Biodiversity & Conservation

LS.LGS.S.Tal

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Substratum loss, in this instance, the deposited macroalgae and other organic debris, would cause a loss of habitat for the strand-line community. Intolerance has been assessed to be high. Species utilizing the stranded material are likely to be removed along with the material and the habitat would be destroyed.
The benchmark against which intolerance is assessed assumes a single event, so following deposition of fresh macroalgae, recovery of the community would be expected to be very rapid in terms of the species present (e.g. many species would migrate to the strand-line from the terrestrial habitats and sand hoppers would buried in the substratum awaiting the arrival of a new strand-line) but may not attain their former abundance for several moths as a considerable proportion of characterizing species would be lost. At the benchmark level, a recoverability of very high has been made.
However, repeated removal of the substratum within a short space of time, e.g. as a result of mechanical raking for the purposes of beach cleaning, would be expected to impact upon the recovery of the strand-line community. A proportion of the population (e.g. sand hoppers, beetles, mites, flies etc.) would be removed or disturbed each time, including important juvenile stages, so that recovery would have to occur from a diminishing population and may take a considerable period of time from the point that the activity ceased. Some species in particular would be at risk. Amphipods, such as Talitrus saltator have an annual univoltine reproductive cycle (only one generation reaches maturity each year) (Williams, 1978). Newly hatched juveniles are unable to bury themselves in the sand to avoid desiccation and remain in amongst the freshly deposited strand-line debris, which maintains an 85-90% relative humidity over low tide (Williamson, 1951). The continuous removal of strand-line algae, even over the summer months will in the long term, effectively destroy the population (Llewellyn & Shackley, 1996). A much longer recovery period would be expected and it is questionable whether the community would recover at all following an impact of extended duration. For instance, the ability of amphipods to colonize over wider areas (e.g. > 200m) may be restricted by their endogenous pattern of activity that generally restricts movement over a relatively short distance in the intertidal zone (see Bregazzi & Naylor, 1972; Lincoln, 1979; Scapini et al., 1992 ).
Smothering
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Many of the species inhabiting the biotope are highly mobile adult forms, e.g. wrack flies, that would avoid being physically covered by additional sediment. A uniform layer of 5 cm of sediment would bury the strand-line material and the species active within it. The habitat would be temporarily lost to those species, mainly terrestrial, that were able to move away. Adult sand hoppers, such as Talitrus saltator, are likely to be capable of burrowing through additional sediment, as the species are capable of burrowing to depths between 10-30 cm (Williams, 1983b). Newly hatched juveniles are unable to bury themselves in the sand to avoid desiccation and remain in amongst the freshly deposited strand-line debris, which maintains an 85-90% relative humidity over low tide (Williamson, 1951). Although juveniles may not be able to bury through the additional sediment to regain the surface and fresh deposits of macroalgal debris, it is likely that the seaweed debris would itself maintain a sufficiently open structure under the sediment for vulnerable juvenile stages to survive. Intolerance has been assessed to be low, but would be expected to be higher if the smothering material was viscous. Recoverability, in terms of the species present and abundance, has been assessed to be immediate (within a few days) as characterizing species would either remain in situ or are sufficiently mobile to rapidly return, e.g. flies.
Increase in suspended sediment
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The community is unlikely to be affected by an increase in the concentration of suspended sediment in the water column, as the habitat is created by the deposition of macroalgae and other organic debris on the ebb tide. An intolerance assessment was not considered relevant.
Decrease in suspended sediment
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The community is unlikely to be affected by a decrease in the concentration of suspended sediment in the water column, as the habitat is created by the deposition of macroalgae and other organic debris on the ebb tide. An intolerance assessment was not considered relevant.
Desiccation
