The Marine Life Information Network

Substratum loss

Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details

Evidence

Crangon crangon is found on sandy and muddy ground, showing a preference for grain sizes between 125 and 710 µm (Pinn & Ansell, 1993). Crangon crangon buries itself to ambush prey and to avoid predation (Pinn & Ansell, 1993). It feeds mainly on benthic infauna and 0-group flatfish and if the substratum was removed, most of the Crangon crangon would be removed with it. Those individuals that escaped would have greatly increased predation from demersal fish e.g. gadoids and would have greatly decreased foraging success and mortality would probably be high. Crangon crangon needs areas with fine silt bottoms as nursery grounds for juveniles and land reclamation in the Wadden Sea has been stated as a threat to recruitment (Boddeke, 1982). Therefore, an intolerance of high and a recoverability of very high have been recorded.

Smothering

Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details.

Evidence

The effect of smothering on Crangon crangon is probably dependent on the nature of the deposited material. Crangon crangon is a very motile organism and therefore should be able to avoid burial but will probably be adversely affected if the deposited material is anything other than sand or mud as it will not be able to forage or escape predation by burying. Crangon crangon needs areas with fine silt bottoms as nursery grounds for juveniles and land reclamation in the Wadden Sea has been stated as a threat to recruitment (Boddeke, 1982). To account for a worst-case scenario an intolerance of intermediate has been recorded. A recoverability of very high has been recorded

Increase in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Crangon crangon inhabits areas with extremely high quantities of suspended sediment (Addison et al., 2003; Lloyd & Yonge, 1947) and, therefore, is likely to be tolerant of an increase in suspended sediment.

Decrease in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Crangon crangon is found in very clear and very turbid waters (Addison et al., 2003) and is likely to be tolerant of a decrease in suspended sediment.

Desiccation

1. A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour.
2. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details.

Evidence

Despite the fact that Crangon crangon is found intertidally, it is not adapted for exposure to air, instead seeking refuge in intertidal pools at low tide. Adults are mostly subtidal but juveniles move into intertidal areas with the flood tide to feed and are carried back out to sea on the ebb (Cattrijsse et al., 1997; Lloyd & Yonge, 1947). An intolerance of high has been recorded to account for any individuals that may become stranded, which will probably die from water loss very quickly. For recoverability see below.

Increase in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Crangon crangon is rarely stranded on sand exposed to the air, burying into the sand just below the low water mark. It has endogenous circatidal rhythms of activity and shows peak emergence around high tide so that it is carried upshore no further than mean tide level to forage and is carried back downshore on the ebb tide (Al-Adhub & Naylor, 1975). Activity is suppressed by light (Addison et al., 2003; Al-Adhub & Naylor, 1975) so a change in emergence regime would not affect timing of emergence during the day when Crangon crangon is most vulnerable to predation. Crangon crangon does occur in the intertidal but due to the reasons stated above is not subject to emersion and not relevant has been recorded.

Decrease in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Crangon crangon is rarely stranded on sand exposed to the air, burying into the sand just below the low water mark. It has endogenous circatidal rhythms of activity and shows peak emergence around high tide so that it is carried upshore no further than mean tide level to forage and is carried back downshore on the ebb tide (Al-Adhub & Naylor, 1975). Activity is suppressed by light (Addison et al., 2003; Al-Adhub & Naylor, 1975) so a change in emergence regime would not affect timing of emergence during the day when Crangon crangon is most vulnerable to predation. Crangon crangon does occur in the intertidal but due to the reasons stated above is not subject to emersion and not relevant has been recorded.

Increase in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Crangon crangon has a preference for strong tidal currents (Henderson et al., 1990) but is less common where current speeds exceed 1.5 knots (Hostens, 2000) even though these speeds probably do not displace standing or walking individuals (Huddart & Arthur, 1971). An increase in the water flow rate at the benchmark level would probably lead to a population of Crangon crangon being swept away by the flow. However, since Crangon crangon uses tidal currents to make annual migrations (Boddeke, 1975) and can move more than 12 km in a week (Huddart & Arthur, 1971) there probably would not be any mortality as a result but some perturbation, and an intolerance of low has been recorded.

