BIOTIC

BIOTIC Species Information for Ophiothrix fragilis

Researched by

Lizzie Tyler

Data supplied by

University of Sheffield

Refereed by

This information is not refereed.

Taxonomy

Scientific name

Ophiothrix fragilis

Common name

Common brittlestar

MCS Code

ZB124

Recent Synonyms

None

Phylum

Echinodermata

Subphylum

Asterozoa

Superclass

Class

Ophiuroidea

Subclass

Order

Ophiurida

Suborder

Family

Ophiotrichidae

Genus

Ophiothrix

Species

fragilis

Subspecies

Additional Information

No 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 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?

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,

Distribution and Habitat

Distribution in Britain & Ireland

All British and Irish coasts, except for the east coast of Scotland, around the Humber Estuary and north East Anglia and south Kent coast.

Global distribution

Widely distributed in the eastern Atlantic from northern Norway to the Cape of Good Hope.

Biogeographic range

Not researched

Depth range

Migratory

Non-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 preferences

Bedrock
Large to very large boulders
Small boulders
Cobbles
Pebbles
Gravel / shingle
Maerl
Muddy gravel
Under boulders
Crevices / fissures
Other species (see additional information)

Physiographic preferences

Open coast
Offshore seabed
Strait / sound

Biological zone

Lower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Upper Circalittoral
Lower Circalittoral

Wave exposure

Extremely Exposed
Very Exposed
Exposed
Moderately Exposed
Sheltered
Very Sheltered

Tidal stream strength/Water flow

Strong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)

Salinity

Low (<18 psu)
Full (30-40 psu)
Variable (18-40 psu)
Reduced (18-30 psu)

Habitat Preferences Additional Information

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 type

Gonochoristic

Developmental mechanism

Planktotrophic

Reproductive Season

June to October

Reproductive Location

Insufficient information

Reproductive frequency

Annual episodic

Regeneration potential

Yes

Life span

6-10 years

Age at reproductive maturity

<1 year

Generation time

Insufficient information

Fecundity

Egg/propagule size

Fertilization type

Insufficient information

Larvae/Juveniles
Larval/Juvenile dispersal potential	>10km	Larval settlement period	August to September
Duration of larval stage	11-30 days

Reproduction Preferences 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,