Biodiversity & Conservation

SS.SSa.SSaVS.NintGam

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The important characterizing species may be relatively unaffected by substratum loss as they are mobile and rest upon the surface as opposed to burrowing into it, so would probably relocate. However, intolerance of the biotope to substratum loss has been assessed to be high owing to the fact that at the benchmark level all of the substratum is removed by an activity such as dredging and in the absence of the sand the biotope would not necessarily be recognized. The biotope should recover assuming that sand is re-deposited, therefore recoverability has been assessed to be very high.
Smothering
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The important characterizing species of the biotope are mobile, able to both swim and crawl and would therefore probably escape smothering. Consequently an intolerance assessment of not relevant has been made.
Increase in suspended sediment
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In the estuarine environment the concentration of suspended sediment is typically very high. Increased suspended sediment may bring additional food for Neomysis integer which suspension feeds upon phytoplankton and detrital material, although an excess of suspended matter may also have some adverse effects, e.g. clogging feeding structures. However on balance, an assessment of not sensitive at the benchmark level has been suggested.
Decrease in suspended sediment
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A decrease in suspended sediment would reduce the detrital food source available to the species, but at the benchmark level a decrease in suspended sediment is not likely to have a detectable effect on survival of the important characterizing species for a period of one month and an assessment of not sensitive has been made.
Desiccation
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The biotope is subtidal and therefore desiccation is not relevant.
Increase in emergence regime
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The biotope is subtidal and therefore a change in the emergence regime was not considered to be relevant.
Decrease in emergence regime
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The biotope is subtidal and therefore a change in the emergence regime was not considered to be relevant.
Increase in water flow rate
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Neomysis integer actively seeks regions where water flow rate is not in excess of 0.2 knots (10 cm/sec) such as at the waters edge or boundary layer. Normally the biotope experiences strong to moderately strong water flow rates and the benchmark increase would expose the community to currents in excess of 6 knots (> 3 m/sec). Species present in the biotope would probably experience difficulty in maintaining a position and be washed from the biotope. Sand is also likely to be swept away by increased tidal flow. In the absence of the important characterizing species the biotope would not be recognised and intolerance has therefore been assessed to be high. On resumption of a normal flow regime the species that may have been lost will probably recolonize from adjacent areas and recovery has been assessed to be very high assuming suitable substrate is deposited.
Decrease in water flow rate
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A decrease in water flow rate, in the absence of wave action determining substratum type would probably favour the accretion of finer silts and clays which, over a period of a year may serve to stabilise the surface sediment and enable the colonization of oligochaetes tolerant of conditions of low fluctuating salinity such as Limnodrilus hoffmeisteri and Tubifex tubifex. Consequently the biotope may no longer be recognisable and intolerance to a decreased water flow rate has been assessed to be high. Resumption of moderately strong to strong water flow rates would winnow away fine particulate matter that had accumulated and probably suppress the viability of species not normally present in the biotope, therefore recovery is likely to be high.
Increase in temperature
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Specimens of Gammarus salinus were tolerant of temperature fluctuations between 8 °C and 20 °C over a period of up to four weeks, acute temperature changes caused additional stress but did not result in mortality (Furch, 1972). The distribution of Neomysis integer extends to the south of the UK, along the Atlantic coast of Spain so the species may be able to tolerate a chronic change of 2 °C. However, Kuhlman (1984) found that over-wintering and summer generations of Neomysis integer had different upper temperature tolerances. Consequently, an acute increase in temperature may be particularly damaging to the population during the spring when the over-wintering population commences breeding than at other times of the year. Intolerance of the biotope fauna to an acute increase in temperature has been assessed to be intermediate. Recovery of the fauna is likely to be relatively rapid as recruitment will occur within in the year along with migration of the important characterizing species from other adjacent biotopes.
Decrease in temperature
