Biodiversity & Conservation

SS.IGS.Mrl.Lgla

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Lithothamnion glaciale is the key structural species within the biotope and is highly intolerant of substratum loss. The selected important, functional or characterizing species in the biotope such as (Ophiothrix fragilis, Psammechinus miliaris and Hyas araneus) are also likely to be highly intolerant of substratum loss, as will the many abundant but less obvious infaunal species. Lithothamnion glaciale has a very low recoverability from substratum loss. Without this species the biotope would not exist. The species selected as representative of biotope intolerance (e.g. Ophiothrix fragilis, Psammechinus miliaris) are likely to return within a few years given the presence of a suitable substratum. Loss of the substratum as well as the structural, functional and characterizing species in the biotope will result in a major decline in species richness for the biotope. Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. J. Hall-Spencer (pers. comm.) has observed that colonization of new locations by maerl can be mediated by a 'rafting' process where maerl thalli are bound up with other sessile organisms that are displaced and carried by currents (e.g. Saccharina latissima (studied as Laminaria saccharina) holdfasts after storms). Growth and development of unattached maerl thalli from crustose individuals is very slow and likely to take a long time.
Smothering
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Lithothamnion glaciale is the key structural species within the biotope and is highly intolerant of smothering. The selected important, functional or characterizing species in the biotope such as Ophiothrix fragilis, Psammechinus miliaris and Hyas araneus are also likely to be highly intolerant of smothering as will the many, abundant but less obvious infaunal species. Lithothamnion glaciale has a very low recoverability from smothering. Without this species the biotope would cease to exist and so intolerance is set to high. Loss of the substratum as well as the structural, functional and characterizing species in the biotope will result in a major decline in species richness for the biotope.
Increase in suspended sediment
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Lithothamnion glaciale is the key structural species within the biotope and is likely to be intolerant of increases in suspended sediment due to restriction of photosynthesis (Birkett et al., 1998) - see section on turbidity below. Recoverability for this key structural species is recorded as very low. Many of the species in this biotope live between the maerl nodules. Some of these species may benefit by increases in siltation (e.g. suspension feeders, species that use particles in construction (e.g. Lanice conchilega) whilst others will decline due to subsequent changes in granulometry of the habitat. Decreases in siltation may have the reverse effects.
Decrease in suspended sediment
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Desiccation
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Maerl species such as Lithothamnion glaciale are highly intolerant of desiccation (Birkett et al., 1998). As the key structural species within the biotope, loss of this species will mean the biotope ceases to exist. Recoverability of Lithothamnion glaciale from total loss is very low. Many of the species associated with maerl biotopes (always subtidal) are likely to be intolerant of desiccation. Although some of the species selected as being representative of the biotope are also found in the intertidal, they are typically found sheltering under boulders or weed (e.g. Psammechinus miliaris and Ophiothrix fragilis). Exposure to desiccating influences for an hour is likely to cause many species to die. See additional information for recovery.
Increase in emergence regime
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Maerl species such as Lithothamnion glaciale are highly intolerant of desiccation, a consequence of emersion (Birkett et al., 1998). As the key structural species within the biotope, loss of this species will mean the biotope ceases to exist. Recoverability of Lithothamnion glaciale from total loss is very low. Although some species associated with this biotope are also found in the intertidal, live maerl beds are entirely sub-tidal (with one exception, Birkett et al., (1998)). Species in sub-tidal biotopes will tend to be intolerant of emergence. See additional information below for recovery.
Decrease in emergence regime
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Increase in water flow rate
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Lithothamnion glaciale is the key structural species within the biotope and is intermediately intolerant of decreases in water flow rate. Lithothamnion glaciale has a low recoverability from changes in water flow rate. Many of the species in this biotope live within the structure provided by the maerl nodules, where there is protection from changes in water flow rate. Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. Vegetative propagation by growth and division of unattached maerl thalli is very slow and likely to take a considerable time.
Decrease in water flow rate
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Increase in temperature
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Lithothamnion glacialeis a northern species so may be intolerant of increases in temperature. Adey (1970) found optimal growth rates at between 10-12 C. Development of reproductive conceptacles in Lithothamnion glaciale requires winter temperatures of between 1-5 °C (Adey, 1970). Long term chronic increases in temperature may prevent sexual or asexual reproduction from occurring. Other species selected as being representative of the intolerance of the biotope (Psammechinus miliaris and Ophiothrix fragilis) also have intermediate intolerance to short term acute changes in temperature. Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. Vegetative propagation by growth and division of unattached maerl thalli is very slow and likely to take a considerable time.
Decrease in temperature
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Increase in turbidity
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Depth distribution of photosynthesising coralline algae is strongly affected by available light. The low clarity of coastal waters of the British Isles restricts the distribution of maerl beds to shallow waters - typically less than 10 m but occasionally down to around 30 m. An increase in turbidity would reduce photosynthesis but is unlikely to result in mortality, the maerl regaining photosynthetic vigour immediately after water clarity returned to previous conditions. Decreases in turbidity would facilitate photosynthesis and benefit the biotope. Faunal species tend to be less directly intolerant of changes in water clarity although reductions in light penetration may restrict the amount of food (phytoplankton) available to suspension feeders such as Ophiothrix fragilis. See additional information for recovery.
Decrease in turbidity
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Increase in wave exposure
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Maerl beds with loose-lying nodules are restricted to less wave exposed areas (e.g. sea lochs for Lithothamnion glaciale beds). Some wave action may be beneficial in creating the 'streaming water' flow that this biotope requires. Strong wave action can break up the nodules into smaller pieces and scatter them from the maerl bed. Wave action during storms can be very important in determining the loss rates of thalli from maerl beds (Birkett et al., 1998). Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. Vegetative propagation by growth and division of unattached maerl thalli is very slow and likely to take a considerable time.
Decrease in wave exposure
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Noise
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Noise vibrations may possibly elicit escape responses in Ophiothrix fragilis (mechanical disturbance causes predator avoidance behaviour) but this will not have any effect on the biotope as a whole.
Visual Presence
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None of the selected key or important species in this biotope are intolerant of visual disturbance. It is also unlikely that any of the infaunal and epifaunal species associated with this biotope are sensitive to visual disturbance.
Abrasion & physical disturbance
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Abrasion and physical disturbance may break up loose-lying maerl nodules or highly branching crustose plants into smaller pieces resulting in easier displacement by wave action. Abrasion may also disrupt the physical integrity of accreted maerl beds. Boat moorings and dragging anchor chains have been noted to damage the surface of maerl beds, as has demersal fishing gear (BIOMAERL team, 1999). Hall-Spencer & Moore (2000a, c) reported that a single pass of a scallop dredge could bury and kill 70% of the living maerl (usually found at the surface), redistributed coarse sediment and affected the associated community. Dredge tracks remained visible for 2.5 years. Hall-Spencer & Moore (2000a, c) suggested that repeated anchorage could create impacts similar to towed fishing gear. Overall, Hall-Spencer & Moore (2000a, c) concluded that maerl beds were particularly vulnerable to damage from scallop dredging activities.