Decrease in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Crangon crangon relies on currents to move up and down sandy shores for foraging (Al-Adhub & Naylor, 1975) and to perform seasonal migrations (Boddeke, 1975) but also occurs in lagoons (Gelin et al., 2000) with negligible water flow. Therefore Crangon crangon is unlikely to be affected by a decrease in water flow rate at the benchmark level and tolerant has been recorded.

Increase in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

Crangon crangon can survive 6-30°C (Abbott & Perkins, 1977; Jeffery & Revill, 2002; Lloyd & Yonge, 1947) and is likely to be tolerant of an increase in temperature at the benchmark level. However, elevated temperatures (20°C +) may cause increased vulnerability to synthetic chemicals (Drewa, 1988; McLeese & Metcalf, 1979), oxygen depletion (Hagerman & Szaniawska, 1986; Sedgwick, 1981), organic enrichment (Costello et al., 1993) and hydrocarbons (Palgan et al., 1988). (see chemical factors below).

Decrease in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

Crangon crangon can survive 6-30°C (Abbott & Perkins, 1977; Jeffery & Revill, 2002; Lloyd & Yonge, 1947) and is likely to be tolerant of a decrease in temperature at the benchmark level, especially as the populations migrate offshore in winter (Boddeke, 1989; Henderson & Holmes, 1987). However, sublethal effects of decreased temperature include less frequent moulting and a decreased ability to escape from e.g. trawls (Jeffery & Revill, 2002). After ice winters in the Wadden Sea, Crangon crangon abundances are very high as its main predators are excluded by the low temperatures (ICES, 1996). Crangon crangon does not seem to be affected by a decrease in temperature and in some cases can benefit and tolerant has been recorded.

Increase in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Crangon crangon is found in areas of extremely high turbidity (Addison et al., 2003; Lloyd & Yonge, 1947). In clear water in The Wash, Crangon crangon is only active at night to avoid predation (Addison et al., 2003) but in the very turbid waters of the Bristol Channel, Crangon crangon is active day and night (Lloyd & Yonge, 1947). Therefore an increase in turbidity is likely to be of benefit to Crangon crangon by increasing foraging time and tolerant* has been recorded.

Decrease in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Crangon crangon occurs in varying turbidity from clear water to extremely high turbidity (Addison et al., 2003) and therefore is likely to be tolerant of a decrease in turbidity.

Increase in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Densities of Crangon crangon reached 394 per 100m² on the Belgian coast and seemed to be unaffected by wind speed and wave height (Beyst et al., 2001). Therefore tolerant has been recorded.

Decrease in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Crangon crangon occurs in lagoons (Gelin et al., 2000) and estuaries where wave exposures are very low. Therefore a decrease in wave exposure is unlikely to adversely affect the population and tolerant has been recorded.

Noise

1. Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods.
2. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details

Evidence

Crangon crangon has highly sensitive antennae and is probably able to detect vibrations in the water. However, at the benchmark level the limit of response to noise is probably that Crangon crangon will bury itself for a short time but suffer no other perturbation and tolerant has been recorded.

Visual presence

Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details

Evidence

Crangon crangon has compound eyes and probably has good visual acuity. The presence of large, unnatural objects is likely to cause them to remain inactive as a predator avoidance response and although mortality is unlikely, it may affect population dynamics especially if the disturbance occurs during the main summer breeding season. Emergence behaviour of Crangon crangon is controlled by light, with most activity occurring at night (Addison et al., 2003; Al-Adhub & Naylor, 1975). Therefore, the presence of lights due to human activity will impact on the rhythmical behaviour of Crangon crangon and probably reduce its foraging success. Neither of the scenarios described above are likely to cause mortality but will probably reduce the viability of the population and an intolerance of low has been recorded.

