Ophiothrix fragilis

Researched ByLizzie TylerData Supplied ByUniversity of Sheffield
Refereed byThis information is not refereed.
Taxonomy
Scientific nameOphiothrix fragilisCommon nameCommon brittlestar
MCS CodeZB124Recent SynonymsNone
PhylumEchinodermataSubphylumAsterozoa
SuperclassClassOphiuroidea
SubclassOrderOphiurida
SuborderFamilyOphiotrichidae
GenusOphiothrixSpeciesfragilis
Subspecies  
Additional InformationNo text entered
Taxonomy References Howson & Picton, 1997, Fish & Fish, 1996, Hayward et al., 1996, Campbell, 1994, Picton & Costello, 1998, Hayward & Ryland, 1995b, Migné & Davoult, 1997(c), Lefebvre & Davoult, 1997, Sides & Woodley, 1985, Hughes, 1998
General Biology
Growth formRadial, StellateFeeding methodPassive suspension feeder, Active suspension feeder, Surface deposit feeder, Sub-surface deposit feeder
Mobility/MovementCrawlerEnvironmental positionEpibenthic
Typical food typesPhytoplanktonHabitFree living
BioturbatorNot relevantFlexibilityLow (10-45 degrees)
FragilityFragileSizeMedium(11-20 cm)
HeightGrowth Rateaverage 1.1mm increase disc diameter per month
Adult dispersal potential1km-10kmDependencyIndependent
SociabilityGregarious
Toxic/Poisonous?No
Additional Information
  • This species can be found in very high densities of up to 2000 individuals per square metre (Davoult, 1989).
  • The smallest brittle stars found have a disk diameter of 2 mm and two segments per arm.
  • Some gonad development is present in individuals with disks of 3 mm although full sexual maturity is probably achieved at about 10 mm disk diameter (Gage, 1990).
  • Growth rate estimates vary considerably. Growth in juveniles may be between 1.6-3.1 % and 3.5-10.3 % increase in body disk diameter per day (Davoult et al., 1990) On average the body disk diameter is estimated to increase by 1.1 mm per month. Other growth rate estimates are much slower (Gage, 1990)
  • Optimal feeding can occur at water flow rates below 20 cm per second (Davoult & Gounin, 1995). Water moving at above 25 cm per second causes the arms to be brought down from being extended in the water column (Warner & Woodley, 1975; Hiscock, 1983). Water flow rates refer to water movements at the seabed. Surface flow rates will be considerably higher.
  • Although not an important dietary component, Ophiothrix fragilis may be found in the stomach contents of most common predators (Warner, 1971). Ophiothrix fragilis avoids predation by moving away from sources of mechanical disturbance (Warner, 1971). The escape response of Ophiothrix fragilis is slow in comparison to other brittle stars and it avoids visual predation through sheltering in crevices etc. and cryptic colouration (Sköld, 1998). Predatory starfish such as Asterias rubens and Marthasterias glacialis produce steroid glycoside chemicals that elicit an avoidance response in Ophiothrix fragilis (Mackie, 1970). Although not toxic, Ophiothrix fragilis achieves unpalatability through heavy calcification and possession of glassy spines (Sköld, 1998).
  • Brittle stars, such as Ophiothrix fragilis, have symbiotic subcuticular bacteria. The host-bacteria association can be perturbed by acute stress and changes in bacterial loading may be used as an indicator of sub-lethal stress (Newton & McKenzie, 1995)
  • The strong tidal current, coarse sediment communities from the English Channel are dominated by Ophiothrix fragilis, Urticina felina and Alcyonium digitatum (Migné & Davoult, 1997(c)).
Biology References Picton & Costello, 1998, Hayward & Ryland, 1995b, Migné & Davoult, 1997(c), Gorzula, 1976, Smaal, 1994, Davoult et al., 1993, Lefebvre & Davoult, 1997, Davoult, 1990, Broom, 1975, Warner & Woodley, 1975, Warner, 1971, Sköld, 1998, Emson & Wilkie, 1980, Wilkie, 1978, Sides & Woodley, 1985, Newton & McKenzie, 1995, Gage, 1990, George & Warwick, 1985, Mackie, 1970, Holme, 1984, Allain, 1974, Ware et al., 1992, Davoult, 1989, Migné & Davoult, 1997(b), Davoult & Gounin, 1995, Hiscock, 1983, Hughes, 1998, Wolff, 1968, Hayward & Ryland, 1990, Julie Bremner, unpub data, Mortensen, 1927
Distribution and Habitat
Distribution in Britain & IrelandAll British and Irish coasts, except for the east coast of Scotland, around the Humber Estuary and north East Anglia and south Kent coast.
Global distributionWidely distributed in the eastern Atlantic from northern Norway to the Cape of Good Hope.
Biogeographic rangeNot researchedDepth range
MigratoryNon-migratory / Resident
Distribution Additional Information
  • Ophiothrix fragilis may be found in low densities on Crepidula fornicata (slipper limpet) beds (Bourgoin et al., 1985) or also overlying Modiolus shells (Magorrian et al., 1995)
  • Wolff, (1968) notes the species occurring in normal salinities of 16 psu and even persisting down to 10 psu.