Other species in the biotope, including those selected as being representative of the sensitivity of the biotope also have intermediate intolerance to abrasion (e.g. the brittle test of Psammechinus miliaris and the fragile arms of Ophiothrix fragilis are easily damaged by impact). Many of the species in the biotope live buried within the maerl bed and will receive some protection from abrasion. However, megafauna on or in the top 10 cm of maerl were either removed or damaged and left on the dredge tracks, susceptible to subsequent predation (Hall-Spencer & Moore, 200a). For example; crabs, Ensis species, the bivalve Laevicardium crassum, and sea urchins. Deep burrowing species such as the sea anemone Cerianthus lloydii and the crustacean Upogebia deltaura were protected by depth, although torn tubes of Cerianthus lloydii were present in the scallop dredge tracks (Hall-Spencer & Moore, 2000a). Hall-Spencer & Moore, (2000a) reported that sessile epifauna such as Modiolus modiolus or Limaria hians, sponges and the anemone Metridium senile where present, were significantly reduced in abundance in dredged areas for 4 years post-dredging.

Overall, an intolerance of high has been recorded. See additional information for recovery.

Displacement
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Lithothamnion glaciale nodules in maerl beds are unattached and generally loose-lying (although may be interlinked and bound together by other species). Many of the species in the biotope have an active, infaunal burying habit. Displacement of the key or important species in the biotope is not likely to cause many of the other species living within the biotope to die.