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The distribution of both Neomysis integer and Gammarus salinus extends to the north of the UK, so the fauna of the biotope would probably be tolerant of a chronic decrease in temperature of 2 °C. Acute decreases in temperature may cause death of vulnerable proportions of the population owing to additional stress, e.g. those that are parasitized, and intolerance has been assessed to be intermediate. Recovery of the fauna is likely to be relatively rapid as recruitment will occur within the year along with migration of the important characterizing species from other adjacent biotopes
Increase in turbidity
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The Humber Estuary, in which the IGS.NeoGam biotope occurs is naturally highly turbid (Uncles et al., 2001). On a spring ebb tide in November 1995 concentrations of surface suspended particulate matter (SPM) were measured to be from 6 in the upper estuary to 13 g per litre at the confluence with the River Ouse which, would drastically reduce light penetration. Consequently, it is unlikely that the benchmark increase in turbidity would be of significance to the fauna and the biotope has been assessed not to be sensitive.
Decrease in turbidity
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Estuarine waters such as that of the Humber, in which the IGS.NeoGam biotope occurs, are typically turbid. The benchmark decrease in turbidity is unlikely to be of any significance to the fauna of the biotope and an assessment of not sensitive has been made.
Increase in wave exposure
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The biotope occurs in very sheltered to extremely sheltered locations where tidal flow is normally more important than wave action as a structuring factor. Increased wave exposure would probably result in displacement of the substratum. Over one year, sufficient layers of the substratum might be lost so that the biotope substratum changes to a different one, e.g. exposed rock. The important characterizing species, Neomysis integer and Gammarus spp. are relatively robust, epibenthic mobile species whose presence in the biotope is not especially determined by the nature of the substratum. However, they both utilize surface features and aggregate at the shallow waters edge in order to seek shelter from faster currents against which they cannot swim. Wave induced turbulence is likely to displace them and they may be washed from the biotope. Owing to the combination of a change in biotope substratum and potential loss of important characterizing species intolerance to increased wave exposure has been assessed to be high as the biotope would not be recognised. The important characterizing species have a very high capacity for recovery but owing to removal of the sandy substratum recovery of the biotope as a whole is likely to take longer and has been assessed to be moderate.
Decrease in wave exposure
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The biotope occurs in very sheltered to extremely sheltered locations where tidal flow is probably more important than wave action as a structuring factor. A reduction in wave action is therefore unlikely to have a significant effect. Therefore the biotope has been assessed to be not sensitive.
Noise
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Gammarus spp. and Neomysis integer may respond to vibrations caused by noise, but are likely to be not sensitive to noise at the benchmark level.
Visual Presence
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Gammarus spp. and Neomysis integer are unlikely to have the visual acuity to detect the presence of for instance boats travelling over the biotope. although, it is likely that they observe predators and react to them. An assessment of visual presence is related to human activity to which the community is considered to be not sensitive.
Abrasion & physical disturbance
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Elliot et al. (1998) reported that subtidal mobile sand banks were colonized by infaunal or epifaunal small bivalves, crustaceans and polychaetes adapted to a changeable hydrography and substratum. Species living in mobile substrata are able to reburrow quickly after being washed out of the sediment, e.g. Nephtys cirrhosa and amphipods. Continual sediment disturbance results in a large number of opportunistic species, e.g. Chaetozone setosa (Elliot et al., 1998). Subtidal mobile sandbanks are the result of high energy conditions and naturally disturbed by hydrographic conditions such as storms. Therefore, Elliot et al. (1998) suggested that the community is likely to recover from sediment disturbance, since the associated species are predominately mobile, able to tolerate sediment movement, and the influx of sediment from natural or man-made sources (e.g. dredged spoil). For example, Jennings & Kaiser (1998) reported that in experiments in the Irish Sea, the effects of beam trawl disturbance could not be detected in mobile sediments, which was attributed to the levels of natural disturbance in megaripple habitats. Animals living in the troughs of sediment ripples were less likely to be disturbed by since fishing gear rode over the crests of the sand waves (Jennings & Kaiser, 1998). Therefore, an assessment of not sensitive has been recorded.
Displacement
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The important characterizing species of the IGS.NeoGam are mobile species, therefore an intolerance assessment for displacement was not considered relevant.

