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

Carcinus maenas displays very little preference for substratum, inhabiting everything from mudflats to bedrock. Therefore, it is unlikely to be affected by the loss of a particular substratum although its foraging success may be decreased and an intolerance of low has 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

Carcinus maenas is an extremely mobile organism and is capable of burrowing into sediment with its legs for shelter or when searching for prey such as the cockle Cerastoderma edule or the clam Mya arenaria. Therefore, it is unlikely to be significantly perturbed by a layer of sediment and tolerant has been recorded. Recruitment may be affected however, as mortality of post-settlement Carcinus maenas on sand flats is 80-90% (Moksnes et al., 1998). Therefore, if a large area of previously complex habitat was covered in sediment, post-settlement mortality would be much higher than before the deposition of the sediment.

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

Carcinus maenas shows very little habitat preference and are found in clear rocky shore waters all the way through to turbid estuarine waters. Therefore, they are unlikely to be affected by 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

Carcinus maenas shows very little habitat preference and are found in clear rocky shore waters all the way through to turbid estuarine waters. Therefore, they are unlikely to be affected by 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

Young crabs have been reported to survive for 10 days in moist air (Crothers, 1968) and can probably survive dry air for some time as well. Therefore, tolerant at the benchmark level has been recorded.

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

The activity rhythms of adult Carcinus maenas are entrained by salinity, hydrostatic pressure and temperature, and are therefore unaffected behaviourally by an increase in emergence. Juvenile crabs are entrained to some extent by periodicity of inundation and emergence (Reid et al., 1992), and may become active before immersion by the tide and become more vulnerable to predation by birds. Physiologically, Carcinus maenas is exceptionally tolerant (e.g. Ameyaw-Akumfi & Naylor, 1987; Crothers, 1968; Hill et al., 1991; Naylor, 2000) and will probably survive an extra hour of emergence until it can re-entrain to the new tidal cycle and migrate downshore to a suitable habitat. First and second instar Carcinus maenas live in the high intertidal and have finely tuned endogenous rhythms to ensure moulting occurs during inundation on spring tides (Zeng et al., 1999). A sudden increase in emergence coupled with these rhythms, which persist for 8 days in constant conditions (Zeng et al., 1999), could lead to moulting becoming dislocated from inundation on spring tides. However, mortality of Carcinus maenas due to an increase in emergence is unlikely and an intolerance of low 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

A decrease in emergence would allow Carcinus maenas to forage for longer and increase its food intake, especially on mussel or cockle beds. This would increase its growth rate and fecundity (Klein Breteler, 1975). Predation by fish, cephalopods and other crustaceans would probably increase but this would probably be tempered by reduced predation from birds, and tolerant 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

Carcinus maenas is replaced in high energy sand areas by Portumnus latipes, Corystes cassivelaunus, Liocarcinus depurator andLiocarcinus holsatus (Crothers, 1968), and so is likely to migrate away from an area where water flow rate increases. Mortality is likely to be low so a 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

Carcinus maenas can be found in salt marsh creeks and rockpools where water flow can be very low or non-existent and therefore a decrease in water flow is unlikely to affect Carcinus maenas 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

At the benchmark level, Carcinus maenas is unlikely to be harmed by an increase in temperature as it can survive at least 23°C at the southern limit of its range in the Mediterranean Sea (Sprung, 2001). However, the adults will not breed over 18°C (Crothers, 1967) so summer breeding may be affected by a chronic increase. However, an increase in temperature also increases moulting rate (Klein Breteler, 1975), feeding rate (Sanchez-Salar et al., 1987) and salinity tolerance (Crothers, 1967) and therefore is likely to be of benefit to a population. Therefore, tolerant* has been recorded.

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

Carcinus maenas can tolerate a temperature range of at least 5 -26°C (Truchot, 1973) and therefore is unlikely to suffer mortality from a decrease in temperature at the benchmark level. Since increased temperature increases feeding rate (Sanchez-Salar et al., 1987) and moulting rate (Klein Breteler, 1975) it follows that a decrease in temperature would slow down feeding rate and growth rate. This is only a perturbation, however, and there would probably not be any mortality at the benchmark level and therefore tolerant has been recorded. However, in the severe winter of 1962-63, when water temperatures around the British coast fell to -1.5°C, large numbers of adult Carcinus maenas were caught in dredges and washed up upon the shore. Juveniles seemed to be unaffected (Crisp, 1964).

