Biodiversity & Conservation

SS.IMS.Sgr.Rup

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum would remove Ruppia spp. and their associated epiphytes and invertebrates, together with roots, rhizomes and the seed bank. Therefore, an intolerance of high has been recorded.
Recovery will depend on recolonization by Ruppia spp. propagules (rhizomes or seed), which may take many years (see additional information). However, the associated community of epiphytes and invertebrates will probably colonized re-established Ruppia stands rapidly.
Smothering
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Ruppia spp. probably traps sediment and increases accretion rates, although little information on accretion rates in Ruppia beds was found. Smothering by 5cm of sediment will shade and damage buried leaves and stems resulting in loss of a proportion of the vegetation above the sediment surface, including the algal mats and epiphytes. Kantrup (1991) suggested that, although most seeds occur in the top 5cm of sediment, seeds buried more than 10cm in sediment would probably not germinate, so that smothering by 5cm of sediment may reduce germination. Smothering in early spring may have a marked effect of the growth of Ruppia spp. stands, especially annuals that are primarily dependant on seed. Most members of the invertebrate fauna will probably be able to burrow through or avoid smothering. However, some hydrobid snails may be lost due to smothering and cockles (Cerastoderma sp.) have limited ability to burrow and may be adversely affected. Therefore, an overall intolerance of intermediate has been recorded.
After a month (the benchmark level) the Ruppia stand and its associated community will probably recover rapidly (see additional information below).
Increase in suspended sediment
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Tidal waters with dense stands of Ruppia spp. were usually clear in the growing season but occasionally turbid with sediment due to storms or flooding. However, areas which consistently carried suspended sediment supported only sparse growth (Robertson, 1980; cited in Kantrup, 1991). Ruppia spp. has been recorded from waters containing 17.5-42.5 ppm suspended sediment and wetlands are recommended to be managed within 25 -55 ppm suspended sediment for Ruppia spp. cultivation (Kantrup, 1991). Therefore, an increase in suspended sediment at the benchmark level is likely to have a significant effect. The most important effect of increased suspended sediment on Ruppia spp. is increased turbidity and light attenuation and is addressed under turbidity below.
Increased accretion in shallow water habitats could increase the bed height, which would bring the Ruppia bed closer to light. However, in the longer term, increased sedimentation may result in drying of the shallowest parts of the beds and replacement of the Ruppia beds with a hydrosere of reeds, sedge or other saltmarsh species. Most other members of the community are probably tolerant of increased suspended sediment since they inhabit estuarine or lagoonal habits where periodic resuspension of sediment or siltation occur. Overall, therefore, increased suspended sediment is may result in loss of a proportion of the Ruppia beds either due to succession or drying and an intolerance of intermediate has been recorded.
Recovery will depend of recolonization from the established bed and of associated species from the surrounding area, and is likely to be rapid (see additional information below).
Decrease in suspended sediment
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Little information concerning accretion or erosion rates in Ruppia beds was found. Decreased suspended sediment concentration will increase water clarity and hence growth, seed set and productivity in Ruppia spp. and the associated algal communities. Overall, the community is likely to benefit. However, seagrass beds are know to depend on a balance between accretion and erosion, and to be intolerant of changes in sedimentation rates, which depend in part on suspended sediment levels (see £IMS.Zmar£). Therefore, a decrease in sedimentation that results in net erosion of the sediment is likely to result in loss of Ruppia spp. stands.
Desiccation
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Examples of this biotope (IMS.Rup) that occur in the shallow subtidal are unlikely to experience desiccation except due to exceptionally low tides or changes in emergence regime. However, Ruppia spp. communities also occur in more temporary waters (e.g. ditches and pools), especially annuals, where drying is likely. Verhoeven (1979) stated that the resistance of Ruppia spp. to drought was very low and that after desiccation all plant parts except ripe seeds die within a few days. Similarly, seed will not germinate in moist soil but need to be covered with water (Kantrup, 1991). Therefore, an increase in desiccation at the benchmark level is likely to result in loss of the affected stands of Ruppia spp.
