The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

Calocaris macandreae is abundant in muddy sediments around the British east and west coasts, extending from North Norway to West Africa and the Mediterranean (Buchanan, 1963; Christiansen, 2000; Ingle & Christiansen 2004; Pinn & Atkinson, 2010). OBIS (2022) includes records of Calocaris macandreae where sea surface temperatures ranged in temperate from 0-25°C, although the majority of records were reported at 10-15°C. Hughes (1998) noted that shallow sea lochs, where burrowed mud megafauna are abundant, usually experience seasonal changes in temperature of 10°C, i.e. between ca 5 and 15°C.  The stability of the population of Calocaris macandreae off the coast of Northumberland, over a 10-year period suggests it can withstand long-term seasonal changes in temperature. Also, the depth of the biotope (>50 m) combined with the Calocaris macandreae burrowed habit probably buffers its exposure to fluctuations in the temperature of the surface water (Hughes, 1998). 

Sensitivity assessment. Calocaris macandreae is recorded from the north and south of the UK from northern Norway to the Adriatic in the Mediterranean. Short-term acute changes in temperature and long-term chronic changes in temperature at the pressure benchmark are unlikely to adversely this biotope as its distribution suggests that Calocaris macandreae and the dominant polychaetes can potentially adapt to a wide range of temperatures experienced in both northern and southern waters.  Therefore, resistance is assessed as 'High', albeit at Low confidence due to the lack of direct evidence. Hence, resilience is assessed as 'High' and sensitivity as 'Not sensitive' at the benchmark level. 

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

Calocaris macandreae is abundant in muddy sediments around the British east and west coasts, extending from North Norway to West Africa and the Mediterranean (Buchanan, 1963; Christiansen, 2000; Ingle & Christiansen 2004; Pinn & Atkinson, 2010). OBIS (2022) includes records of Calocaris macandreae where sea surface temperatures ranged in temperate from 0-25°C, although the majority of records were reported at 10-15°C. Hughes (1998) noted that shallow sea lochs, where burrowed mud megafauna are abundant, usually experience seasonal changes in temperature of 10°C, i.e. between ca 5 and 15°C.  The stability of the population of Calocaris macandreae off the coast of Northumberland, over a 10-year period suggests it can withstand long-term seasonal changes in temperature. Also, the depth of the biotope (>50 m) combined with the Calocaris macandreae burrowed habit probably buffers its exposure to fluctuations in the temperature of the surface water (Hughes, 1998). 

Sensitivity assessment. Calocaris macandreae is recorded from the north and south of the UK from northern Norway to the Adriatic in the Mediterranean. Short-term acute changes in temperature and long-term chronic changes in temperature at the pressure benchmark are unlikely to adversely this biotope as its distribution suggests that Calocaris macandreae and the dominant polychaetes can potentially adapt to a wide range of temperatures experienced in both northern and southern waters.  Therefore, resistance is assessed as 'High', albeit at Low confidence due to the lack of direct evidence. Hence, resilience is assessed as 'High' and sensitivity as 'Not sensitive' at the benchmark level. 

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

No evidence was found to assess the salinity tolerance of Calocaris macandreae.  This biotope is found in fully marine conditions (JNCC, 2022), while Calocaris macandreae is recorded from sites where sea surface salinity ranged from 15-35 psu although most records were from 30-35 psu (OBIS, 2022). 

An increase in salinity at the benchmark level would result in a salinity of >40 psu, and as hypersaline water is likely to sink to the seabed, the biotope may be affected by hypersaline effluents. Ruso et al. (2007) reported changes in the community structure of soft sediment communities due to desalinisation plant effluent in Alicante, Spain. In particular, in close vicinity to the effluent, where the salinity reached 39 psu, the community of polychaetes, crustaceans and molluscs was lost and replaced by one dominated by nematodes. Roberts et al. (2010b) suggested that hypersaline effluent dispersed quickly but was more of a concern at the seabed and in areas of low energy where widespread alternations in the community of soft sediments were observed. In several studies, echinoderms and ascidians were amongst the most sensitive groups examined (Roberts et al., 2010b).

Sensitivity assessment.  An increase in salinity from full to >40 psu is probably detrimental to the important characteristic species of the biotope. Hypersaline water could sink to the seabed and potentially into the sediment via burrows. Although there is no direct evidence of the effects of hypersaline water, the stenohaline nature of the community suggests that hypersaline conditions may cause mortality. Therefore, a resistance of 'Low' is recorded but at Low confidence.  Resilience would probably be 'Low', so sensitivity may be 'High'. 

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

No direct evidence was found to assess the salinity tolerance of Calocaris macandreae.  This biotope is found in fully marine conditions (JNCC, 2022), while Calocaris macandreae is recorded from sites where sea surface salinity ranged from 15-35 psu although most records were from 30-35 psu (OBIS, 2022). 

The effects of low salinity exposure and emersion were tested to simulate the conditions experienced by discarded Nephrops in the Kattegat area as these are transported through the halocline (Harris & Ulmestrand, 2004).  Nephrops exposed to 15 psu (for <2 hr) suffered mortalities of 25-42% overall.  Exposed animals gained mass rapidly as water was absorbed and showed delayed or absent responses to stimulation following their return to waters of 33 psu (Harris & Ulmestrand, 2004; Johnson et al., 2013).  In addition, Nephrops was reported to survive at 28 psu but experience 50% mortality at 25 psu and 100% mortality at 21 psu (Harris & Ulmestrand, 2004).

Sensitivity assessment.  A decrease in salinity from full to reduced (18-30 psu) is likely to be detrimental to most of the important characteristic species in the biotope. This Calocaris macandreae dominated biotope is only recorded from full (30-35) saline conditions as are most habitats in which it is abundant (Buchanan, 1974; Hughes, 1998; JNCC, 2022). The evidence for the similar species Nephrops shows that short, acute reductions in salinity result in mortality but also that reduced salinity results in mortality. Therefore, a reduction in salinity for a year may cause significant mortality. Therefore, a resilience of 'Low' is recorded but with 'Low' confidence due to the lack of direct evidence. Resilience would probably be 'Low', so sensitivity may be 'High'. 

