Biodiversity & Conservation

LS.LMp.Sm

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
(View Benchmark)
Removal of the substratum will remove the vegetation and infauna. Recovery will be dependant on recruitment. Pioneer species such as Salicornia sp. and Aster tripolium are likely to recover quickly whereas Spartina sp. will depend on transport of plant fragments and seed. Infaunal recovery will be dependant on recruitment form neighbouring intertidal populations and may take up to 5 years depending on the species, although mobile species will colonize quickly (e.g. ca I year).
Smothering
(View Benchmark)
Smothering by 5cm of sediment may cover small plants, removing them from light. However, saltmarsh plants are adapted to accreting environments and may not be adversely affected by smothering for a month, depending on the species and the grain size of the smothering material e.g. die back of Spartina anglica in the Solent, southern England was associated with accumulation of very fine sediment. The intolerance of epifaunal burrowers and suspension feeders was higher than deep burrowing siphonate species (Hall, 1994).
Increase in suspended sediment
(View Benchmark)
Salt marshes are dependant on suspended sediment to grow (accretion) and vulnerable to erosion, although a dynamic balance or erosion and accretion is probably normal. Die back of Spartina anglica in the Solent, southern England was associated with accumulation of very fine sediment, and changes in sediment type may affect saltmarsh communities (Holt et al., 1995). Increased siltation may increase sedimentation rates above growth rates resulting in smothering, whereas decreases siltation rates may reduce the rate of growth of the saltmarsh and subject it to increased erosion. Overall, any activity that changes the sedimentary regime could potentially have marked effects on saltmarsh. Therefore, an intolerance of high and a recoverability of moderate has been suggested (see additional information below).
Decrease in suspended sediment
(View Benchmark)
Desiccation
(View Benchmark)
Drought may control the salinity levels and the community in the high marsh. In warm dry summers the marsh become hypersaline, dry out and crack. In the dry summer of 1967, drought on the north Irish coast caused extensive die-back of Spartina anglica even though it is tolerant of salinities in excess of normal seawater (Packham & Willis, 1997). Desiccation at the above level is likely to significantly affect epifauna and infauna. An increase in desiccation, equivalent to an increase or decrease of the level on the shore is likely to change the community from pioneer to low-mid saltmarsh or intertidal flat communities or biotopes.
Increase in emergence regime
(View Benchmark)
Decreased emergence, for example due to sea level rise or barrages, may move the high water mark further up shore but this is not possible in the presence of sea defences. The low water mark moves inshore, effectively reducing the area available for invertebrates and feeding of birds and fish, so called 'coastal squeeze'. Resultant increased water depth changes infaunal feeding types and increases area available to predatory fish, and hence the community. Similarly it reduces the area available to shore birds and reduces the carrying capacity of the area for wildfowl. Increased emergence will allow species typical of higher saltmarsh to invade while allowing the pioneer species to colonize further offshore. However, decreased emergence is likely to decrease the extent of the saltmarsh, moving the pioneer community up shore.
Decrease in emergence regime
(View Benchmark)
Increase in water flow rate
(View Benchmark)
Change in water flow rate and hence the hydrographic regime will change the accretion and erosion rates in the saltmarsh. 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. Recovery will depend the accretion of eroded sediment and subsequent recruitment of the pioneer species (see additional information below).
Decrease in water flow rate
(View Benchmark)
Increase in temperature
(View Benchmark)
Increases in temperature are likely to result in increased evaporation and desiccation (see above). However, vascular plants are terrestrial in origin and adapted to relatively wider extremes of temperature than intertidal species.
Decrease in temperature
(View Benchmark)
Increase in turbidity
(View Benchmark)
Saltmarsh are accreting habitats and probably turbid. Turbidity reduces the light attenuation through water. However, salt marsh vegetation is emersed for the majority of the tidal cycle and able to photosynthesize.
Decrease in turbidity
(View Benchmark)
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 at low water 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. Recovery will depend replacement of eroded sediment and the subsequent recruitment of the pioneer species (see additional information below).
Decrease in wave exposure
(View Benchmark)
Noise
(View Benchmark)
Disturbance by noise and visual presence of human activities to bird populations are difficult to separate and have been considered together. The level of disturbance is dependant on the species considered. Some species habituate to noise and visual disturbance while others 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)
Disturbance by noise and visual presence of human activities to bird populations are difficult to separate and have been considered together (see above).
Abrasion & physical disturbance
(View Benchmark)
Abrasion in saltmarsh biotopes is 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). It is likely that succulents, such as Salicornia sp. are intolerant of trampling. Trampling may also affect the substratum, either through destabilization of creek walls and loss of vegetation, or may result in compaction of sediments and reduced aeration. Some plants will be damaged and invertebrates may be displaced but effects are likely to be restricted in area, therefore, an intolerance of intermediate has been recorded.
Displacement
(View Benchmark)
Once removed vascular plants can not reattach and will be lost. However, Spartina sp. can establish colonies from remaining fragments and may recover quickly. Most infaunal species can burrow back into sediment, but may suffer significant predation as a result of being removed from the sediment.

