Biodiversity & Conservation

LS.LMU.Sm.SM13

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
(View Benchmark)
Removal of the substratum (by e.g. erosion, tuft cutting, or via borrow pits) will remove the vascular plants, algal mats, infauna and their associated community. Therefore, an intolerance of high has been recorded.
Recovery will depend on recruitment of the plant communities and their invertebrate fauna and a recoverability of moderate has been recorded (see additional information below).
Smothering
(View Benchmark)
Saltmarsh is a sedimentary habitat dependant on accretion and erosion of sediment. Therefore, most communities and associated species are probably adapted to levels of sedimentation and occasional smothering. For example, Puccinellia maritima can tolerate accretion rates of 5cm /year (Packham & Willis, 1997). Swards of tall Puccinellia maritima can be up to 80cm in height and are unlikely to be adversely affected by smothering at the benchmark level. However, in areas influenced by grazing, Puccinellia maritima may form prostrate growth, as little as 1cm high, which would be liable to smothering. However, Gray & Scott (1977) suggested that Puccinellia maritima was extremely tolerant of burial by wind or water borne sediment. Algal mats may not survive smothering for a month. Burrowing infaunal species such as Hediste diversicolor, Arenicola marina, oligochaetes, nematodes and possible burrowing beetles will probably be little affected by smothering a the benchmark level. However, suspension feeding Cerastoderma edule and Mya arenaria may be adversely affected. The Puccinellia sward will probably survive, while some members of the community may be lost. Therefore an intolerance of low has been recorded with a reduction in species richness
The vascular plant sward and most of the community will probably recover in less than 6 months, although some bivalve species may take longer to return (see additional information).
Increase in suspended sediment
(View Benchmark)
Saltmarsh habitats are dependant on a balance of accretion and erosion. For example, Ranwell (1964) reported a regular summer accretion and winter erosion pattern in the Bristol Channel, a pattern typical of most salt marshes (Holt et al., 1995). Under suitable conditions the saltmarsh may accrete, gain in height and increase in seaward extent (prograde) (Packham & Willis, 1997). Increased sedimentation may, therefore, benefit pioneer or low marsh communities (e.g. Puccinellia communities) by providing additional sediment to colonize. However, gains in the lower marsh will be compensated by loss of extent, due to competition with more terrestrial species, in the higher marsh (e.g. Festuca rubra). Packham & Willis (1997) reported that Puccinellia maritima could tolerate accretion rates of 5cm /year, while Gray & Scott (1977) reported accretion rates of 10cm /yr. in the Puccinellia maritima zone. Sedimentation rates, and hence accretion rates vary between sites e.g. 8mm /year at Scolt Head, east England and 78mm /year in the Dovey estuary, Wales, and are determined by the hydrographic regime, and sediment supply from eroding cliff or riverine sources. Most of the marine species associated with the biotope are probably relatively tolerant of increased sedimentation, except Mya arenaria, which is more intolerant. Therefore, an increase in sedimentation rate is likely to change the extent and distribution of Puccinellia maritima communities (depending on the local hydrographic regime) and an intolerance of intermediate has been recorded. A recoverability of high has been recorded (see additional information below).
Decrease in suspended sediment
(View Benchmark)
Saltmarsh habitats are dependant on a balance of accretion and erosion. For example, Ranwell (1964) reported a regular summer accretion and winter erosion pattern in the Bristol Channel, a pattern typical of most salt marshes (Holt et al., 1995). Decreases in sedimentation may result in net erosion of the saltmarsh and a decrease in deposition of organic particulates affecting productivity, especially secondary. Holt et al. (1995) suggested that saltmarsh should be regarded as highly intolerant of changes in sedimentation. Any activity that affects the sedimentary regime is likely to have a marked effect on net erosion and the long term stability of the saltmarsh, especially the lower marsh. Therefore an intolerance of high has been recorded.
Desiccation
(View Benchmark)
Gray & Scott (1977a) reported that the aerial leaves of Puccinellia maritima died back after exposure to prolonged summer drought but rapidly regrew from leaf bases. Gray & Scott (1977a) also suggested that autumn and spring drought were critical for the survival of seedlings, extensive drought being detrimental. Puccinellia maritima is restricted to waterlogged soils by competition with more terrestrial species such as Festuca rubra. However, an increase in desiccation equivalent to an increase in one vertical biological zone on the shore (the benchmark) is likely to increase competition and effectively result in a regression of succession and loss of the upper portion of the Puccinellia maritima sward. Therefore, an intolerance of intermediate has been recorded. A recoverability of high has been recorded (see additional information below).
Increase in emergence regime
(View Benchmark)
The degree and periodicity of inundation by tides controls the amount of water in the sediments, the sediment chemistry, and salinity fluctuations. Therefore, the tidal regime controls the zonation and succession of vascular plant communities and the marine or terrestrial species associated with them. Treherne & Foster (1979) suggested that tidal regime was of overwhelming importance to the insect fauna of saltmarsh communities.