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

Calocaris macandreae was restricted to the muddier bottom areas at 70-100 m of the coast of Northumberland, where silt and clay content was greater than 20%, mixed with fine sand, but reached its highest density where silt and clay were >60% (Buchanan, 1963; Hughes, 1998). This biotope is recorded from weak (<0.5 m/s) tidal streams on mud and muddy sands, typical of low flow, wave-sheltered conditions.  A further decrease in flow is unlikely. An increase of 0.2 m/s may begin to erode the mud surface where the site is already subject to flow (e.g. weak flow at the seabed), based on the Hjulstrom-Sundborg diagram (Wright et al., 2001).  However, given the depth of mud that characterizes the biotope only the surface of the mud may be removed within a year (the benchmark).  Hence, the deep burrowing community may remain intact but the surface infauna may reduce in abundance. Therefore, a resistance of 'High' is recorded but with Low confidence.  Hence, resilience is probably High and sensitivity is assessed as 'Not sensitive' at the benchmark level. However, greater changes in water flow e.g. due to storms may reduce the area of mud or muddy sand, or temporarily deposit coarse sediment, which would alter the character of the biotope. 

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

This biotope occurs at 50 - 150 m so emergence is 'Not relevant'.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

This biotope (SS.SMu.OMu.CalPol) occurs in low-energy environments, very sheltered from wave exposure (JNCC, 2022), a prerequisite for the muddy sediments that characterize the biotope (JNCC, 2022). In addition, the biotope is found to considerable depths, at which, wave action is unlikely to be significant. Therefore, a decrease in wave exposure is 'Not relevant'. Any activity or climatic effect that increased wave action or storminess could have a significant effect on the shallower examples of the biotope, due to the removal or modification of the sediment. However, a change of 3-5% in significant wave height (the benchmark) is unlikely to be significant. Therefore, the biotope is probably 'Not sensitive' (resistance and resilience are High) at the benchmark level.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

Rygg (1985) examined benthic macrofauna communities in areas of Norwegian fjords with different levels of heavy metal pollution.  While Pb and Zn gave a weak negative correlation with diversity, Cu showed a strong negative correlation due to its toxicity to a large number of species.  Rygg (1985) identified 20 of the 50 most common species as significantly missing from stations where the Cu concentration was >200 ppm.  These non-tolerant species included Calocaris macandreae, Glycera unicornis (syn. rouxii) and Nucula sulcata, which characterize this biotope (OMu.CalPol).  Tolerant species were all polychaetes.  Atkinson & Taylor (2005) noted that bioturbation of sediments by thalassinideans has been shown to redistribute radionuclides in the Red Sea, a Pacific lagoon and the Irish Sea, although no effects on the species were given.

Sensitivity assessment.  The evidence suggests that copper (Cu) pollution could result in a significant reduction in the abundance of Calocaris macandreae and possibly other members of the community and, hence, a reduction in the extent of the biotope.  Therefore, resistance is assessed as ‘Low’ although only a single metal was implicated.  Hence, resilience is assessed as ‘Low’ and sensitivity as ‘High’.

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

Daan et al. (1992) found that Callianassa subterranea decreased in density towards drilling sites contaminated by oil-based muds in the North Sea.  For example, Daan et al. (1992) reported that at 1 km, where the oil concentration of the sediment was 16 mg/kg the abundance of Callianassa subterranea was significantly reduced.  They suggested that it was one of the more sensitive species in the sediment fauna, and experienced environmental stress even at distances of 1 - 2 km from the contaminant (Daan et al., 1992; Hughes, 1998).

Sensitivity assessment. Although no evidence of the effects of hydrocarbons on Calocaris spp. was found, the evidence from the similar species Callianassa spp. suggests that Calocaris spp. may be affected in a similar way.  Therefore, resistance is assessed as ‘Low’ but with ‘Low’ confidence.  Hence, resilience is assessed as ‘Low’ and sensitivity as ‘High’.

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

Hughes (1998) noted that the pesticide Ivermectin (once used in salmon farming to control sea lice) was reported to be highly toxic to sediment-dwelling polychaetes (Black et al., 1997; Thain et al., 1997) and epibenthic shrimps (Burridge & Haya, 1993), and suggested that it might be toxic to burrowing crustaceans.

Feldman et al. (2000) reviewed the use of pesticides to control burrowing thalassinidean shrimp (the ghost shrimp Neotrypaea californiensis and the mud shrimp Upogebia puggettensis) on oyster grounds in Willapa Bay and Grays Harbor, Washington State.  The aerial application of the pesticide Carbaryl (1-Naphthalenol methylcarbamate) to mudflats at 11.02 kg/ha between 1963 and 1984 was shown to kill 90-95% of the targeted shrimp on treated beds.  Ghost shrimp areas could be treated ‘effectively' at 2-5 kg/ha for 2-5 hours while mud shrimp grounds required 7-9 kg/ha for 1.5-3 hours.  They also reported that mud shrimp sediments (silty muds) could remain toxic to juveniles for 28 days while ghost shrimp sites remained toxic for 12 days.  Stewart et al. (1967) reported an 1-day LC₅₀ (death or irreversible paralysis) of 0.03- 0.16 mg/l Carbaryl and a 1-day LC₅₀ of 6.2-13.7 mg/l of 1-naphthol (the pesticide precursor) larval Upogebia pugettensis; and a 1-day LC50 of 0.13 mg/l Carbaryl and 1-day LC50 of 6.6 mg/l of 1-naphthol in adult Neotrypaea californiensis.  Dumbauld et al. (1997) reported a 1-day LC₉₀ (90% mortality) of 7.0 kg/ha in Upogebia pugettensis in the field, and a LOEC of 5.6 kg/ha after 30.4 days based on changes in population abundance.

