BIOTIC Species Information for Ophiothrix fragilis
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Researched byLizzie Tyler Data supplied byUniversity of Sheffield
Refereed byThis information is not refereed.
General Biology
Growth formRadial
Feeding methodPassive suspension feeder
Active suspension feeder
Surface deposit feeder
Sub-surface deposit feeder
Environmental positionEpibenthic
Typical food typesPhytoplankton HabitFree living
BioturbatorNot relevant FlexibilityLow (10-45 degrees)
FragilityFragile SizeMedium(11-20 cm)
Height Growth Rateaverage 1.1mm increase disc diameter per month
Adult dispersal potential1km-10km DependencyIndependent
General Biology 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,
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