Puccinellia maritima communities occur primarily in saline influenced, waterlogged substrata routinely inundated by the sea. Puccinellia communities may experience between 150 -225 submergences per year on Scolt Head, Norfolk salt marshes and over 350 submergences /year at their lower limit in Morecambe Bay (Gray & Scott, 1977b; Rodwell, 2000). Beeftink (1979) reported that the Volkerak barrage (built in 1969) stopped tidal influence in some areas of saltmarsh resulting in desiccation, desalination (due to rainfall and lowered water table), increased aeration of sediments, increase mineralization of nutrient and loss of the original halophyte community within 1 -7 years and Puccinellia communities within 3 years. The halophytes being replaced by glycophytic communities.

At the benchmark level, the Puccinellia communities are likely to suffer increased desiccation and reduced salinity, resulting in their replacement by high marsh communities such as Festuca rubra and Agrostis stolonifera communities. The insect fauna will probably benefit whereas the marine fauna will restricted to the lower levels of the marsh. However, a reduction in tidal regime will probably allow the Puccinellia communities to colonize adjacent mudflat, allowing recovery within about five years (see Cefni marsh example in Packham & Willis, 1997). Therefore, the extent of Puccinellia maritima communities will probably be reduced temporarily and an intolerance of intermediate has been recorded with a recoverability of high.
Decrease in emergence regime
(View Benchmark)
The degree and periodicity of inundation by tides controls the amount of water in the sediments, the sediment chemistry, and salinity fluctuations. Therefore, the tidal regime controls the zonation and succession of vascular plant communities and the marine or terrestrial species associated with them (see above)
Beeftink (1979) reported that increases in tidal height (decreased emergence) resulted in changes in the plant communities, equivalent to regression succession towards lower marsh communities. Puccinellia dominated communities were able to tolerate an increase in tidal height of about 10cm, whereas Puccinellia - Armeria communities only tolerated about a 3-5 cm increase. Increases >30cm resulted in replacement of the Puccinellia community with Salicornia dominated communities in the Netherlands Scheldt. Plant communities stabilized within about 2-4 years. Similarly, Dijkema et al. (1990) concluded that accretion in salt marsh may kept up with the predicted sea level rise due to climate change in the Wadden Sea but that pioneer communities were more intolerant due to the increased erosion.

