|Researched by||Angus Jackson||Refereed by||Dr Maeve Kelly|
|Authority||(P.L.S. Müller, 1771)|
|Other common names||-||Synonyms||-|
An almost round, slightly flattened urchin that grows up to 57 mm in diameter (although more typically to 35 mm diameter). It is greenish in colour with distinctive violet tips to the spines. The spines are robust, short and closely packed.
MarLIN would like to thank Dr Maeve Kelly for her comments and significant additions to the review.
- none -
|Phylum||Echinodermata||Starfish, brittlestars, sea urchins & sea cucumbers|
|Class||Echinoidea||Sea urchins, heart urchins and sand dollars|
|Authority||(P.L.S. Müller, 1771)|
|Typical abundance||High density|
|Male size range||typically <40mm|
|Male size at maturity||8-10mm|
|Female size range||8-10mm|
|Female size at maturity|
|Growth rate||See additional information|
|Body flexibility||None (less than 10 degrees)|
|Characteristic feeding method||Active suspension feeder|
|Typically feeds on||Macroalgae, hydroids, bryozoans, boring sponges, barnacles, mussels, cockles and worms (see Lawrence, 1975).|
See additional information.
|Is the species harmful?||No|
See additional information
In Scotland Psammechinus miliaris typically occurs in dense, localized populations in sheltered areas of sea lochs on the west coast (Davies, 1989; Holt, 1991). Densities have been recorded of 18 individuals per 100 g dry weight of sea weed (Bedford & Moore, 1985); several /m² in beam trawls in the Wadden Sea (Cranmer, 1985); 34 individuals per m² in a subtidal Saccharina latissima (studied as Laminaria saccharina) bed, 182.4 /m² in a shallow bed of Zostera and 28.4 /m² on adjacent mud surfaces (Comely, 1979) and 352 /m² for littoral populations (Kelly, 2000) where individuals in one 0.25 m² quadrat ranged from 3.7 to 24.2 mm horizontal test diameter. Densities of several individuals /m² have been recorded in the German Waddensea (Ursin, 1960). Larsson (1968) found up to 10 individuals /m² in Saltkälle Fjord, Sweden.
Maximum size varies with location. In some places the maximum diameter reached is small (< 20 mm (Jensen, 1969); around 35 mm (Bedford & Moore, 1985; Gage, 1991; Bull, 1939) although others have recorded diameters up to 57.5 mm (Allain, 1978) or up to 50 mm (Massin, 1999b; Aquascope, 2000a). The minimum diameter at maturity recorded (Brattström, 1941 cited in Jensen, 1969) is 6-7 mm but more usually 8-10 mm.
Estimates of growth rate vary. Gage, (1991) tried to relate growth bands found in the calcified plates of the test to seasonal differences in skeletal growth rate. This approach can be used reasonably accurately for estimating age of young urchins. However, when growth slows down, the reduced distance between bands make it difficult to distinguish individual markings. Bull, (1939) recorded growth up to 20 mm test diameter in the first year which then slowed considerably. In the second year mean diameters increased from 20 to 26.2 mm and by the sixth year saw growth of only a further 12 mm or so. Jensen, (1969) found that newly settled urchins (in August) grew 2 mm in the first 2 months and had reached 5.8 mm by the following July. Growth was recorded as maximal in spring and early summer by Gage (1991) and Bedford & Moore (1985) but work by Jensen, (1969) showed no growth between May and October. Growth rates of cultivated Psammechinus miliaris are given by Cook et al. (1998).
Locomotion is mediated by the movable spines attached to the test. The echinoid test is very brittle and easily damaged by impact. The spines which are articulated at the base and controlled by muscles may provide some cushioning to impact but overall the flexibility is negligible.
Psammechinus miliaris has been recorded as feeding on a wide variety of species (see Lawrence, 1975). Loose lying brown macro algae, particularly Saccharina latissima (studied as Laminaria saccharina), is probably the main nutrient source although softer green algae such as Ulva lactuca may be important when small (Cook et al., 1998). The green sea urchin also feeds on epifauna such as hydroids, barnacles, small bivalves, boring sponges (e.g. Cliona), worms (e.g. Polydora) (Hancock, 1957; Lawrence, 1975).
