|Researched by||Dr Heidi Tillin||Refereed by||Admin|
|EUNIS 2008||A2.223||Amphipods and Scolelepis spp. in littoral medium-fine sand|
|JNCC 2015||LS.LSa.MoSa.AmSco||Amphipods and Scolelepis spp. in littoral medium-fine sand|
|JNCC 2004||LS.LSa.MoSa.AmSco||Amphipods and Scolelepis spp. in littoral medium-fine sand|
|1997 Biotope||LS.LGS.S.AP||Burrowing amphipods and polychaetes in clean sand shores|
Mobile clean sandy beaches on exposed and moderately exposed shores, with sediment grain sizes ranging from medium to fine, often with a fraction of coarser sediment. The sediment contains little or no organic matter, and usually no anoxic layer is present at all. It tends to be well-drained, retaining little water at low tide, though the sediment of the AmSco.Pon sub-biotope may remain damp throughout the tidal cycle. These beaches usually occur under fully marine conditions, though the AmSco.Eur sub-biotope may occur under moderately exposed lower estuarine conditions. The mobility of the sediment leads to a species-poor community, dominated by polychaetes, isopods and burrowing amphipods. Scolelepis spp. can tolerate well-drained conditions, and are often present in well-draining, coarser sand. Burrowing amphipods that often occur in this biotope include Bathyporeia spp., Pontocrates arenarius, and Haustorius arenarius. The isopod Eurydice pulchra is also often present. On semi-exposed beaches with a moderate tide range where there is a marked high-shore berm, there can be a marked seepage at the foot of the berm that probably carries the products of the organic matter derived from strand line breakdown. Here in a narrow zone, exceptionally high populations of Bathyporeia pilosa, sometimes above 10000 per square metre, may occur. The zone may be narrower than the strandline and could easily be missed on surveys were only a few levels are sampled. Three sub-biotopes are described for this biotope, based principally on differences in infaunal species composition (JNCC, 2015).
The biotope description and characterizing species are taken from JNCC (2015). This sandy beach biotope is characterized by mobile clean sand sediments on exposed and moderately exposed shores, with sediment grain sizes ranging from medium to fine, often with a fraction of coarser sediment. The mobility of the sediment leads to a species-poor community, dominated by polychaetes (Scolelepis squamata), isopods (Eurydice pulchra) and burrowing amphipods (Bathyporeia spp., Pontocrates arenarius, and Haustorius arenarius). The sediments and wave exposure are key factors maintaining the biotope and are considered in the sensitivity assessments where the pressure may alter these. Three variant sub-biotopes are described for this biotope, based principally on differences in infaunal species composition. The sensitivity assessments are applicable to all three variant biotopes.
The species inhabiting this biotope are characteristic of sandy beaches and are adapted to the high levels of disturbance from mobile sediments. Exposed beaches where this biotope typically occurs may change seasonally where winter storms remove large amounts of material that are then re-deposited over the following weeks and months as material is shifted from the subtidal (Quartel et al., 2008; Douglas et al., 1998). For instance, at Village Bay on St Kilda, an island group far out into the Atlantic west of Britain, an expanse of sandy beach was removed offshore as a result of winter storms to reveal an underlying rocky shore (Scott, 1960). Yet in the following summer the beach was gradually replaced when wave action was less severe. In view of such observations, that many sandy beaches disappear in winter and reappear in spring, it is likely that physical recovery of sediments would occur in less than a year ,although longer time periods may be required for unusually severe erosion events (Douglas et al., 1998).
The species present in the biotope must either be able to withstand mobile sediments through physical robustness, mobility and ability to re-position within sediments and/or to recover rapidly to sustain population losses following severe erosion. Characterizing species typically have opportunistic life history strategies, with short life histories (typically two years or less, see below), rapid maturation and extended reproductive periods. Typically they produce juveniles that are either brooded (amphipods) and therefore present to repopulate the disturbed habitat directly or have pelagic larvae capable of dispersal within the water column.
The polychaete Scolelepis squamata is a widespread species typical of sandy beaches but occurring in a range of sediment types. Populations are likely to be interconnected, supporting recolonization, as this species produces pelagic larvae. Scolelepis squamata exhibits an extended reproductive period allowing it to produce larvae over an extended period. In a Belgian population, Scololepis squamata were semelparous (breeding once and then dying) and lived for 24 months (Speybroeck et al., 2007). Fertilization is external and the larva is free swimming for about five weeks before settlement (Fish & Fish, 1996). Recruitment in Belgium was observed from July until October (Speybroek et al., 2007). Scolelepis squamata has been observed to swim and significant seasonal changes in its distribution within the swash and surf zones have been reported, indicating that the species is able to re-establish itself within the substratum following displacement
The amphipods characterizing this biotope are found in sediments subject to physical disturbance, as a result of wave action or in wave sheltered biotopes, strong tidal streams. This group is therefore tolerant of disturbed environments and can recover quickly. Bathyporeia spp. are short lived, reaching sexual maturity within 6 months with 6-15 eggs per brood, depending on species. Reproduction may be continuous (Speybroeck et al., 2008) with one set of embryos developing in the brood pouch whilst the next set of eggs is developing in the ovaries. However, specific reproductive periods vary between species and between locations (Mettam, 1989) and bivoltine patterns (twice yearly peaks in reproduction) have been observed (Mettam, 1989; Speybroeck et al., 2008). In Pontocrates arenarius from Irish Sea coasts breeding has been recorded throughout the year (Fish & Fish, 1996). Little is known of the breeding patterns of Haustorius arenarius populations in Britain, but females with eggs are found during the summer months and longevity is believed to be two, possibly three years (Fish & Fish, 1996). Adult amphipods are highly mobile in the water column and recolonization by the adults is likely to be a significant recovery pathway. The life history traits of rapid sexual maturation and production of multiple broods annually support rapid local recolonization of disturbed sediments where some of the adult population remains. The isopod Eurydice pulchra also produces brooded young, but only produces a single brood a year, reproducing twice in its two year lifespan (Fish, 1970; Jones, 1970).
Leewis et al. (2012) investigated the recovery of the characterizing species, Scolelepis squamata, Eurydice pulchra, Haustorius arenarius and Bathyporeia sarsi, following beach nourishment by comparing beaches that had been exposed at different times. The lengths of beach nourished varied from 0.5 kn to > 7 km and nourishment is likely to kill all animals present, so the results are applicable to broad-scale disturbance and defaunation. Recovery to original abundances appeared to occur within one year for the characterizing species which were in agreement with other studies (Leewis et al., 2012 and references therein).
Resilience assessment. As a consequence of the dynamic nature of the habitat the faunal component of the biotope is very sparse and low in species richness. Therefore, the community might be considered 'mature' only a few days or weeks after the last storm event, as the mobile species displaced from the biotope and those from adjacent area colonize the substratum via the surf plankton. Even following severe disturbances recovery would be expected to occur within a year, supported by the study by Leewis et al. (2012) and life-history traits. Resilience is therefore assessed as ‘High’ for any level of impact (Resistance is ‘None’, ‘Low’ or ‘Medium’.