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Moisture conservation is a major stress factor to crustaceans on intertidal beaches (Hurley, 1959, 1968) and high-shore and terrestrial sandy beach amphipods such as Talitrus saltator are highly dependant on behavioural mechanisms to locate and maintain humid microhabitats during the diurnal, quiescent phase of their activity cycle (e.g. Williamson, 1951). An intolerance of high would have been recorded but for the ability of the species to avoid exposure to desiccating conditions. For instance, Williams (1983b) found a significant statistical correlation between the distribution of Talitrus saltator and sand moisture content. Talitrus saltator burrows down into the beach until sand with at least 2 % moisture content is encountered. The burrows of Talorchestia deshayesii are usually associated with the immediate area of the high water mark and freshly deposited algae, which would ameliorate moisture conservation problems, whilst Orchestia spp. combat desiccation by remaining burrowed within strand-line debris and below stones during its diurnal quiescent period in a manner similar to juvenile infaunal talitrids (Williams, 1983b). Unprotected individuals of Talitrus saltator above the substratum survived only approximately 0.5 -1 hours in air, a longer period than Talorchestia deshayesii and Orchestia gammarellus (Williamson, 1951). An intolerance assessment of not relevant has been made because the strand-line populations are protected from desiccation by their activity cycle and behaviour, otherwise desiccation would cause considerable mortalities.
Increase in emergence regime
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The strand-line habitat is created as the tide, which carries macroalgal debris towards the shore, ebbs and deposits the material on the shore. The biotope has been assessed to be not sensitive to emergence, because it is created when the tide is out.
Decrease in emergence regime
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A decrease in emergence is a factor considered not to be of relevance to this biotope as the habitat is created by the deposition of macroalgal debris on the shore as the tide ebbs.
Increase in water flow rate
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The community is unlikely to be affected by an increase in water flow rate, as the habitat is created by the deposition of macroalgae and other organic debris on the ebb tide. An intolerance assessment was not considered relevant.
Decrease in water flow rate
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The community is unlikely to be affected by a decrease in water flow rate as the habitat is created by the deposition of macroalgae and other organic debris on the ebb tide. An intolerance assessment was not considered relevant.
Increase in temperature
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The important characterizing species of the strand-line, Talitrus saltator, occurs to the south of the British Isles, so is likely to be tolerant of a chronic temperature increase of 2°C. Bregazzi & Naylor (1972) observed that the timing of activity was temporarily advanced by increased temperature but otherwise the activity pattern possessed a large measure of temperature independence. Specimens brought in to laboratory conditions from a field temperature of 10.5°C were introduced to (within 3 hours) and maintained for 15 days at constant temperatures of 15, 20 and 25°C. For Talitrus saltator maintained at the highest temperatures the activity mid-point advanced by as much as three hours to occur before midnight. However, alterations in activity were compensated for within two to ten days. Acute temperature increases may therefore temporarily disrupt activity of the sand hopper and other similar species, but owing to insufficient evidence for adverse effects in the field intolerance has been assessed to be low. Immediate recovery has been recorded as the locomotor activity rhythm is synchronized within a few days.
Decrease in temperature
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The important characterizing species of the strand-line, Talitrus saltator, remains inactive in high shore burrows for much of the winter in more northern latitudes. In the laboratory, exposure to low temperature (2 or 3°C) was accompanied by the onset of inactivity, a precipitous decrease in oxygen uptake and a marked increase in the concentrations of the major ions in the haemolymph (Spicer et al., 1994). In addition to causing a complete cessation of activity, chilling (2-3°C for 8 hours) also causes a delay in the successive activity peaks following return to normal temperatures. Maximum delay occurred if chilling began during the inactive period of the sand hopper and was of equal duration to that of the chill. At other times the delay was less than that of the chill (Bregazzi, 1972). Thus it is possible that exposure to decreased temperatures in the field would enforce a period of inactivity causing disruption to the species normal behaviour with potential consequences for the maintenance of a position with appropriate moisture, e.g. the substratum may be come too dry or the temporary burrow become inundated with water. The effects of an unusually cold winter are likely to be a simple physical one, whereby quiescent sand hoppers freeze within the substratum, causing cell and tissue damage and eventually rupture of cell and body walls. Other supralittoral members of the Talitridae with a similar habit to Talitrus saltator were reported to be adversely affected by the severe winter of 1962/63. In particular, sand hoppers of the genus Orchestia were found dead in considerable numbers (Crisp, 1964). However, intolerance has been assessed to be low at the benchmark level as the behaviour of the sand hopper is likely to be disrupted by mild chilling, whilst death as a result of freezing is probable only in severe winters. Recovery from mild chilling has been assessed to be immediate following an initial disruption to its activity.