Psammechinus miliaris (as well as other echinoderms) frequently harbours a polychaete, Flabelligera affinis amongst the spines.
The gonads of Psammechinus miliaris, but more commonly Paracentrotus lividus, are eaten as a delicacy in Mediterranean countries. As wild populations of Psammechinus miliaris typically have small gonads, its potential for aquaculture is being investigated (Kelly et al., 1998).
|Physiographic preferences||Open coast, Offshore seabed, Strait / sound, Sea loch / Sea lough, Ria / Voe|
|Biological zone preferences||Lower circalittoral, Lower eulittoral, Lower infralittoral, Mid eulittoral, Sublittoral fringe, Upper circalittoral, Upper infralittoral|
|Substratum / habitat preferences||Macroalgae, Artificial (man-made), Bedrock, Cobbles, Gravel / shingle, Large to very large boulders, Mixed, Muddy gravel, Muddy sand, Rockpools, Small boulders, Under boulders|
|Tidal strength preferences||Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.)|
|Wave exposure preferences||Extremely sheltered, Moderately exposed, Sheltered, Very sheltered|
|Salinity preferences||Full (30-40 psu), Variable (18-40 psu)|
|Depth range||0 -100 m|
|Other preferences||No text entered|
|Migration Pattern||Non-migratory / resident|
On the west coast of Scotland Psammechinus miliaris typically occurs in dense, localized populations in sheltered areas of sea lochs (Davies, 1989; Holt, 1991). Its distribution frequently coincides with that of the brown seaweed Saccharina latissima, with Psammechinus miliaris occurring on the fronds as well as on rock surfaces below the fronds. Some populations are exposed to air at low spring tides, and are found attached to the underside of rocks, boulders and seaweed, or shallowly buried under gravel on the foreshore (Kelly, 2000). Individuals from the intertidal and subtidal habitats on the west coast of Sweden were termed 'Z' and 'S' forms by Lindahl & Runnström (1929). The 'Z' form lived in the 'seaweed region' and were larger and darker than the 'S' forms found at greater depths.Comely (1979) described a population of Psammechinus miliaris from a Zostera marina bed in a stable salinity, shallow inlet in Loch Sween, Scotland. Theses individuals were found on the bottom mud and attached to the rhizomes of Zostera at depths of 1 -2 m. Very young individuals have been found in the holdfasts of Laminaria from the Clyde Sea, Scotland (Moore, 1971).
Psammechinus miliaris is often found on man-made surfaces such as bridge supports and wrecks.
|Reproductive type||Gonochoristic (dioecious)|
|Reproductive frequency||Annual protracted|
|Fecundity (number of eggs)||>1,000,000|
|Generation time||1 year|
|Age at maturity||1 year|
|Season||May - October|
|Life span||5-10 years|
|Duration of larval stage||1-2 months|
|Larval dispersal potential||Greater than 10 km|
|Larval settlement period||Insufficient information|
The MarLIN sensitivity assessment approach used below has been superseded by the MarESA (Marine Evidence-based Sensitivity Assessment) approach (see menu). The MarLIN approach was used for assessments from 1999-2010. The MarESA approach reflects the recent conservation imperatives and terminology and is used for sensitivity assessments from 2014 onwards.