NB: The resilience and the ability to recover from human induced pressures is a combination of the environmental conditions of the site, the frequency (repeated disturbances versus a one off event) and the intensity of the disturbance. Recovery of impacted populations will always be mediated by stochastic events and processes acting over different scales including, but not limited to, local habitat conditions, further impacts and processes such as larval-supply and recruitment between populations. Full recovery is defined as the return to the state of the habitat that existed prior to impact. This does not necessarily mean that every component species has returned to its prior condition, abundance or extent but that the relevant functional components are present and the habitat is structurally and functionally recognizable as the initial habitat of interest. It should be noted that the recovery rates are only indicative of the recovery potential.
Intertidal species are exposed to extremes of high and low air temperatures during periods of emersion. They must also be able to cope with sharp temperature fluctuations over a short period of time during the tidal cycle. In winter air temperatures are colder than the sea, conversely in summer air temperatures are much warmer than the sea. Species that occur in the intertidal are therefore generally adapted to tolerate a range of temperatures, with the width of the thermal niche positively correlated with the height of the shore that the animal usually occurs at (Davenport & Davenport, 2005). The species present in this biotope are present in the mid and/or upper shore and therefore are likely to have broad temperature tolerances and to be tolerant of temperature fluctuations.
Many intertidal species can alter metabolic activity, burrow deeper in sediment or move to deeper water to tolerate or escape unfavourable conditions. At low tide, air temperature becomes critically important to intertidal animals: on sandy beaches the substratum, from the surface to a depth of several centimetres, can experience large variations in temperature during a single tidal cycle and throughout the year (Hayward, 1994). For instance, Khayrallah & Jones (1980b) reported the temperature range of sand at a depth of 1 cm during neap tides to be from -2°C in February 1973, to a maximum of 25°C in July 1977. Although adapted to temperature change, severe acute change may result in seasonal reduction in species richness and abundance, but the effects of an acute temperature increase are not necessarily direct and may be more related to the resultant changes in other factors, especially reductions in oxygen resulting from enhanced microbial activity (Hayward, 1994; Eltringham, 1971).
The amphipods and isopods that occur within this habitat are mobile and can avoid unfavourable conditions to some extent. The isopod Eurydice pulchra, was observed to migrate seasonally off-shore in the Dovey Estuary (Wales). Bathyporeia life cycles vary between locations and this is related to temperature (Mettam, 1989). Preece (1971) tested temperature tolerances of Bathyporeia pelagica and Bathyporeia pilosa in the laboratory. Individuals acclimated to 15oC for 24 hours were exposed to temperature increases (water temperature raised by 0.2oC/minute). As test temperature were reached individuals were removed, placed in seawater at 4oC and allowed to recover for 24 hours at which point mortalities were tested. Amphipods were also allowed to bury into sediments and held at test temperatures for 24 hours of 32.5 oC, 31.8oC and 29.5oC before being allowed to recover in fresh seawater at 15oC for a further 24 hours, before mortalities were assessed. Upper lethal temperatures (the temperature at which 50% of individuals died for adult males and gravid females of Bathyporeia pilosa were 37.5oC and 39.4oC, respectively. Bathyporeia pelagica exhibited lower tolerances and adult males and gravid females had upper lethal temperature tolerances of 33.4 and 34.2oC respectively. These tests measures short-term exposure only and species had lower tolerance for longer-term (24 hour exposure). No mortality occurred for Bathyporeia pilosa individuals held at 29.5oC and 30.8oC; however 15% of individuals exposed to water temperatures of 31.8oC and 96% at 32.5oC died. Bathyporeia pelagica exhibited lower tolerances, 11% of individuals died after 24 hr exposure to 29.5oC and 100% mortality occurred at 30.8oC and above (Preece, 1971).
Tolerances for temperature changes may, therefore, vary between even closely related characterizing species and some shifts between the variant sub-biotopes may occur although the biotope LS.LSa.MoSa.AmSco would still be recognisable. The amphipod Bathyporeia pilosa, for example, tends to occur higher on the shore than Bathyporeia sarsi (Degraer et al., 2003) and Bathyporeia pelagica (Preece, 1971) and this may be linked to a greater physiological tolerance for temperature extremes. Other species of the community, such as Scolelepis squamata are infaunal and their environmental position and ability to bury deeper into the sand is likely to protect them from desiccation. Scolelepis squamata appears to be capable of tolerating the well-drained sediments of this biotope and generally demonstrates a high tolerance to different environmental conditions (Souza & Borzone, 2000).
Scolelepis squamata is a widespread species occurring on sandy beaches in the North and South Atlantic, North pacific, Indian Ocean, and the Mediterranean (Souza & Borzone, 2000), with the latitudinal range from 58oN to 35oS (Bayed et al., 2006). Over its range it is exposed to both higher and lower temperatures than experienced in the UK, suggesting a broad thermal tolerance. Widely separated populations may be genetically distinct and acclimated to local conditions so that the distribution may not necessarily represent temperature tolerance.
Sensitivity assessment. Typical surface water temperatures around the UK coast vary seasonally from 4-19 oC (Huthnance, 2010). A chronic increase in temperature throughout the year of 2oC may fall within the normal temperature variation and an acute increase in water temperatures from 19 to 24oC for a month may be tolerated by the characterizing species supported by deeper burrowing and/or migration. For Bathyporeia spp. temperature increases above 30oC appear to be critical based on Preece (1971). For intertidal biotopes air temperature may be more critical in the hottest parts of the year although nocturnal emergence of Bathyporeia spp. and isopods, or thr burrowing life habit may also enhance survival. Biotope resistance is therefore assessed as ‘High’ and resilience as ‘High’ so that the biotope is assessed as ‘Not sensitive’. Increased water and air temperatures and desiccation may lead to greater synergistic effects and the loss of characterizing amphipods and isopods may result in shifts between the variant sub-biotopes.
Intertidal species are exposed to extremes of high and low air temperatures during periods of emersion. They must also be able to cope with sharp temperature fluctuations over a short period of time during the tidal cycle. In winter air temperatures are colder than the sea; conversely in summer air temperatures are much warmer than the sea. Species that occur in the intertidal are therefore generally adapted to tolerate a range of temperatures, with the width of the thermal niche positively correlated with the height of the shore that the animal usually occurs at (Davenport & Davenport, 2005).
Crisp (1964) reported that species of amphipod and isopods seemed to be unharmed by the severe winter of 1962-1963. This may be due to burial in sediments buffering temperature or seasonal migration to deeper waters to avoid freezing. In the winter, Eurydice pulchra , for example, migrates into the sublittoral zone, thus escaping extreme temperatures (Jones, 1970b) and winter migrations have also been observed for Bathyporeia spp. (Fish & Fish, 1978; Fish & Preece, 1970).