Sensitivity assessment.  Although no direct evidence of the effects of synthetic compounds on Calocaris spp. was found, the above evidence suggests that pesticides (e.g. insecticides) have the potential to cause significant or severe (>75% mortality) on thalassinidean shrimp depending on the type of pesticide, the amount applied and duration of application, and its behaviour in the environment (e.g. retention by sediment).  Therefore, resistance is assessed as ‘None’ as a precaution.  Hence, resilience is assessed as ‘Low’ and sensitivity as ‘High’.

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

Communities similar to this biotope containing abundant burrowing megafauna and sea pens were found to exist in areas heavily contaminated by radionuclides, in particular near Sellafield, Cumbria, due to the activities of the British Nuclear Fuels Plc reprocessing plant (Hughes & Atkinson, 1997) but no information on the level of radiation was provided.  Atkinson & Taylor (2005) noted that bioturbation of sediments by thalassinideans has been shown to redistribute radionuclides in the Red Sea, a Pacific lagoon and the Irish Sea, although no effects on the species were given.

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

No evidence was found.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

Low oxygen concentration, reduced pH and sulphide are probably typical of crustacean burrows (Atkinson & Taylor, 2005).  For example, the oxygen concentration in Calocaris macandreae was reported to be between 20 and 40 Torr (ca 1.17 and 2.34 mg O₂/l ) (Anderson et al., 1991; Atkinson & Taylor, 2005). Calocaris macandreae irrigates its burrow for short intermittent periods of time.  However, a significant increase in irrigations only occurs once the oxygen partial pressure (PO₂) has fallen to low levels (Anderson et al., 1991; Atkinson & Taylor, 2005).

Mud shrimps are highly tolerant of hypoxia and the critical PO₂ below which normal oxygen consumption cannot occur is lower in thalassinideans than other decapods not normally exposed to hypoxia (Atkinson & Taylor, 2005).  For example, the critical PO₂ of Calocaris macandreae was reported to be 10-20 Torr (ca 0.58-1.17 mg O₂/l).  Their ability to maintain oxygen consumption under hypoxia is aided by the high oxygen affinities of their haemocyanins.  As oxygen levels fall, especially in the presence of sulphide, mud shrimp can switch to anaerobic respiration resulting in the formation of lactate.  For example, Calocaris macandreae switched to anaerobic respiration when PO₂ fell to =<10 Torr (ca =<0.58 mg O₂/l) (Anderson et al., 1994; Atkinson & Taylor, 2005). Sufficient concentrations of sulphide only occur in anoxic conditions but thalassinideans are able to metabolise sulphide to thiosulphate in the presence of oxygen, i.e. in hypoxia.  For example, in Calocaris macandreae more thiosulphate is produced under normoxic than hypoxic conditions but Calocaris macandreae is able to maintain aerobic metabolism under hypoxia (20 Torr) when exposed to 25 µM sulphide (Johns et al., 1997).  At higher concentrations of sulphide, it switched to anaerobic metabolism (Johns et al., 1997; Atkinson & Taylor, 2005). Johns et al. (1997) reported an LT₅₀ of 28 hours at 1 mM sulphide in Calocaris macandreae.

Sensitivity assessment.  The evidence suggests that Calocaris macandreae and mud shrimps in general are highly tolerant of hypoxic and anoxic conditions.  Therefore, a decrease in oxygen levels to below 2 mg/l for a week is unlikely to affect the abundance of the dominant mud shrimp in this biotope significantly.  Hence, resistance and resilience are assessed as ‘High’, and sensitivity as ‘Not sensitive’ at the benchmark level.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

Burrowing megafauna, e.g mud shrimps, flourish in areas where the sediments are naturally high in organic matter, such as sheltered sea lochs (Hughes, 1998).  Mud shrimps such as Calocaris macandreae are adapted to conditions associated with organic-rich muds and eutrophication such as hypoxia, anoxia and sulphide contamination but their burrowing activities oxidise the sediment, cycle nutrients to the overlying water and can moderate the effects of organic enrichment (Atkinson & Taylor, 2005).

No information on the effect of eutrophication was found.  However, Stachowitsch (1984) recorded individuals of Upogebia tipica, Jaxea nocturna and Axius stirhynchus abandoning their burrows during a severe episode of oxygen depletion, possibly due to a halocline, in the Gulf of Trieste, northern Adriatic, although Calocaris macandreae is more tolerant of hypoxia than Upogebia or Jaxea spp. (Hughes, 1998; Atkinson & Taylor, 2005). Pinn & Atkinson (2010) reported that the levels of nitrite, phosphate and ammonia in Calocaris macandreae burrows were higher than the overlying water in mesocosm studies, although only phosphate levels were significant. They reported average values of ca 0.1 mg/l N (nitrite), ca 0.4 mg/l N (nitrate), ca 0.4 mg/l N (ammonia), and ca 0.6 mg/l phosphate in their burrows (values extrapolated from Pinn & Atkinson, 2010; Figure 2). 

Sensitivity assessment. No evidence was found to compare against the benchmark. However, mud shrimps such as Calocaris macandreae are adapted to conditions associated with eutrophication such as hypoxia, anoxia and sulphide contamination.  Therefore, resistance is assessed as 'High', resilience as 'High' and sensitivity as 'Not sensitive' at the benchmark but with 'Low' confidence. 

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

Burrowing megafauna, e.g mud shrimps, flourish in areas where the sediments are naturally high in organic matter, such as sheltered sea lochs (Hughes, 1998). For example, Nephrops norvegicus was present in high densities in Loch Sween, Scotland where the organic content was about 5% and as high as 9% in some patches (Atkinson, 1989). Callianassa subterranea is found in sediments with a range of organic content. In the soft, organically enriched sediments (typical organic carbon values of 3.6 - 7.8%) of Loch Sween, a sea loch in Scotland, Callianassa subterranea was present as a significant megafaunal burrower (Atkinson, 1989). The maximum depth of the species burrows has been recorded as 86 cm, which Nickell & Atkinson (1995) suggest is an underestimate, indicating a nutritional requirement for sub-surface organic matter. In the North Sea, where sediments have a low organic content Rowden & Jones (1997) found Callianassa subterranea had to construct much more complex burrows to support their energetic costs.

