A benthic survey was carried out from November
1998 to December 1999 in the tidal flats of Bahía
Samborombón (Río de la Plata estuary, Argentina),
in order to study the population structure,
reproductive aspects, growth and secondary
production of Capitella capitata (Fabricius, 1780).
Growth was analyzed using ELEFAN routine, and
the secondary production was estimated by Hynes
and Coleman's method (1968). C. capitata did not
present periods of very important recruitments
throughout the year; however, the abundance of
smallest size classes was higher during summer and
autumn. The summer cohort showed a growth rate
(K) of 2.05 and a seasonal growth oscillation (C) of
0.6, pointing out that worms grew very slowly
during winter months. The life span of this cohort
was 13 months. The autumn cohort showed a lower
growth rate (K= 1.5) and its growth was lowest
during winter. The life span was 15 months for this
cohort. C. capitata in Punta Rasa presented an
extended reproductive period, with absence of
activity during winter months. The type of eggs and
larvae suggest that C. capitata has benthic larval
development in the study area, destining its reproductive effort to the production of a low number of eggs, and assuring larvae survival through incubation in brooding tubes. The annual mean biomass in Punta Rasa was 0.117 g m-2 (AFDW), with a mean secondary production of 0.23 g m-2 y-1 and a P/B ratio of 1.96 y-1. The relatively low density, biomass production and P/B ratio of C.
capitata in Punta Rasa can be considered as reference values for this species inhabiting undisturbed or moderately disturbed areas