This study aimed to describe the ecological distribution and the effects of environmental factor oscillation on the life cycle of Penaeus schmitti along the coastal area of Cananéia, southern São Paulo state, Brazil. Shrimp and environmental factors were sampled monthly from July 2012 to May 2014 at seven sampling stations covering both estuarine and marine environments, using a shrimp fishing boat. A total of 273 juveniles and 829 adults were sampled, and there were significant differences in body size (carapace length -CL) throughout the seasons (ANOVA). Smaller animals were observed in the summers of 2013 and 2014 and at sites closer to the coast, which are under estuarine influence. Adults were observed mostly in autumn and in deeper regions. We detected a positive relationship between the abundance of juveniles and the bottom water temperature and between the abundance of adults and the water salinity (canonical correspondence analysis). The presence of smaller individuals in the estuarine environment demonstrates the importance of the estuaries in this species' ontogeny, mainly concerning their protection, since this environment has physical (depth) and physiological (salinity) barriers to their predators. Furthermore, we could clearly observe the plasticity of juveniles in relation to environmental factors. In contrast, adults were less tolerant to the variation in environmental factors, mainly water salinity, which was a limiting factor of their distribution. Seasonal differences in body size could be directly associated to this species' life cycle and characterized by trophic and reproductive migratory activities between the estuarine and oceanic regions. ARTICLE HISTORY

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This study evaluated the temporal and bathymetric distribution of the speckled swimming crab Arenaeus cribrarius from coastal waters of southern Brazil. Monthly samples were taken at five distinct depths throughout one year in the adjacent area from Babitonga Bay, Southern Brazil. Data on environmental conditions (temperature, salinity, granulometry and organic matter) were collected and their association was tested using Multiple Linear Regression and Principal Component Analysis. Juveniles and adults showed different distribution patterns according to depth, with juveniles being more abundant in the shallower areas. The increase in temperature favors the juvenile distribution, while the distribution of adults was related to finer sediments. The pattern of distribution observed for adults might be associated with burrowing habits, or with the search for colder (and consequently deeper) waters, which are richer in nutrients. The high abundance of juveniles in shallower areas might be influenced by the Coastal Water mass that provides higher water temperatures in the summer, and by the Babitonga Bay estuarine complex, which can be an important source of organic matter. We conclude that this region represents a nursery ground for the studied species and is essential to preserve Babitonga Bay in order to maintain A. cribrarius in this region, since this area has suffered from anthropic impacts.