Increase in turbidity
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The community is unlikely to be affected by the light attenuating effects of an increase in turbidity within the water column, as the habitat is created by the deposition of macroalgae and other organic debris on the ebb tide. An intolerance assessment was not considered relevant.
Decrease in turbidity
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The community is unlikely to be affected by a decrease in turbidity in the water column, as the habitat is created by the deposition of macroalgae and other organic debris on the ebb tide. An intolerance assessment was not considered relevant.
Increase in wave exposure
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The species characteristic of the biotope are unlikely to be directly affected by an increase in wave exposure. However, increased wave exposure may be of indirect benefit to strand-line populations. Storm wave erosion is likely to be an important factor in determining the quantity and quality of strand-line debris deposited on the beach. Increased wave exposure onshore is likely to increase the quantity of debris washed-up and available for colonization by strand-line fauna. For example, Shackley & Llewellyn (1994) recorded a positive correlation between strand-line debris weight and total amphipod numbers at beaches in South Wales. The community would benefit from the additional habitat/food resources and an intolerance assessment of not sensitive* has been made.
Decrease in wave exposure
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The species characteristic of the biotope are unlikely to be directly affected by a decrease in wave exposure. However, decreased wave exposure may affect the abundance of shore strand-line populations. Storms are likely to be an important factor in determining the quantity of strand-line debris deposited on the beach. Reduced wave exposure over the period of a year is likely to affect the quantity of debris washed-up on the shore. As a consequence of reduced habitat availability the abundance of strand-line invertebrate populations may be reduced, owing to increased competition for resources. As the viability of some species may be affected an intolerance assessment of low has been made. However, fluctuation in the quantity of stranded debris is likely to be a normal feature of the biotope, as it is characteristically ephemeral, and species populations are likely to be able to cope but may fluctuate accordingly. Recoverability has consequently been assessed to be very high.
Noise
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The invertebrate fauna of the biotope are unlikely to be sensitive to noise at the benchmark level. However, birds that frequent the biotope to feed may be disrupted and their feeding efficiency impaired, although this would benefit invertebrate species. An assessment of not sensitive* has been made.
Visual Presence
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The invertebrate fauna of the biotope possess visual acuity and are able to detect changes in light for purposes of navigation and probably are able to detect prey items within their visual envelope. However, apart from flies which would be temporarily disturbed by the approach of machinery, other important characterizing species of the biotope are unlikely to be disturbed by visual presence. Some species of bird that frequent the biotope to feed are likely to be disturbed by the visual presence of machinery and people in the vicinity of the strand-line, and their feeding efficiency reduced, although this would benefit invertebrate species. An assessment of not sensitive* has been made.
Abrasion & physical disturbance
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This biotope is subject to physical disturbance due to the rising and falling of the tide, wave action, and the movement of marine debris, including strand line material. Human trampling, and in this specific case, mechanical beach cleaning/raking, are potential sources of additional abrasion and physical disturbance. Adults of the many terrestrial species that exploit the biotope are highly mobile, e.g. wrack flies, and are likely to avoid disturbance. During the day, species such as Talitrus saltator, usually remain burrowed in the sand or amongst the algal debris (to avoid desiccation), so their environmental position may offer considerable protection from physical disturbance caused by trampling. Therefore, an overall assessment of not sensitivte has been made. However, the biotope is likely to be highly intolerance of substratum loss caused by mechanical beach cleaning/raking (see 'substratum loss', above).
Displacement
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Species within the biotope are mobile and in the event of displacement form strand-line material, would be able to rapidly recolonize debris elsewhere in the vicinity. An assessment of not sensitive has been made.

