Étude dynamique de la population de Nucula nucleus (bivalve, protobranche) du cap de Flamanville (Manche)

Annual production and turnover rate of biomass are estimated on a population of the bivalve, Nucula nucleus, dominant on the sublittoral area of Cap de Flamanville (Manche). Investigations on reproductive cycle established on the gonads maturity index over one year indicate a single spawning period in autumn. Age is determined from a study of the ring pattern on the shells, in which annual signification is outlined. The Von Bertalanffy curve and the exponential function give an adequate description of growth and mortality. The studied population is considered as near a theoretical population with constant recruitment and mortality; this simplification is discussed through the comparison of the demographie structures obtained in the same station in 1978 and 1979. One objective of the study is to provide, by simulation procedure, an assessment of the uncertainty of the calculated P/B ratio taking in account the variability of the length and the effectives by age classe. The mean biomass is equal to 16,6 g dry ftesh weightjm2 and production 9,3 g dry weight, m2/year. P/B ratio is equal to 0,56 with a confidence interval between 0,49 and 0,62 (ex = 5 %).