Preece (1971) tested the temperature tolerances of Bathyporeia pelagica and Bathyporeia pilosa in the laboratory. Individuals acclimated to 15oC for 24 hours were placed in a freezer in wet sediment. As test temperatures were reached individuals were removed and allowed to recover for 24 hours at which point mortalities were tested. Amphipods were also allowed to bury into sediments and held at test temperatures of -1oc, -3oC and -5oC for 24 hours before being allowed to recover in fresh seawater at 15oC for a further 24 hours before mortalities were assessed. Lower lethal short term tolerances of Bathyporeia pilosa and Bathyporeia pelagica were -13.6oC and -6.4oC respectively. Sensitivity to longer-term exposure is greater, especially for Bathyporeia pelagica. Bathyporeia pilosa individuals could withstand temperatures as low as -1oC for 24 hours, while 42% of Bathyporeia pelagica died. At -3oC 5% of Bathyporeia pilosa died (100% of Bathyporeia pelagica) but this rose to 82% at -5oC.
Sensitivity assessment. Typical surface water temperatures around the UK coast vary seasonally from 4-19 oC (Huthnance, 2010). A chronic decrease in temperature throughout the year of 2oC may fall within the normal temperature variation but an acute decrease in water temperatures from 4oC to -1oC at the coldest part of the year may lead to freezing and lethal effects on for a month may be tolerated by the characterizing species supported by deeper burrowing and/or migration. For Bathyporeia spp. seawater temperature decreases below -1oC appear to be critical based on Preece (1971). For intertidal biotopes air temperature may be more important than seawater temperatures in the coldest parts of the year and nocturnal emergence of Bathyporeia spp. and isopods or burrowing life habit may reduce survival, although these species are more likely to be quiescent during cold periods or to have migrated to the subtidal. Biotope resistance is therefore assessed as ‘High’ and resilience as ‘High’ so that the biotope is assessed as ‘Not sensitive’
|No evidence (NEv)||No evidence (NEv)||No evidence (NEv)|
This biotope is found in full salinity (30-35 ppt) habitats (JNCC, 2015), a change at the pressure benchmark is therefore assessed as a change to hypersaline conditions. Little evidence was found to assess responses to hypersalinity. However, monitoring at a Spanish desalination facility where discharges close to the outfall reached a salinity of 53, found that amphipods were sensitive to the increased salinity and that species free-living in the sediment were most sensitive. The study area did not host any of the species characterizing this biotope but the results indicate a general sensitivity (De-la-Ossa-Carretero, et al., 2016).
Sensitivity assessment. Not assessed, ‘No evidence’.
The biotope is found in full salinity habitats (JNCC, 2015). A change at the pressure benchmark refers to a decrease from full to variable (18-35 ppt), or to reduced salinity (18-30 ppt). Intertidal species tend to be euryhaline as they experience periods of higher salinities where freshwater evaporates from interstitial spaces and decreased salinities when rainfall is high. Short-term tolerance is likely to be high but changes in salinity over the longer time may affect the biological assemblage. Eurydice pulchra was found to be relatively euryhaline (Jones, 1970b), whilst Bathyporeia pelagica migrates seaward in response to reduced salinities, the effect of which is enhanced by higher temperature (Preece, 1970). Bathyporeia pilosa is, however, more tolerant of low salinities and is capable of reproducing at salinities as low as 2 (Khayrallah, 1977). Populations of Bathyporeia pilosa within the upper reaches of the Severn Estuary experience wide fluctuations in salinity ranging from 1-22 depending on the season and tidal cycle (Mettam, 1989). The physiological stress for this environment affects size and reproduction (Mettam, 1989). Speybroeck et al. (2008) noted that Bathyporeia pilosa tends to occur subtidally in estuarine and brackish conditions. Local populations may be acclimated to the prevailing salinity regime and may exhibit different tolerances to other populations subject to different salinity conditions and, therefore, caution should be used when inferring tolerances from populations in different regions.
Sensitivity assessment. A decrease in salinity may lead to some changes in species abundance and this may lead to some changes in classification between the sub-biotope variants. Bathyporeia pilosa has high salinity tolerances and may replace more sensitive species, however, the biotope would still be recognisable as a LS.LSa.MoSa habitat and may retain its identity as LS.LSa.MoSa.AmSco.Sco . As some changes in species richness and abundance may occur, resistance is assessed as ‘Medium’ and resilience as ‘High’ (following restoration of typical habitat conditions). Sensitivity is therefore assessed as ‘Low’. Replacement of amphipods by an oligochaete dominated community would lead to reclassification to the biotope LS.LSa.MoSa.Ol.VS.
Water movement is a key factor physically structuring this biotope, with sediment sorting and mobilisation by tidal streams and wave action modifying the sediments present and the level of disturbance. Where this biotope occurs in more wave sheltered areas the biological structure alters in response to the decrease in sediment mobility and the presence of finer sand fractions and may become classified as one of the sub-biotopes LS.LSa.MoSa.AmSco.Eur orLS.LSa.MoSa.AmSco.Pon, depending on the species present and abundance. In areas sheltered from wave action, water flow may become a more important factor but the threshold for changes is less clear. Some changes between biotope types may also be cyclical and/or vary naturally depending on seasonal patterns.
A change in water flow at the pressure benchmark may, however, be significant as sand fractions are not cohesive (particularly where these occur higher on the shore and are coarser and drier) and are eroded at lower current velocities that muds and silts. Sand particles are most likely to be eroded at about 0.20 m/s (based on the Hjulström-Sundborg diagram, Sundborg, 1956).
Of the species present, Scolelepis squamata occurs in the broadest range of sediment types (see physical change pressures) and may have the greatest tolerance for changes in flow speeds, based on its habitat distribution. This species may respond to decreased water flows by switching from suspension feeding to deposit feeding (Dauer,1983).
Sensitivity assessment. The sediments that characterize this biotope and sub-biotopes are mobile sands that range from coarse to fine, a change at the pressure benchmark (increase or decrease) may lead to some changes in sediment sorting and the biotope classification may revert to different sub-biotopes within the biotope LS.LSa.MoSa.AmSco based on sediment changes. However, it is unlikely that a change would lead to a sandy mud or mud sediment developing as fine silts require lower velocities to deposit than erode. The wave action typically experienced by the exposed habitats this biotope occurs in will maintain a recognisable species-poor sand biotope. Biotope resistance is therefore assessed as ‘High’ and resilience as ‘High’ (by default), so that the biotope is assessed as ‘Not sensitive’. Changes in water flow coupled with wave action could lead to more severe physical changes with the deposition of fine sediments (see physical change pressures).
This biotope is found on the mid and lower shore (JNCC, 2015). On sandy shores (as in rocky shores) zonation of species occurs in relation to tidal height. The degree of wave exposure and sediment characteristics (notably drainage) influences the zonation patterns observed (McLachlan et al., 1995). Under more exposed conditions this biotope may occur below BarSa, or BarSh (JNCC, 2015). Under more sheltered conditions, it may occur above the LS.LSa.FiSa communities. The biotope LS.LSa.St.Tal may be present on the same shores where driftlines of decomposing seaweed and other debris occur on the upper shore.
