidity. Alaria esculenta occurs at considerable depths in EIR.Ala.AnSC on Rockall and increased turbidity is likely to reduce its depth range at this site.
Decrease in turbidity
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Increase in wave exposure
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Alaria esculenta is associated with strong wave action and moderately strong to weak water flow rates. It is likely to be intolerant of any reduction in wave exposure, which will subject it to more intense competition from other Laminarians. Increased wave exposure may remove fronds of Corallina officinalis however calcification is thought to an adaptation to mechanical damage (Little & Kauker 1984) and the fronds grow as a compact (short) turf in wave exposed conditions. Within the biotope, increases of wave exposure may favour EIR.Ala.Myt over EIR.Ala.Ldig which prefers less exposure (Connor et al. 1997b). Equally reduced wave exposure may enable Laminaria digitata to invade EIR.Ala.Myt to form EIR.Ala.Ldig. Although increasing wave exposure may result in a minor decline in species richness, a decrease in wave exposure favouring EIR.Ala.Ldig may increase species richness.
Decrease in wave exposure
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Noise
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Macroalgae have no known sound or vibration receptors. The response of macroinvertebrates are not known.
Visual Presence
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Macrophytes have no known visual sensors. Most macroinvertebrates have poor or short range visual perception and unlikely to be affects by visual disturbance such as shading.
Abrasion & physical disturbance
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Moderate trampling on articulated coralline algal turf in the New Zealand intertidal (Brown & Taylor 1999; Schiel & Taylor 1999) resulted in reduced turf height, declines in turf densities, and loss of crustose bases in some case probably due to loss of the canopy algae and resultant desiccation. Calcification is thought to an adaptation to grazing and sediment scour (Littler & Kauker 1984). The sublittoral fringe is unlikely to be significantly impacted by trampling due to its position of the lower shore but may be prone to abrasion from moorings or low tide landings. Given its resilience to wave action Alaria esculenta is unlikely to be significantly damaged by abrasion although the under canopy coralline turf may suffer some damage. The coralline turf meiofauna will probably be lost as a result of trampling.
Displacement
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Displaced fronds of Corallina officinalis can reattach and grow if they contact suitable substrata (Thomas Wiedemann pers. comm.). The crustose bases are difficult to remove from the substratum and appreciable cover can return in 3-12 months (Seapy & Littler 1982; Littler & Kauker 1984). Removal of the Alaria esculenta canopy would result in increased risk of desiccation (see above) for the coralline algae, understory foliose red algae and macroinvertebrates. Although Alaria esculenta may recolonize or grow from dormant gametophytes and small juveniles and recover quickly the understory community is likely to take longer to recover.