Abrasion & physical disturbance

Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details.

Evidence

Crangon crangon suffers exoskeleton damage when it is trawled or dredged. Such damage allows infection of the exoskeleton by chitin digesting bacteria that cause black spot disease (Nottage, 1982). Although mortality from black spot disease is very low (Dyrynda, 1998; Nottage, 1982) prey perception and motility might be affected and therefore an intolerance of low has been recorded.

Displacement

Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details

Evidence

Lancaster & Frid (2002) reported that 99% of undersized shrimp discarded from a trawl catch are alive when returned to the sea and that 92% were alive 24 hours later. Most of the mortality resulted from seabirds consuming discards before they could swim down out of reach. Crangon crangon uses tidal currents to make annual migrations (Boddeke, 1975) and can move more than 12 km in a week (Huddart & Arthur, 1971). Therefore, if a Crangon crangon population was displaced by less traumatic means than trawling and release, it is unlikely that they would be significantly perturbed and tolerant has been recorded.

Synthetic compound contamination

Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example:

• evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity;
• evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity;
• evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity.

The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details.

Evidence

In the 1980s the amount of detergents polluting water bodies increased, reaching extremes of 40 mg/l but more commonly around 5 mg/l. A 5 mg/l concentration of the surfactant alkylobenzene sulphonate (ABS) caused 100% mortality of Crangon crangon in 18 days at 15°C and in 15 days at 20°C in normoxic conditions (8.6-9.3 mg O₂ l). Hypoxia (4.4-5.3 mg O₂ l) increased surfactant toxicity and halved the time taken to reach total mortality (Drewa, 1988). ABS caused vacuolization of hepatopancreas cells (presumably as an attempt to detoxify the chemical) and a total cessation of cell proliferation at 5 mg/l (Zbytniewski & Drewa, 1988). Even if Crangon crangon was not exposed to ABS for long enough to cause mortality, it probably suffers serious physiological effects.
Ivermectin is used in fish farms to treat salmon for fish lice. In solution, it had no effect on Crangon septemspinosa, a North American relative of Crangon crangon, but when presented in fish food (used to treat salmon prophylactically), Ivermectin caused 50% mortality in 96 hours at only 8.5 µg ivermectin per g of fish food (Burridge & Haya, 1993). Crangon crangon beneath fish cages are likely to suffer high mortality if they feed upon waste food impregnated with Ivermectin.
Some polychlorobiphenyls (PCBs) are toxic to Crangon crangon but only at concentrations far higher than normally found in the sea. PCB15 caused 50% mortality at 500 µg/l but concentrations of PCB in nature are rarely higher than 1.7 µg/l (general levels for the North Sea are 5 ng/l) and only 9% of PCB in nature is PCB15 (Smith & Johnston, 1992). Therefore Crangon crangon is unlikely to be killed directly by PCBs, however, a concentration of 0.5 µg/l of PCB15 caused an approximately 40% drop in haemocyte numbers making Crangon crangon more susceptible to bacterial infection (Smith & Johnston, 1992).
Modern oil dispersants are less toxic than those used for e.g. the Torrey Canyon oil spill but they are not without their effects. The dispersant 'SOLO' caused a 50% reduction in arylsulphatase activity, which is the enzyme responsible for post-moult exoskeleton hardening (Drewa et al., 1978). The dispersants Tween 80, BP1100X and Slickgone LT2 did not cause mortality at a concentration of 10 ppm but decreased food consumption and ability to detect food by Crangon crangon. The exposed Crangon crangon recovered their appetite after 4 hours in clean seawater (Evans et al., 1977).
Creosote is lethal to Crangon crangon at 0.13 mg/l at 10°C and at 0.11 mg/l at 20°C (McLeese & Metcalfe, 1979). Abele-Oeschger et al. (1997) reported a 26% reduction in aerobic metabolic rate in 0.68 mg/l of hydrogen peroxide but did not report a lethal concentration.
Crangon crangon has been shown to be intolerant of a wide variety of synthetic chemicals at varying concentrations but long time periods or high concentrations are needed to cause 100% mortality and intermediate has been recorded to represent the conditions that Crangon crangon is likely to be subject to in nature. Crangon crangon is also very sensitive to sulphide pollution (see oxygenation below).