The marine fauna, infauna, gastropods and intertidal fish would probably benefit from an decrease in the emergence regime, whereas the insect fauna would probably retreat further up the shore. High saltmarsh communities will probably retreat further inland where possible but if prevented by sea defences these communities will be lost. Overall, the Puccinellia communities may experience a temporary reduction in extent and species richness while they adapt to the new regime, at the benchmark level. Therefore, an intolerance of intermediate has been recorded. Once the tidal regime returned to prior level community will recover rapidly, probably within five years.
Increase in water flow rate
(View Benchmark)
Salt marshes develop in sheltered environments where sediments accumulate. Increased water flow rate will change the accretion and erosion rates in the saltmarsh, especially at low water exposed to immersion for longer periods. Increases in water flow rate may erode areas at the face of the raised salt marsh, resulting in a 'cliff' and may undermine the edges of creeks. Most of the invertebrate marine infauna may be adversely affected by increased water flow due to loss or changes in the sediment. Therefore, increases in water flow at the benchmark level are likely to remove lower marsh communities such as Puccinellia dominated communities, their substratum and associated species and an intolerance of high has been recorded. Recovery will depend on recruitment of the plant communities and their invertebrate fauna and a recoverability of moderate has been recorded (see additional information below).
Decrease in water flow rate
(View Benchmark)
Salt marshes develop in sheltered environments and any further decrease in water flow is likely to increase sedimentation rates, especially in the lower marsh, but otherwise have minor effects. Decreased water flow may reduce the distribution and hence recruitment of saltmarsh species, e.g. of plants by seed and vegetative fragments and by insects due to rafting.
Increase in temperature
(View Benchmark)
Vascular plants communities are exposed to greater fluctuations in day and night temperatures than their marine counterparts, and are probably tolerant. In addition, flood tides result in temperatures shocks, e.g. in winter the frozen marsh surface may be exposed to tidal waters 10 °C warmer. Although temperature shock probably has physiological effects, they have not been studied (Adam, 1993). Puccinellia maritima was thought to be limited to habitats below 70 deg N, Norway in the eastern Atlantic (62 deg N in southern Greenland, western Atlantic) by temperature and day-length and rarely flowers in the northern limits of its range (Gray & Scott, 1977a). However, Puccinellia maritima extends south to Spain and is, therefore, probably tolerant of summer temperatures in Britain and Ireland.
Increased temperatures may affect reproduction in the polychaetes Hediste diversicolor and Arenicola marina, whereas Hydrobia ulvae can survive exposure to the air for several days. However, the marine infauna of the lower marsh are probably at the upper limit of their range and their abundance may decrease, or they may be lost as a result of an increase in temperature. Therefore, although the vascular plant communities are relatively tolerant of temperature increases and temperature shock and of low intolerance, several marine species may be lost, reducing species richness.
Decrease in temperature
(View Benchmark)
Vascular plants communities are exposed to greater fluctuations in day and night temperatures than their marine counterparts, and are probably tolerant. In addition, flood tides result in temperatures shocks, e.g. in winter the frozen marsh surface may be exposed to tidal waters 10 °C warmer. Although temperature shock probably has physiological effects, they have not been studied (Adam, 1993).
Puccinellia maritima extends to 70 deg N and is probably tolerant of winter temperatures in the UK. Gray & Scott (1977a) reported that established Puccinellia maritima plants were rarely, if ever, killed by even exceptional frosts in Britain. However, several marine infaunal species are known to be susceptible to severe winters, e.g. Cerastoderma edule, Mya arenaria, Arenicola marina and Gobius spp. Decrease in temperature at the benchmark level are likely to reduce their extent or abundance. Terrestrial fauna may be less intolerant of temperature extremes or over-winter as dormant stages. Overall, the Puccinellia dominated communities are likely to survive although their species richness may be slightly decreased.
Increase in turbidity
(View Benchmark)
The vascular plants photosynthesise at low tide and are probably not completely covered at high tides, so that the turbidity of the water is probably not relevant. Macroalgal mats and microphytobenthos are probably covered by some tides, and photosynthesis reduced, but will probably compensate when exposed to air and low tides.
Decrease in turbidity
(View Benchmark)
The vascular plants photosynthesise at low tide and are probably not completely covered at high tides, so that the turbidity of the water is probably not relevant. Macroalgal mats and microphytobenthos are probably covered by some tides, and photosynthesis reduced, but will probably compensate when exposed to air and low tides.
Increase in wave exposure
(View Benchmark)