Hydrobia ulvae is known to tolerate emersion for long periods of time, although other hydrobids may be more intolerant. Gammarids and isopods will probably be killed by prolonged desiccation but tend to remain in moist areas of weed or to burrow into the sediment. Juvenile bivalves in the top layer of the sediment and Cerastoderma glaucum, where present are probably highly intolerant of desiccation and excluded from the more ephemeral habitats. Benthic infauna, such as burrowing polychaetes are protected form the effects of desiccation by their infaunal habit and the water retention of the sediments. However, in ephemeral habitat prolonged drying of pools will exclude these species. Therefore, an overall intolerance of high has been recorded.
Recovery will depend in part on recolonization by Ruppia spp. propagules (seeds and rhizomes) but also recovery from the resident seed bank. Recolonization by propagules may take many years however, if the seed bank survives recovery will be more rapid. Annual Ruppia species (e.g. Ruppia maritima) are adapted to the more ephemeral habitats and produce enormous numbers of seed rather than vegetative shoots, and will recover rapidly as soon as favourable conditions return (Verhoeven, 1979; Kantrup, 1991). Therefore a recoverability of high has been recorded (see additional information below).
Increase in emergence regime
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Ruppia dominated communities can occur in tidal areas, from mean high to mean low water. It was reported to be common or restricted to intertidal areas exposed for 4hrs daily or 6.96hrs per low tide but quickly disappeared from areas emersed for longer periods (Kantrup, 1991). Therefore, while Ruppia spp. are relatively tolerant of fluctuating water levels an increase in emergence within tidal Ruppia beds is likely to result in reduced growth, production and the loss of the upper portion of the population, especially on hot sunny days. An increase in emergence in a normally submerged bed may have only sublethal effects.
Hydrobia spp. inhabit salt marshes and are tolerant of emersion. Gammarids and isopods either migrate to deeper water, burrow in the sediment of shelter in damp weed to avoid the effects of emergence. Algal mats retain water, and while their surface may be bleached or desiccate in hot sunny weather, they are likely to recover quickly. Arenicola marina and Pygospio elegans together with several bivalve species recorded in the biotope occur in the intertidal and would probably tolerate an increase in emergence at the benchmark level. However, where present, Cerastoderma glaucum is thought to be intolerant of changes in emergence and may be lost. Overall, an increase in emergence may result in a reduction in the upper shore extent of the Ruppia spp. bed and some intolerant species may be lost. Therefore, a biotope intolerance of intermediate has been recorded.
Recolonization by Ruppia spp. and its associated community will probably occur from the surrounding communities and via the remaining seed bank and is likely to be rapid (see additional information below). Therefore a recoverability of high has been suggested.
Decrease in emergence regime
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In shallow subtidal areas a decrease in emergence may increase the relative water depth, increasing light attenuation and reducing growth and productivity. However, in deeper water the growth form of Ruppia spp. produces longer stems and concentrates the leaves higher in the water column (Kantrup, 1991). An increase in immersion may allow intertidal stands of Ruppia to colonize further up the shore and increase in extent. Therefore, decreased emergence is likely to have only sublethal effects and may allow the population to increase in extent, therefore not sensitive* has been recorded.
Increase in water flow rate
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The IMS.Rup biotope is found in extremely sheltered conditions in very weak tidal streams. An increase in water flow at the benchmark level (i.e. from very weak to moderately strong) is likely to damage leaves and shoots and probably remove the vegetation and a proportion of the root system. The root system of Ruppia spp. is poorly developed consisting of horizontal runners a few mm below the sediment surface and only 1-2 thin roots per 10-20cm along the rhizome. Therefore, Ruppia spp. are not very resistant of water flow and are limited to still, sheltered waters such as lagoons and bays where current flow is less than in adjacent channels and tidal rivers (Verhoeven, 1979; Kantrup, 1991). Verhoeven (1979) suggested that Ruppia maritima was particularly intolerant while Ruppia cirrhosa occurred in larger waters at more exposed but still sheltered sites. In addition, turbulent water flow resulting in resuspension of sediment can indirectly reduce Ruppia productivity due to increased turbidity (see below). Kantrup (1991) reported that Ruppia spp. can occur in areas of 'considerable' current flow, e.g. Ruppia beds fertilized in situ with phosphorus were found to grow well in currents up to 4cm/s. However, 4cm/s is considered to be negligible (see benchmark). Epiphytes and algal mats would also be lost. Therefore, an intolerance of high has been recorded.
Most of the benthic infauna are found in areas of stronger currents (e.g. Arenicola marina), and many of the mobile species (e.g. amphipods, isopods, shrimp, crabs and fish) would migrate to other suitable substrata or habitats. However, where present Cerastoderma glaucum is only found in areas of weak water flow and may be lost.