Heavy metal contamination

Evidence

• Andersen et al, (1984) measured metal concentrations in wild Crangon crangon from the Seine Bay estuary and found 5.25 mg mercury, 2.35 mg cadmium, 121.5 mg copper, 316 mg zinc and 247 mg iron per kg dry weight of tissue.
• In the Bristol Channel, cadmium, zinc and copper were found at levels of 1.4-15.4, 29-136 and 76-107 mg per kg dry weight respectively (Culshaw et al., 2002).
• Price (1979) investigated the toxicity of metals in solution and found that toxicity was temperature dependent with higher temperatures increasing toxicity. In 96 hour exposures, copper caused 50% mortality at 21 mg/l at 5°C, 9.5 mg/l at 10°C, 6 mg/l at 15°C and 4.5 mg/l at 20°C. Zinc is much less toxic to Crangon crangon and caused 50% mortality at 56, 19, 12 and 10 mg/l at 5, 10, 15 and 20°C respectively. Cadmium was the most toxic of the metals tested by Price (1979) and caused 50% mortality at 2.54, 0.65, 0.4 and 0.3 mg/l at 5, 10, 15 and 20°C respectively.
• Crangon crangon exposed to very low concentrations of metals, 0.005 mg/l cadmium, 0.75 mg/l copper and 5.5 mg/l zinc, for 42 days suffered 40-60% mortality at 5-20°C (Price, 1979).
• Crangon crangon is tolerant of arsenate, which becomes toxic at 25 mg/l but takes over 7 days to cause 50% mortality at 50 mg/l in small Crangon crangon and more than 14 days in larger specimens (Madsen, 1992). Crangon crangon did not accumulate arsenic from seawater but it was rapidly accumulated from food, especially organic forms such as arsenobetaine, which reached levels 40 times those of control animals in a 16 day exposure (Hunter et al., 1998).

Several authors have reported sublethal effects of heavy metals.

• Johnson (1988) reported a reduction in osmoregulatory ability at 25% oxygen saturation and 0.25 mg/l of copper or zinc.
• A reduction in osmoregulatory ability at 0.5 mg/l zinc was reported by Rasmussen et al. (1995).
• Copper, cadmium and zinc at around 1 mg/l caused increased heart beat and gill ventilation but an escape response (emergence from the sediment and rapid tail flicking) was not observed until a metal concentration of 20 mg/l (Price & Uglow, 1980).
• Very low concentrations of cadmium damaged mitochondria and inhibited the transportation of salts, enzyme activity and protein synthesis in the gill epithelium (Papathanassiou, 1985).
• Crangon crangon is a strong bioaccumulator of cadmium and does not have an efficient method of excretion (Culshaw et al., 2002).

High levels of metal pollution cause significant mortalities of Crangon crangon and an intolerance of intermediate has been recorded. As important, however, is the fact that Crangon crangon accumulates high levels of toxic metals that will be concentrated by consumers, including humans.

Hydrocarbon contamination

Evidence

Crangon crangon exposed to light diesel fuel oil, heavy fuel oil and crude oil were found to be most susceptible to light diesel fuel oil. In brackish (7 psu) water at 20°C, light diesel fuel oil caused 50% mortality in 96 hours at 10 ppm, heavy fuel oil had the same effect at 20 ppm and crude at 25 ppm. Long term exposures to 5 ppm of all 3 oil types at 15°C caused total mortality in 9 days (Palgan et al., 1988). After the Sea Empress oil spill, Crangon crangon 3 km from the wreck were found to be lethargic and failed to exhibit a normal escape response (Rutt et al., 1998). Different hydrocarbons have different toxicities in short exposures but all are very toxic if Crangon crangon is exposed for many days. Therefore an intolerance of high has been recorded.