Change in wave exposure and hence the hydrographic regime will change the accretion and erosion rates in the salt marsh, especially on the low marsh exposed to immersion for longer periods. Increases in wave action may erode areas at the face of the raised salt marsh, resulting in a 'cliff' and may undermine the edges of creeks. Low marsh pioneer communities are likely to be the most intolerant. Holt et al. (1997) suggested that saltmarsh were relatively tolerant of wave action, presumably since their low profile attenuates the wave energy and the sediment is bound by plant material. However, an increase in wave exposure above 'sheltered' will probably result in net erosion and loss of pioneer communities, including Puccinellia maritima, and their associated fauna. Therefore, an intolerance of intermediate has been recorded. A recoverability of high has been recorded (see additional information below).
Decrease in wave exposure
(View Benchmark)
Saltmarsh habitats occur in areas of net accretion, sheltered from wave action. A further decrease in wave action is unlikely to has a significant effect.
Noise
(View Benchmark)
Wildfowl and seabirds are important grazers within this biotope. Disturbance by noise and visual presence of human activities to birds population will be considered together. Disturbance is species dependant, some species habituating to noise and visual disturbance while other become more nervous. For example, brent geese, redshank, bar-tailed godwit and curlew are more 'nervous' than oyster catcher, turnstone and dunlin. Turnstones will often tolerate one person within 5-10m. However, one person on a tidal flat can cause birds to stop feeding or fly off affecting c. 5 ha for gulls, c.13ha for dunlin, and up to 50 ha for curlew (Smit & Visser, 1993). Goss-Custard & Verboven (1993) report that 20 evenly spaced people could prevent curlew feeding over 1000 ha of estuary. Industrial and urban development may exclude shy species from adjacent tidal flats. Disturbance causes birds to fly away, increasing energy demand and feeding on the flats later or cause them to move to alternative sites. Least human disturbance is likely in winter, however during breeding period for some species and moulting periods of northerly breeding species in late summer and early autumn most recreational activity takes place. Removal of predators may allow some species to dominate, enable recruitment of others and affect the community structure. However, visual or noise disturbance is unlikely to affect epibenthic or infaunal species, therefore although wildfowl may be regarded as highly intolerant, and overall assessment of intermediate is given. Recovery of birds population may be immediate for some species, while shy species may find more isolated sites.
Visual Presence
(View Benchmark)
Wildfowl and birds are important grazers within this biotope. Disturbance by noise and visual presence of human activities to birds population have been considered together (see above).
Abrasion & physical disturbance
(View Benchmark)
Abrasion in saltmarsh biotopes is most likely to result from trampling and vehicle use. In coastal plant communities trampling may favour plants with high growth rates, basal meristems, and low growth forms. Low levels of trampling encourage growth and species richness but these fall as trampling increases (Packham & Willis 1997). Puccinellia maritima was reported to colonize slumps sides of creeks, ruts lefts by vehicles or animals, areas of turf cutting, ditches and even reclaimed land (Gray & Scott, 1967, 1977a; Rodwell, 2000). Most of the marine infaunal species are likely to be adversely affected by abrasion that penetrates the sediment, and a proportion of the population will probably be lost. Mobile species such as fish are unlikely to be directly affected. Burrowing insects may also be adversely affected, and sucking insects such as aphids may be displaced or crushed. However, aphids in particular reproduce rapidly (most species are parthenogenic) and will recover quickly. Insects capable of flight will avoid the impact, while small birds are likely to benefit from the flushing of insects from the saltmarsh sward. Overall, an intolerance of intermediate has been recorded.
However, it should be noted that, disturbance by grazing birds releases vegetative fragments of the plant, which are important for dispersal and the establishment of pioneer communities while Puccinellia maritima plants may be damaged by physical disturbance, disturbance may allow the Puccinellia communities to colonize the high marsh and result in a more heterogeneous and diverse saltmarsh. Therefore, Puccinellia communities and their associated species are likely to recover within about 5 year or less (see additional information).
Displacement
(View Benchmark)
Removal of the vascular plants from their substratum will probably result in their break-up and loss. However, vegetative fragments of Puccinellia maritima are capable of colonizing available habitat and will probably regrow from plant fragments left in the soil. Most infaunal species can burrow back into sediment, but may suffer significant predation as a result of being removed from the sediment. Hydrobia ulvae can survive on a wide variety of substrata and exhibits mucus rafting and is unlikely to be affected. Mobile fish and insects will be unaffected, and aphid and most plant feeding species will find other plant species or other Puccinellia swards up which to feed, although they may suffer predation as a result of displacement. Overall, an intolerance of high has been recorded to represent the damage to the plant communities. Recovery is likely to take 5-10 years (see additional information below)