The effects of organic enrichment on burrowing megafauna and other infauna depended on the degree of enrichment and any resultant hypoxia, which depend on the sediment type and local hydrology.  For example, in a survey of Garoch Head sludge dumping grounds, Firth of Clyde, the burrowing megafauna (Nephrops norvegicus, Callianassa subterranean, Calocaris macandreae, Lumpenus lampraetiformis and Cepola rubsecens) were abundant where organic content was <4% but absent where the organic content exceeded 6% (Smith, 1988, cited in Hughes, 1998). Calocaris macandreae did not extend as far into the gradient as Nephrops norvegicus or Lumpenus lampraetiformis (Smith, 1988, cited in Hughes, 1998). Similarly, Feder & Pearson (1988) reported that Calocaris macandreae was present in Loch Eil in 1980 and 1982 after 16-18 years of pulp and paper mill effluent but not in the prior survey in 1963. Nevertheless, Calocaris macandreae was recorded at 6.3 and 9.2 km from the outfall but not at 3.3 km from the outfall (Feder & Pearson, 1988).

In Caol Scotnish, Loch Sween, bacterial mats of Beggiatoa were reported in the immediate vicinity of salmon cages in 1987. The burrowing megafauna (Maxmuelleria lankesteri, Callianassa subterranea and Jaxea nocturna) were abundant in unimpacted areas. But by 1988, the bacterial mats covered most of the seabed in the basin, the sediment was close to anoxic, and the burrows of megafauna were restricted to small areas free of Beggiatoa. After the removal of salmon cages in 1989, some recovery was apparent by 1990 with more burrows apparent. However, the size of the individuals of Maxmuelleria lankesteri, Callianassa subterranean suggested that they had survived the loch basin during the peak of enrichment (Hughes, 1998).  Stachowitsch (1984) recorded individuals of Upogebia tipica, Jaxea nocturna and Axius stirhynchus abandoning their burrows during a severe episode of oxygen depletion in the Gulf of Trieste, northern Adriatic, although Calocaris macandreae is more tolerant of hypoxia than Upogebia or Jaxea spp. (Hughes, 1998; Atkinson & Taylor, 2005). 

Sensitivity assessment. Mud shrimps such as Calocaris macandreae are adapted to conditions associated with organic-rich muds such as hypoxia, anoxia and sulphide contamination but their burrowing activities oxidise the sediment, cycle nutrients to the overlying water and can moderate the effects of organic enrichment (Atkinson & Taylor, 2005). Gitterberger & Van Loon (2011) ranked the mud shrimp Callianassa subterranea as a 'species tolerant to excess organic matter enrichment' and Upogebia deltaura as a 'species indifferent to enrichment'.  The above evidence suggests that mud shrimp can survive all but gross organic enrichment but the absence of Calocaris macandreae from the centre of Garoch Head sludge dumping grounds suggests that its resistance has limits. Therefore, resistance is assessed as 'Medium' as a precaution and, as resilience is probably 'Medium', sensitivity is assessed as 'Medium'. 

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’).  Sensitivity within the direct spatial footprint of this pressure is, therefore ‘High’.  Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

If sedimentary substrata were replaced with rock substrata the biotope would be lost, as it would no longer be a sedimentary habitat and would no longer support sea pens and burrowing megafauna. Resistance to the pressure is considered ’None‘, and resilience ’Very low‘ or ‘None’ (as the pressure represents a permanent change), and the sensitivity of this biotope is assessed as ’High’.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

The mud shrimp Calocaris macandreae burrows in organically rich soft muds. Calocaris macandreae was restricted to the muddier bottom areas at 70-100 m of the coast of Northumberland, where silt and clay content was greater than 20%, mixed with fine sand, and reached its highest density where silt and clay were >60% but is not found in sandy sediments (Buchanan, 1963; Hughes, 1998). It is a deposit feeder and omnivore (Buchanan, 1963; Atkinson & Taylor, 2005; Pinn & Atkinson, 2010). In addition, this biotope is only recorded from mud and sandy mud (JNCC, 2022). A change in sediment type of one Folk class (see benchmark) to sand and muddy sand or to mixed sediments would result in the loss of the biotope and its community. Therefore, resistance is assessed as 'None', resilience as 'Very low' (permanent change) and sensitivity as 'High'. 

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

No direct evidence was found to assess the impacts of this pressure. Calocaris macandreae creates burrows with a total depth of 21 cm in muddy sediments with a high silt content (Buchanan, 1963; Hughes, 1998a).  Based on burrow depths extraction (of 30 cm of sediment) is likely to disturb and remove the majority of the population of Calocaris macandreae within the affected area. Therefore, resistance is assessed as 'None' (removal of >75% of individuals) and resilience is assessed as 'Low'. Hence, sensitivity is assessed as 'High'. Confidence in the quality of evidence for this assessment is Low as it is based on expert judgement, informed by the life habit of the species assessed.

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Species living in deep subtidal mud habitats are considered to be more vulnerable to physical disturbance as they are adapted to stable conditions (Pommer et al., 2016).  In general, species with large body size, low dispersal, late maturation and long lifespan are considered sensitive to physical disturbance (Bolam et al., 2014; Pommer et al., 2016). Large bioturbating or bio-irrigating species may be especially sensitive and their loss may affect the community (Widdicombe et al., 2004; Pommer et al., 2016).