Radionuclide contamination

Evidence

Crangon crangon accumulates ⁶⁰cobalt and ⁶⁵zinc from liquid radioactive waste but most is lost at ecdysis as they are concentrated in the exoskeleton (van Weers, 1975). No information on the toxicity of radionuclides has been found and there is insufficient information to assess an intolerance.

Changes in nutrient levels

Evidence

Phospho-gypsum, a by-product of the fertilizer industry, caused total mortality of Crangon crangon in 24 hours in a 1% solution. Long term exposures in 0.25% and 0.5% phospho-gypsum caused less mortality but reduced haemolymph protein with consequences for oxygen transport and immunity (Zbytniewski & Pautsch, 1973).
Adult Crangon crangon exposed to 1% sewage sludge in seawater at 10°C for 96 hours suffered 50% mortality. Sediments consisting of more than 6% sewage sludge were avoided by Crangon crangon but they would bury in sediments containing 1.6% sewage sludge (Costello et al., 1993).
However, nutrient inputs can be of benefit to Crangon crangon. In the Wadden Sea, phosphate enrichment from riverine industrial inputs was cut by a factor of 3 between 1981 and 1991. This caused a decrease in primary and secondary (calanoid copepod) production and a drop in Crangon crangon abundance from 4,000-6,000/1000m² to <2000/1000m² (Boddeke, 1996) showing that the enrichment was of benefit to Crangon crangon.
The sandy bottoms of the North Sea have a poor infauna and in these areas the main recruitment of Crangon crangon in May-July coincides with the calanoid copepod bloom, which is an important food source for 10-20 mm Crangon crangon. In the Hook of Holland, where nitrogen in seawater (as nitrate and ammonium) increased 5-fold from 1945-75, recruitment of Crangon crangon occurred April-October since the eutrophication generated a rich benthic infauna for small post-settlement Crangon crangon to exploit (Boddeke et al., 1986). Mortality from nutrient enrichment is likely to be very localized at point sources and have little impact on Crangon crangon populations whereas widespread dilute inputs are likely to be of benefit but intermediate has been recorded to account for the worst case scenario.

Increase in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Crangon crangon can tolerate salinities of 7-40 psu and can survive extremes if previously acclimated to the high or low end of its tolerance. For example, individuals acclimated to 40 psu survived 50 psu for 38 hours in comparison 16 hours by those previously acclimated to 7 psu (McLusky et al., 1982). Therefore tolerant has been recorded.

Decrease in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Crangon crangon can tolerate salinities of 7-40 psu (Mclusky et al., 1982) and can survive fresh water for up to 8 hours (Lloyd & Yonge, 1947). Nevertheless, prolonged decreases in salinity are not without their effects and Crangon crangon migrate offshore in winter to avoid low salinities (Henderson & Holmes, 1987). At 25 psu female Crangon crangon become berried as normal but at 15 psu egg attachment to the abdominal appendages (pleoplods) is delayed and there is a complete failure of spawning at 5 psu (Gelin et al., 2001). Decreased salinity also increases the susceptibility of Crangon crangon to hypoxia (Johnson, 1988; Sedgwick, 1981). Low salinity is unlikely to cause mortality of adult Crangon crangon but may affect the viability of a population and an intolerance of low has been recorded.

Changes in oxygenation

Benchmark.  Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details.

