BIOTIC Species Information for Eurydice pulchra
|Researched by||Lizzie Tyler||Data supplied by||University of Sheffield|
|Refereed by||This information is not refereed.|
|Scientific name||Eurydice pulchra||Common name||Speckled selouse|
|MCS Code||S854||Recent Synonyms||None|
|Additional Information||British coastal isopods have been described by Naylor (1972, 1990). A second intertidal species of Eurydice, Eurydice affinis Hansen, is also found on British shores. It is distinguished from Eurydice pulchra by an overall paler appearance, with black spots only on its dorsal surface. In Britain it has a more restricted distribution than Eurydice pulchra, from south-west England into North Wales, where it occurs amongst populations of Eurydice pulchra.|
|Taxonomy References||Howson & Picton, 1997, Naylor, 1972, Naylor, 1990, Hayward & Ryland, 1995b, Hayward, 1994, Hayward et al., 1996, Fish & Fish, 1996,|
|Typical food types||Other infaunal invertebrates associated with sandy shores and dead organic material.||Habit||Free living|
|Bioturbator||Flexibility||High (>45 degrees)|
|Height||Insufficient information||Growth Rate||0.3 mm/month|
|Adult dispersal potential||1km-10km||Dependency||Independent|
|General Biology Additional Information||Feeding
Eurydice pulchra is a highly predatory carnivore, its mouthparts are adapted for tearing and macerating animal tissue (Naylor, 1972).
Endogenous swimming rhythm
Eurydice pulchra has been shown to have an endogenously controlled circatidal rhythm cycle of swimming that is coupled to a circasemilunar pattern of emergence from the substratum (Alheit & Naylor, 1976; Jones & Naylor, 1970).
On the beach, the animals rely on the cue of increasing water agitation caused by the flood tide to swim from the sand, the endogenous component of the rhythm ensuring that they swim for up to 5-6 hours before reburying in the sand in a restricted zone between mean tide level (MTL) and high water neaps (HWN).
Eurydice pulchra swims mostly at night. Animals emerging from the sand, or washed out by turbulence during the day show photonegative behaviour and immediately bury themselves again.
|Biology References||Naylor, 1972, Hayward, 1994, Fish & Fish, 1996, Fish, 1970, Jones, 1970, Salvat, 1966, Jones & Naylor, 1970, Alheit & Naylor, 1976, Hayward & Ryland, 1990,|
|Distribution and Habitat|
|Distribution in Britain & Ireland||Widespread on open coast and estuarine sandy beaches, with reduced abundance in south-east England.|
|Global distribution||Eurydice pulchra is found from Norway and the outer Baltic to the Atlantic coast of Morocco, but not in the Mediterranean (Soika, 1955).|
|Biogeographic range||Not researched||Depth range|
|Distribution Additional Information||Population densities
Eurydice pulchra populations may occur at densities of 1500 per m² or more and, on a South Wales beach studied by Jones (1970b), the population exceeded 4000 per m².
Eurydice pulchra lives on the upper half of the shore, generally being most abundant between mean tide level (MTL) and mean high water of neap tides (MHWN). Eurydice pulchra relies upon the cue of increasing wave action caused by the flood tide (Jones, 1970b) to initiate swimming from the substratum. It swims in search of food, and buries itself in the sand again as the tide ebbs. As the fortnightly spring tides carry water further up the shore, so Eurydice pulchra moves up, and it can be found in the sand right up to the mean high water of spring tides. When the tidal cycles swings again towards neaps, the Eurydice population also moves down shore again, and avoids being stranded above the neap high water mark (Fish, 1970).
|Substratum preferences||Coarse clean sand
Fine clean sand
Strait / sound
Enclosed coast / Embayment
|Biological zone||Upper Eulittoral
|Tidal stream strength/Water flow||Salinity||Full (30-40 psu)
|Habitat Preferences Additional Information|
|Distribution References||Naylor, 1972, Hayward & Ryland, 1995b, Hayward et al., 1996, Fish, 1970, Jones, 1970b, Alheit & Naylor, 1976, Soika, 1955, Jones & Naylor, 1967, Hayward & Ryland, 1990,|
|Reproductive Season||See additional information||Reproductive Location||As adult|
|Reproductive frequency||Annual episodic||Regeneration potential||No|
|Life span||1-2 years||Age at reproductive maturity|
|Generation time||<1 year||Fecundity||32|
|Egg/propagule size||Fertilization type||Internal|
|Reproduction Preferences Additional Information||Fecundity
The number of eggs carried by females of Eurydice pulchra was reported to vary in populations from different localities. In a population from the Dovey Estuary, west Wales, Fish (1970) observed the total number of eggs in any one female to vary between 22 to 54. Jones (1970) found that small females, 4.5 mm body length, carried a minimum of 10 eggs, whilst larger females, 7 mm body length, carried up to 40 eggs. In France, Salvat (1966) reported females of 6.0 mm body length to carry at least 45 eggs.
Fish (1970) and Jones (1970) describe the reproductive cycle of two British populations of Eurydice pulchra from an estuarine and open coast location respectively. Some differences concerning the duration of the breeding period, number of eggs carried by females of a particular size were found.
The sexes are separate and pair whilst swimming. Development of the embryo occurs within the internal brood pouch (marsupium) of the female, and the incubation period takes 7-8 weeks. Embryonic development is similar to that for other isopods (Forsman, 1944; Kjennerud, 1950; Naylor, 1955b, cited in Fish, 1970), and four distinct stages are recognised, the last stage being a miniature version of the adult. The minimum recorded length of newly emerged juveniles is 1.7 mm and they are able to swim and feed immediately.
Early broods released during July were reported by Jones (1970), to reach maturity before winter within the same year, breed early during the following spring and consequently provide the first broods of that year, before dying in their second autumn after a total life span of approximately 15 months. Broods released in August and September, initially grew as rapidly as the early spring brood but did not reach maturity and consequently overwintered as juveniles. Over-wintering juveniles matured as late as July and themselves produced the late broods of the following year. In contrast, on the west coast of Wales, sexually immature specimens of Eurydice pulchra overwintered twice and took 20 months to attain sexual maturity, produced only one brood per year and had a life span of about 2 years (Fish, 1970). Furthermore, Salvat (1966) reported a population of Eurydice pulchra from Arcachon, France, to have an annual reproductive cycle with sexual maturity being reached within 8 months. It is suspected (Fish, 1970; Jones, 1970; Salvat, 1966), that these variations in reproductive life cycle are related to the significant temperature differences between localities. The effect of temperature being reflected in the duration of the post-hatching growth stages, which are accelerated at higher temperatures.
|Reproduction References||Fish, 1970, Jones, 1970, Salvat, 1966,|