|Psammechinus miliaris lives and feeds on a variety of substrata. Loss of substratum will cause mortality. Adult urchins are mobile but probably not active over large distances so recolonization is unlikely to occur through adult immigration. Psammechinus miliaris is quite long lived (up to 12 years) (Allain, 1978), and can breed within one year of settlement (Kelly, 2001). Breeding occurs in spring and summer each year (Mortensen, 1927; Sukarno et al., 1979; Kelly, 2000), fecundity is likely to be high (MacBride, 1903) and the larvae are long lived (20-40 days) (Jensen, 1969; Massin, 1999b; Kelly et al., 2000). Dispersal potential is therefore large and recoverability is likely to be high.|
|Psammechinus miliaris is an epibenthic species that, although mobile, is not highly active and moves using mobile spines. This urchin species is quite small (typically up to 40 mm) and is likely to be completely covered by 5 cm of sediment. It is probable that the urchin would be unable to 'dig out' of the sediment. Adult urchins are mobile but probably not active over large distances so recolonization is unlikely to occur through adult immigration. Psammechinus miliaris is quite long lived (up to 12 years) (Allain, 1978), and can breed within one year of settlement (Kelly, 2001). Breeding occurs in spring and summer each year (Mortensen, 1927; Sukarno et al., 1979; Kelly, 2000), fecundity is likely to be high (MacBride, 1903) and the larvae are long lived (20-40 days) (Jensen, 1969; Massin, 1999b; Kelly et al., 2000). Dispersal potential is therefore large and recoverability is likely to be high.|
|Low||Very high||Very Low||Low|
|It is unlikely that changes in siltation rate will have a great effect on this species. Psammechinus miliaris grazes on macroalgae and some encrusting faunal species so increases in siltation are unlikely to affect feeding. Increases in siltation rate will increase the amount of sediment settling out onto the urchin. There may be an increased energetic cost to clearing these particles. Energetic expenditure may result in loss of condition or compromise gonadal and somatic growth. On removal of the factor, recovery should take only a short time.|
|Psammechinus miliaris is found subtidally and intertidally. In intertidal regions the urchin is typically found in crevices and under boulders or weed where the risk of desiccation is minimized. However, relative humidity and temperature strongly influence survivorship of Psammechinus miliaris. Cook (1999) found that Psammechinus miliaris from littoral populations were more tolerant of an increased temperature and decreased relative humidity during aerial exposure than those from subtidal populations. Psammechinus miliaris from the littoral zone show slightly more tolerance to exposure at 60% relative humidity and 10 °C than those from sublittoral populations. At high relative humidity (95%), 95% of Psammechinus miliaris can withstand 72 hours exposure to air if kept chilled at 5 °C. But at 20 °C and 95% humidity, no Psammechinus miliaris survived 72 hours exposure (Cook, 1999; Dr Maeve Kelly, pers comm.). Therefore, it is likely that individuals exposed to an increase in desiccation at the benchmark level will die. Therefore, an intolerance of high has been recorded. Recruitment to the remaining population will probably occur by larval settlement from the plankton. Recoverability is likely to be high (see additional information).|
|Psammechinus miliaris is unlikely to be intolerant of changes in emergence regime. Although not highly active, the species is sufficiently mobile to be able to relocate to more suitable conditions.|
|Low||Very high||Very Low||Low|
|Psammechinus miliaris holds itself onto the substratum using suction pads at the end of its tube feet (Massin, 1999b) Large increases in water flow rate may make it more difficult to remain on the substratum. The urchin Echinus esculentus has been observed to be 'rolled' by water currents (Comely & Ansell, 1988). Displacement from the substratum is unlikely to cause damage or death. Relocation back to a suitable or preferred location will incur an energetic cost. Energetic expenditure may result in loss of condition or compromise gonadal and somatic growth. On removal of the factor, recovery should take only a short time.|