Recovery will depend on recolonization by Ruppia spp. propagules (rhizomes or seed) , which may take many years (see additional information). However, the associated community of epiphytes and invertebrates will probably colonized re-established Ruppia stands rapidly.
Decrease in water flow rate
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This biotope occurs in very weak tidal streams. A decrease in water flow will result in negligible flow. Kantrup (1991) suggested that stable water provided good growing conditions for Ruppia spp. However, negligible water flow increases deposition of fine, flocculent muds and clays, and the potential for deoxygenation of the water column or sediment, which may reduce Ruppia productivity. Therefore, an intolerance of low has been recorded, at very low confidence.
Increase in temperature
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The temperature regime is important for reproduction in Ruppia spp. Germination and budding begin when the water temperatures rise in early spring above a min/max of 10/15 °C, with reproduction (flowering) commencing at 15-19 °C but reproduction falls above 30 °C .Therefore, the timing of growth and reproduction in Ruppia spp. are temperature dependant and are probably earlier in warm years and later in cold years. Optimum temperatures for vegetation growth was reported to be 12-13 °C, and 15-20 °C for seedlings. although local adaptation occurs (Verhoeven, 1979; Kantrup, 1991). Verhoeven (1979) noted that all Ruppia taxa survive between 0 -38 °C, grow exponentially at 10 -30 °C and survive daily fluctuations of 15 °C in culture. However, Kantrup (1991) suggested that temperatures above 30 °C were probably harmful and noted that Ruppia spp. were replaced by Potamogeton pectinatus in the vicinity of a thermal effluent where temperatures sometimes reached 35 °C. Verhoeven (1979) concluded that Ruppia spp. were well adapted to the temperature conditions found in small shallow waters. Therefore, Ruppia spp. are probably not sensitive to temperature increase at the level of the benchmark.
Species inhabiting lagoons and shallow lochs are probably adapted to fluctuating temperatures, while mobile species are likely to move to deeper waters. Benthic infauna are likely to be protected form temperature extremes by their benthic habit, however, a proportion of the Arenicola marina population may be lost at temperatures above 20 °C, and excluded from habitats suffering from more extreme fluctuations in temperature. Therefore, an increase in temperature at the benchmark level may not adversely affect the Ruppia spp. beds but is likely to result a reduction in species richness.
Decrease in temperature
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A decrease in temperature is likely to delay the onset of budding and germination and subsequent reproduction in Ruppia spp., which may be of particular importance for annual species (see above). Verhoeven (1979) noted that all Ruppia taxa survive between 0 -38 °C, grow exponentially at 10 -30 °C and survive daily fluctuations of 15 °C in culture. Kantrup (1991) reported that in North American wetlands that freeze in winter, Ruppia spp. behaved as annuals. Verhoeven (1979) reported that the distribution of Ruppia maritima and Ruppia cirrhosa extended north to Norway (ca 69 deg N and 68 deg N respectively), suggesting that these species would be tolerant of the average winter temperatures encountered in the UK. Therefore, Ruppia spp. are probably not sensitive to temperature increase at the level of the benchmark.
Many of the species found within the Ruppia spp. communities are typically lagoonal or shallow water species, adapted to fluctuating temperatures. Infaunal polychaetes are protected from temperature extremes by their burrowing habit, however, a proportion of the Arenicola marina population may be lost below 5 °C on in areas subject to extreme fluctuations in temperature. Overall, the Ruppia spp. stand will not be damaged by a decrease in temperature at the benchmark level but some species will reduce in abundance while mobile species may move to deeper water resulting in a reduced species richness.
Increase in turbidity
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Ruppia spp. require high light levels and only normally develop well in clear water and are always reduced or absent from turbid waters (Verhoeven, 1979). Increased turbidity results from increases in dissolved organics (e.g. humic acids or gelbstoff), organic particulates and suspended sediment (see above), or blooms of phytoplankton and zooplankton (see nutrients below). Large beds of Ruppia spp. were reported to have disappeared due to rapid increases in turbidity (Anderson, 1970; cited in Kantrup, 1991). Ruppia spp. beds may tolerate occasional turbid events, e.g. from storms or flooding but grow sparsely in turbid waters (Richardson, 1990; cited in Kantrup, 1991). A 40% reduction in light intensity was reported to result in a 50% reduction in Ruppia spp. Standing crop (Congdon & McComb, 1979; cited in Kantrup, 1991). Kantrup (1991) concluded that control of water clarity was of utmost importance to establish or maintain Ruppia spp. beds.