Chemical Factors

Synthetic compound contamination
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In general, crustaceans are widely reported to be intolerant to synthetic chemicals (Cole et al., 1999) and intolerance to some specific chemicals has been observed in amphipods. Amphipods have been reported to be intolerant to TBT and leachates from antifouling paints (Laughlin et al., 1982). Numbers of the sand hopper, Talitrus saltator, were found in a lethargic state at the base of dunes at Constantine Bay (Cornwall), after spraying with the BP1002 an oil dispersant detergent after the Torrey Canyon oil spill (Smith, 1968). Intolerance has been assessed to be high.
Recovery assumes the deterioration of the contaminant, but is likely to be variable. In the case of the important characterizing species, Talitrus saltator, if a remnant population of young adults survived to breed, recovery would begin within a year. However, it has an annual univoltine reproductive cycle (only one generation reaches maturity each year) (Williams, 1978). So if a population were to be killed, recovery would take much longer and be reliant on the recolonization of adults able to breed. However, the ability of amphipods to colonize over wider areas may be restricted by their endogenous pattern of activity that generally restricts movement over a relatively short distance in the intertidal zone (see Bregazzi & Naylor, 1972; Lincoln, 1979; Scapini et al., 1992 ). Recoverability has been assessed to be high.
Heavy metal contamination
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Talitrus saltator has been used as a spatial and temporal heavy metal biomonitor (Rainbow et al., 1989, 1998; Fialkowski et al., 2000). Bioavailable sources of trace metals to talitrids are available in solution and in food, the latter consisting of decaying macrophytic material on the strand-line. Such material acts as an adsorption site for heavy metals locally, as sandy substrata does not adsorb contaminants as easily as other substrata. The species is an efficient bioaccumulator of heavy metals whose moult cycle does not interfere with its biomonitoring potential. Specimens of the sand hopper from the Isle of Cumbrae, a non metal polluted site in the Clyde, Scotland, had zinc concentrations between 145-181 µg /Zn/g and copper concentrations of 35.8 µg/Cu/g (Rainbow & Moore, 1990). In comparison, Talitrus saltator from a heavy metal polluted site in Dulas Bay, Anglesey, Wales (Foster et al., 1978; Boult et al., 1994) had a zinc concentration of 306 µ g/Zn/g and a copper concentration of 112 µg/Cu/g. In the Gulf of Gdansk, Poland, comparable concentrations for zinc were in the region of 200-400µ g/Zn/g with bottom sediment zinc concentrations of 0-20 µg/g and 40µ g/g in the most polluted areas (Fialkowski et al., 2000). It is likely that the most significant contamination pathway to the amphipod is that of pollutants adsorbed to vegetative matter that is consumed rather than that concentrated in the water column. However, insufficient information has been recorded as no evidence concerning the effects of heavy metal contamination on the community as a whole was found.
Hydrocarbon contamination
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intolerance to hydrocarbon contamination has been assessed to be high. Supralittoral sediment habitats immediately adjacent to the littoral zone can be susceptible to damage from oil pollution and any subsequent attempts to remove the oil by scraping off the sediment surface. Oil which reaches the shore following a pollution incident generally gets concentrated along the high tide mark. Oil deposits on the strand-line and amongst seaweed would probably incapacitate and kill, by smothering and toxic effects, a considerable proportion of invertebrates that are found in strand-line debris. For instance, following the Torrey Canyon oil tanker spill in 1967 quantities of Talitrus saltator were found dead at Sennen, Cornwall, as were other scavengers of the strand-line, e.g. Ligia and Orchestia. Signs of oil dispersant detergent damage were reported at Constantine Bay (Cornwall) where sand hoppers were found in a lethargic state at the base of dunes after spraying with detergent (Smith, 1968).