Substratum preferencesBedrock, Large to very large boulders, Small boulders, Cobbles, Pebbles, Gravel / shingle, Maerl, Muddy gravel, Under boulders, Crevices / fissures, Other species (see additional information)Physiographic preferencesOpen coast, Offshore seabed, Strait / sound
Biological zoneLower Eulittoral, Sublittoral Fringe, Upper Infralittoral, Lower Infralittoral, Upper Circalittoral, Lower CircalittoralWave exposureExtremely Exposed, Very Exposed, Exposed, Moderately Exposed, Sheltered, Very Sheltered
Tidal stream strength/Water flowStrong (3-6 kn), Moderately Strong (1-3 kn), Weak (<1 kn)SalinityLow (<18 psu), Full (30-40 psu), Variable (18-40 psu), Reduced (18-30 psu)
Habitat Additional Information
AMBI Group (Borja et al., 2000)I 
Distribution References Fish & Fish, 1996, Hayward et al., 1996, Campbell, 1994, Bruce et al., 1963, MBA, 1957, JNCC, 1999, Picton & Costello, 1998, Hayward & Ryland, 1995b, Migné & Davoult, 1997(c), Gorzula, 1976, Lefebvre & Davoult, 1997, Davoult, 1990, Migné et al., 1998, Warner & Woodley, 1975, Warner, 1971, Bourgoin et al., 1985, George & Warwick, 1985, Davoult et al., 1990, Holme, 1984, Migné & Davoult, 1997(b), Hughes, 1998, Magorrian et al., 1995, Wolff, 1968, Hayward & Ryland, 1990, Julie Bremner, unpub data, Mortensen, 1927
Reproduction/Life History
Reproductive typeGonochoristic Developmental mechanismPlanktotrophic
Reproductive SeasonJune to OctoberReproductive LocationInsufficient information
Reproductive frequencyAnnual episodic Regeneration potentialYes
Life span6-10 yearsAge at reproductive maturity<1 year
Generation timeInsufficient informationFecundity
Egg/propagule sizeFertilization typeInsufficient information
Larvae/Juveniles
Larval/Juvenile dispersal potential>10kmLarval settlement periodAugust to September
Duration of larval stage11-30 days  
Additional Information
  • Longevity estimates vary from 9 months (Davoult et al., 1990) to over 10 years (Gage, 1990). Work by Gage (1990) on skeletal growth bands in Ophiothrix fragilis indicate a slow rate of growth and considerable longevity suggesting that individuals with a disk diameter of 13mm are around 10 years old (disk diameters reach 20mm). N.B. This is not yet a validated age determining mechanism.
  • Davoult et al., (1990) consider development to maturity to take 6-10 months depending on the cohort and time of recruitment. Gonads are most developed in May-July (George & Warwick, 1985). Some gonad development is present in individuals with disks of 3 mm although full sexual maturity is probably achieved at about 10 mm disk diameter (Gage, 1990). Development of sexual maturity is dependent on day length and temperature although temperature is not believed to be a trigger for spawning (Davoult, et al., 1990).
  • Gamete release - Davoult et al., (1990) record spawning in the eastern Channel from mid July to mid August. Spawning in the Plymouth area has been recorded from June to the start of September (Davoult et al., 1990) and in October (Marine Biological Association 1957). In Kinsale Harbour on the south coast of Ireland Ball et al. (1995) found that Ophiothrix fragilis had a long breeding season, extending from May to January, with peak activity in summer/autumn, a small percentage of the population can breed throughout most of the year in certain regions. The evidence suggests that each animal spawns only once during a breeding season, although spawning may take place as several bursts over the period based on the presence of a number of different size classes of oocytes within the gonad at any particular time. Further north, in Sweden, spawning is recorded from August and September (Davoult et al., 1990).
  • Recruitment from the planktonic larvae occurs from August to September (Allain, 1974). Davoult et al., (1990) consider there to be multiple recruitments in the eastern Channel, a primary one in September and three secondary ones in February, April and June. Individual cohorts can be followed for 4-6 months after which variable growth rates and overlap in size precludes their separation. These multiple recruitments indicate more than one discrete spawning episode.
  • Larvae appear in the water column about a week after gamete release and fertilisation of the eggs. The larvae metamorphose into juvenile brittlestars whilst still in the plankton. The pelagic phase lasts about 26 days (MacBride, 1907).
  • The larvae may undertake a passive migration in areas such as the English Channel where there are strong water flow rates (Davoult et al., 1990). Here, with water that may move over 4 km per day and a larval duration of 26 days, the larvae can disperse up to 70-100 km. This may preclude auto-recruitment of local populations (Davoult at al., 1990).
  • Mean disk diameter can decrease by up to 20 % during gamete production (Davoult et al., 1990).
  • Although the species is gonochoristic Davoult et al., (1990) record a 1 % incidence of hermaphroditism.
  • Recruitment success is heavily dependent on environmental conditions including temperature and food availability. In years after mild winters Ophiothrix fragilis occurred in extremely high densities in the Oosterschelde estuary in Holland (Smaal, 1994). Populations seem to be stable in the long term although there may be strong variation from year to year. A multi annual cycle of around 4 years may exist in the eastern English Channel (Davoult et al., 1993). However, Holme, (1984) notes long term changes in Ophiothrix fragilis populations in the western Channel, possibly linked with predator abundance (Luidia ciliaris and Luidia sarsi) and water quality.
    Reproduction References Bruce et al., 1963, MBA, 1957, Davoult et al., 1993, Lefebvre & Davoult, 1997, Davoult et al., 1990, Pedrotti, 1993, Allain, 1974, Hughes, 1998, Julie Bremner, unpub data