|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.