|The species is recorded as occurring in water temperatures of between 4-17 °C. Ursin (1960) reported that Psammechinus miliaris had a high tolerance of low temperatures and that it is found in Limfjord, Denmark, where winter temperatures are just above zero. It reproduces in waters around the Faeroes where the summer temperatures seldom exceed 11 °C (Ursin, 1960). The geographical distribution of Psammechinus miliaris extends to the north and south of the British Isles into colder and warmer waters respectively. Consequently, long term chronic changes in temperature are unlikely to have a great effect on populations of Psammechinus miliaris in the British Isles. Therefore, an intolerance of low has been recorded. Recoverability is likely to be rapid. However, exposure to high temperatures in the intertidal will increase the risk of desiccation (see above).|
|Low||Very high||Very Low||Moderate|
|Moore (1977) suggested that Echinus esculentus was unaffected by turbid conditions. Psammechinus miliaris can inhabit similar kelp habitats to Echinus esculentus and may be similarly tolerant. However, increased turbidity and resultant reduced light penetration is likely to affect macroalgal populations e.g. kelps, which are a preferred food species for Echinus esculentus. However, it can feed on alternative prey, detritus or dissolved organic material (Lawrence, 1975, Comely & Ansell, 1988). Conversely, decreases in turbidity may benefit algal growth. Reduced food availability may cause loss of condition or compromise gonadal and somatic growth. When food availability is returned to 'normal' recovery should take only a short time.|
|Psammechinus miliaris occurs both in subtidally and inter-tidally from coasts all round the British Isles but is typically found in more sheltered environments. It has a lower tolerance of wave exposure than Echinus esculentus and Paracentrotus lividus, the latter being found on the exposed. It is likely that high levels of wave exposure limits the distribution of Psammechinus miliaris in the intertidal and subtidal (Dr Maeve Kelly, pers comm.). As Psammechinus miliaris feeds on a wide selection of algae and encrusting organisms (Lawrence, 1975) its distribution is thought to be limited more by physical parameters than food availability (Faller-Fritsch & Emson, 1972; cited in Lawrence, 1975). Therefore, an increase in wave exposure at the benchmark level is likely to remove at least a proportion of the population and an intolerance of intermediate has been recorded. Recruitment to the remaining population will occur by larval settlement from the plankton. Recoverability is likely to be high.|
|Tolerant||Not relevant||Not sensitive||Very low|
|No evidence of sound or vibration reception in echinoids was found.|
|Low||Very high||Very Low||Moderate|
|Psammechinus miliaris is likely to have slight intolerance to visual disturbance. Like many other echinoids it avoids bright light (Massin, 1999(b)). This species is recorded as having a behavioural response to changes in shading. Sudden shading results in withdrawal of the tube feet (Millott & Yoshida, 1956) The degree of response depends on light intensity and the degree of intensity change. Other echinoid species are also recorded as having a shading response, with spines being brought round to point in the direction of the stimulus as a protective mechanism. The reaction is likely to be short lived and insignificant. This response may interfere with feeding and if this occurs repeatedly then loss of condition or reduced somatic and gonadal may result. On removal of the stimulus, recovery of condition should not take long.|
|The test of Psammechinus miliaris is brittle and easily damaged by impact or abrasion. Spines and podia may be damaged or broken off. The spines may provide some degree of cushioning for the test. Beam trawling was reported to remove ca 20 to 50% of this species (Kaiser & Spencer, 1994a), and the impact of scallop dredging is likely to be similar. Damage to the test will generally be lethal, if not outright because internal organs become exposed to predators and possible infection. However, the frequency of occurrence of Psammechinus miliaris was reported to increase markedly over an 80 year period in trawled areas in the southern North Sea (Rumohr & Kujawski, 2000). Overall, the evidence from Kaiser & Spencer (1994a) suggests that a proportion of the population is likely to be removed and intolerance has been assessed as intermediate. Some repair and regrowth of minor damage to the test and spines may be possible. Recoverability is likely to be high (see additional information below).|
|Tolerant||Not relevant||Not sensitive||High|
|Psammechinus miliaris is mobile and may be also regularly displaced by wave action or water currents. Some damage may be caused by loss of tube feet during a displacement event but this is repairable. As with Echinus esculentus (Lewis & Nichols 1979b), displaced specimens are able to relocate. This will probably have negligible effect on the species.|