Evidence

Crangon crangon can maintain its use of oxygen independent of dissolved oxygen down to 2 mg/l and does not commence anaerobic respiration until 0.9 mg/l (Hagerman & Szaniawska, 1989). Sedgwick (1981) reported 99% survival at 27 psu and 20°C in 1.7 mg O₂/l and 99% mortality at 0.9 mg O₂/l. However, hypoxia tolerance in Crangon crangon is temperature and salinity dependent. At 20°C, buried Crangon crangon emerge from the sand at 4-5 mg O₂/l but remain buried until 2 mg O₂/l at 9°C (Hagerman & Szaniawska, 1986). Tolerance to very low oxygen is salinity dependent. An oxygen concentration of 1 mg O₂/l at 10 psu incurred 50% mortality in 4.5 hours but at 20 psu 50% mortality occurred after 6 hours. Very low mortalities occurred at either salinity at 2 mg O₂/l (Hagerman & Szaniawska, 1986). At the benchmark level, Crangon crangon is unlikely to suffer mortality from prolonged hypoxia but there are physiological perturbations and low has been recorded. Despite a high tolerance to hypoxia, Crangon crangon is surprisingly intolerant of anoxia when it is considered that it shares a habitat with organisms such as the green shore crab Carcinus maenas which can tolerate anoxia for up to 18 hours. In anoxic conditions at 30 psu and 18°C 50% mortality occurred in 2.5 hours. In combination with 17 µg sulphide (H₂S)/l, anoxia caused 75% mortality in 1.5 hours (Hagerman & Vismann, 1995). Crangon crangon is intolerant of H₂S in the presence of oxygen. At 3.4 µg/l it emerged from the sand and began to swim, at 6.8 µg/l panic ensued and rapid tail flicking was exhibited in an attempt to escape the pollution. At 13.6 µg/l H₂S, Crangon crangon is paralysed (Vismann, 1996).

Introduction of microbial pathogens/parasites

Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details.

Evidence

Black spot shell disease, caused by chitin digesting bacteria, is common in Crangon crangon with an incidence of 13% in the Solway Firth (Nottage, 1982), up to 87% in Poole Harbour (Dyrynda, 1998) and 58% in the Elbe and Weser estuaries (Knust, 1990). Incidence increases with age: only 4.4% of 25 mm Crangon crangon were infected but 34.6% of 60 mm were infected (Knust, 1990). High incidences of black spot disease are believed to be related to damage by fishing gear and pollution, especially heavy metals (Knust, 1990; Nottage, 1982). Infected Crangon crangon have black lesions on the limbs, scaphocerites and antennae that make the exoskeleton very brittle leading to breakages. Mortality due to black spot disease is very low but infected individuals may have reduced prey perception and motility (Dyrynda, 1998) and an intolerance of low has been recorded.

Introduction of non-native species

Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details.

Evidence

No information was found on the effects of non-native species on Crangon crangon.

Extraction of this species

Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

There are important fisheries for Crangon crangon around the British Isles (Addison et al., 2003; Henderson et al., 1990; Lancaster & Frid, 2002; Lloyd & Yonge, 1947 ) and on the coasts of the Netherlands, Germany and Belgium (Boddeke, 1989) with landings reaching a peak in 1997 at nearly 29,000 t (ICES, 2001). The high fecundity, prolonged breeding, rapid growth and maturity of Crangon crangon has meant that stocks have barely been affected (ICES, 2001). Crangon crangon are marketable when the carapace length is 9 mm or more (Lancaster & Frid, 2002) and fishing mortality amongst this population is high and an intolerance of intermediate has been recorded to account for this. Since most of the Crangon crangon that reproduce and contribute to the commercial catch are less than 1 year old (ICES, 2001), the turnover and hence recoverability is rapid.

Extraction of other species

Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Crangon crangon densities increased in the tracks of blue mussel dredges for 7 days after dredging. This was presumed to be due to the dredge exposing large numbers of polychaetes upon which the Crangon crangon were feeding (Dolmer et al., 2001). Therefore tolerant* has been recorded.