Established beach fauna, exhibit physiological and behavioural adaptations to the drying out of sediments that accompanies the tidal cycle (Eltringham, 1971). The characterizing amphipod species are mobile, with an endogenous swimming rhythm that is coupled to circasemilunar pattern of emergence, which serves to reduce the risk of animals being stranded high on the shore (Jones & Naylor, 1970; Fish & Fish, 1972; Alheit & Naylor, 1976). Tolerances for emergence may vary between species and some shifts may occur although the biotope would still be recognisable. The amphipod Bathyporeia pilosa, for example, tends to occur higher on the shore than Bathyporeia sarsi (Degraer et al., 2003) and Bathyporeia pelagica (Fish & Preece, 1970). Other characterizing species, ioncluding Scolelepis squamata are also infaunal and their environmental position and ability to bury deeper into the sand is likely to protect them from desiccation. Scolelepis squamata appears to be capable of tolerating the well-drained sediments of this biotope and generally demonstrates a high tolerance to different environmental conditions (Souza & Borzone, 2000).
Changes in emergence are likely to alter suspension feeding by Scolelepis squamata which will be restricted to periods when immersed in water. Drying of sediments may prevent feeding by Bathyporeia spp. (Fish & Preece, 1970). An increase in emergence could therefore affect both these species but may not directly inhibit the predator Eurydice pulchra.
Changes in emergence may result in sub-biotope shifts between the LS.LSa.MosSa.AmSco.Eur sub-biotopes as the characterizing species for the biotopes exhibit some zonation (Degraer et al., 2003) , influenced also by wave exposure and sediment sorting and degree of water retention (Defeo & McLachlan, 2005). The sub-biotope LS.LSa.MoSa.AmSco.Eur may occur on the mid and upper shore together with LS.LSa.MoSa.AmSco.Sco, or above LS.LSa.MoSa.AmSco.Pon and the Po communities. Under more exposed, open conditions, LS.LSa.MoSa.AmSco.Eur may be restricted to the lower part of the shore, Where LS.LSa.MoSa.AmSco.Pon occurs on the mid shore in relatively sheltered conditions, finer sand biotopes (LS.LSa.FiSa.Po) may be present on the lower shore. Talitrid dominated biotopes may occur above this biotope group where driftlines of fucoids and other debris occur on the upper shore.
In summary, changes in emergence are likely to result in some shifts in the shoreward or landward extent of the biotope group due to changes in the length of time the biotope is uncovered and covered. Where the changes are relatively small the changes may simply be shifts between sub-biotopes. However more significant changes could lead to biotopes at the lower shore becoming sub-littoral or colonized by bivalves and more species rich assemblages. Similarly upper shore biotopes that are at the limit of the ebbing tide could revert to strandline biotopes LS.LSa.St.Tal or tend to revert to the species poor biotope LS.LSa.MoSa or the Scolelepis squamata dominated variant (LS.LSa.MoSa.AmSco.Sco) due to the species tolerance for well-drained habitats
Sensitivity assessment. Sandy beaches exhibit vertical zonation of biotopes due to species differing tolerances for emergence. Species within the biotope exhibit physiological and behavioural adaptations to changes and the biotope as a group is unlikely to be very sensitive to changes in emergence that do not alter the shore zone (from mid-eulittoral to supralittoral, for example). Changes in emergence may result in some changes in upper and lower extents of the biotope and the sub-biotopes and biotope resistance is therefore assessed as ‘Medium’, resilience is assessed as ‘High’ and biotope sensitivity is therefore ‘Low’.
Water movement is a key factor physically structuring this biotope, with sediment sorting and mobilisation by tidal streams and wave action modifying the sediments present and the level of disturbance. The LS.LSa.MoSa.BarSa biotope group tends to be found on exposed shores (very exposed to moderately exposed, JNCC, 2015). In sandy habitats that are more sheltered from wave action, finer sands are deposited that are less mobile, more cohesive and hold more water. This allows more species rich and diverse assemblages to develop, such as the sub-biotope LS.LSa.MoSa.AmSco.Eur In more wave sheltered areas the barren sand biotope may be present on the upper shore only.
Sensitivity assessment. Wave action is a key factor structuring this biotope and moderately exposed examples may contain the more species rich sub-biotopes. As the biotope occurs across three wave exposure categories (JNCC, 2015) this is considered to indicate, by proxy, that a change in wave exposure at the pressure benchmark is less than the natural range of wave heights experienced. Biotope resistance to this pressure is therefore assessed as ‘High’ and resilience as ‘High (by default) so that the biotope is considered to be ‘Not sensitive’ at the pressure benchmark.
|Not relevant (NR)||Not relevant (NR)||Not sensitive|
Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.
Levels of contaminants that exceed the pressure benchmark may cause impacts. For most metals, toxicity to crustaceans increases with decreased salinity and elevated temperature, therefore marine species living within their normal salinity range may be less susceptible to heavy metal pollution than those living in salinities near the lower limit of their salinity tolerance (McLusky et al., 1986). Jones (1973; 1975b) found that mercury (Hg) and copper (Cu) reacted synergistically with changes in salinity and increased temperature (10°C) to become increasingly toxic to species of isopod, including Eurydice pulchra.
|Not relevant (NR)||Not relevant (NR)||Not sensitive|
Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.
Similar biotopes have been shown to recover rapidly from exposure to oil pollution from single events. The exposed sandy beach of Ladeira (Corrubedo Bay, NW Spain) was sampled during seven years (2003-2009) after the Prestige oil spill (winter 2002-03), to determine interannual variations in the macroinfaunal community in two ways: (i) through ecological indices (species richness and abundances, Shannon's diversity and Pielou's evenness) and (ii) through the density of the most representative species (Junoy et al., 2013). A clear zonation pattern was found, consisting of two zones: (i) the supralittoral, occupied by talitrid amphipods, isopods and insects, and (ii) the intertidal, where marine crustaceans and polychaetes prevailed. The amphipods Talitrus saltator and Talorchestia deshayesii dominated from the drift line upwards, and isopods (Eurydice spp.), polychaetes (Scolelepis spp.) and the amphipod Pontocrates arenarius dominated the intertidal. Univariate indices remained constant throughout the study period in the supralittoral, but they varied widely in the intertidal zone. Multivariate analysis showed that the Prestige oil spill scarcely affected the macroinfaunal community structure during the study period (2003-2009) and its effect was limited just to the first campaign (2003), six months after the Prestige accident (Junoy et al., 2013).
|Not relevant (NR)||Not relevant (NR)||Not sensitive|
Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.
|No evidence (NEv)||No evidence (NEv)||No evidence (NEv)|
|Not relevant (NR)||Not relevant (NR)||Not sensitive|
The mobile sands that characterize this biotope may have relatively high oxygen concentration and a lack a black reducing layer (JNCC, 2015). Brafield (1964) concluded that the most significant factor influencing the oxygenation is the drainage of the beach which, in turn, is determined by the slope and particle size.
