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Population structure and secondary production of Heteromastus filiformis (Polychaeta: Capitellidae) in the Loire estuary, France

A survey was carried out from April 1998 to June 2000 to study the structure and the secondary production of the population of Heteromastus filiformis in the Loire estuary. Each month, samples were collected in the intertidal zone of Mindin harbour. The length of the thorax (L12) was correlated with the fresh weight (FW) with the relation FW=1·49848 L12–3·62804 (r=0·92). In 1999, the mean density was 2184 ind m−2 with a minimum of 1104 ind m−2 in December and a maximum of 3328 ind m−2 in March. The mean annual biomass was 15·4 g m−2 with a minimum of 2·6 g m−2 in December and a maximum of 28·2 g m−2 in March. Most of the histograms of size–frequency are unimodal and could be considered a single cohort except in May and November/December 1999. The abundance and biomass of the population of H. filiformis decreased during summer and winter which are mortality periods and increase during spring and autumn which are recruitment periods for the population. The life time for a cohort was from six to nine months depending on the recruitment period and on the inter-annual variations. The secondary production was estimated by the method of Crisp (1971). The annual secondary production in 1999 was P=104·3 g m−2 with B¯=15·4 g m−2 and P:B¯=6·8. The quantity of sediment reworked by H. filiformis is about 116 l m−2 y−1 or 65 kg m−2 y−1 which is approximately a deep-sediment layer of 12 cm transported to the surface annually.