Chemical Factors

Synthetic compound contamination
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Estuaries may receive effluent discharges which contain a variety of synthetic chemicals. In general, crustaceans are widely reported to be intolerant of synthetic chemicals (Cole et al., 1999). Neomysis integer was found to be intolerant of exposure to the organophosphate pesticide, Chlorpyrifos. Following 7 days of exposure to a concentration of 0.038 µg /l, its swimming behaviour was disrupted, an effect which would compromise the ability of Neomysis integer to maintain its position in the estuarine environment (Roast et al., 2000b). In addition, synthetic chemicals have been reported to affect species of Gammarus related to Gammarus salinus. Pentachlorophenol (PCP) and benzo[a]pyrene (B[a]P) impaired swimming stamina and disrupted embryo development in Chaetogammarus marinus (Lawrence & Poulter, 2001). Owing to the likelihood of a consequential reduction in abundance and viability of the crustacean populations in the biotope, intolerance has been assessed to be intermediate. The important characterizing species have a very high capacity for recovery assuming degradation of the synthetic contaminants.
Heavy metal contamination
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The salinity-temperature dependent toxicity of cadmium and other heavy metals to marine and estuarine invertebrates is well documented (reviewed in McLusky et al., 1986). Wildgust & Jones (1998) found that mortalities of Neomysis integer resulting from free cadmium ion exposure were greater at salinities of 28 and 12 psu than at 20 psu. However, the swimming behaviour and orientation of Neomysis integer was disrupted following exposure to 0.5 µg Cd (aq)2+ per litre, a significantly lower cadmium concentration than that causing mortality (Roast et al., 2000). The significance of this sub-lethal effect is that Neomysis integer would be unable to maintain its position within the estuary, resulting in reduced abundance of the population. Similarly, Lawrence & Poulter (2001) observed disrupted embryogenesis and swimming stamina in Chaetogammarus marinus, a species related to Gammarus salinus. Intolerance of the biotope fauna has been assessed to be intermediate owing to reduced abundance as a result of reduced swimming ability. The important characterizing species have a very high capacity for recovery assuming degradation of the synthetic contaminants.
Hydrocarbon contamination
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Amphipods are generally very sensitive to oil pollution (Suchanek, 1993). Ponat (1975) observed the narcotic effect of crude oil on Gammarus salinus, which reduced the species oxygen consumption to 40 % of normal levels. Lindén (1976) also observed narcosis in Gammarus oceanicus, a species related to Gammarus salinus, exposed to concentrations of oil between 5 to 20 mg /l, which followed an initial period of hectic swimming and then deterioration of crawling ability. Furthermore, sub-lethal concentrations of crude oil (1-40 µg/l) proved to be responsible for a reduction in the numbers of sexually mature adults of Gammarus oceanicus entering precopula, a requirement for successful fertilization (Lindén, 1976b). The intolerance of the biotope to hydrocarbon contamination has been assessed to be high owing to the probable destruction of the important characterizing Gammarus species.
Radionuclide contamination
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Radionuclides can accumulate within substrata. However, there is little information concerning their biological effects (Cole et al., 1999).
Changes in nutrient levels
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Primary productivity within in the biotope is extremely limited. Nutrient enrichment at the benchmark level which directly or indirectly enhances the supply of detrital organic material available to the fauna for consumption is likely to be beneficial and an intolerance assessment of not sensitive * has been made.
Increase in salinity
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Neomysis integer and Gammarus salinus are euryhaline species. However, whilst Gammarus salinus may tolerate salinities of 30 psu, Neomysis integer was found to have an upper salinity tolerance between 20-25 psu, with death occurring at 30 psu (Kuhlman, 1984). An intolerance assessment of high has been made owing to the fact that the biotope is characterized by species tolerant of lower salinities, increased salinity would cause physiological stress to the important characterizing species and favour the establishment of fully marine species and the IGS.NeoGam biotope would temporarily not be recognised. On return to a brackish water salinity regime, recovery of the important characterizing species has been assessed to be very high owing to immigration and rapid reproduction.
Decrease in salinity
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Neomysis integer is tolerant of salinities as low as 0.5 psu (Koepke & Kausch, 1996) and Gammarus salinus can tolerate a salinity of 2 psu. A further reduction in salinity at the extreme of their salinity tolerance range would expose them to freshwater. Neomysis integer successfully made the transition to freshwater environments but presumably over an extended period of time. An intolerance assessment of high has been made as freshwater species may successfully penetrate the biotope and the IGS.NeoGam biotope would temporarily not be recognised. On return to a brackish water salinity regime, recovery of the important characterizing species has been assessed to be very high owing to migration and rapid reproduction.
Changes in oxygenation
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Gammarus salinus demonstrated negative rheotaxis (swimming away ) in response to a current of sub-lethal and lethal concentrations of oxygen (Vobis, 1973). It is also probable that as a mobile species Neomysis integer would also avoid decreased oxygen concentrations to which it is intolerant. Consequently, in the absence of the important characterizing species the biotope would temporarily not be recognized and intolerance has been assessed to be high. On return to prior conditions, repopulation is likely to occur rapidly as the species move into feed.

Biological Factors

Introduction of microbial pathogens/parasites
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Neomysis integer may be parasitized by the third larval stage of the nematode Thynnascaria adunca (Astthorsson, 1980). Both Gammarus salinus and Gammarus zaddachi are important host species for the transmission of fish and bird parasites (Voigt, 1991).
Introduction of non-native species
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No information concerning non-native species that might affect the abundance or survival of the important characterizing species of the IGS.NeoGam biotope was found.
Extraction
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It is extremely unlikely that any of the species indicative of sensitivity 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

Recoverability
No evidence concerning community development was found. However, it is expected that the community, which consists entirely of swimming species, could establish very rapidly as migration from other populations would occur in addition to any larval recruitment. The length of time for recruitment to occur might be a few hours but 'maturity' would not be expected for several weeks in the case of extensive defaunation of the substratum. Recoverability has therefore been assessed to be very high in general.

This review can be cited as follows:

Budd, G.C. 2002. Neomysis integer and Gammarus spp. in low salinity infralittoral mobile sand. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 23/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=51&code=2004>