A study on the temporal distribution, sex ratio, reproductive period, recruitment of juveniles and size composition of individuals of the fiddler crab Uca (Leptuca) uruguayensis was carried out in a population living in the Garças River mangrove, Guaratuba Bay, Paraná State, Brazil. Eight square samples of 0.25 m² (0.50 m side) were obtained on a monthly basis, from April/2011 to March/2012. The crabs were collected through the excavation of burrows and their carapace width (CW) was measured. Air and water temperatures varied from 19.0 to 29.5ºC and 17.0 to 27.0ºC, respectively, the salinity from 7 to 23 and the soil temperature from 19.0 to 29.2ºC. A total of 1,099 fiddler crabs were collected, being 529 males, 520 females (of these, 9 ovigerous) and 50 sexually undifferentiated individuals. The average density of the population ranged from 12 (June/11) to 71 ind.m-² (May/11), but its annual fluctuation was not correlated to abiotic variables. The sex ratio was 1:1 all year round and in all CW classes. Although in low abundance, ovigerous females were recorded in six months and juvenile crabs were present all year round, indicating a continuous reproduction and recruitment of the species. The CW of males ranged from 2.33 to 8.33 mm and that of females, from 2.52 to 7.79 mm: these data showed that this population is composed of smallest individuals among those studied
Annual fluctuation; reproductive period; recruitment; sex ratio