Hinz et al. (2009) noted that different studies on the effects of otter trawl disturbance in muddy sediments gave mixed results and that the effect on abundance, biomass and diversity at a community level were largely inconsistent between studies. For example, experimental studies on short-term effects showed modest changes in the benthic communities (e.g. Tuck et al., 1998) and meta-analysis suggested that otter trawling on muddy sediments had one of the least negative impacts on the benthos (Kaiser et al., 2006). However, other studies showed that areas of seabed protected by wrecks from Nephrops trawls had higher abundance and biomass of benthos (Ball et al., 2000), while Smith et al. (2000) showed significantly lower abundance, biomass and species richness of benthos in high-intensity trawling lanes. Hinz et al. (2009)  suggested that the differences in results were the result of differences in statistical analysis, prior fishing intensity and duration of the studies. Hinz et al. (2009) reported that chronic otter trawling from a Nephrops fishery had significant negative effects on the benthic macrofauna. Hinz et al. (2009) concluded that while the initial impact of otter trawl on muddy sediments was modest, the long-term disturbance could lead to profound changes in the benthic communities, especially epifauna and shallow burrowing infauna.

Nephrops norvegicus fisheries could, therefore, affect burrowing megafauna and sea pen biotopes. Nephrops is a commercially targeted species that is harvested by static and mobile gears. Information on the European fisheries for this species is summarised by Ungfors et al. (2013). It is difficult to conduct stock assessments on Nephrops, which can only be harvested selectively by trawls and static gears. Nephrops cannot be aged directly. European Nephrops fisheries are managed as Functional Units (FUs), which are smaller than the usual ICES sub-regions due to the limited dispersal abilities of Nephrops. The estimates of abundance, and hence the recommended maximum sustainable yield (MSY), the related Biomass trigger points and fishing mortality (F_MSY), estimated harvest rates and ICES recommended limits on landings and by-catch vary between FUs, (Ungfors et al., 2013; Marine Scotland, 2016).  For example, harvest rates (ratio of total catch to absolute abundance) vary from ca 5-25% between 2007 and 2015 in the Farn Deeps, to ca 5-30% between 2005 and 2015 in South Minch (Marine Scotland, 2016). Marine Scotland (2016) suggested that the abundance of most stocks in the North Sea had declined to the MSY Biomass trigger point but remain above the F_MSY trigger point. However, in West Scotland, most stocks were above the Biomass trigger point but fluctuate around the F_MSY (Marine Scotland, 2016). Nevertheless, landings of Nephrops in 2014 were 13,700 tonnes in the North Sea and 12,800 in West Scotland (Marine Scotland, 2016).

Calocaris macandreae is suggested to rarely venture onto the surface (Nash et al. 1984).  Bergmann et al. (2002) noted that small numbers of Calocaris macandreae were bycatch in Nephrops trawls in the Clyde Sea. Comparisons between grab samples collected at trawled and untrawled sites in the Oslofjord, a northern branch of the Skagerrak in the North Sea, showed that Calocaris macandreae were depleted at trawled sites. The mean abundance of Calocaris macandreae was 41.5 individuals per m² (ca ±9.91) in non-trawled areas and 14.5 individuals per m² (ci.±4.99) in trawled areas (Olsgard et al., 2008). Trawled areas were visited by otter trawlers targeting Pandalus montagui between 50 and 100 times per year, and based on the size of the trawls and the boat speed, each part of these areas is trawled on average 2–3 times per year (Olsgard et al., 2008).  It is not clear whether the impact is cumulative with decreases in the population occurring incrementally or if the first pass removes the most vulnerable individuals, and those that remain are either new recruits or individuals that are more resistant due to factors such as burrow depth. However, Pommer et al. (2016) did not find a significant difference in the abundance of Calocaris macandreae with trawling intensity in the Kattegat. Duineveld et al. (2007) reported a higher species diversity and abundance of mud shrimps (Callianassa subterranea and Upogebia deltura) with a fisheries exclusion zone in the North Sea than in the surrounding area.

Based on burrow depths surface abrasion is unlikely to likely to disturb or remove the majority of the population of Calocaris macandreae, Callianassa subterranea, or Nephrops norvegicus within the affected area. The burrow openings may be damaged but observations from Loch Sween suggest that they are re-established soon after disturbance (Marrs et al., 1998; Hughes, 1998). Atkinson (1989) suggested that trawling was unlikely to affect burrowing megafauna (other than Nephrops) to ‘any great extent’.  Similarly, Vergnon & Blanchard (2006; OSPAR, 2010) noted that burrowing megafauna (Nephrops and other non-commercial crustaceans) did not show any reduction in total biomass or abundance in highly exploited sites. In their study, Nephrops norvegicus, Munida rugosa and Liocarcinus depurator dominated highly exploited sites in the Bay of Biscay (Vergnon & Blanchard, 2006).

Sensitivity assessment. The burrowing habit of the important characterizing species probably confers some protection from direct impacts of surface abrasion.  Therefore, resistance is assessed as 'Medium' (loss of <25% of individuals) as some individuals may be exposed within the direct footprint when on the surface.  Most Nephrops populations are reported to be resilient to fishing activity and the majority of the population will probably remain to support recovery.  However, there is the potential for overfishing in populations enclosed by hydrology (e.g. in the Irish Sea) or in sea lochs. In addition, while Callianassa subterranea may recover quickly, Calocaris macandreae may take longer to recover due to its benthic larvae and lower fecundity with stable populations and low recruitment rates. Therefore, resilience is assessed as 'Medium' and sensitivity is assessed as 'Medium'.  

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Species living in deep subtidal mud habitats are considered to be more vulnerable to physical disturbance as they are adapted to stable conditions (Pommer et al., 2016).  In general, species with large body size, low dispersal, late maturation and long lifespan are considered sensitive to physical disturbance (Bolam et al., 2014; Pommer et al., 2016). Large bioturbating or bio-irrigating species may be especially sensitive and their loss may affect the community (Widdicombe et al., 2004; Pommer et al., 2016).