Chemical Factors

Synthetic compound contamination
(View Benchmark)
Sheltered, low energy areas in enclosed bays or estuaries act as a sink for sediment and detritus. Low dispersion within these areas also acts as a sink for complex mixtures of pollutants, especially since many become adsorbed onto organic particulates and fine sediments e.g. chlorinated hydrocarbons, DDT (Clark 1997). Therefore the sediments act as a sink for a wide variety of contaminants, many with a long half life in the environment, e.g. PCBs, dieldrins, and pesticides. Some pollutants may bioaccumulate within the food chain, e.g. PCBs and mercury. The sublethal or toxic effects vary with concentration, the bio-availability of the contaminant, and the physiology of the affected organism (Nedwell 1997 cited in Elliot et al. 1998). Recovery requires dilution, biodegradation or removal of the contaminant from the sediments. Contaminants with long half lives may remain in sediments for decades, at least, in sheltered areas with little dispersion. Intertidal sediments in Southampton Water and the Tees had reduced benthic communities due to contamination with phenols, oil effluent, sulphides and nitrogen compounds (Elliot et al. 1998).
Cole et al. (1999) suggested that herbicides (e.g. atrazine) were very toxic to marine macrophytes, which is probably true of most plants. Beeftink (1979) demonstrated that Puccinellia maritima was one of the first species to recolonize areas of marsh denuded by herbicide treatment (see additional information below). Tributyl tin has been shown to cause mortality or impair reproduction in marine bivalves such as Cerastoderma edule, Mya arenaria and Macoma baltica. Arenicola marina and Hediste diversicolor has been found to be intolerant of the pesticide ivermectin, and may be intolerant of pesticides with similar molecular structures. Similarly, Gobius spp. are thought to be intolerant of pesticides. It is highly likely that the resident insect fauna will be intolerant of insecticides by design. Therefore, it the absence other evidence, it is likely that the build up of pesticides, TBT or other synthetics in the marsh may adversely affect primary and secondary productivity and may result in loss of a proportion of the plant and animal communities. An intolerance of intermediate has been recorded. Recovery is likely to take about 6-10 years based on the results of Beeftink (1979) (see additional information below).
Heavy metal contamination
(View Benchmark)
Sediment particulates, organic or inorganic adsorb heavy metals, so that saltmarsh may act as a sink for heavy metals. Saltmarsh plants take up heavy metals through their roots, and is affected by soil chemistry. Uptake is species specific but in general monocotyledons (such as Puccinellia maritima) tend to exclude heavy metals while dicotyledons tend to accumulate. Williams et al. 1994 list levels of heavy metals found in Puccinellia maritima and other saltmarsh plants. Symptoms of acute toxicity in halophytes have not been reported (Adam, 1993; Packham & Willis, 1997). Williams et al. (1994) suggested that the concentrations of heavy metals in most estuaries was not sufficient to cause ill effects to saltmarsh plants.
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. Gobies were reported to be particularly intolerant of Hg (see Pomatoschistus minutus). Bryan (1984) reported sublethal effects of heavy metals in crustaceans at low (ppb) levels. Bryan (1984) suggested that polychaetes are fairly resistant to heavy metals, based on the species studied. Short term toxicity in polychaetes was highest to Hg, Cu and Ag, declined with Al, Cr, Zn and Pb whereas Cd, Ni, Co and Se were the least toxic. However, he suggested that gastropods (were relatively tolerant of heavy metal pollution. Heavy metals have been shown to bioaccumulate in wading birds (Parslow 1973). Overall, Holt et al. (1995) concluded that saltmarsh may be relatively tolerant of heavy metals. Therefore, an intolerance of low has been recorded. However, some marine infaunal species may be lost, or reduced in extent suggesting a loss of species richness.
Hydrocarbon contamination
(View Benchmark)
Salt marshes are very sensitive to oil spills since they trap sediments, adsorb oils, and occur in sheltered environments where the oils persist (Holt et al., 1997) The effect of spills depends on the type of oil and its extent with lighter oils being the most toxic. Heavy oils tend to cause death by smothering (Baker, 1979). In successive experimental oiling Baker (1979) demonstrated the 5 levels of intolerance to Kuwait crude oil, for example:
  • very susceptible, Salicornia sp., Suaeda maritima and seedling of all species were quickly killed by a single spill;
  • intermediate, species that recovered well from up to four spills but rapidly succumbed if further oiled, e.g. Puccinellia maritima, Spartina anglica and Festuca rubra;
  • resistant due to underground storage organs e.g. Armeria maritima, Plantago maritima and Triglochin maritima.
Therefore, the Puccinellia maritima sub-communities may differ in their response, depending on the frequency of oiling and the sub-communities species composition.
Chronic hydrocarbon pollution may also greatly affect saltmarsh communities, e.g. Dicks & Hartley (1982) reported that large areas of vegetation were lost due to refinery discharges between 1953 and 1970 at Fawley (Holt et al., 1995). Trampling and disturbance caused by clean up operations may increase the levels of damage.
Long term chronic petrochemical effluent also affects the infauna (McLusky, 1982). Studies of intertidal mudflats in the Forth estuary contaminated by petroleum effluent discharge showed that Hydrobia ulvae, Macoma baltica and Hediste diversicolor survived at low abundance in severely polluted areas of low oxygen content, and increased in abundance in polluted areas while oligochaetes and spionids were able to colonize. Cerastoderma edule, Corophium volutator and Mya arenaria were more intolerant being restricted to areas of moderate pollution (McLusky, 1982). No information concerning insect fauna was found, however a proportion of the fauna is likely to be adversely affect or leave the saltmarsh. The intolerance of bird species is well known.
