Ecology of the polychaete Nereis diversicolor in the Canal de Mira (Ria de Aveiro, Portugal):: Population dynamics, production and oogenic cycle

The population of Ner-eis diversicolor O.F. Muller was studied in 1993 and 1994 at three intertidal areas along the estuarine gradient in the Canal de Mira (Ria de Aveiro). The population dynamics, secondary production and growth were followed for the 2-year period, whereas in the second year, a study on the oogenic cycle was also carried out. For the population dynamics and production studies, core samples were collected monthly at each site, and for the study of the oogenic cycle, medium size and large individuals were sampled from the sediment. Mean annual densities were higher (573-718 ind.m(-2)) at a station located in the middle zone of the channel, followed by the outer (190-275 ind.m(-2)) and the innermost (43-94 ind.m(-2)) stations. A cohort analysis by 'Bhatta' software enabled the separation of the cohorts present at each date, and two cohorts were followed from recruitment to extinction. The secondary production ranged from 15.9 to 74.2 g ash free dry weight.m(-2).year(-1) and the P/(B) over bar ratio from 4.4 to 7.9. The average body growth rate varied between 0.16 and 0.20 mm.d(-1) for worms longer than 2 cm. Two recruitment seasons were detected each year. Two spawning periods were also observed, one in the spring and the other in early autumn. (C) 1999 Editions scientifiques et medicales Elsevier SAS.