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

Carcinus maenas is not reliant on clear water for any part of its adult life and so is unlikely to be affected by an increase in turbidity. One consequence may be increased productivity of filter-feeding prey items such as the mussel Mytilus edulis or the cockle Cerastoderma edule and therefore improved feeding for Carcinus maenas .

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

Carcinus maenas is not reliant on clear water for any part of its adult life and so is unlikely to be affected by 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

Carcinus maenas is typical of sheltered shores (Crothers, 1968) and estuaries (Ingle, 1997) and an increase in wave exposure may force Carcinus maenas out of areas where it is at the limit of its tolerance. An intolerance of intermediate has been recorded since some crabs are likely to be washed out of refuges by large waves and killed by further wave action or consumption by predators.

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

Carcinus maenas is typical of sheltered shores (Crothers, 1968) and estuaries (Ingle, 1997) and a decrease in wave exposure is likely to increase the available habitat for Carcinus maenas 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

Carcinus maenas is unlikely to be affected by noise at the benchmark level.

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

Carcinus maenas may adjust its behaviour in response to the presence of machinery or people, it will often adopt a defensive posture upon the approach of a person but mortality or emigration is unlikely and tolerant 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

During the construction of the "EUROPIPE" gas pipeline in the Wadden Sea, Carcinus maenas abundance was affected by construction activities across the route of tidal migration: crabs were most likely scared away and unable to migrate upshore than killed. The difference in Carcinus maenas abundance compared to pre-construction levels lasted only a few months (van Bernem, 1999). Physical disturbance will probably cause short term effects with rapid recovery due to the mobility and fecundity of Carcinus maenas.

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

Translocated crabs quickly orient to concealment (Bliss, 1983) and are easily kept in captivity at high density. Therefore, they are tolerant of displacement as long as there is suitable refuge in the new area.

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

Cypermethrin is an insecticide used to treat salmon for fish lice. At the concentration used on fish farms (5 µg/l) half the exposed Carcinus maenas died within 96 hours. However, most of the crabs displayed sublethal effects of stiffened limbs, outstretched chelae and unresponsiveness to visual or mechanical stimuli after 5 hours in cypermethrin treated water (Gowland, 2002). In the wild, this would make active crabs vulnerable to predation.
Exposure to sublethal concentrations of the oil dispersant BP1100WD caused increased locomotory activity, cardiac output and respiratory rate for the first 24 hours of exposure and prevented feeding for the entire six weeks of the trial (Depledge, 1984). Exposure to dispersant will probably affect moulting and reproduction because they both have high energy requirements that are unlikely to be met after a period of dispersant-induced starvation.

A solution of 200 ng/l of DDT (a concentration that may be found in the aquatic environment) inhibited Na K ATPase and Mg ATPase in the gills of Carcinus maenas and decreased the crabs' ability to osmoregulate. This effect was cumulative and increased with exposure time (Jowett et al., 1981) and would probably decrease the ability of Carcinus maenas to survive low salinity environments. Exposure to synthetic chemicals is likely to cause high mortality in Carcinus maenas populations and an intermediate intolerance has been recorded.

Heavy metal contamination

Evidence

Carcinus maenas is very tolerant of zinc pollution and was found to have loadings from 2087-3859 µg Zn per 10 g dry weight of crab; 60-80% of which was deposited in the exoskeleton (Chan & Rainbow, 1993) and was presumably lost at moulting. Even at very high concentrations, zinc does not cause significant mortality but it is not without metabolic effects. Carcinus maenas exposed to hypoxia (1.5 mg O₂/l) and zinc pollution (0.25 mg/ l) switched to anaerobic respiration sooner than those exposed to hypoxia only (Johnson, 1987). In low salinity, in addition to zinc contamination and hypoxia, osmoregulation was interrupted by zinc but the experimental Carcinus maenas survived 96 hours in these conditions and then fully recovered in clean normoxic water (Johnson, 1988).
Johnson (1988) also conducted experiments under the same conditions described above with copper, with similar results. Copper contamination can be lethal or cause severe sublethal effects. As described above, 0.25 mg/l caused some perturbation but not mortality of Carcinus maenas (Johnson, 1987; 1988), 0.5 mg/l caused gill damage including vacuolisation and necrosis of gill cells and reducing blood oxygen levels, and 2 mg/l caused 50% mortality in five days (Nonnotte et al., 1993). Low salinity caused synergistic effects with copper, a 10 ppm copper solution caused a 50-60% reduction in Na K ATPase (needed for ionic regulation) activity in 10 psu water and some mortality as a result (Hansen et al., 1992).