Hinz et al. (2009) noted that different studies on the effects of otter trawl disturbance in muddy sediments gave mixed results and that the effect on abundance, biomass and diversity at a community level were largely inconsistent between studies. For example, experimental studies on short-term effects showed modest changes in the benthic communities (e.g. Tuck et al., 1998) and meta-analysis suggested that otter trawling on muddy sediments had one of the least negative impacts on the benthos (Kaiser et al., 2006). However, other studies showed that areas of seabed protected by wrecks from Nephrops trawls had higher abundance and biomass of benthos (Ball et al., 2000), while Smith et al. (2000) showed significantly lower abundance, biomass and species richness of benthos in high-intensity trawling lanes. Hinz et al. (2009)  suggested that the differences in results were the result of differences in statistical analysis, prior fishing intensity and duration of the studies. Hinz et al. (2009) reported that chronic otter trawling from a Nephrops fishery had significant negative effects on the benthic macrofauna. Hinz et al. (2009) concluded that while the initial impact of otter trawl on muddy sediments was modest, the long-term disturbance could lead to profound changes in the benthic communities, especially epifauna and shallow burrowing infauna.

Nephrops norvegicus fisheries could, therefore, affect burrowing megafauna and sea pen biotopes. Nephrops is a commercially targeted species that is harvested by static and mobile gears. Information on the European fisheries for this species is summarised by Ungfors et al. (2013). It is difficult to conduct stock assessments on Nephrops, which can only be harvested selectively by trawls and static gears. Nephrops cannot be aged directly. European Nephrops fisheries are managed as Functional Units (FUs), which are smaller than the usual ICES sub-regions due to the limited dispersal abilities of Nephrops. The estimates of abundance, and hence the recommended maximum sustainable yield (MSY), the related Biomass trigger points and fishing mortality (F_MSY), estimated harvest rates and ICES recommended limits on landings and by-catch vary between FUs, (Ungfors et al., 2013; Marine Scotland, 2016).  For example, harvest rates (ratio of total catch to absolute abundance) vary from ca 5-25% between 2007 and 2015 in the Farn Deeps, to ca 5-30% between 2005 and 2015 in South Minch (Marine Scotland, 2016). Marine Scotland (2016) suggested that the abundance of most stocks in the North Sea had declined to the MSY Biomass trigger point but remain above the F_MSY trigger point. However, in West Scotland, most stocks were above the Biomass trigger point but fluctuate around the F_MSY (Marine Scotland, 2016). Nevertheless, landings of Nephrops in 2014 were 13,700 tonnes in the North Sea and 12,800 in West Scotland (Marine Scotland, 2016).

Calocaris macandreae is suggested to rarely venture onto the surface (Nash et al. 1984).  Bergmann et al. (2002) noted that small numbers of Calocaris macandreae were by-catch in Nephrops trawls in the Clyde Sea. Comparisons between grab samples collected at trawled and untrawled sites in the Oslofjord, a northern branch of the Skagerrak in the North Sea, showed that Calocaris macandreae were depleted at trawled sites. The mean abundance of Calocaris macandreae was 41.5 individuals per m² (ca ±9.91) in non-trawled areas and 14.5 individuals per m² (ci.±4.99) in trawled areas (Olsgard et al., 2008). Trawled areas were visited by otter trawlers targeting Pandalus montagui between 50 and 100 times per year, and based on the size of the trawls and the boat speed, each part of these areas is trawled on average 2–3 times per year (Olsgard et al., 2008).  It is not clear whether the impact is cumulative with decreases in the population occurring incrementally or if the first pass removes the most vulnerable individuals, and those that remain are either new recruits or individuals that are more resistant due to factors such as burrow depth. However, Pommer et al. (2016) did not find a significant difference in the abundance of Calocaris macandreae with trawling intensity in the Kattegat. Duineveld et al. (2007) reported a higher species diversity and abundance of mud shrimps (Callianassa subterranea and Upogebia deltura) with a fisheries exclusion zone in the North Sea than in the surrounding area.

Based on burrow depths surface abrasion is unlikely to likely to disturb or remove the majority of the population of Calocaris macandreae, Callianassa subterranea, or Nephrops norvegicus within the affected area. The burrow openings may be damaged but observations from Loch Sween suggest that they are re-established soon after disturbance (Marrs et al., 1998; Hughes, 1998). Atkinson (1989) suggested that trawling was unlikely to affect burrowing megafauna (other than Nephrops) to ‘any great extent’.  Similarly, Vergnon & Blanchard, (2006; OSPAR, 2010) noted that burrowing megafauna (Nephrops and other non-commercial crustaceans) did not show any reduction in total biomass or abundance in highly exploited sites. In their study, Nephrops norvegicus, Munida rugosa and Liocarcinus depurator dominated highly exploited sites in the Bay of Biscay (Vergnon & Blanchard, 2006).

Sensitivity assessment. The burrowing habit of the important characterizing species probably confers some protection from direct impacts depending on the depth of penetration of the passing fishing gear or other penetrative activity.  Penetration of the substratum surface may shallow burrowed specimens of the burrowing megafauna, especially juveniles, and disturb and damage the burrow network within the sediment. Therefore, resistance is assessed as 'Low' (loss of 25%-75% of individuals) as some individuals may be exposed within the direct footprint on the surface or in shallow parts of their burrows. Calocaris macandreae may take longer to recover due to its benthic larvae and lower fecundity and its low recruitment potential. Therefore, resilience is assessed as 'Low' and sensitivity is assessed as 'High'.  

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

Mud shrimps, such as Calocaris macandreae are important bioturbators and influence the chemical, physical and biochemical properties of the sediment, and burrow irrigation draws oxygenated waters into the sediment while denitrification circulates nitrogen within the system and overlying waters above the sediment (Atkinson & Taylor, 2005; Pinn & Atkinson, 2010). Mud shrimp burrows expel suspended sediment during excavation, and due to feeding and respiratory currents (Atkinson & Taylor, 2005). For example, Gagnon et al. (2013) reported that Calocaris templemani reworked sediment to a depth of 15 cm at a rate of 8 L/m²/yr in a mesocosm study. Gittenberger & Van Loon (2011) ranked the mud shrimp Callianassa subterranea and Upogebia deltaura as 'species insensitive to higher amounts of sedimentation'. 

