|Reproduction Preferences Additional Information||This polychaete has a life span of up to four years in British waters (Rouse & Pleijel, 2001) and has a polymodal population structure of three to five year classes (Menard et al., 1990). The mortality rate increases gradually with age but suddenly increases in the fourth year of life (Menard et al., 1990).
Growth is rapid in summer, slows in the autumn and is negligible in winter, resuming in April each year.
Owenia fusiformis is an annual breeder, gonochoric, with external fertilization (Rouse & Pleijel, 2001). Up to 70,000 oocytes mature from September to April (Gentil et al., 1990) and are spawned during May and June (Rouse & Pleijel, 2001). Oocytes are up to 100 µm in diameter (Rouse & Pleijel, 2001).
The sex ratio is female biased and is around 0.86:1. Maturity is size-dependent and all worms 6 cm long or more are mature but some individuals reach maturity at 2.4 cm. Some individuals may breed in their first year if they can grow fast enough (Gentil et al., 1990).
In late May, larval densities can be up to 100,000 per m3 (Thiebaut et al., 1992) and settled densities vary from 4,000 to 15,000 juveniles per m² (Menard et al., 1990).