Population dynamics and secondary production of Owenia fusiformis Delle Chiaje (Polychaeta) from the Bay of Seine (eastern English Channel)

Abstract

The life cycle, population dynamics and production of Owenia fusiformis Delle Chiaje from the muddy fine sand community in the Bay of Seine were studied at two stations from May 1981 to September 1983. Densities showed large and synchronized variations at both stations; means were 1110 and 327 ind · m−2, respectively. Recruitment occurred at the end of the spring or during the summer. The number of recruits varied strongly from one year to another. Recruitments were marked in 1983 and weak in 1981–82. Growth of young individuals was rapid during the summer and the beginning of the autumn, then slowed down in October and stopped during autumn and winter. Growth resumed in April for the overwintered specimens and continued during the spring and the summer. Growth rates were similar from one year to another for all the year classes. The mortality rate was higher for the 4th yr of life than it was for the first 3 yr of life. The maximum life span was 4 yr at both stations but the mean life span did not exceed 3 yr at Station A and 2–3 yr at Station B. Production was estimated for two annual cycles at both stations. Growth production varied from 4.2 to 18.8 g DW · m−2 · yr−1 and elimination production from 1.7 to 33.6 DW · m −2 · yr−1. P/B̄ ratios ranged from 0.75 to 1.55 and E/B̄ ratios from 0.6 to 1.85. Production, and P/B̄ ratios, are compared with previously published data for other populations of Polychaetes which live ⩾3yr.