Carcinus maenas starves immediately before moulting and the breakdown of energy stores and catabolism of body tissue releases bound metals and increases the total body concentration even though no more metal has been absorbed (Scott-Fordsmand & Depledge, 1993). This may affect metal toxicity and Carcinus maenas may be more vulnerable to metal pollution just before and just after moulting. Low salinity also increases the uptake of cadmium (by up to twice as much) from solution and during long exposures whole body levels of cadmium can be 6-18 times higher than that of the surrounding water (Bjerregaard & Depledge, 1994: Wright, 1977). Nevertheless, Carcinus maenas tolerated a body loading of 33.7 mg Cd per kg wet weight and cleared half of the cadmium from its body in 11 days in clean water (Wright, 1977). This is presumably due to the excretion of metallothioneins.

Carcinus maenas is also tolerant of selenium, an essential micronutrient, but toxic at high concentrations (as are many other metals including copper and zinc). As with most metals, selenium is concentrated in the hepatopancreas and bound with metallothionein. It was found at 4.5 ppm in sampled Carcinus maenas (Zatta et al., 1985). Interestingly, selenium binds with other metals and forms metal-selenides that are less toxic than the metal or selenium alone (Zatta et al., 1985).

In contrast to other metals, arsenic is found at the highest concentrations in the gill tissue of Carcinus maenas this may be due to absorption at this site or elimination. Gill arsenic concentrations were found to be 179-483 µg per g dry weight and Carcinus maenas is assumed to be tolerant to arsenic pollution (Anderson & Depledge, 1994).

Mercury is by far the most toxic metal to Carcinus maenas, 0.05 mg/l caused an increase in locomotory activity and disrupted endogenous rhythms with possible ecological implications (Depledge, 1984a). A 10 hour exposure to 1 mg Hg/l caused 100% mortality within 48 hours (Depledge, 1984a).

Overall, Carcinus maenas is very tolerant of metal contamination although mortality may occur at high concentrations of mercury. However, heavy metal contamination causes a wide range of metabolic effects and, therefore, an intolerance of low has been recorded.

Hydrocarbon contamination

Evidence

Carcinus maenaspopulations were extinguished on some shores by oiling from the Torrey Canyon oil spill (Smith, 1968) and many were killed by effluent discharged into saltmarsh creeks from a Milford Haven refinery (Baker, 1976).
Sublethal concentrations of the water soluble fraction of oil caused increased locomotory activity, cardiac output and respiratory rate for the first 24 hours of exposure. Feeding was inhibited for at least 8 days. A combination of oil and dispersant had synergistic effects and inhibited feeding for longer than either oil or dispersant alone (Depledge, 1984b). An intolerance of high has been recorded.

Radionuclide contamination

Evidence

Carcinus maenas accumulates antimony¹²⁴ from its food (Weers & Louwrier, 1981) and uranium from water (Chassard-Bouchaud, 1983). Both are concentrated in the hepatopancreas and seem to cause little harm to Carcinus maenas even though concentrations of uranium can be 100 times higher in contaminated individuals compared to uncontaminated ones. Carcinus maenas is capable at least of detoxifying itself of uranium by moulting and voiding spherocrystals in which the uranium is bound (Chassard-Bouchaud, 1983). However, no evidence of adverse effects of radionuclides on Carcinus maenas was found and tolerant has been recorded.

Changes in nutrient levels

Evidence

Carcinus maenas is probably tolerant of nutrient input as it is tolerant of hypoxia that is often associated with organic enrichment. In addition, Carcinus maenas preys on species that can benefit from organic inputs, especially bivalve molluscs. Carcinus maenas normally excretes ammonium through the gills but in response to increased ammonium concentration, Carcinus maenas increases urea production and consequently has to increase gill permeability to take up more water for urine production. This in turn means that the affected Carcinus maenas has to increase energy expenditure on active ion transport, especially in low salinities (Spaargaren, 1990). Therefore, high energy demands may exclude Carcinus maenas from areas of organic enrichment in low salinity waters. The megalopae of Carcinus maenas select filamentous algae for settlement to avoid predation from cannibalistic juveniles (Moksnes et al., 1998; Moksnes, 2002). Eutrophication has been shown to cause algal mats to form on estuarine mudflats which may increase recruit survivorship. Therefore, tolerant has been recorded.

