Population dynamics and production of Streblospio benedicti (Polychaeta) in a non-polluted estuary in the Basque coast (Gulf of Biscay)

Abstract

Population dynamics and production of a population of Streblospio benedicti from the Gernika estuary (Basque coast, Gulf of Biscay) were studied monthly for one year, from May 1991 to May 1992. S. Benedicti was present in the muddy sand community of Gernika throughout the period of study except in March, when it all but disappeared. Continuous recruitment was observed throughout the year, even though it was stronger in autumn. Abundance fluctuations were principally due to the incorporation of recruits and so the highest density in Gernika was recorded in autumn, and the lowest in spring, with an annual mean of 6346 ± 4582 ind m^-2. The same pattern of seasonal variation was shown in biomass: the annual mean biomass of S.benedicti in Gernika was estimated at 0.80 ± 0.54 g dry weight m-2. Secondary production was 3.57 g dry weight m-2 year, giving a P/B ratio of 4.46. S. benedicti in Gernika behaved similarly to those described for Mediterranean Streblospio populations as regards practically continuous recruitment, but the number of individuals and the annual average density were considerably lower on the Basque coast.