BIOTIC

BIOTIC Species Information for Ophiothrix fragilis
All Taxonomy Biology Distribution Reproduction

Researched by	Lizzie Tyler	Data supplied by	University of Sheffield
Refereed by	This information is not refereed.
General Biology
Growth form	Radial Stellate	Feeding method	Passive suspension feeder Active suspension feeder Surface deposit feeder Sub-surface deposit feeder
Mobility/Movement	Crawler	Environmental position	Epibenthic
Typical food types	Phytoplankton	Habit	Free living
Bioturbator	Not relevant	Flexibility	Low (10-45 degrees)
Fragility	Fragile	Size	Medium(11-20 cm)
Height		Growth Rate	average 1.1mm increase disc diameter per month
Adult dispersal potential	1km-10km	Dependency	Independent
Sociability	Gregarious
Toxic/Poisonous?	No
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,