Sensitivity assessment.  The biotope occurs in sheltered areas, in fine sediments, and subject to high suspended sediment loads. Therefore, the important characteristic species are unlikely to be impacted by an increase in suspended sediments.  Calocaris macandreae lives in deep burrows and only emerges for short periods of time (Nash et al., 1984) and is unlikely to be affected by the resultant increase in turbidity.  Therefore, resistance is, assessed as 'High' based on its burrowing habit, resilience as 'High', and the biotope is assessed as ‘Not sensitive’.

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

The important characteristic burrowing megafauna Calocaris macandreae is unlikely to be affected adversely as it is an active borrower and important bioturbator.  Calocaris macandreae and Callianassa subterranea were reported within the Garroch Head (Firth of Clyde) sludge dumping ground (Smith, 1988; cited in Hughes, 1998).  In addition, if the deposited sediment occludes burrow openings, then they would be reopened quickly. Observations from Loch Sween suggest that burrows are re-established soon after experimental disturbance (Hughes, 1998).  This biotope (OMu.CalPol) occurs in deep, sheltered muddy habitats where the accretion rates are potentially high. Therefore, it is probable that the deposition of 5 cm of fine sediment will have little effect other than to temporarily suspend feeding and the energetic cost of burrowing. Therefore, resistance is assessed as 'High', resilience as 'High' and sensitivity assessed as 'Not sensitive' at the benchmark level. 

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

The important characteristic burrowing megafauna Calocaris macandreae is unlikely to be affected adversely as it is an active borrower and important bioturbator.  Calocaris macandreae and Callianassa subterranea were reported within the Garroch Head (Firth of Clyde) sludge dumping ground (Smith, 1988; cited in Hughes, 1998).  In addition, if the deposited sediment occludes burrow openings, then they would be reopened quickly. Observations from Loch Sween suggest that burrows are re-established soon after experimental disturbance (Hughes, 1998).  This biotope (OMu.CalPol) occurs in deep, sheltered muddy habitats where the accretion rates are potentially high. Therefore, it is probable that the deposition of 30 cm of fine sediment will have little effect other than to temporarily suspend feeding and the energetic cost of burrowing. Therefore, resistance is assessed as 'High', resilience as 'High' and sensitivity assessed as 'Not sensitive' at the benchmark level. 

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

No evidence was found

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

Most of the species are infaunal and unlikely to respond to noise disturbance at the benchmark level. Therefore, this pressure is probably Not relevant in this biotope.

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

Calocaris macandreae rarely or infrequently emerges from its burrow system (Nash et al., 1984; Hughes, 1998; Gagnon et al., 2013). Light is probably not relevant in the deep examples of this biotope.  Pinn & Atkinson (2010) observed their behaviour in mesocosms under 'subdued' lighting while Gagnon et al. (2013) observed the behaviour of Calocaris templemani in situ under low-intensity red light. These precautions suggest that the behaviour of Calocaris macandreae may be affected by bright light or sudden shading (similar to the approach of a predator) but no information on the response of Calocaris macandreae to light was found. 

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Not relevant – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of seed, larvae or other propagules but propagule dispersal is not considered under the pressure definition and benchmark.

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

Not relevant to seabed habitats. 

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

Calocaris macandreae rarely or infrequently emerges from its burrow system (Nash et al., 1984; Hughes, 1998; Gagnon et al., 2013). Pinn & Atkinson (2010) observed their behaviour in mesocosms under 'subdued' lighting while Gagnon et al. (2013) observed the behaviour of Calocaris templemani in situ under low-intensity red light. These precautions suggest that the behaviour of Calocaris macandreae may be affected by bright light or sudden shading (similar to the approach of a predator) but no information on the response of Calocaris macandreae to light was found. It is unlikely to have the visual acuity or range to respond to visual disturbance from passing boats or divers etc, especially at depth. Therefore, this pressure is probably 'Not relevant'. 

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

No evidence of genetic modification, breeding, or translocation in burrowing mud shrimps was found.

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

The red king crab Paralithodes camtschaticus is a voracious, omnivorous benthic predator that has spread from the Barents Sea to the coast of Norway, where it is a threat to shellfisheries and demersal fisheries. It has not been recorded in UK waters to date (GBNNSIP, 2011). No direct evidence of the effect of non-native species on burrowing mud shrimp was found. However, this assessment should be revisited in light of new evidence.

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

Mud shrimp are parasitized by parasitic isopods called bopyrids. The parasite lives in the gills and reduces reproductive output (Hughes, 1998). Rowden & Jones (1994) reported that 11% of Callianassa subterranea in the southern North Sea were infected.  Other than a reduction in reproduction, no other effects were reported (Hughes, 1998). Calderon-Perez (1986) reported the presence of larval nematodes (Ascarophis sp., Proleptus obtusus and Hysterothylacium aduncum) in Calocaris macandreae from the Irish Sea. However, no effect on host mortality was observed.

The bryozoan Triticella flava grows as a dense ‘furry’ covering on the antennae, mouthparts and legs of burrowing crustaceans. It occurs most commonly on Calocaris macandreae but has also been found on Nephrops norvegicus, Goneplax rhomboides, Jaxea nocturna and Upogebia spp (Hughes, 1998). On Calocaris macandreae, its coverage is densest in late summer but it is shed when the mud shrimp moults in September-October (Buchanan, 1963). However, the reproductive cycle of Triticella is synchronized with the moult cycle of its host and larvae are available to recolonize the crustacean body after the moult (Eggleston, 1971; Hughes, 1998).

Sensitivity assessment. As bopyrids could result in a decrease in reproduction and recruitment, resistance is assessed as 'Medium' albeit with 'Low' confidence. Hence, resilience is assessed as 'Medium' and sensitivity as 'Medium'.

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

Calocaris macandreae is not part of a targeted fishery so this pressure is 'Not relevant' technically, although the species may be taken as bycatch. 