|Considerable observations and work, mainly on Echinus esculentus but also on Psammechinus miliaris (Smith, 1968; Gomez & Miguez-Rodriguez, 1999; Dinnel et al., 1988 ) indicate high intolerance to synthetic contaminants. Newton & McKenzie (1995) state that echinoderms tend to be very intolerant of various types of marine pollution, but there is little more detailed information than this. Following the Torrey Canyon incident, large numbers of dead Psammechinus miliaris in the vicinity of Sennen, presumably due to the heavy spraying of dispersants in that area and exposure to the oil spill (Smith, 1968). Therefore, an intolerance of high has been reported. Recoverability is likely to be high (see additional information below).|
|Little is known about the effects of heavy metals on adult echinoderms although Newton & McKenzie (1995) state that echinoderms tend to be very sensitive to various types of marine pollution. In an area around Naples, with high concentrations of lead, zinc and copper, the urchins Paracentrotus lividus and Arbacia lixula were smaller than those at unpolluted sites further along the coast (Sheppard & Bellamy, 1974) probably due to either restricted growth or individuals dying before reaching adult size. Abundance was also lower in polluted sites and so intolerance of adults has been assessed as intermediate. Echinoderm larvae are know to be especially intolerant of heavy metals (Bryan, 1974). Recoverability is likely to be high (see additional information below).|
|Echinoderms seem especially sensitive to the toxic effects of oil, likely because of the large amount of exposed epidermis (Suchanek, 1993). Following the Torrey Canyon incident, large numbers of dead Psammechinus miliaris in the vicinity of Sennen, presumably due to exposure to the oil spill and the heavy spraying of hydrocarbon based dispersants in that area (Smith, 1968). Other significant effects have been observed in other species of urchins. For example, mass mortality of the echinoderm Echinocardium cordatum was observed shortly after the Amoco Cadiz oil spill (Cabioch et al., 1978) and reduced abundance of the species was detectable up to > 1000m away one year after the discharge of oil-contaminated drill cuttings in the North Sea (Daan & Mulder, 1996). In the Mediterranean around Naples, urchins were absent from areas which has visible signs of massive pollution of both sewage and oil. Echinus esculentus populations in the vicinity of an oil terminal in A Coruna Bay, Spain, showed developmental abnormalities in the skeleton. The tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gomez & Miguez-Rodriguez 1999). But the observed effects may have been due to a single contaminant or synergistic effects of all present. However, it appears likely that echinoids such as Psammechinus miliaris are highly intolerant of hydrocarbon contamination. Recoverability is likely to be high (see additional information below).|
|No information||No information||No information||Not relevant|
|Low||Very high||Very Low||Moderate|
|It is unlikely that changes in nutrient concentration will directly affect Psammechinus miliaris populations. The addition of nutrients may encourage the growth of ephemeral and epiphytic algae and therefore increase the food available to populations of grazing sea-urchins such as Psammechinus miliaris. Conversely, decreases in nutrient availability may limit growth of algae used as a nutrient source. Lawrence (1975) reported that sea urchins had persisted over 13 years on barren grounds near sewage outfalls, presumably feeding on dissolved organic material, detritus, plankton and microalgae, although individuals died at an early age. The ability to absorb dissolved organic material has been suggested by Comely & Ansell (1988). Reduced food availability may cause loss of condition or compromise gonadal and somatic growth. Increased food availability may cause the population to expand in number or extent. When food availability is returned to 'normal', recovery should take only a short time.|
|Echinoderms are generally unable to tolerate low salinity (stenohaline) conditions and possess no osmoregulatory organ (Boolootian, 1966). There is some evidence for intracellular regulation of osmotic pressure due to increased amino acid concentrations. Populations of Psammechinus miliaris occur both in the sub-tidal and inter-tidal. The latter must encounter reduced salinity due to fresh water runoff or heavy rain and hence be able to tolerate variable salinity. Lindahl & Runnström (1929) showed through acclimatisation experiments that Psammechinus miliaris from the littoral (Z form) and sublittoral (S form) had different salinity optima. Gezelius (1962) showed that eggs from the Z and S forms of Psammechinus miliaris differed in the range of salinities they would tolerate and over which fertilization would successfully occur, 20-32 psu and 26-38 psu at 17-19 °C respectively. At low salinity urchins gain weight and the epidermis loses its pigment as patches are destroyed; prolonged exposure is fatal. Therefore, a short term acute decrease in salinity may cause mortality, especially in sublittoral populations, and an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).|