On exposed shores the sand sediments are coarser and more porous and therefore have a higher oxygen content. Oxygen depletion becomes a severe problem at all states of the tide on only the very finest grained beaches, and as a general rule, if the percentage of particles of less than 0.25 mm median diameter exceeds 10% of a sediment, then the oxygen concentration of its interstitial water will be less than 20% of the air saturation level, and will drop rapidly during low tide periods (Brafield, 1964). Fine sands tend to have lower oxygen levels because their lower permeability leads to the trapping of detritus which, together with the large surface area for microbial colonisation, leads to higher oxygen uptake (Eagle, 1983).
Laboratory studies by Khayrallah (1977) on Bathyporeia pilosa, indicated that it has a relatively poor resistance to conditions of hypoxia in comparison to other interstitial animals. However, Mettam (1989) and Sandberg (1997) suggest that Bathyporeia pilosa can survive short-term hypoxia.
Sensitivity assessment. This biotope is intertidal and is characterized by mobile sands on wave exposed beaches. Exposure to air and the mixing effect of wave action will limit the intensity and duration of exposure to deoxygenated waters. The species characterizing the biotope are also mobile and able to migrate vertically or shorewards to escape unsuitable conditions. Biotope resistance is therefore assessed as ‘High’ and resilience as ‘High’ (by default) so that the biotope is considered to be ‘not sensitive’.
In-situ primary production is limited to microphytobenthos within and on sediments and the high levels of sediment mobility may limit the level of primary production as abrasion would be likely to damage diatoms (Delgado et al., 1991). The characterizing polychaete Scolelpis squamata is a suspension and depost feeding polychaete (Dauer, 1983) while the amphipods feed on epipsammic diatoms attached to the sand grains (Nicolaisen & Kanneworff, 1969). Both these groups may benefit from slight nutrient enrichment if this enhanced primary production.
Sensitivity assessment. Nutrient level is not a key factor structuring the biotope at the pressure benchmark. In general however, primary production is low and this biotope is species poor and characterizing species may be present at low abundances (depending on wave exposure). Biotope resistance is therefore assessed as ‘High’, resilience as ‘High’ (by default) and the biotope is considered to be ‘Not sensitive’. Changes in nutrient status may indirectly affect this biotope where these result in changes in diatom production and inputs of macroalagal debris.
The biotope occurs in mobile sand sediments where wave action leads to particle sorting, in-situ primary production is restricted to microphytobenthos although sediment mobility may restrict production levels (Delgado et al., 1991). An input of organic matter would provide a food subsidy to the suspension/deposit feeding Scolelepis squamata and may be utilised by amphipods also. In organically enriched areas Scolelepis squamata switch from suspension to deposit feeders (Weston, 1990). In Loch Eil where sediments were enriched with organic matter from pulp mill effluent, the congener Scolelepis fuliginosus was a co-dominant with Capitella capitata (Gray, 1979). The congener, Scolelepis fuliginosa, has also been reported to colonise the anoxic and surrounding enriched sediments beneath fish pens in the Aegean and in Scottish Waters (Klaoudatos et al., 2006; Brown et al., 1987).
The biotope description (JNCC, 2015) notes that inputs of organic matter seeping from the driftline can result in high abundances of Bathyporeia pilosa. Organic matter is unlikely to accumulate as sediment mobility and re-suspension by wave action will result in removal of fine organic matter deposits. The isopod Eurydice pulchra is an aggressive and very mobile predator, feeding on polychaetes and amhipods, including Bathyporiea pilosa, Bathyporeia sarsi and Scolelepuis squamata (Jones, 1968). An increase in secondary production of prey species would therefore be of benefit to this species.
An increase in organic enrichment that exceeded the pressure benchmark may impact the habitat and biological assemblage, particularly in more sheltered areas where deposits can accumulate. For instance, prior to the introduction of a sewage treatment scheme in the Firth of Forth (Scotland) , the communities of several sandy beaches were considerably modified by gross sewage pollution (Read et al., 1983). The west end of Seafield beach exhibited extremely reduced diversity with a community dominated by Scolelepis fuliginosa and Capitella capitata, to the almost exclusion of all other species of macrofauna. However, at Portobello beach, a reduction in the number of species was recorded and the presence of a 'dominant' replacement community was less obvious. Furthermore, in 1977, before the introduction of the sewage scheme, meiofauna population counts at Seafield and Portobello were also conspicuously lower than for other Scottish beaches (McIntyre, 1977). Many of the major taxa commonly associated with marine intertidal meiobenthos were scarce or absent. Only nematodes, gastrotriches, harpacticoids and turbellarians were commonly identified from samples, nematodes being the most abundant taxon. Following sewage pollution abatement in 1977, dramatic changes in the macrofauna occurred. The Scolelepis / Capitella community declined steadily throughout 1978-1979, so that by spring 1980 species normally associated with 'cleaner' sandy beaches were recorded e.g. Microthalmus sp., Ophiodromus flexuosus, Eulalia viridis, Eurydice pulchra Monoculodes sp., but not at pre-impact abundances. There was also an increase in meiofaunal diversity and reduction in dominance by certain taxa.
Sensitivity assessment. At the pressure benchmark organic inputs are likely to represent a food subsidy for the characterizing species and are unlikely to significantly affect the structure of the biological assemblage or impact the physical habitat. Biotope sensitivity is therefore assessed as ‘High’ and resilience as ‘High’ (by default) and the biotope is therefore considered to be ‘Not sensitive’.
All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’). Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.
The biotope is characterized by the sedimentary habitat (JNCC, 2015), a change to an artificial or rock substratum would alter the character of the biotope leading to reclassification and the loss of the sedimentary community including the characterizing amphipods and Scolelepis squamata that live buried within the sediment (Van Tomme et al., 2013).
Sensitivity assessment. Based on the loss of the biotope, resistance is assessed as ‘None’, recovery is assessed as ‘Very low’ (as the change at the pressure benchmark is permanent and sensitivity is assessed as ‘High’.
The pressure benchmark refers to the simplified Folk classification developed by Long (2006) and the UK Marine Habitat Classification Littoral and Sublittoral Sediment Matrices (Connor et al., 2004). The biotope occurs on mobile sands, a change at the pressure benchmark refers to a change to sandy muds or muddy sands or to coarser gravel sediments. Experiments by Van Tomme et al. (2013) have shown that the optimal sedimentary habitats for the species that characterize this biotope vary slightly. Bathyporeia pilosa and Eurydice pulchra prefer the finest sediments, although at a subtidal dredge disposal site the change to a finer sediment led to a reduction in the abundance of Bathyporeia pilosa (Witt et al., 2004).
Bathyporeia sarsi has a broader preference and also occurred in medium-coarse sediments (Van Tomme et al., 2013). The polychaete Scolelepis squamata exhibits the broadest preferences and occurrs in muddy sands, sands and coarse sediments (Speybroek et al. 2007; Van Tomme et al., 2013).