Loss of the Ruppia vegetation would result in loss of substratum, refuge, productivity, and the associated community. Benthic infauna would loose a significant source of primary productivity but would likely survive in the absence of Ruppia spp. The Ruppia spp. bed may be replaced by Potamogeton species in low salinity habitats. Overall, the biotope is likely to be lost an intolerance of high has been recorded.
Recovery will depend on recolonization by Ruppia spp. propagules (rhizomes or seed), which may take many years (see additional information below). Therefore a recoverability of moderate has been recorded.
Decrease in turbidity
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Ruppia spp. beds are likely to occur in clear waters, however, any further decrease in turbidity is likely to increase productivity and seed set and may allow the Ruppia spp. bed to extend its range. Therefore, the biotope and its associated community is likely to benefit.
Increase in wave exposure
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Kantrup (1991) reported that wave action damaged Ruppia plants stems and leaves and Verhoeven (1979) noted that the base of leaves detached easily in turbulent water to avoid damage to the root system. However, the root system is weak (see water flow) and Ruppia beds are restricted to areas protected from wave action and with little fetch and wind induced water turbulence. Wave action also resuspends sediment, increasing turbidity and hence reducing productivity. This biotope (IMU.Rup) is found in extremely sheltered areas, therefore, and increase in wave action at the benchmark level is likely to remove the surface vegetation and the majority of the root system.
Most lagoonal species are adapted to sheltered conditions and are likely to be adversely effected by increases in wave exposure, e.g. Gammarus insensibilis and Cerastoderma edule, at the benchmark level resulting in loss of a proportion of the population. The resident gastropods e.g. Hydrobia ulvae are unlikely to be directly affected, and will switch to alternative food supplies, however, should the increase in wave exposure be significant enough to change the sediment type, e.g. to coarse sands, they are likely to be lost. Benthic species, such as Arenicola marina can tolerate sheltered to moderately exposed conditions and would probably be little affected at the benchmark level. Overall, therefore, although most of the benthic infauna will remain, loss of the Ruppia stands will result in loss of its associated epiphytic flora and fauna and the biotope as a whole. Therefore, an intolerance of high has been recorded.
Decrease in wave exposure
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This biotope occurs in extremely sheltered condition and any further decrease in wave exposure, i.e. to ultra sheltered is unlikely to have an adverse affect, although the risk of anoxia may be increased (see below).
Noise
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The majority of species in Ruppia dominated communities are unlikely to react to noise at the benchmark level. Wildfowl, however, are intolerant of disturbance from noise from e.g. shooting (Madsen, 1988) and from coastal recreation, industry and engineering works. For example, Percival & Evans (1997) reported that wigeon were very intolerant of human disturbance and, where wildfowling was popular, wigeon avoided Zostera noltii beds at the top of the shore.
Visual Presence
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The majority of species in Ruppia dominated communities have poor, if any, visual acuity, and are unlikely to react to visual disturbance. However, mobile fish may be disturbed by passing boats but probably with minimal effect. Wildfowl, however, are intolerant of disturbance from noise from e.g. shooting (Madsen, 1988) and from coastal recreation, industry and engineering works. For example, Percival & Evans (1997) reported that wigeon were very intolerant of human disturbance and, where wildfowling was popular, wigeon avoided Zostera noltii beds at the top of the shore.
Abrasion & physical disturbance
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Ruppia stems and leaves are damaged by wave action or water turbulence and the root system is shallow and weak (Verhoeven, 1979; Kantrup, 1991). Therefore, it is likely that Ruppia spp. are intolerant of physical disturbance and that a proportion of the vegetation may be removed and rhizomes broken by anchorage or mooring (see benchmark). Benthic infauna such as polychaetes (e.g. Arenicola marina or Pygospio elegans) are partly protected from abrasion due to their infaunal habit but a proportion are likely to be killed by any mechanical disturbance that penetrates the sediment (e.g. anchors). Similarly, the shell of Cerastoderma glaucum is relatively thin and individuals are likely to be damaged or killed by abrasion. Macroalgae and relatively flexible and unlikely to be damaged. However, resident grazers (e.g. gammarid amphipods, isopods, or gastropods) are likely to be killed by direct physical contact, although they are generally small enough to be swept aside, or able swimmers and most will probably escape.
Overall, a proportion of the Ruppia beds will be removed, together with a proportion of the associated community and benthic infauna. Therefore, an intolerance of intermediate has been recorded.

