A study of the population of the xanthid crab Pilumnus dasypodus Kingsley, 1879 from rocky shore at the Farol Isle (25º51'S and 48º32'W) was carried out in the following aspects: temporal and spatial distributions of density, annual fluctuation of the sex ratio, size composition of the population and reproductive activities of the species. Monthly, four leveis in relation to emmersion time within intertidal zone were sampled, from May/90 to April/91, but Pilumnus dasypodus was obtained only in the levels 2, 3 and 4. The surface water temperature ranged from 16.0ºC (July/90) to 28.0ºC (February/91). A total of 775 individuais of Pilumnus dasypodus were collected among which, 92 were ovigerous females. The population density ranged from 14.63 ind.m-3 (February/91) to 148.00 ind.m-3 (March/91). Higher densities were observed in the level 4, a local of permanent submersion. The sex ratio was 1:1 in almost all months. The carapace width varied from 1.01 to 8.28 mm for males, from 1.01 to 7.18 mm for females and 0.01 to 1.00 mm for juveniles. The fecundity ranged from 81 to 1834 eggs per female. The species has continuous reproduction with two peaks of recruiting in the year. There was a positive relationship, with weak correlation rate, between the carapace width of the ovigerous females and the number of eggs in the abdomen. The rocky shore at Farol Isle is a complex environment which harbor the decapod Pilumnus dasypodus, for breeding and surviving.
Pilumnus dasypodus; population structure; Farol Isle; Paraná State