Sensitivity assessment. Although Scolelepis squamata has broad sediment preferences a change to either a finer muddy sediment or a coarser sediment, would lead to loss of the biotope and the characterizing species. Based on the loss of the biotope, resistance is assessed as ‘None’, recovery is assessed as ‘Very low’ (as the change at the pressure benchmark is permanent and sensitivity is assessed as ‘High’.
Bathyporeia pelagica lives infaunally in the uppermost 3 cm of sandy substrata as does the isopod Eurydice pulchra (Fish, 1970). The burrowing polychaete Scolelepis squamata may burrow more deeply (depths of 40cm have been quoted but a citation for this depth was not found). Extraction of the sediment to 30cm is likely to remove all amphipods and isopods within the footprint (although if disturbed some may be able to escape). Most Scolelepis squamata are also likely to be removed.
Removal of some beaches by storm action is normal and recovery is likely to occur within one-two years depending on local sediment supply and water transport.
Sensitivity assessment. Biotope resistance to extraction of sediment and characterizing species is assessed as ‘None. Resilience is assessed as ‘High’, as sediment recovery will be enhanced by wave action and mobility of sand. The characterizing species are likely to recover through transport of adults in the water column or migration from adjacent patches. Biotope sensitivity is therefore assessed as ‘Medium’.
This biotope group is present in mobile sands, the associated species are generally present in low abundances and adapted to frequent disturbance suggesting that resistance to surface abrasion would be high. The amphipod and isopod species present are agile swimmers and are characterized by their ability to withstand sediment disturbance (Elliott et al. 1998). Similarly, the polychaete Scolelepis squamata is adapted to life in unstable sediments and survives through rapid burrowing (McDermott, 1983, cited from Elliott et al., 1998). This characteristic is likely to protect this species from surface abrasion.
Comparisons between shores with low and high levels of trampling found that the amphipod Bathyporeia pelagica is sensitive to human trampling, other species including Pontocrates arenarius and the isopod Eurydice affinis also decreased in response to trampling but Bathyporeia pelagica appeared to be the most sensitive (Reyes-Martínez et al., 2015). Changes in abundance of talitrid amphipods on urban beaches subject to high levels of recreational use was also observed by Bessa et al. (2014), this study compared abundances between samples taken ten years apart and thus the trends observed were not directly attributable to trampling vs beach cleaning or other pressures although they illustrate a general trend in density patterns as recreational use increases. Ugolini et al. (2008) carried out a controlled trampling experiment on Talitrus saltator. Plastic cylinders of 110 cm diameter (area 0.95 m2) were placed in the sand and all individuals trapped and counted, and 400 steps were made in a cylinder in 15 minutes after the amphipods had reburied. The trampling rate was based on observed number of beach users and therefore represents a realistic level of exposure. Alive sandhoppers were counted at the end of the experiment and 24 hours after. Trampling significantly reduced abundance of the amphipods and after 24 hours the percentage of surviving amphipods dropped to almost zero, while survival rates of control (untrampled) amphipods were unaffected. Abrasion and compaction can, therefore, kill buried amphipods within sediments.
Sensitivity assessment. The trampling experiment (Ugolini et al., 2008) represents a high intensity of abrasion with multiple steps on the sediment within a short time period. The experimen, does, however, demonstrate that amphipods are sensitive to abrasion and compaction of the sediment and these results are observed by comparisons between heavily and lightly used areas (Reyes-Martínez et al., 2015; Bessa et al., 2014). Resistance to a single abrasion event is therefore assessed as ‘Low’ based on the characterizing species. Resilience is assessed as ‘High’, based on migration from adjacent populations and in-situ reproduction by surviving amphipods. Sensitivity is therefore assessed as ‘Low’. This assessment may underestimate sensitivity to high-levels of abrasion (repeated events within a short period). The trampling evidence and the evidence for penetration from mobile gears (see below) differ in the severity (resistance) of impact. This may be due to different levels of intensity (multiple trampling/abrasion events vs single penetration/towed gear impacts) or the nature of the pressure. Abrasion from trampling also involves a level of compaction that could collapse burrows and damage species through compression. Penetration may, however, break sediments open allowing mobile species to escape or species may be pushed forwards from towed gear by a pressure wave where this is deployed subtidally (Gilkinson et al., 1998). This suggests that exposure at different states of tide will mediate impacts. Both risk assessments are considered applicable to single events based on the evidence and the sensitivity assessment for both pressures is the same although resistance differs.
This biotope group is present in mobile sands, the associated species are generally present in low abundances and adapted to frequent disturbance suggesting that resistance to abrasion and penetration and disturbance of the sediment would be high. The amphipod and isopod species present are agile swimmers and are characterized by their ability to withstand sediment disturbance (Elliott et al. 1998). Similarly, the polychaete Scolelepis squamata is adapted to life in unstable sediments and survives through rapid burrowing (McDermott, 1983, cited from Elliott et al., 1998). This characteristic is likely to protect this species from surface abrasion.
Bergman and Santbrink (2000) found that direct mortality of gammarid amphipods, following a single passage of a beam trawl (in silty sediments where penetration is greater) was 28%. Similar results were reported from experiments in shallow, wave disturbed areas, using a toothed, clam dredge. Bathyporeia spp. experienced a reduction of 25% abundance in samples immediately after intense clam dredging, abundance recovered after 1 day (Constantino et al. 2009). Experimental hydraulic dredging for razor clams resulted in no statistically significant differences in Bathyporeia elegans abundances between treatments after 1 or 40 days (Hall et al., 1990), suggesting that recovery from effects was very rapid. Ferns et al. (2000) examined the effects of a tractor-towed cockle harvester on benthic invertebrates and predators in intertidal plots of muddy and clean sand. Harvesting resulted in the loss of a significant proportion of the most common invertebrates from both areas. In the muddy sand, the population of Bathyporeia pilosa remained significantly depleted for more than 50 days, whilst the population in clean sand recovered more quickly. These results agree with other experimental studies that clean sands tend to recover more quickly that other habitat types with higher proportions of fine sediment (Dernie et al., 2003).
Sensitivity assessment. Based on the evidence above it is considered that Bathyporeia spp. and other characterizing species will have ‘Medium’ resistance (mortality <25%) to abrasion, their small size, infaunal position and mobility enabling a large proportion of the population to escape injury. Recovery is assessed as ‘High’ and sensitivity is therefore categorised as ‘Low’.The trampling evidence (see above) and the evidence for penetration from mobile gears differ in the severity (resistance) of impact. This may be due to different levels of intensity (multiple trampling/abrasion events vs single penetration/towed gear impacts) or the nature of the pressure. Abrasion from trampling also involves a level of compaction that could collapse burrows and damage species through compression. Penetration may, however, break sediments open allowing mobile species to escape or species may be pushed forwards from towed gear by a pressure wave where this is deployed subtidally (Gilkinson et al., 1998). This suggests that exposure at different states of tide will mediate impacts. Both risk assessments are considered applicable to single events based on the evidence and the sensitivity assessment for both pressures is the same although resistance differs.