Chemical Factors

Synthetic compound contamination
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Cole et al. 1999 suggest that macrophytes are generally intolerant of herbicides such as atrazine, simazine, diuron and linuron e.g. atrazine was lethal to Laminaria hyperborea sporophytes at 1mg/l and suppressed growth at 0.01mg/l (Hopkin & Kain 1978). Smith (1968) noted that Corallina officinalis was killed in areas of heavy spraying after the Torrey Canyon oil spill and affected at 6 m depth in areas of high wave action. High water specimens were more affected than low water specimens, presumably because they are emerged for longer and had more contact with oil and dispersants. However exposure to pine oil disinfectant had little effect on Corallina officinalis productivity. Gastropods are known to be highly sensitive to endocrine disrupters such as TBT. Crustaceans (e.g. amphipods, isopods, ostracods, copepods and barnacles) are also susceptible to endocrine disruption by synthetic chemicals. It is likely therefore that some members of the population, especially grazing invertebrates and meiofauna will be intolerant of synthetic chemical contamination and the biotope will be at least of intermediate intolerance.
Heavy metal contamination
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Mercury (organic > inorganic) is highly toxic to macrophytes (Bryan 1984; Cole et al. 1999). Mercury and copper we lethal at 0.05mg/l and 0.1mg/l respectively and toxic at 0.05mg/l and 0.01mg/l respectively in Laminaria hyperborea. Zinc and Cadmium were lethal at 5mg/l and 10mg/l respectively. The presence of alginates in kelp tissue is thought to sequester heavy metals in a biologically unavailable form. It is likely that Laminarians such as Alaria esculenta are relatively tolerant of heavy metals except at high concentrations at high levels Little information on heavy metal tolerance of corallines was found.
Hydrocarbon contamination
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The mucilaginous coating on kelp fronds is thought to protect them from coatings of oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. Reduction in photosynthesis is dependant on the type of oil, its concentration, length of exposure, oil-water mixture and irradiance in experimental trials (Lobban & Harrison 1994). Subtidal populations are only exposed to oil emulsions or oil adsorbed particles. Kelps are relatively insensitive to dispersants (Birkett et al. 1998b). E.g. Laminaria digitata exposed to diesel oil at 0.130mg/l reduced growth by 50 percent in a 2 year experiment. No growth inhibition was noted at 0.03 mg/l and the plants recovered completely in oil free conditions. Corallina officinalis, however, exhibited dramatic bleaching after the Sea Empress oil spill and died after the Torrey Canyon spill (Crump et al. 1999; Smith 1968). Encrusting corallines and Corallina officinalis recovered from the Sea Empress spill quickly, bleaching only affecting the fronds or surface of crustose forms. Grazing gastropods, e.g. limpets are highly intolerant of oil spillage and if not killed are narcotinized and washed offshore and/or consumed by predators. The lower littoral populations are likely to be most vulnerable to oil spill and sublittoral fringe would be particularly affected at low tide. Although Alaria esculenta may not be affected severely, the articulated coralline turf may be lost but recover quickly although the red algae may be intolerant. Grazers such as limpets, barnacles and meiofaunal crustaceans may also be lost from the community. EIR.Ala.Ldig may be the most intolerant and loose understory red and coralline algae together with some epifauna, although the kelp species will probably survive.
Radionuclide contamination
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Insufficient information
Changes in nutrient levels
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Increased nutrients are associated with eutrophication, increased siltation and turbidity (see above) (Fletcher 1996). Eutrophication is associated with loss of perennial algae, reduction of the depth range of algae (due to turbidity), replacement by mussels or opportunistic algae (Fletcher 1996). Alaria esculenta is probably not light limited in this biotope. Increased nutrients may favour Mytilus edulis in EIR.Ala.Myt which may increase in cover and abundance. Increased abundance of Mytilus edulis may reduce species richness. However Corallina officinalis is also tolerant of polluted waters (Kindig & Littler, 1980). Alaria esculenta occurs at considerable depths in EIR.Ala.AnSC on Rockall and increased turbidity is likely to reduce its depth range at this site. However, an intermediate intolerance has been recorded to represent to indirect effects of turbidity and siltation.
Increase in salinity
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Kelps are stenohaline (Birkett et al. 1998b). Alaria esculenta sporophytes grew poorly at salinities below 25 psu (Sundene 1962). Corallina officinalis is restricted to full salinity waters in the Baltic and grows maximally between 33 and 38 psu in Texan lagoons (Kinne 1971). This biotope is likely to be exposed to short term freshwater runoff at low tide but is likely to be intolerant of long term changes in salinity, which are likely to depress its upper limit and reduce the extent of the population.
Decrease in salinity
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Changes in oxygenation
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Macroalgae may be relatively tolerant of deoxygenation since they can produce their own oxygen. They may be more intolerant of night time deoxygenation when they only respire. Corallines may be more tolerant due to their low respiration rates (Littler & Kauker 1984). However, grazers and mobile meiofauna in the coralline turf are probably intolerant and may be lost of move out of the affected area.

Biological Factors

Introduction of microbial pathogens/parasites
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Streblonema sp. is associated with spot disease in kelps and has been found growing on Alaria esculenta (Lein et al. 1991) but no incidence of disease or information was found. Corallina officinalis may host several epiphytes of which Titanoderma corallinae is thought to cause tissue damage. However, no evidence of losses of this biotope due to disease were found.
Introduction of non-native species
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The Japanese kelp Undaria pinnatifida (wakame) has recently spread to south coast of England from Brittany where it was introduced for aquaculture. It may spread in ballast water of commercial or recreational boats and shipping. Its potential competition with native kelps need further study (Birkett et al. 1998b), however the wave exposed habitat of EIR.Ala may protect it from potential competition.
Extraction
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Alaria esculenta is eaten fresh or cooked in Greenland, Iceland, Scotland and Ireland. It may be used as a fodder additive and is grazed by sheep in Orkney. In Ireland it is collected and sold as a health food 'Atlantic Wakame'. Corallina officinalis is collected for medical purposes; the fronds are dried and converted to hydroxyapatite and used as bone forming material (Ewers et al. 1987). It is also sold as a powder for use in the cosmetic industry. There is little evidence on the effects of harvesting Alaria esculenta populations. However removal of the algal canopy would expose the understory fauna and flora to increased desiccation (see above). Corallina officinalis turf provides substratum for various epiphytes, and supports a diverse, species rich invertebrate community some of which would be lost if it was collected.

Intolerance to extraction has been assessed as intermediate. Alaria esculenta is an opportunistic species and it probably recovers quickly. Corallina officinalis produces spores over a protracted period and can colonize artificial substratum within one week in the intertidal (Harkin & Lindbergh 1977; Littler & Kauker 1984). The crustose base enables Corallina officinalis to survive loss of fronds and recovery is therefore expected to be high.


This review can be cited as follows:

Tyler-Walters, H. 2000. Alaria esculenta on exposed sublittoral fringe bedrock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 02/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=165&code=1997>