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 sediment 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). Spartina alterniflora was found to accumulate high levels of cadmium, lead and zinc in experiments with sewage sludge treatment in the USA (Long & Mason, 1983).
Heavy metal contamination
(View Benchmark)
Flocculation, salinity and pH changes within estuaries, in particular result in the preferential precipitation of some heavy metals, e.g. Fe and Cu (Bryan, 1984). As above sediments act as sinks for contaminants including heavy metals. Spartina alterniflora was found to accumulate high levels of cadmium, lead and zinc in experiments with sewage sludge treatment in the USA (Long & Mason, 1983). Packham & Willis (1997) note that acute toxicity to heavy metals has not been reported in saltmarsh plants. However, different members of the community are likely to vary in their intolerance to heavy metal pollution.
Hydrocarbon contamination
(View Benchmark)
Salt marshes are very intolerant of 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 oilings 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.
Annual species are most intolerant and are either killed or their reproduction is repaired. Shallow rooted Salicornia sp. and Suaeda sp. are susceptible since they have few food reserves, whereas plants with underground storage organs are resistant, e.g. Armeria maritima and Plantago maritima. Experiments show that most species succumbed after more than four oilings and 8 -12 oiling resulted in significant die back (Baker, 1979). Chronic hydrocarbon pollution may also greatly affect saltmarsh communities. Dicks & Hartley (1982) reported that discharge of refinery effluent (containing oils and other chemicals), together with small accidental discharges from Fawley terminal, Southampton (1953-1970) caused loss of vegetation from a large area of the adjacent saltmarsh (Holt et al., 1995). Trampling and disturbance caused by clean up operations may increase the levels of damage (Holt et al., 1995).
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 sensitivity 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) reported that reduction of hydrocarbons content and discharge rate took place between 1970 and 1975 in the Fawley marsh. By 1980 vegetation had recolonized much of the area, pioneer species such as Salicornia sp. and Aster tripolium recolonized quickly followed, slowly by Spartina anglica but the sediment remained contaminated and supported an impoverished fauna, which rare oligochaetes and reduced numbers of Nereis diversicolor. Dicks & Levell (1989) reported that annual species (e.g. Salicornia sp. and Suaeda maritima) and the perennial Spartina anglica had colonized most of the previously denuded area by 1987, although Spartina anglica recovery was aided by transplantation. Dicks & Levell (1989) suggested that areas recolonized by Spartina anglica in 1977 had begun to resemble healthy marshes by 1987 (10 years), although recovery of the whole area would probably take another 5-10 years. 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. Overall, the above evidence suggests that annual species would probably recover within a few years while perennial species such as Spartina anglica would take between 10 to 20 years. Therefore, a recoverability of low has been recorded.
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. 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).
Increase in salinity
(View Benchmark)
Saltmarsh plants live inhabit an environment hostile to terrestrial plants and are tolerant of fluctuating salinity, especially at the lower shore.
Decrease in salinity
(View Benchmark)
Changes in oxygenation
(View Benchmark)
Vascular plants may be not sensitive to 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. However, other members of the community, such as infauna are intolerant of deoxygenation.

Biological Factors

Introduction of microbial pathogens/parasites
(View Benchmark)
Although pathogens of Spartina anglica are known they have not been implicated in die backs. No information on pathogens of other important species was found.
Introduction of non-native species
(View Benchmark)
Introduction of North American cord grass Spartina alterniflora to stabilize and reclaim high intertidal mudflats has significantly altered UK saltmarsh. Spartina alterniflora hybridized 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. 1997).
Extraction
(View Benchmark)
Saltmarsh is subject to grazing in the UK. Grazing prevents invasion of the upper saltmarsh by scrub species. Grazing by livestock causes trampling and introduces nutrients (faeces). Salicornia europaea, Puccinellia maritima and Armeria maritima are favoured by grazing while Spartina anglica and Limonium vulgare are harmed (Long & Mason 1983). Grazing favours prostrate plants over tall plants and increases species richness. Saltmarsh are also grazed by brent geese and wigeon. Grazing also slows floral succession. Overall intolerance has been assessed as intermediate with a high recovery.

Additional information icon Additional information

Recoverability
Pioneer species such as Salicornia sp. and Aster tripolium are likely to recover quickly whereas Spartina sp. will depend on transport of plant fragments and seed. For example, Suaeda maritima recolonized within a year after water-logging, and Suaeda maritima and Salicornia europaea recolonized within three years of chemical destruction of the Haliminone portulacoides community. The time take for recovery depended on the initial level of disturbance to the Haliminone portulacoides community, taking less time after minimal disturbance (Beeftink, 1979). Infaunal recovery will be dependant on recruitment form neighbouring intertidal populations and may take up to 5 years depending on the species, although mobile species will colonize quickly (e.g. ca I year). Overall, pioneer saltmarsh will probably recover within less than 5 years of disturbance. Where the sediment has been eroded, recovery will probably be delayed until the sediment levels has built up again.

This review can be cited as follows:

Tyler-Walters, H. 2001. Pioneer saltmarsh.. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 20/04/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=25&code=2004>