The characterizing species live within the sand and are unlikely to be directly affected by an increased concentration of suspended matter in the water column. Within the mobile sands habitat storm events or spring tides may re-suspend or transport large amounts of material and therefore species are considered to be adapted to varying levels of suspended solids.
Scolelepis squamata is a suspension feeder (Dauer, 1983) and may also deposit feed so may benefit from increased organic particles in suspension or deposited on the surface. Bathyporeia spp. feed on diatoms within the sand grains (Nicolaisen & Kanneworff, 1969), an increase in suspended solids that reduced light penetration could alter food supply. However, diatoms are able to photosynthesise while the tide is out and therefore a reduction in light during tidal inundation may not affect this food source , depending on the timing of the tidal cycle. The isopod Eurydice pulchra feeds on the amphipod and polychaete characterizing species and, it may therefore be indirectly affected by changes in food supply if other species are impacted by changes in suspended solids.
Amphipods and isopods may be regular swimmers within the surf plankton, where the concentration of suspended particles would be expected to be higher (Fincham, 1970a). Furthermore, during the winter, when Bathyporeia pelagica extends its distribution into the mouths of estuaries the species may encounter concentrations of suspended sediment measurable in grams per litre (benchmark is mg/l) (Cole et al. 1999).
Sensitivity assessment. Increased organic solids in suspension may provide food to the key characterizing species Scolelepis squamata. Increased inorganic suspended solids may increase abrasion but it is likely that the infaunal species would be unaffected. The biotope is considered to be ‘Not sensitive’ to a decrease in suspended solids that does not affect sediment transport and supply to the biotope. Biotope resistance is assessed as ‘Medium’ as some effects on feeding and diatom productivity may occur from increases in suspended solids, resilience is assessed as ‘High’, following a return to usual conditions and sensitivity is assessed as ‘Low’. This more precautionary assessment is presented in the table. Indirect effects such as deposition, erosion and associated sediment change that may result from changes in suspended solids in the long-term are assessed separately.
Evidence for the effects of siltation by thick layers of added sediment from beach nourishment is described for the heavy deposition pressure below. The pressure benchmark for light deposition refers to the addition of a relatively thin layer of deposits in a single event. Species adapted to coarse sediments may not be able to burrow through fine sediments, or experienced reduced burrowing ability. For example, Bijkerk (1988, results cited from Essink 1999) found that the maximal overburden through which Bathyporeia could migrate was approximately 20 cm in mud and 40 cm in sand. No further information was available on the rates of survivorship or the time taken to reach the surface.
To allow respiration, Scolelepis squamata requires permeable sediments (Dauer, 1985). Increased siltation that leads to surficial layers of fine sediment will inhibit permeability of surface sediments and reduce habitat suitability for this species. In a review that developed new sensitivity indices, Scolelepis squamata was characterized as AMBI Sedimentation Group II-Species sensitive to high sedimentation. They prefer to live in areas with some sedimentation, but don’t easily recover from strong fluctuations in sedimentation (Gittenberger & van Loon, 2011). However, Scolelepis squamata has been found to rapidly recover following disturbance, with some increase from original population size (Peterson et al., 2006; Leewis et al., 2012, Manning et al., 2014), recovering within nine months following nourishment (Menn et al., 2003, Leewis et al., 2012).
Sensitivity assessment. As the biotope is associated with wave exposed beaches, some sediment removal will occur, mitigating the effect of deposition. The mobile amphipods and the isopod Eurydice pulchra are likely to be able to burrow through a 5cm layer of fine sediments. Scolelepis squamata is also likely to be able to survive some burial and to reposition. Biotope resistance is therefore assessed as ‘High’ and resilience as ‘High’ (by default). The biotope is therefore considered to be ‘Not sensitive’ to this pressure. Repeated deposits or deposits over a large area or in sheltered systems that were shifted by wave and tidal action may result in sediment change (see physical change pressure).
Studies have found that beach ‘replenishment’ or ‘nourishment’ that involves the addition of sediments on beaches can have a number of impacts on the infauna (Peterson et al., 2000, Peterson et al., 2006). Impacts are more severe when the sediment added differs significantly in grain size or organic content (Nelson et al., 1989, Peterson et al., 2000). For example, Maurer et al. (1981) found that the amphipod Parahaustorius longimerus which occurs intertidally in clean, well-sorted sands and is an active, effective burrower was able to regain the surface after being buried by sand far more easily than when buried under silt/clay mixtures.
A thick layer of sediment has a smothering effect and in most instances buried species will die although some polychaetes can escape up to 90cm of burial In response to nourishment (Speybroek et al., 2007, references therein). Peterson et al. (2000) found that the dominant macrofauna were reduced by 86-99% 5-10 weeks after the addition of sediment that was finer than the original sediments but with a high shell content.
Little empirical information was found for the ability of characterizing species to reach the surface after burial. Bijkerk (1988, results cited from Essink 1999) found that the maximal overburden through which Bathyporeia could migrate was approximately 20 cm in mud and 40 cm in sand. No further information was available on the rates of survivorship or the time taken to reach the surface and no information was available for other characterizing species.
Leewis et al. (2012) investigated the recovery of the characterizing species, Scolelepis squamata, Eurydice pulchra, Haustorius arenarius and Bathyporeia sarsi, following beach nourishment by comparing beaches that had been exposed at different times. The lengths of beach nourished varied from 0.5 kn to > 7 km. Recovery to original abundances appeared to occur within one year for the characterizing species which were in agreement with other studies (Leewis et al., 2013 and references therein). Scolelepis squamata has been found to rapidly recover following disturbance, with some increase from original population size (Peterson et al., 2006; Leewis et al., 2012, Manning et al., 2014), recovering within nine months following nourishment (Menn et al., 2003, Leewis et al., 2012).
Repeated events are not considered at the pressure benchmark but it is noted that annual beach nourishment can alter beach sediments (see physical change pressure) and result in suppression of macroinvertebrate populations (Manning et al., 2014).
Sensitivity assessment. The thickness of sediment applied during beach nourishment is likely to exceed the 30cm pressure benchmark but the results from studies on the activity are informative, particularly with regard to recovery rate. Sediment removal by wave action could mitigate the level of effect but overall smothering by fine sediments is likely to result in mortality of characterizing amphipiods and isopods and possibly Scolelepis squamata. Biotope resistance is, therefore, assessed as ‘Low’ and resilience as 'High' (based on Leewis et al., 2012) so that biotope sensitivity is, therefore, assessed as ‘Low’.
|Not Assessed (NA)||Not assessed (NA)||Not assessed (NA)|
This pressure is not assessed. Amphipods may also consume microplastics although no negative effects have been documented. Ugolini et al.,( 2013) found that Talitrus saltator could consume polyethylene microspheres (diameter 10-45 mu m). Most microspheres were expelled in 24 h. and were totally expelled in one week. microsphere ingestion on the survival capacity in the laboratory. Analyses carried out on faeces of freshly collected individuals revealed the presence of polyethylene and polypropylene, confirming that microplastic debris could be swallowed by Talitrus saltator in natural conditions. The talitrid Orchestia gammarellus has also been recorded as ingesting microplastics in the size range 20-200µm (Thompson et al., 2004).
|No evidence (NEv)||No evidence (NEv)||No evidence (NEv)|
No evidence for the characterizing species was found to assess this pressure. For some amphipods there is evidence for geomagnetic orientation being inhibited or disrupted by the presence of electromagnetic fields or by changing magnetic fields. Arendse & Barendregt (1981) manipulated magnetic fields to alter orientation of the talitrid amphipod Orchestia cavimana.