The Ruppia beds will probably recover relatively rapidly from the surrounding plants, the seed bank and fragments of rhizome remaining in the sediment.

Displacement
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Ruppia can be transported as floating rhizomes, that root, sink and colonize new substratum. Amphipods and isopods are good swimmers and able to colonize most algae, and unlikely to be affected by displacement. Benthic polychaete species may suffer predation when displaced but can burrow rapidly into suitable substratum. Arenicola marina, can swim and may be transported passively to colonize new sediment. Broström & Bonsdorff (2000) noted that the abundance of nematodes, oligochaetes, chironomids, copepods and Macoma baltica increased in their artificial seagrass stands after strong winds, suggesting that these species colonized by passive transport, hence, that they were not sensitive to displacement. Similarly, Cerastoderma glaucum established itself in Emsworth Harbour by displacement of animals from adjacent lagoon habitats (Barnes, 1973).
However, physical displacement of Ruppia will probably reduce the plants to fragments, remove the resident population of the Ruppia beds and destroy part of the biotope. Therefore, an intolerance of intermediate has been recorded.
Subsequent recovery of the Ruppia beds from the effectively transplanted rhizome, plant fragments and attached seed if present will be relatively rapid (see (additional information below).

Chemical Factors

Synthetic compound contamination
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Johnston & Bird (1995) demonstrated that photosynthesis in Ruppia maritima was less intolerant of the effects of herbicides than other aquatic plants. Although photosynthesis was reduced by 0.05mg/l atrazine after 35 days exposure, growth was reduced at atrazine concentrations <5mg/l but continued at 10mg/l. Atrazine concentrations required to reduce growth were higher than normally occurred in estuaries (Johnston & Bird, 1995). However, Kantrup (1991) reported that herbicides (atrazine and alachlor) in agricultural runoff reduced Ruppia growth and biomass in Chesapeake bay and noted that 1.0 ppm of atrazine had been used to control Ruppia growth in wetlands. Only small numbers of plants survived 4 years after treatment with the herbicide 2,4 D-ester at 112kg/ha (Kantrup, 1991). Cole et al. (1999) suggested that herbicides were, not surprisingly, very toxic to algae and macrophytes.
Similarly, most pesticides and herbicides were suggested to be very toxic for invertebrates, especially crustaceans (amphipods isopods, mysids, shrimp and crabs) and fish (Cole et al., 1999). For example, Lindane was shown to be very toxic to gobies (Gobius spp.: see Pomatoschistus minutus) (Ebere & Akintonwa, 1992) . The pesticide ivermectin is very toxic to crustaceans, and has been found to be toxic towards some benthic infauna such as Arenicola marina (Cole et al., 1999).
Therefore, synthetic chemicals found in agricultural, urban and industrial discharges are likely to adversely affect the biotope. Herbicides in particular are likely to reduce growth and productivity of the Ruppia beds, and may result in its loss. In addition, loss of particularly intolerant crustaceans may result in unchecked growth of epiphytes, which would again reduce photosynthesis and productivity of the Ruppia beds. Overall, synthetic chemical contamination will at the least result in a reduction in productivity, seed set and ultimately the extent of the Ruppia bed. Therefore, given the intolerance of Ruppia spp. to herbicides an intolerance of high has been recorded.
Recovery will depend on recolonization by Ruppia spp. propagules (rhizomes or seed) , which may take many years (see additional information below).
Heavy metal contamination
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No information concerning the effects of heavy metals on Ruppia spp. was found. However, Cole et al. (1999) suggested that Hg was very toxic to macrophytes.
Cole et al. (1999) suggested that Pb, Zn, Ni and As were very toxic to algae, while Cd was very toxic to Crustacea (amphipods, isopods, shrimp, mysids and crabs), and Hg, Cd, Pb, Cr, Zn, Cu, Ni, and As were very toxic to fish. Gobies were reported to be particularly intolerant of Hg (see Pomatoschistus minutus). Bryan (1984) reported sublethal effects of heavy metals in crustaceans at low (ppb) levels. Bryan (1984) suggested that polychaetes are fairly resistant to heavy metals, based on the species studied. Short term toxicity in polychaetes was highest to Hg, Cu and Ag, declined with Al, Cr, Zn and Pb whereas Cd, Ni, Co and Se were the least toxic. However, he suggested that gastropods were relatively tolerant of heavy metal pollution.
The intolerance of crustaceans to heavy metal contaminants suggests that amphipod and isopod grazers would be lost, allowing rapid growth of epiphytes, and reduced turnover of the detrital food chain. Additional growth by the epiphytes and algal mats, unless there are adversely affected themselves, could potentially compete with Ruppia stands for light and nutrients reducing productivity. Overall, therefore, in the absence of other evidence, the Ruppia beds would probably survive, with reduced productivity, but that several members of the community may be lost (e.g. fish and crustaceans) resulting in a reduced species richness.
Recovery is likely to be rapid (see additional information below).
Hydrocarbon contamination
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Little information on the effects of hydrocarbon contamination from, for example oil spills, on Ruppia beds was found. Where they occur, oil spills are likely to persist for some time in sheltered, soft sediment habitats.