|Under hypoxic conditions echinoderms become less mobile and stop feeding. Death of a bloom of the phytoplankton Gyrodinium aureolum in Mounts Bay , Penzance in 1978 produced a layer of brown slime on the sea bottom. This resulted in the death of fish and invertebrates, including Echinus esculentus, presumably due to anoxia caused by the decay of the dead dinoflagellates (Griffiths et al., 1979). Spicer (1995) investigated the effects of environmental hypoxia on the oxygen and acid-base status of Psammechinus miliaris. Oxygen uptake is not regulated by this species during progressive hypoxia. The habitat of this species includes rock pools on the shore that can experience quite severe hypoxia or even anoxia. Psammechinus miliaris must be able to tolerate low oxygen conditions provided the event is brief. In prolonged events, subtidal Psammechinus miliaris would presumably react in a similar fashion to the Echinus esculentus above. Recoverability is likely to be high (see additional information below).|
|Psammechinus miliaris is susceptible to 'Bald-sea-urchin disease', which causes lesions, loss of spines, tube feet, pedicellariae, destruction of the upper layer of skeletal tissue and death (Maes et al., 1986). It is thought to be caused by the bacteria Vibrio anguillarum and Aeromonas salmonicida. This disease has been recorded from Psammechinus miliaris from the French Atlantic coast. Although associated with mass mortalites of Strongylocentrotus franciscanus in California and Paracentrotus lividus in the French Mediterranean there is no evidence of mass mortalities of Psammechinus miliaris associated with this disease around Britain and Ireland. an intolerance of intermediate has therefore been recorded. Recoverability is likely to be high (see additional information below).|
|Tolerant||Not relevant||Not sensitive||Low|
|No alien or non-native species is known to prey on, compete with or adversely (or otherwise) affect Psammechinus miliaris.|
|Psammechinus miliaris is now targeted as a potential aquaculture species since when fed a nutritious diet in culture, the gonad biomass rapidly proliferates (Kelly et al., 1998). A study of a littoral and sublittoral population, Kelly (2000) concluded that there was no evidence of an opportunity for a commercial fishery because of the low gonad content of wild populations. However, some extraction of Psammechinus miliaris may conceivably develop for roe-enhancement through feeding artificial or nutrient enriched diets (Dr Maeve Kelly pers comm.). Therefore, an intolerance of intermediate has been recorded. The aquaculture potential of this smaller species is being investigated (Kelly et al., 1998). Recoverability is likely to be high (see additional information below).|
|Both sub-tidal and inter-tidal populations of Psammechinus miliaris are often intimately associated with macro algae, particularly with kelp beds, both attached and loose lying. Physical effects associated with removal of other species (such as kelp) are addressed in the relevant factors above. Therefore, extraction of seaweed species is likely to result in the loss of some individuals of Psammechinus miliaris. This species may also suffer as a result of trawling or dredging for other benthic species. Species with fragile tests such as urchins have been reported to be particuarly sensitive to damage from mobile fishing gear (see Jennings & Kaiser, 1998; Bergman & van Santbrink, 2000). Kaiser & Spencer (1994a) reported a ca 20 - 50% mortality in Psammechinus miliaris as a result of a single pass of an experimental 4 m beam trawl. However, the frequency of occurrence of Psammechinus miliaris was reported to increase markedly over an 80 year period in trawled areas in the southern North Sea (Rumohr & Kujawski, 2000). Overall, the evidence from Kaiser & Spencer (1994a) suggests that a proportion of the population is likely to be removed and intolerance has been assessed as intermediate. Recoverability is likely to be high (see additional information below).|
- no data -
|National (GB) importance||-||Global red list (IUCN) category||-|
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This review can be cited as:
Last Updated: 08/05/2008