Deep-water amphipods Gondogenia arctica have been shown to be sensitive to even weak electromagnetic fields which cancel magnetic orientation (Tomanova & Vacha, 2016). Loss of orientation was observed at a radiofrequency electromagnetic field of 2 nT (0.002 µT) (Tomanova & Vacha, 2016).
|Not relevant (NR)||Not relevant (NR)||Not relevant (NR)|
As this feature is not characterized by the presence of primary producers it is not considered that shading would alter the character of the habitat. No specific evidence was found to assess sensitivity of the characterizing species to this pressure. Changes in light level may, however, affect activity rhythms of the invertebrates. Amphipods within the biotope prefer shade and therefore an increase in light may inhibit activity, particularly at night when they emerge from the sediment and are most active (Jelassi et al., 2015; Ayari, 2015). Hartwick (1976) found that artificial lighting interfered with learning or orientation cues by Talitrids.
Orientation by light has been well studied for intertidal amphipods (particularly Talitrus saltator). Intertidal amphipods orientate themselves by a range of factors that include (but are not limited to) visual cues based on solar or astronomic cues such as the moon and the geomagnetic field (Scapini, 2014). Activity patterns are also linked to internal biological clocks that respond to diel, tidal, lunar and seasonal cycles, so that animals are active during the most suitable time of day or night (Scapini, 2014). The introduction of light or an increase in shading could therefore alter behavioural patterns and navigation. As responses may be species specific or vary according to local factors or individual needs such as feeding, mating, it is not possible to provide a simple assessment for this species. Some sensitivity is however likely if incident light levels were altered. This will depend, however, on the footprint and intensity of impact. Fanini et al., (2014) found no difference in abundance of Talitrus saltator between Greek beaches that frequently hosts small scale beach-parties with lights at night and those that were not used in this way.
Changes in light and level of shade may indirectly affect the characterizing Bathyporeia spp. through changes in bwehaviour and food supply via photosynthesis of diatoms within sediments. Benthic microalgae play a significant role in system productivity and trophic dynamics, as well as habitat characteristics such as sediment stability (Tait & Dipper, 1998). Shading couldprevent photosynthesis leading to death or migration of sediment diatomsaltering sediment cohesion and food supply to the grazing amphipods.
Sensitivity assessment. Changes in light are not considered to directly affect the biotope however, some changes in behaviopur or food supply for Bathyporeia spp could result. Sensitivity is assessed as ‘Medium’ and resilience is assessed as ’High’. Biotope sensitivity ids therefore assessed as ‘Low’.
As the amphipods and isopods that characterize this biotope have benthic dispersal strategies (via brooding), water transport is not a key method of dispersal over wide distances, as it is for some marine invertebrates that produce pelagic larvae such as the characterizing Scolelepis squamata. Barriers that limit tidal excursion and flushing may reduce connectivity or help to retain larvae.
Sensitivity assessment. The biotope (based on the biological assemblage) is considered to have ‘High’ resistance to the presence of barriers that lead to a reduction in tidal excursion, resilience is assessed as ‘High’ (by default) and the biotope is considered to be ‘Not sensitive’.
|Not relevant (NR)||Not relevant (NR)||Not relevant (NR)|
Not relevant’ to seabed habitats. NB. Collision by grounding vessels is addressed under ‘surface abrasion.
No evidence was found to assess visual perception for Scolelepis squamata. The characterizing species are likely to be able to detect light and some movement but are unlikely to have any visual acuity and are considered to not be sensitive to this factor. The amphipods emerge from the sediments at night and are unlikely to be disturbed although like many species they may flee from movements.
Sensitivity assessment. Biotope resistance is assessed as ‘High’ and resilience as ‘High’ so that the biotope is assessed as ‘Not sensitivie’.
|Not relevant (NR)||Not relevant (NR)||Not relevant (NR)|
Key characterizing species within this biotope are not cultivated or translocated. This pressure is therefore considered ‘Not relevant’ to this biotope group.
The sediments characterizing this biotope are coarse, mobile and free-draining, this limits establishment of marine and coastal invasive non-indigenous species as the habitat conditions are unsuitable for most species, as exemplified by the low species richness characterizing this biotope. This biotope is therefore considered to have 'High' resistance to this pressure and high resilience (by default), so that it is assessed as 'Not sensitive' to this pressure.
|No evidence (NEv)||No evidence (NEv)||No evidence (NEv)|
The polychaete Scolelepis squamata may be parasitized externally by a nematode, Theristus polychaetophilus, (Hopper 1966). Amphipods may also be infected by a number of parasites or pathogens that alter population numbers through changes in host condition, growth, behaviour and reproduction (Green Extabe & Ford, 2014). Infection by acanthocephalan larvae, for example, may alter behaviour and responses of gammarid amphipods (Bethel & Holmes, 1977).
No evidence was found for pathogen/parasite outbreaks that may result in mass-mortalities in the characterizing species and this pressure is not assessed.
|Not relevant (NR)||Not relevant (NR)||Not relevant (NR)|
No species characterizing the biotope are targeted by commercial or recreational fishers or harvesters. This pressure is therefore considered ‘Not relevant’.
The loss of the key characterizing species through unintentional removal would alter the character of the biotope and, depending on prey selection, could mean temporary reversion to another biotope within the LS.LSa.MoSa (depending on the identities and abundance of species remaining) . The ecosystem services such as secondary production and food for higher trophic levels would be lost. The polychaete Scolelepis squamata and the amphipods are predated on by wading birds and flat fish and other invertebrate predators during tidal inundation (Speybroeck et al., 2007; Van Tomme et al., 2014).
Sensitivity assessment. Biotope resistance to loss of the characterizing species is assessed as ‘Low’ as the burrowing lifestyle and mobility of species mean that a proportion of the population may escape incidental removal. Resilience is assessed as ‘High’ based on in-situ recovery and migration from adjacent populations and sensitivity is therefore assessed as ‘Low’. Despite the loss of a high proportion of the characterizing species the biotope would still be classified as belonging to the LS.LSa.MoSa group as some examples, particularly those that are very exposed to wave action, contain few species at low abundance (JNCC, 2015).
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Last Updated: 13/06/2016