Overall, saltmarsh habitats are considered to by highly sensitive to oil spills (Gundlach & Hayes, 1978; Holt et al., 1995; Packham & Willis, 1997). Therefore, an intolerance of high has been recorded.
Recovery depends on the retention of oil within the saltmarsh, e.g. after the Amoco Cadiz spill some areas of saltmarsh still had oily footprints 5 years later (Holt et al., 1995). Similarly Baker (1979) reported that the effects of oiling were still apparent 10 years after oiling. Dicks & Hartley (1982) suggested that saltmarsh could recover in 10 years once chronic pollution had been removed, and Seneca & Broome (1982; cited in Holt et al., 1995) suggested that recovery from the Amoco Cadiz spill would have taken 5-10 years without restoration.
Radionuclide contamination
(View Benchmark)
Insufficient information
Changes in nutrient levels
(View Benchmark)
Moderate enrichment with nutrients may be beneficial to both plant and infaunal communities. Nitrogen was reported to be limiting in many salt marsh ecosystems and added nitrogen resulted in increased primary production, decomposition and animal growth rates (Valiela & Teal, 1974; Long & Mason, 1983) although Holt et al. (1995) suggested care should be taken when applying this conclusion in all salt marshes. Increased nutrient levels has been associated with increased algal mats, which may smother some burrowing specie, such as Mya arenaria. (Packham & Willis, 1997). Higher levels of nutrient enrichment may result in a decrease in the oxygen levels of the sediment (see below). Plots of salt marsh treated with sewage sludge in Massachusetts, USA, stimulated growth of Spartina alterniflora which eliminated other plants from the area (Long & Mason 1983). However, at the benchmark level, an increase in nutrients is unlikely to have a significant effect on communities.
Increase in salinity
(View Benchmark)
Puccinellia maritima was reported to be highly salt tolerant, communities growing at 12-30 g/l in the Exe estuary, while Puccinellia maritima can grow at 0, 10 and 30 g/l, although it is probably exposed to much higher salinities due to evaporation (Gray & Scott, 1977a; Rodwell, 2000). The salinity in salt pans may vary markedly and Puccinellia maritima was found to grow around the edge of pans in the high marsh. However, with increasing height the salinity decreases due to percolation or rainwater. Increases in salinity are likely to favour Puccinellia maritima, by excluding its competitors (Gray & Scott, 1967, 1977b). Increases in salinity may allow more marine species to colonize further into the marsh, for example salt pans often have marine fauna such as Carcinus maenas and Sphaeroma sp. Terrestrial fauna may become reduced and restricted to the high marsh, for example the aphid Macrosiphoniellia asteris selects stems of Aster tripolium with the lowest salt content, and survived on plants grown in 0, 15 and 30% seawater but died quickly on plants grown in 60% seawater. Overall, therefore, the relative composition of marine and terrestrial species is likely to change but the Puccinellia maritima communities may be able to expand due to increased salinity.
Decrease in salinity
(View Benchmark)
Puccinellia maritima was reported to be highly salt tolerant, communities growing at 12-30 g/l in the Exe estuary, while Puccinellia maritima can grow at 0, 10 and 30 g/l (Gray & Scott, 1977a; Rodwell, 2000). However, in areas of low sodium content (reduced salinity) such as the high marsh, or areas affected by freshwater runoff, Puccinellia maritima is replaced by high marsh species such as Festuca rubra (Gray & Scott, 1967, 1977b). Therefore, the Puccinellia communities will probably be lost in areas subject to reduced salinity and an intolerance of high has been recorded. The marine fauna will also probably reduce in extent while the terrestrial fauna will probably expand.
Changes in oxygenation
(View Benchmark)
Oxygen levels in the soils in Puccinellia communities vary markedly with neap or spring tides (Packham & Willis, 1997). Free sulphide was not recorded in soil occupied by Aster tripolium, Puccinellia maritima, Spartina anglica and Suaeda maritima and growth of Puccinellia maritima was significantly inhibited by sulphide while Salicornia europaea was not (Packham & Willis, 1997). However, the waterlogged soils of salt marshes, favoured by Puccinellia maritima are generally anoxic. Vascular plants may not be intolerant of deoxygenation since photosynthesis liberates oxygen, they are uncovered for the majority of the tidal cycle, and in some species, e.g. Spartina alterniflora air spaces in the leaf sheaths aid gas transport to the roots. Most infaunal polychaetes and oligochaetes are probably tolerant of low oxygen conditions, while some species of oligochaete and nematode may be dependant on the locally oxygenated areas around the roots of vascular plants. Hydrobia ulvae can tolerate emersion for several days and many insects live on stems and leaves of vascular plants and avoid anoxic conditions, e.g. aphids. However, Cerastoderma edule is probably intolerant to anoxic conditions and would be lost from the lower marsh. Overall, the vascular plants are probably tolerant of anoxic soils and are exposed to the air at low tide, so that the Puccinellia communities would probably be little affected by increases in hypoxia at the benchmark level, whereas a few fauna may be lost. Therefore an intolerance of low has been recorded. Recovery will probably be rapid (see additional information below).

