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ABSTRACT. The population dynamics and reproductive strategy of the polychaete Scolelepis goodbodyi (Jones, 1962), were investigated between June 2009 and May 2010 at Manguinhos beach, southeastern, Brazil. A total of 9,242 individuals were collected. The density did not differ significantly from one month to another. The estimated values of the growth, recruitment, and mortality rates were studied using the width of the third setiger and the growth curves for the populations were adjusted by the Bhattacharya method (Lϱ= 1.23, K = 1.2, mortality = 0.73). Two annual cohorts were identified in the period. Significant differences between males and females were observed in the population ( 2 = 71.6, p < 0.01) and between sexually defined and sexually indeterminate individuals ( 2 = 158.4, p < 0.01). Five stages of gonadal development were identified. The coexistence of recruits and mature individuals throughout the study period suggests that this population presented continuous reproduction.

Representatives of the Family Orbiniidae are very common in marine sediments and are found in both shallow and deep waters. Currently, 26 species and 10 genera have been recorded along the Brazilian coast. The specimens examined in this study were collected at depths ranging from 25 to 400 m in the Campos Basin (20-24ºS; 39-42ºW), Rio de Janeiro, in the summer and winter of 2008 and 2009. We describe two new species, Orbinia sagitta n. sp. and Orbinia camposiensis n. sp., and record the occurrences of Orbinia johnsoni (Moore, 1909), which was originally described in California, and Orbinia oligopapillata (López, Cladera & San Martin, 2006), which was previously described from the Pacific coasts of Panama. We provide a key for all the species of Orbinia recorded in the Campos Basin.

The secondary production is the result of the functional response of populations subject to various environmental factors. Marine habitats vary in terms of quantity and quality of food supply, and the use of secondary production values, as well as renewal rates (P/B), may be used as estimates for understanding the incorporation of organic matter and energy per unit, population or community in each area. This estimative was performed for the population of Scolelepis goodbodyi in a tropical beach in the Southwestern Atlantic, located in an upwelling area. A comparison of Spionidae and non-spionid populations from different latitudes was also done. The Mass Specific Growth Rate method (MSGR) and the Production/Biomass ratio (P/B) were used to estimate the somatic annual production and average annual biomass. The mean density and biomass were 16.38 ind. m-2 and 2.78 g AFDW m-2,respectively. The secondary production and P/B were 8.3 g AFDW m-2 y-1 and 2.98 y1, respectively. The growth rate in weight was greater for the small size than the large size classes. The largest individuals (W3C = 1.0 mm) showed the lowest biomass and secondary production values. The observed high rates of secondary production and P/B suggest that this S. goodbodyi population can transfer large amounts of biomass to higher trophic levels of the local food web. Studies of the secondary production of spionidae populations in different latitudes, including the population of S. goodbodyi in the beach of Manguinhos, showed variability in their rates probably due to the differences of several factors such as life history and environmental variability