POPULATIONS OF STREBLOSPIO (POLYCHAETA, SPIONIDAE) IN TEMPERATE ZONES- DEMOGRAPHY AND PRODUCTION

The life cycle, seasonal dynamics and production of two populations of Streblospio species (Annelida: Polychaeta), S. benedicti Webster, 187 9, from muddy sediments of the Great Sippewissett Salt Marsh (southern New England, USA), and S. shrubsolii (Buchanan, 1890), from muddy are as of the Alfacs Bay (north-eastern Spain), were studied from November 1986 to September 1988. Both species have life-cycles shorter than on e year. The American population showed a unimodal distribution most of the year while in the European population polymodal distributions wer e common. Average density of S. benedicti over the two-year period ran ged from 24,086 to 677 individuals m-2 (annual average 4,554). The obs erved numbers of S. shrubsolii ranged from 65,668 to 2,579 individuals m-2 (average 35,311). The biomass of the American population ranged f rom 2.1 to 0.04 g dry weight m-2 (average 0.5). The values obtained fo r the European population ranged from 5.9 to 0.1 g dry weight m-2 (ave rage 4.1). Secondary production was higher in the European population (15.65 g dry weight m-2 y-1) than in the American population (3.0 g dr y weight m-2 y-1). Production to mean biomass ratios were 4.4 y-1 for S. shrubsolii and 5.4 y-1 for S. benedicti. Population densities are c ompared with previously published data for other Streblospio populatio ns.