Biological Factors

Introduction of microbial pathogens/parasites
(View Benchmark)
Puccinellia maritima may develop saprophytic fungi or 'rust' fungus on its leaves and 'choke' disease may prevent flowering. Nematodes are know to infect Puccinellia maritima, e.g. Ditylenchus radicicola while Anguina spp. and Anguillulina argostis occur in inflorescences (Gray & Scott, 1977a). A number of aphid species also feed of Puccinellia maritima, although not exclusively (Gray & Scott, 1977a). Most of the above diseases and parasites probably impair production and flowering but no mass mortalities were reported, therefore an intolerance of low has been recorded.
Introduction of non-native species
(View Benchmark)
Introduction of North American cord grass Spartina alterniflora to stabilise and reclaim high intertidal mudflats has significantly altered UK saltmarsh. Spartina alterniflora hybridised with native Spartina maritima producing an infertile hybrid (Spartina townsendii) which gave rise to fertile Spartina anglica. Spartina anglica. is fast growing and aggressive and has colonized extensive areas of intertidal mudflats, increasing the area of saltmarsh in the UK but reducing intertidal feeding grounds for shorebirds. The success of Spartina anglica may dominate the community to the detriment of other species reducing species richness (Eno et al. 2000).
Extraction
(View Benchmark)
Saltmarsh is subject to grazing by wildfowl, rabbits and livestock in the Britain and Ireland (see ecological relationships). Grazing is important in maintenance of Puccinellia communities although the response of species varies between sites (Rodwell, 2000). Grazing by livestock causes trampling and introduces nutrients (faeces). Grazing varies with species, livestock probably removing only the leaves while some species of wildfowl also remove or disturb the roots. Grazing affects the species composition of the sward Salicornia europaea, Puccinellia maritima and Armeria maritima are favoured by grazing while Spartina anglica and Limonium vulgare are harmed by intensive grazing. (Long & Mason 1983). Grazing favours prostrate growth of Puccinellia maritima over tall plants, increases species richness, and controls the balance between Puccinellia maritima and Festuca rubra, which is less tolerant of grazing. Grazing, therefore, also slows floral succession (Packham & Willis, 1997; Rodwell, 2000).
Removal of 50% of the biomass (the benchmark level) would result in an intolerance of intermediate being returned, but the extent and longevity of Puccinellia communities benefits form low to moderate grazing, so that a rank of not sensitive* is more appropriate. However, over intensive or inappropriate grazing may result in loss of the vascular plant communities, disturbance and erosion of the marsh,

