Bending fatigue strength of a steel, DistaloyAE : P. Beiss et al. (Aachen University of Technology, Aachen, Germany.)

Abstract

A survey was carried out from April 1998 to June 2000 to study the structure of the population and the secondary production of Hediste diversicolor (Copenhagen 32 (1776) 274) in the Loire estuary, Atlantic coast of France. Each month, samples were collected in the intertidal zone of the Mindin harbour. In 1999, the mean annual density was 900±594 individuals (ind.) m−2 with a minimum of 304 ind. m−2 in February and a maximum of 2560 ind. m−2 in April. The mean annual biomass (dry weight) was B̄=9.1 g m−2 with a minimum of 1.2 g m−2 in January and a maximum of 26.0 g m−2 in July 1999. The density and the biomass of the population of H. diversicolor decreased during winter and increased during spring/summer. Size frequency histograms allowed the analysis of cohorts and gave the growth curves. Two recruitment periods were detected each year, in June/July and October. The secondary production was estimated by the method of Crisp (Methods for the study of marine benthos, Blackwell, Oxford, 1971). From June 1998 to May 1999, P=5.1gm−2 with B̄=4.6gm−2 and the ratio P/B̄=1.1 and from June 1999 to May 2000, P=34.4gm−2 with B̄=9.6gm−2 and P/B̄=3.6. The annual secondary production in 1999 was P=32.5gm−2 with B̄=9.1gm−2 and P/B̄=3.6. The differences observed between the 1986–1988 and 1998–2000 populations of H. diversicolor in the Loire estuary are discussed and could be explained by environmental changes, as competition or by migration of individuals.