BIOTIC Species Information for Psammechinus miliaris
|Researched by||Lizzie Tyler||Data supplied by||University of Sheffield|
|Refereed by||This information is not refereed.|
|Scientific name||Psammechinus miliaris||Common name||Green sea-urchin|
|MCS Code||ZB193||Recent Synonyms||None|
|Taxonomy References||Howson & Picton, 1997, Hayward & Ryland, 1995b, Hayward et al., 1996, Hancock, 1957, Mortensen, 1927, Massin, 1999(b), Aquascope, 2000(a), Bull, 1939, Lindahl & Runnström, 1929, Comely, 1979,|
|Typical food types||Macroalgae, hydroids, bryozoans, boring sponges, barnacles, mussels, cockles and worms (see Lawrence, 1975).||Habit||Free living|
|Bioturbator||Not relevant||Flexibility||None (< 10 degrees)|
|Height||Growth Rate||See additional information|
|Adult dispersal potential||100-1000m||Dependency||Independent|
|General Biology Additional Information||Abundance
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 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.
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).
Psammechinus miliaris has been recorded as feeding on a wide variety of species (see Lawrence, 1975). Loose lying brown macro algae, particularly 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).
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).
|Biology References||Gage, 1991, Cranmer, 1985, Bedford & Moore, 1985, Cook et al., 1998, Hancock, 1957, Mortensen, 1927, Jensen, 1969, Massin, 1999(b), Aquascope, 2000(a), Bull, 1939, Kelly et al., 1998, Boolootian, 1966, Kelly & Cook, 2001, Kelly, 2000, Lindahl & Runnström, 1929, Comely, 1979, Lawrence, 1975, Davies, 1989, Holt, 1991, Ursin, 1960, Larsson, 1968, Hinegardner, 1969, Hayward & Ryland, 1990, Julie Bremner, unpub data,|
|Distribution and Habitat|
|Distribution in Britain & Ireland||All British and Irish coasts. Evenly distributed in the southern North Sea but scarce in northern North Sea.|
|Global distribution||From Trondheim Fjord in northern Norway, inner Danish waters from the Skaw into the western Baltic, Iceland, British Isles, south to the Atlantic coast of Morocco and the Azores. Not in Greenland, the Mediterranean or Atlantic coasts of America.|
|Biogeographic range||Not researched||Depth range||0 - 100 m|
|Migratory||Non-migratory / Resident|
|Distribution Additional Information||The species is found in the intertidal and subtidal, occasionally as deep as 100 m (Mortensen, 1927) but more commonly between 16 -70 m (Cranmer, 1985) or 0 -10 m in Scottish sea lochs (Kelly, 2000).
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 %Laminaria saccharina%, 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.
|Substratum preferences||Large to very large boulders
Artificial (e.g. metal/wood/concrete)
Gravel / shingle
|Physiographic preferences||Open coast
Strait / sound
Ria / Voe
|Biological zone||Mid Eulittoral
|Wave exposure||Moderately Exposed
|Tidal stream strength/Water flow||Moderately Strong (1-3 kn)
||Salinity||Variable (18-40 psu)
Full (30-40 psu)
|Habitat Preferences Additional Information|
|Distribution References||Hayward & Ryland, 1995b, Hayward et al., 1996, Gage, 1991, Cranmer, 1985, Bedford & Moore, 1985, Allain, 1978, Hancock, 1957, Rasmussen, 1973, Mortensen, 1927, Jensen, 1969, Bruce et al., 1963, MBA, 1957, Massin, 1999(b), Aquascope, 2000(a), Kelly & Cook, 2001, Lindahl & Runnström, 1929, Comely, 1979, Davies, 1989, Holt, 1991, Ursin, 1960, Larsson, 1968, Leighton, 1995, Moore, 1971, Hayward & Ryland, 1990, Julie Bremner, unpub data,|
|Reproductive Season||June to August in UK||Reproductive Location||Water column|
|Reproductive frequency||Annual protracted||Regeneration potential||No|
|Life span||6-10 years||Age at reproductive maturity||1 year|
|Generation time||1 year||Fecundity||2500000|
|Egg/propagule size||Fertilization type||External|
|Reproduction Preferences Additional Information||Longevity
Gage (1991) tried to use skeletal growth bands to estimate the age of urchins but this approach proved to be difficult to use in older specimens due to the proximity of growth lines during slow growth in older individuals. Bull, (1939) estimated longevity to be up to 6 years, Jensen, (1969) up to 8 years and Alain, (1978) up to 10 or 12 years.
Elmhirst (1922; cited in Gage, 1991) noted that maturity was reached in the first year after settlement. In contrast, Jensen (1969) found 75 % of one year old urchins to have immature gonads in their first summer. However, Kelly (2001) noted that one year old Psammechinus miliaris produced viable gametes and were able to breed in the laboratory.
Spawning (see additional images)
Individuals have been recorded as having ripe gonads from as early as February to as late as November (Orton, 1923; Sukarno et al., 1979; Mortensen, 1927). Actual breeding occurs in spring and early summer (Mortensen, 1927; Sukarno et al., 1979; Kelly, 2000). Psammechinus miliaris is a broadcast spawner (Massin, 1999(b)). The spawning period has been reported to be June to August in the Clyde Sea area (Elmhirst, 1922); June to October near Bergen, Norway (Runnström, 1925; cited in Lindahl & Runnström, 1929); June to October and May to October in West Norway and Denmark (Jensen, 1969); and July and August on the west coast of Scotland (Comely, 1979). Psammechinus miliaris from two typical habitats (littoral and sublittoral) on the west coast of Scotland had a defined annual cycle of gametogenesis with a single spawning period (Kelly, 2000) and gonad indices that peaked in June and July.
Estimates of fecundity suggest that females produce between 80,000 and 2,500,000 eggs in a single spawning event (Dr Maeve Kelly, unpublished observations). Breeding probably occurs over a couple of months (Kelly, 2000) but whether individuals breed for this entire period or whether this duration is for a whole population is uncertain. Orton (1923) suggests there is no evidence for collective spawning.
|Reproduction References||Gage, 1991, Orton, 1923, Allain, 1978, Sukarno et al., 1979, Mortensen, 1927, Jensen, 1969, Massin, 1999(b), Bull, 1939, MacBride, 1903, Boolootian, 1966, Kelly & Cook, 2001, Kelly, 2001, Kelly, 2000, Lindahl & Runnström, 1929, Comely, 1979, Kelly et al., 2000, Hinegardner, 1969, Leighton, 1995, Elmhirst, 1922, Cook et al., 2000, Pantazis, 2000, Julie Bremner, unpub data,|