Suchanek (1993) noted that gastropods, amphipods, infaunal polychaetes and bivalves were particularly sensitive to oil spills. For example substantial kills of Nereis, Cerastoderma, Macoma, Arenicola and Hydrobia were reported after the Sivand oil spill in the Humber (Hailey, 1995). Single oil spills were reported to cause a 25-50% reduction in abundance of Arenicola marina (Levell, 1976). The toxicity of oil and petrochemicals to fish ranges from moderate to high (Cole et al., 1999). The water soluble fraction of oils was shown to cause mortality in sand gobies and fish, especially their larvae, are thought to be intolerant of polyaromatic hydrocarbons (PAHs) (see Pomatoschistus minutus). PAHs are significantly more toxic when exposed to sunlight (Ankley et al., 1997) , and may have a greater effect in clear shallow waters inhabited by Ruppia communities.
Therefore, while there is no evidence to suggest that Ruppia spp. would be directly affected by hydrocarbon contamination, its associated community may be lost. Loss of grazers may increase epiphytic fouling resulting in lower growth and productivity. However, given the likely persistence of oils in sheltered, sedimentary habitats, an overall intolerance of high has been recorded.
Recovery will depend on recolonization by the associated invertebrate community, which is likely to be rapid (see additional information below).
Radionuclide contamination
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Insufficient information
Changes in nutrient levels
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In mesocosm experiments, Ruppia maritima was shown to increase shoot production by >300% over controls after the addition of 10µM water column NO3-N /day (Burkholder et al., 1994). Burkholder et al. (1994) went on to suggest that Ruppia maritima and Halodule wrightii effectively control nitrate uptake and could be transplanted to replace Zostera marina in nitrate-enriched waters where the eelgrass had disappeared. Therefore, it appears that Ruppia spp. will benefit from low nutrient enrichment. Nutrient enrichment is known to have indirect adverse effects. Nutrient enrichment stimulate epiphyte growth, which interfere with the nutrient exchange across the Ruppia leaves and shade out light, reducing primary productivity, growth and reproduction. Similarly, nutrients stimulate phytoplankton blooms that compete for nutrients but more importantly increase the turbidity (see above). and absorb light, reducing Ruppia productivity. Twilley et al. (1985) found that epiphyte growth in nutrient enriched conditions reduced the light incident on Ruppia leaves by >80%, resulting in significant decreases in macrophyte biomass at medium to high levels of enrichment (0.86 and 1.68 g N /m²/ day respectively). Ruppia maritima production collapsed after 6 weeks at high nitrogen levels. However, the epiphytic growth only resulted in loss of macrophytes due to the additional turbidity caused by the phytoplankton Twilley et al., (1985). Kantrup (1991) concluded that while nutrients can stimulate growth, growth is severely limited by phytoplankton and epiphytes in eutrophic conditions.
Ruppia spp. can tolerate organic rich sediments and has been reported to grow in extremely reduced sediments since leaves supply oxygen to the root system (Kantrup). However, Azzoni et al. (2001) noted that the oxygen supply to the roots detoxified the sulphide levels around the root system but that once this capacity was exhausted, perhaps due to additional nutrients or reduction in plant productivity, sulphide rapidly built up and killed the root system and hence the plant.
The nationally scarce foxtail stonewortLamprothamnium papulosum was reported to be absent where the total phosphate concentration was greater than 100µg/l and may be lost due to nutrient enrichment (Bamber et al., 2001). Most grazing and suspension and deposit feeding members of the community will probably benefit from the increased epiphyte and phytoplankton productivity, as would their predators.
However, the productivity and growth of the Ruppia beds are likely to be reduced, and a proportion of the population lost at the benchmark level, while significant increase and eutrophication may result in loss of the biotope. Therefore, an intolerance of intermediate at the benchmark level has been recorded.
Recovery is likely to be rapid (see additional information below).
Increase in salinity
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Ruppia spp. tolerate a wider range of ionic strengths and salinities than any other aquatic angiosperm, occurring between 0.6 -390g/l (Kantrup, 1991). However, the reported salinity tolerances vary with region and with species. Ruppia maritima was reported to be abundant at salinities between 15 ->100g/l in North American wetlands and between 0.57 -27g/l in European sites (Verhoeven, 1979; Kantrup, 1991). Ruppia cirrhosa tolerated 2.7-108.3 g/l in European sites (Verhoeven, 1979). Kantrup (1991) concluded that the optimum salinity for Ruppia spp. Growth was 5-20 g/l while slightly lower salinities early in spring may enhance germination and seed formation. Rapid fluctuations were found to kill Ruppia spp. when salinities rise >ca 18g/l in a few weeks (Verhoeven, 1979). However, Ruppia spp. was also reported to survive a drop of at least 14 g/l in 24 hrs (Kantrup, 1991). Overall, Ruppia spp. are probably not directly sensitive changes in salinity at the benchmark level. Their exclusion from very low to freshwater, or nearly full seawater is probably due to competitive exclusion by other aquatic plants or seagrasses.