Shackley & Llewellyn (1997) monitored shores with dune systems at Pendine and Pembury within Carmarthen Bay, that received oil spilt by the Sea Empress tanker in February 1996. Strand-line material at the two beaches contained quantities of oiled material and small particles of oil (2-5 mm in diameter) became mixed in with the sediment. However, Pendine was amongst the initial areas to become contaminated and received more viscous oil than Pembury, where oil appeared later and in a more weathered form. Tar balls persisted within the sediment at Pendine a year after the spill, whilst very little oiled material was found at Pembury a year later. Whilst physical and biological factors are important in determining the amphipod populations on such shores and differ between localities, differences were found in the abundance of amphipods between the two shores that could not be accounted for by physical and biological processes alone. Shackley & Llewellyn (1997) suspected that the persistence of oil at the strand-line and in the sediment beneath was affecting the strand-line community. Oil amongst strand-line material and in the sediment may affect the viability of species and/or it may simply deter species from colonizing. Recovery of the community is likely to vary according to the extent of oil pollution. Oil may be responsible for the decimation of amphipod populations, unless a remnant population survives buried in the substratum or in refuges higher than the tide mark. Some species in particular would be at risk. Amphipods, such as Talitrus saltator have an annual univoltine reproductive cycle (only one generation reaches maturity each year) (Williams, 1978). Newly hatched juveniles are unable to bury themselves in the sand to avoid desiccation and remain in amongst the freshly deposited strand-line debris, which maintains an 85-90% relative humidity over low tide (Williamson, 1951), so oil pollution could effectively remove the breeding population and recovery consequently protracted. Terrestrial species including coleopteran insects and dipteran flies are likely to colonize the strand-line rapidly following the deterioration of oil. Recoverability has been assessed to be high, as it may take more than a year for amphipod populations to recover to former abundances.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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The community is unlikely to be directly affected by an increase in the concentration of dissolved nutrients in the water column, as the food resource that the community utilizes is in the form of macroalgal debris. An assessment of not relevant has been made.
Increase in salinity
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The strand-line occurs in the supralittoral biological zone, where the benchmark increases in salinity are unlikely to occur. An assessment of not relevant has been recorded.
Decrease in salinity
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The community may experience periods of freshwater inundation owing to episodes of rain. The highly mobile adult forms of wrack flies are likely to go elsewhere, whilst sand hoppers such as Talitrus saltator and other strand-line fauna are likely to seek protection within the strand-line debris. Talitrus saltator demonstrated the ability to hyper-regulate at lower external salinity concentrations, maintaining a haemolymph concentration between 750-850 mOsm (Morritt, 1988). It is likely to tolerate a short term decrease in salinity, resulting from episodes of rain. An assessment of not sensitive has been made.
Changes in oxygenation
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At the benchmark level, intolerance is assessed against changes in the amount of dissolved oxygen in the water column. The strand-line habitat is created as the tide ebbs and deposits organic debris on the shore. Species inhabiting the strand-line are either fully terrestrial, or are marine species that have assumed a terrestrial mode of life, and all can therefore respire in air. An assessment of not relevant has been made.

Biological Factors

Introduction of microbial pathogens/parasites
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Wolbachia are endosymbiotic bacteria known to infect a wide range of arthropods and nematodes (Cordeaux et al., 2001). Wolbachia endosymbionts can alter their hosts reproduction. Cordeaux et al. (2001) found Wolbachia strains in the intertidal amphipods Talorchestia deshayessiiand Orchestia gammarellus living in the same habitats as semi-aquatic isopods whose populations typically have an infection level >35% (e.g. Sphaeroma rugicauda, Sphaeroma hookeri and the sea slater Ligia oceanica). Whilst reproductive impairment has been reported in isopod species, there is insufficient information to assess the likely impact of Wolbachia bacteria on amphipod populations inhabiting the strand-line. Insufficient information has been recorded.
Introduction of non-native species
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No species alien to the British Isles are known to impact upon the community.
Extraction
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It is extremely unlikely that Talitrus saltator would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope.

Additional information icon Additional information

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This review can be cited as follows:

Budd, G.C. 2004. Talitrid amphipods in decomposing seaweed on the strand-line. 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=176&code=1997>