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

Large bioturbating or bio-irrigating species may be especially sensitive to physical disturbance and their loss may affect the community (Widdicombe et al., 2004; Pommer et al., 2016).  Hinz et al. (2009) noted that different studies on the effects of otter trawl disturbance in muddy sediments gave mixed results and that the effect on abundance, biomass and diversity at a community level were largely inconsistent between studies. For example, experimental studies on short-term effects showed modest changes in the benthic communities (e.g. Tuck et al., 1998) and meta-analysis suggested that otter trawling on muddy sediments had one of the least negative impacts on the benthos (Kaiser et al., 2006). However, other studies showed that areas of seabed protected by wrecks from Nephrops trawls had higher abundance and biomass of benthos (Ball et al., 2000), while Smith et al. (2000) showed significantly lower abundance, biomass and species richness of benthos in high-intensity trawling lanes. Hinz et al. (2009)  suggested that the differences in results were the result of differences in statistical analysis, prior fishing intensity and duration of the studies. Hinz et al. (2009) reported that chronic otter trawling from a Nephrops fishery had significant negative effects on the benthic macrofauna. Hinz et al. (2009) concluded that while the initial impact of otter trawl on muddy sediments was modest, the long-term disturbance could lead to profound changes in the benthic communities, especially epifauna and shallow burrowing infauna.

Calocaris macandreae is suggested to rarely venture onto the surface (Nash et al. 1984).  Bergmann et al. (2002) noted that small numbers of Calocaris macandreae were bycatch in Nephrops trawls in the Clyde Sea. Comparisons between grab samples collected at trawled and untrawled sites in the Oslofjord, a northern branch of the Skagerrak in the North Sea, showed that Calocaris macandreae were depleted at trawled sites. The mean abundance of Calocaris macandreae was 41.5 individuals per m² (ca ±9.91) in non-trawled areas and 14.5 individuals per m² (ci.±4.99) in trawled areas (Olsgard et al., 2008). Trawled areas were visited by otter trawlers targeting Pandalus montagui between 50 and 100 times per year, and based on the size of the trawls and the boat speed, each part of these areas is trawled on average 2–3 times per year (Olsgard et al., 2008).  It is not clear whether the impact is cumulative with decreases in the population occurring incrementally or if the first pass removes the most vulnerable individuals, and those that remain are either new recruits or individuals that are more resistant due to factors such as burrow depth. However, Pommer et al. (2016) did not find a significant difference in the abundance of Calocaris macandreae with trawling intensity in the Kattegat. Duineveld et al. (2007) reported a higher species diversity and abundance of mud shrimps (Callianassa subterranea and Upogebia deltura) with a fisheries exclusion zone in the North Sea than in the surrounding area.

Based on burrow depths surface abrasion is unlikely to likely to disturb or remove the majority of the population of Calocaris macandreae, Callianassa subterranea, or Nephrops norvegicus within the affected area. The burrow openings may be damaged but observations from Loch Sween suggest that they are re-established soon after disturbance (Marrs et al., 1998; Hughes, 1998). Atkinson (1989) suggested that trawling was unlikely to affect burrowing megafauna (other than Nephrops) to ‘any great extent’.  Similarly, Vergnon & Blanchard (2006; OSPAR, 2010) noted that burrowing megafauna (Nephrops and other non-commercial crustaceans) did not show any reduction in total biomass or abundance in highly exploited sites. In their study, Nephrops norvegicus, Munida rugosa and Liocarcinus depurator dominated highly exploited sites in the Bay of Biscay (Vergnon & Blanchard, 2006), although Calocaris macandreae was not included in their study. 

Mud shrimps, such as Calocaris macandreae are important bioturbators and influence the chemical, physical and biochemical properties of the sediment, and burrow irrigation draws oxygenated waters into the sediment while denitrification circulates nitrogen within the system and overlying waters above the sediment (Atkinson & Taylor, 2005; Pinn & Atkinson, 2010). For example, Gagnon et al. (2013) reported that Calocaris templemani reworked sediment to a depth of 15 cm at a rate of 8 L/m²/yr in a mesocosm study. Norling et al. (2007) noted that oxygen, ammonia and silicon fluxes were higher in mesocosms in the presence of Calocaris macandreae.  Widdicombe & Austen (2003) noted that the presence of Calocaris macandreae decreased the abundance of burrowing spionid polychaetes and deposit-feeding polychaetes (e.g. Heteromatus filiformis) and the bivalve Nuculoma tenuis compared with controls. They suggested that spionids were excluded due to the reworking of the sediment and resultant smothering by sediment, while deposit feeders may be less abundant because deposit feeding by mud shrimp decreased the availability of organic matter in the sediment. They noted that species tolerant of smothering, i.e. Chaetozone setosa and Cossura longicirrata had higher abundances in mesocosms with low densities of mud shrimp (Widdicombe & Austen, 2003). However, while Calocaris macandreae significantly affected the community it did not significantly affect diversity (Widdicombe & Austen, 2004). Although they rarely leave their burrows, Calocaris macandreae are preyed upon by demersal fish (e.g. cod and haddock) and large decapods (e.g. Nephrops) (Buchanan, 1963; Hughes, 1998). 

Sensitivity assessment.  The above evidence suggests that the populations have been depleted by fisheries in some sites but not others. But this pressure examines the effect of the removal of the characteristic species on the community present in the biotope.  Hughes (1998) suggested that there was no evidence that any single species of megafaunal burrower was dominant or determined the structure or functioning of the burrowing mud communities (see SS.SMu.CFiMu.MegMax). However, this biotope is defined by the abundance of Calocaris macandreae and a few dominant polychaetes. The evidence suggests that Calocaris macandreae is an important bioturbator in this biotope and its community, affects oxygen penetration into the sediment, denitrification and nutrient cycling, and influences community structure within the sediment (e.g. of the associated polychaete species), but not diversity (Widdicombe & Austen, 2003, 2004; Atkinson & Taylor, 2005). Therefore, the loss of a significant proportion of the Calocaris macandreae population could alter the community and the classification of the biotope.  Therefore, resistance is assessed as 'Low'. Hence, resilience is assessed as 'Low' and sensitivity is assessed as 'High'.