As the salinity increases low salinity species are likely to be replaced by comparable marine forms. Typically lagoonal species (e.g. the hydrobids, some gammarids, and Cerastoderma glaucum) are adapted to a wide range of salinities and are unlikely to be affected. Estuarine and low salinity polychaetes present in the benthos are likely to be replaced by more marine species as the salinity increases, e.g. the abundance of Hediste diversicolor is likely to fall while the abundance of Arenicola marina increases. Sticklebacks are found in marine and freshwater habitats and the sand goby tolerates a wide range of salinities.

Therefore, the biotope as a whole will probably be little affected by increases in salinity at the benchmark level, although some species may be replaced by more marine members of the same group. As the salinity increased more marine species would be able to colonize the habitat so that the species richness may increase. Therefore, an intolerance of low has been recorded at the benchmark level. However, should the biotope be exposed to full salinity for a prolonged periods, the biotope may be replaced by seagrass species. Once prior conditions return, recovery is likely to be rapid (see additional information below).
Decrease in salinity
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Ruppia spp. are probably not directly intolerant of changes in salinity at the benchmark level (see above). Their exclusion from very low to freshwater, is probably due to competitive exclusion by other aquatic plants, e.g. Potamogeton pectinatus.
Most of the typically lagoonal species (e.g. Cerastoderma glaucum, Gammarus insensibilis and hydrobids) will be little affected by changes in salinity. However, Gammarus insensibilis was reported to disappear in areas affected prolonged exposure to freshwater. Similarly, Arenicola marina does not tolerate salinities below 24 psu and is likely to be replaced by Hediste diversicolor. Sticklebacks are found in marine and freshwater habitats and the sand goby tolerates a wide range of salinities. As the salinity decreases the species composition is likely to change towards more freshwater tolerant species, including insects, although the functional groups will probably remain, and the species richness may increase.
A short term decrease in salinity is unlikely to affect the biotope adversely. However, prolonged exposure to low salinities or freshwater is likely to result in replacement of the Ruppia community by other aquatic plant communities e.g. Potamogeton pectinatus, therefore an intolerance of intermediate has been recorded. Once prior conditions return recovery is likely to be rapid (see additional information below).
Changes in oxygenation
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Ruppia spp. favour aerobic sediments with low levels of sulphides and free H2S but will grow in reduced conditions, since the leaves supply oxygen to the roots. Senescence and loss of stems can coincide with increases in H2S in the sediment and may be a factor regulating the decrease in Ruppia species in hot summer months (Kantrup, 1991). Germination may also be affected by oxygen levels and seeds in poorly oxygenated sediments lie dormant until the next year (Kantrup, 1991). However, the presence of Ruppia in reduced sediment suggests that it would tolerate low oxygen levels comparable to the benchmark, especially since photosynthesis produces oxygen.
Mud snails ( hydrobids) are relatively tolerant of reduced hypoxic muds, and can tolerate aerial exposure for over a week, suggesting that they are capable of anaerobic respiration. Benthic infaunal species are probably tolerant of hypoxia, e.g. Arenicola marina which can tolerate 9 days without oxygen (Hayward, 1994) and Cerastoderma glaucum which tolerates 84 hrs in the absence of oxygen (Boyden, 1972). Most polychaetes are capable of anaerobic metabolism, while mobile fish and gobies migrate out of the affected area in response to decreasing oxygen levels (Diaz & Rosenberg, 1995). Small mobile shrimp, amphipods and isopods will probably also migrate out of the affected area.
Therefore, the Ruppia stands and benthic infauna will probably tolerate hypoxia at the level of the benchmark and an intolerance of low has been recorded, since increased epiphyte growth due to reduced numbers but not loss of grazers, may reduce Ruppia spp. productivity. However, species richness is likely to decline.
Recovery is likely to be rapid (see additional information below).

