Nassariids have a worldwide distribution and are most often found in sheltered embayments in tropical, subtropical, and temperate zones occurring in intertidal and subtidal areas. Species of this genus are scavengers, constituting a major link in the energy flow between carrion, independent of trophic levels, and the environment. The aims of this study are to compare the distribution pattern and the population biology (growth and mortality) of males and females of Nassarius vibex. Sampling was carried out monthly, at spring low tide, from September 2007 through February 2009 at Flexeiras Beach, located in Rio de Janeiro state (22°), southeastern Brazil. Sampling was conducted according to a systematic design in which biological samples were taken along 6 transects spaced equally and perpendicular to the shoreline. On each transect, 10 equally spaced sampling units (SUs) were established: the first (SU1) at the waterline, the second last (SU9) on the drift line, and the last (SU10) 3 m above the drift line (supralittoral). Highest population abundances were observed in spring for both sexes. There were significant differences in abundance among the levels in both sexes. Females of N. vibex had lower abundance, grew faster, and had higher mortality and shorter life spans than males. Variations in the population parameters of N. vibex might be regulated by phenotypic adjustment in local conditions, food availability, and, apparently, in this case, by exposure to organotin compounds inducing to the imposex.