Chemical Factors

Synthetic compound contamination
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There is insufficient information available to assess the intolerance of Lithothamnion glaciale to synthetic chemical contamination. However, red algae are known to be sensitive to contamination (for instance Hoare & Hiscock, 1974). Other species in the biotope such as Psammechinus miliaris and Ophiothrix fragilis are likely to highly intolerant of this factor. Contamination by synthetic chemicals will probably reduce the species diversity within the maerl beds resulting in at least intermediate intolerance. Many of the infaunal species in maerl beds are molluscs which tend to have high intolerance to chemical contamination. Overall, an intolerance of high is recorded by with very low confidence.
Heavy metal contamination
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There is insufficient information available to assess the intolerance of Lithothamnion glaciale to synthetic chemical contamination. Some species in the biotope such as Psammechinus miliaris are recorded as highly intolerant of heavy metal contamination.
Hydrocarbon contamination
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There is insufficient information available to assess the intolerance of Lithothamnion glaciale to hydrocarbon contamination. However, red algae are known to be sensitive to oil spills. For example, Crump et al. (1999) describe "dramatic and extensive bleaching" of 'Lithothamnia' following the Sea Empress oil spill. Other species in the biotope such as Psammechinus miliaris and Ophiothrix fragilis are likely to highly intolerant of this factor. Many of the infaunal species in maerl beds are molluscs which tend to have high intolerance to hydrocarbons. For recovery see additional information below.
Radionuclide contamination
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Insufficient information
Changes in nutrient levels
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Cabioch (1969) has suggested that maerl is tolerant to increases in nutrients. However, in shallower waters, growth of ephemeral algae may be increased, smothering the maerl beds and restricting photosynthesis. King & Schramm, (1982) report that ionic calcium concentration is the main factor affecting growth of maerl in culture experiments rather than salinity per se (although this has not been shown in the field). Reductions in calcium concentration may theoretically limit growth of maerl nodules. Reductions in nutrient availability may also limit growth of phytoplankton or algal species which are fed on by Ophiothrix fragilis and Psammechinus miliaris respectively.
Increase in salinity
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Unlike Lithothamnion corallioides and Phymatolithon calcareum, Lithothamnion glaciale is tolerant to some variation in salinity. The biotope is found at the head of sea lochs on the west coast of Scotland where riverine in-put and precipitation run-off cause variable salinity. Growth rates are decreased by reduced salinity (Adey, 1970).
Decrease in salinity
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Changes in oxygenation
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Anoxia will kill live maerl (Jason Hall-Spencer, pers. comm.) but reduced oxygen levels for a week are unlikely to kill the algal nodules. Respiration, growth and reproduction may be affected by hypoxia. The loose structure of the maerl bed allows oxygenation to occur to considerable depth and this fact is exploited by many burrowing species. Changes in oxygenation are likely to cause a major decline in species richness.

Biological Factors

Introduction of microbial pathogens/parasites
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No diseases of European maerl species are known. However, the bacterial pathogen 'coralline lethal orange disease' from the Pacific is highly virulent (Littler & Littler, 1985). If this species was introduced to the region then maerl beds could potentially be significantly affected.
Introduction of non-native species
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The introduced species Crepidula fornicata has radically altered the ecology of maerl beds in the Rade de Brest, France through increasing siltation and provision of substrata (J. Hall-Spencer pers. comm.). If this alien species was to extend its distribution to overlap with Lithothamnion glaciale maerl beds, similar alterations may occur.
Extraction
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Maerl beds, of which Lithothamnion glaciale can form an important component, particularly in Scotland, may be subject to exploitation (Flora Celtica Database, 2000). Harvesting of maerl beds is one of the greatest threats. In England only dead maerl is extracted. However, even this can have detrimental effects, resuspending sediments that resettle and cover the algae reducing photosynthesis. In live beds the living nodules are typically on the surface so these are the first to be removed. Lithothamnion glaciale can also be adversely affected indirectly through the removal of other species. Extraction of other organisms such as scallops using dredges can cause great damage through physical disruption, crushing, burial and the loss of stabilizing algae (Hall-Spencer & Moore, 2000(a)). Other large burrowing bivalves such as Ensis sp. and Venerupis sp. are harvested using suction dredging which causes structural damage and resuspends sediment that resettles, covering the algae and reducing photosynthesis (Hall-Spencer & Moore, 2000(a)). These effects are best addressed using the relevant physical factors (see Physical Disturbance) but overall, intolerance has been assessed as high. Recovery is expected to be very low (see additional information).

Additional information icon Additional information

Recoverability
Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. J. Hall-Spencer (pers. comm.) has observed that colonization of new locations by maerl can be mediated by a 'rafting' process where maerl thalli are bound up with other sessile organisms that are displaced and carried by currents (e.g. Saccharina latissima (studied as Laminaria saccharina) holdfasts after storms). Growth and development of unattached maerl thalli from crustose individuals is very slow and likely to take in the order of several decades for a bed to form.

Most of the intolerance assessments are based mainly on Lithothamnion glaciale as this is the key structural species in the biotope. Other species selected to represent the biotope intolerance are not necessarily always present and do not represent particular taxa or groups that feature in the biotope.

This review can be cited as follows:

Jackson, A. 2006. Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 02/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=7&code=1997>