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

Carcinus maenas can tolerate salinities from 4-40 psu (Crothers, 1968; Ameyaw-Akumfi & Naylor, 1987) and has a preference for 27-40 psu, exhibiting halokinesis (non-directional movement in response to salinity) in a salinity gradient (Ameyaw-Akumfi & Naylor, 1987). Carcinus maenas is more tolerant of hypoxia (Legeay & Massabuau, 2000) and heavy metal accumulation (Bjerregard & Depledge, 1994) in higher salinities. Therefore, Carcinus maenas is likely to be tolerant of an increase in salinity at the benchmark level.

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

Carcinus maenas remains in estuaries throughout each tidal cycle (as opposed to migrating in and out with the flood and ebb tides) and experiences from full salinity to almost freshwater twice daily (Ameyaw-Akumfi & Naylor, 1987). Therefore, it is very tolerant of a decrease in salinity. However, decreasing salinity decreases the tolerance of Carcinus maenas to hypoxia and heavy metal accumulation, presumably due to increased energetic demands. Because of the increased energetic demands in low salinity, berried females and parasitized Carcinus maenas avoid brackish water (Crothers, 1968). Overall, Carcinus maenas is probably tolerant of a decrease in salinity at the benchmark level.

Changes in oxygenation

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

Evidence

Carcinus maenas can survive up to 18 hours in complete anoxia by switching to anaerobic respiration and building up lactate. The crabs become inactive in anoxia and metabolic rate drops to <20% of that in normoxic conditions. Carcinus maenas is probably tolerant of hypoxia and is regularly subject to hypoxic conditions in rock pools, especially at night (Brante & Hughes, 2001). Exposure to 1.5 mg O₂/l, about a quarter of normoxic oxygen levels, for 24 hours had little effect on metabolism (Johnson, 1987) and 1 mg O₂/l increased the time taken to glean and consume the flesh of mussels but had no other effect (Brante & Hughes, 2001). Oxygen consumption doubles after feeding but Carcinus maenas can still survive long periods of hypoxia (Legeay & Massabuau, 2000). Hypoxia and low salinity in combination can cause some perturbation in Carcinus maenas. Exposure to 27 psu and 1.5 mg O₂/l for 96 hours had no effect on crabs but when the salinity was reduced to 13 psu, osmoregulation was interrupted but none of the crabs died (Johnson, 1988). However, Carcinus maenas in salinities less than 10 psu in approximately 1.5 mg O₂ l^-1 switched to anaerobic respiration and there was 50% mortality within 24 hours (Legeay & Massabuau, 2000). The tolerance of Carcinus maenas to hypoxia does vary with season and is highest in the spring and summer during intermoult and lowest in winter just before the main moulting period (Legeay & Massabuau, 2000). Tolerant has been recorded because Carcinus maenas is unaffected by hypoxia (and even anoxia) in all but the most extreme conditions.

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

Carcinus maenas can contract bacterial haemolymph infections through wounds which cause death or prolong intermoult and are caused by a variety of bacteria including species of Vibrio, Bacillus and Aerococcus (Bliss, 1983). On very rare occasions, Carcinus maenas may become infected by Anophrys maggii, which consumes blood cells and causes death by anaemia and secondary bacterial infection (Bliss, 1983). Carcinus maenas is parasitized by Proficollis botulus, Fecampia erythrocephalus and Sacculina carcini (see adult general biology). Some mortality in Carcinus maenas populations is caused by microbial and parasitic infections and an intolerance of intermediate 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

The Chesapeake Bay Swimming Crab, Callinectes sapidus, was introduced to southeast England from America (Ingle, 1980; 1997). It has a similar diet to Carcinus maenas and the two species may compete for food (Ropes, 1989).

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

Carcinus maenas is sometimes sold at fish markets in France and Portugal and soft crabs (known as 'peelers') are used as fishing bait but although there is some mortality, neither are at a sufficient magnitude to significantly affect Carcinus maenas populations.

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

Carcinus maenas consumes such a wide range of food items that the extraction of one food type (e.g. mussels Mytilus edulis) would cause Carcinus maenas to switch to a different food type. Therefore, it is probably tolerant of extraction of its prey species.