Biological Factors

Introduction of microbial pathogens/parasites
(View Benchmark)
Kantrup (1991) reported possible pathogenic effects of fungi, that produce 'tubercles' on the Ruppia leaves. Kantrup (1991) also states that 'vegetative reproduction usually allows Ruppia spp. to survive Rhizoctonia infestations' and that Ruppia spp. probably suffer less from diseases than other aquatic angiosperms.
Introduction of non-native species
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No information found.
Extraction
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Ruppia spp. is not subject to any specific extraction within the UK. However, in subtropical areas wintering wildfowl were reported to consume entire stands of Ruppia spp. which grew back in a few weeks (Kantrup, 1991). Similarly, Steiglitz (1966, cited in Kantrup, 1991) suggested that wildfowl could consume 50% of the standing crop without damaging the Ruppia bed. This evidence suggests that Ruppia stands would tolerate grazing and possibly extraction although a proportion of the algal mats and the associated invertebrate fauna would be removed. Therefore, an intolerance of intermediate has been recorded at the benchmark level. Recovery is likely to be rapid (see additional information below).

Extraction of Arenicola marina for bait is likely to disturb the sediment and benthic infauna, although the Ruppia stands themselves would probably recover quickly (see above). Similarly, Arenicola marina populations are thought to recover rapidly, although in isolated areas recovery may take longer due to the lack of a pelagic larvae.

Intolerance has been assessed as intermediate.

Additional information icon Additional information

Recoverability
Zieman et al. (1984) noted that the recovery of seagrass ecosystems depended primarily of the extent or magnitude of damage to the sediments, i.e. the rhizome and root system. This is probably also true of Ruppia dominated communities. Where, the rhizomes remain, recovery is likely to be rapid. For example, in subtropical climates wintering waterfowl were reported to consume entire stands of Ruppia spp., which re-established within weeks in optimal conditions (Kantrup, 1991). Ruppia spp., either annuals or perennials annually die back only to regrow from seed and or over-wintering rhizome the following year. Seed survive in sediment for up to three years and germinate as long as they are not buried by more than 10cm of sediment (Kantrup, 1991). Therefore, if a proportion of the rhizomes or seed bank remains, recovery is likely to be rapid, probably taking a single good growing season or several years in less optimal conditions.

The Ruppia vegetation dies back in autumn and winter, and over-winters either as seed or rhizome, only to germinate or bud in early spring. Therefore, the Ruppia bed and its associated community (except the infauna) develops annually. Micro and macroalgae are ubiquitous and produce numerous spores, while other invertebrates colonize the developing Ruppia spp. from adjacent areas, probably through settlement of pelagic larvae but more importantly passive and active migration by juveniles (Broström & Bonsdorff, 2000). For example, the artificial seagrass habitats tested by Broström & Bonsdorff (2000) were colonized by large numbers of a variety of invertebrates with 57 days (ca 2 months).

Benthic infauna is probably more stable, remaining when the Ruppia spp. die back. However, recolonization is thought to be rapid in Arenicola marina where adjacent population exist. In Broström & Bonsdorff (2000) experiments the polychaete Pygospio elegans and juvenile Macoma baltica had begun to colonize the habitat with 21 days and large numbers of both species were present by day 57. The community is, therefore, likely to recover rapidly, suggesting a recoverability of very high. However, in isolated lagoons and lochs recovery may take longer depending the proximity of similar communities from which recruitment can occur.

If the rhizomes and seed bank is removed recovery may be prolonged. Ruppia spp. seed and rhizomes can be transported considerable distances by wildfowl or by water currents and wind (when dry). Floating fragments of Ruppia spp. grow roots freely, sink and attach to the bottom. Orth & Moore (1982; cited in Kantrup, 1991) reported that sediments denuded by a boat propeller was recolonized at about 0.25m/ year. Therefore, once rhizomes or seed arrive in the habitat recovery may take several years, however, recovery will depend on the time taken for Ruppia propagules to reach the available habitat. In areas connected by water flow or regularly frequented by wildfowl recovery will take many years, but in isolated, habitat recovery may be prolonged, suggesting a recoverability of moderate (5-10 years).

Several factors may inhibit or prevent recovery; loss of preferred habitat, competition and bioturbation or feeding by benthic infauna. Verhoeven (1979) noted that Ruppia spp. have little ability to compete with other, more vigorous aquatic plants and, therefore, most frequently occur in environments of variable salinity and temperature that other species can not endure (Verhoeven, 1979; Kantrup, 1991). Similarly, competition with infauna such as Hediste diversicolor or Arenicola marina have been suggested to hamper potential recruitment in Zostera noltii (see review) (Hughes et al., 2000; Philippart, 1994a) and Corophium volutator has been reported to inhibit colonization of mud by Salicornia sp. (Hughes et al., 2000). Therefore, the above infaunal species could potentially inhibit recruitment and hence recovery in Ruppia spp. when they are abundant.


This review can be cited as follows:

Tyler-Walters, H. 2001. Ruppia maritima in reduced salinity infralittoral muddy sand. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 24/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=266&code=1997>