Additional information icon Additional information

Recoverability
Rates of recovery and recolonization depend on the level of damage or disturbance, and will probably be protracted where the sediment has been disturbed (Beeftink, 1979). Puccinellia maritima acts as a pioneer species and therefore may be expected to colonize relatively quickly as seed but primarily as vegetative fragments, depending on the local hydrographic regime. Subsequent development of an extensive Puccinellia maritima dominated sward may take several years. For example, Gray & Scott (1977a) noted that where the aerial growth died back due to drought, isolated individuals recovered rapidly, regrowing leaves from the base of the plant. Gray & Scott (1969) reported that Puccinellia maritima established 5 -30% cover in bare areas left by turf cutting within 1-2 years. Packham & Willis (1997) reported that Puccinellia maritima formed radially spreading hummocks (clonal growth) and that in the newly expanding Cefni Marsh, Anglesey, roughly circular patches of 120-150cm in diameter formed in the newly developed Puccinellia community with 3 -4 years. After die back of Haliminone portulacoides communities in the Netherlands a successional recolonization occurred, beginning with Suaeda maritima (and sometimes Salicornia sp.) followed by Aster tripolium , then Puccinellia maritima until Haliminone portulacoides returned (Beeftink, 1979). The time taken for recovery depended on the initial level of disturbance to the Haliminone portulacoides community, taking less time after minimal disturbance, e.g. Puccinellia maritima showed the greatest abundance after 4 years after waterlogging, 6-10 year after chemical destruction by herbicides, 5-7 years after changes in tidal regime (Beeftink, 1979). Rodwell (2000) noted that Puccinellia maritima colonizes ruts left by cars or livestock. Glaux maritima and Limonium vulgare sub-communities representing further stages in succession from Puccinellia maritima and would probably take longer to establish. Other pioneer species such as Salicornia sp. and Aster tripolium are likely to recover quickly.

Most mobile species and invertebrates would probably recognize newly established Puccinellia communities relatively rapidly from adjacent sites. Recruitment in infaunal sediment dwelling invertebrates may be patchy and sporadic depending on the hydrographic regime and post-settlement mortality (from scour, smothering and predation). However, polychaetes probably recolonize habitats by a mixture of migration (swimming) and passive transport and thought to be rapid in some species, e.g. Arenicola marina and Hediste diversicolor. Nematodes are ubiquitous are probably colonize by a mixture of larval settlement, and active and passive transport of adults and juveniles. Marine bivalves such as Macoma baltica, Mya arenaria and Cerastoderma edule have sporadic and unpredictable recruitment via settling pelagic larvae or passive bedload transport of juveniles together with significant larval and postsettlement motility. While a single recruitment event may re-establish the population within a year and longer period (e.g. up to 5 years ) has been suggested for recovery (see individual reviews).

Overall, therefore, where disturbance is slight, or only the aerial parts of the plant are damaged, recovery is likely to be rapid due to regrowth (immediate in the summer months, longer in winter) but overall probably taking less than 6 months, including recolonization by most invertebrates and algae. However, where the sediment has been disturbed and plants lost, recovery of plant communities together with infauna may take between 4 -10years.


This review can be cited as follows:

Tyler-Walters, H. 2004. Puccinellia maritima salt marsh community. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 23/07/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=350&code=1997>