ABSTRACT Two populations of the Southwestern Atlantic burrowing crab, Neohelice granulata (Dana, 1851), are separated by only 190 km. They inhabit bays that drain into a Patagonian gulf in the southernmost limit of the geographical distribution of the species: San Antonio Bay (SAO) and San José Gulf (RSJ). The population from SAO has been extensively studied, whereas that of RSJ has not. The main goal of this study is to compare the ecological and habitat characteristics of the two populations, based on samples collected on successive days during the middle of the reproductive season of the crab. The substrate of SAO is composed of a high proportion of gravel and scarce organic matter, whereas the substrate of RSJ presents twice as much silt and clay, and greater organic matter content. Crabs of both sexes were larger at RSJ. Fecundity and reproductive output were greater at RSJ. The size of females at maturity was smaller and their range was shorter at RSJ. Burrows were longer and wider at RSJ. Our results indicate that there are strong differences between the two populations, which might be correlated with local environmental differences, mainly substrate granulometry and food availability.

Environmental aspects and the decapod fauna of several estuaries and coastal lagoons in the southwestern Atlantic, between 25 and 41°S, are compared: Baia de Paranaguá, Manguezal de Itacorubí, Lagoa dos Patos (Brasil), Laguna Castillos (Uruguay), Río de la Plata (Uruguay-Argentina), Laguna Mar Chiquita and Bahía Blanca (Argentina). The information about natural history of crab species (Crustacea: Brachyura) from these estuarine systems is reviewed. The number of crab species falls dramatically between Itacorubí and Lagoa dos Patos, together with a fall in minimum water temperature. Low winter temperatures may affect physiological processes of many species and are related to the disappearance of mangroves, and the variety of microhabitat generated by them. However, temperature alone cannot explain several features of species distribution and life history

Se compara la fauna de decápodos y las características ambientales de varios estuarios y lagunas costeras del Atlántico sudoccidental, ubicados entre los 25 y los 41°S: Baia de Paranaguá, Manguezal de Itacorubí, Lagoa dos Patos (Brasil), Laguna Castillos (Uruguay), Río de la Plata (Uruguay-Argentina), Laguna Mar Chiquita y Bahía Blanca (Argentina). Se revisa la información sobre historia natural de las especies de cangrejos (Crustacea: Brachyura) que los habitan. El número de especies de cangrejos desciende bruscamente entre Itacorubí y Lagoa dos Patos, junto a la disminución de la temperatura mínima del agua. Las bajas temperaturas invernales tienen un efecto directo sobre la fisiología de muchas especies, pero también están relacionadas con la desaparición de los manglares y la variedad de microhabitat que éstos generan. Sin embargo, el efecto de la temperatura no es suficiente para explicar algunos aspectos relacionados con la distribución de las especies y sus historias de vida

A number of 243 species of decapod crustaceans, belonging to 49 families, were found in the southwestern Atlantic, between 25 and 55°S. Suborder Dendrobranchiata includes 6 families with 23 species. Suborden Pleocyemata has 10 families of Caridea with 35 species, 1 family of Astacidea with 2 species, 1 family of Palinura with 1 species, 2 families of Thalassinidea with 7 species, 8 families of Anomura with 44 species and 21 families of Brachyura with 131 species. In the warm-temperate region of the southwestern Atlantic there are 200 species; 73% of them spread to the north ("tropical species"), 27% are found between Río de Janeiro and Tierra del Fuego. From these species, 44 are endemic. The number of tropical species diminishes at higher latitudes, although different families show different patterns; environmental changes at 29º-35°S, mainly the fall in winter temperatures and the effects of La Plata River, seem to limit their southern spread. Cold-temperate region is represented by 39 species; 24 of them also inhabited the southern Pacífic ocean. Many cold-temperate species (50%) reach lower latitudes in the Atlantic (42°S or less), but in deep waters. Information on geographic distribution, life cycles, and economic importance of warm-temperate species is given. The atlantic and pacific decapod fauna of southern South America have a similar number of species and families, but differences in their composition are detected

Se mencionan 243 especies de crustáceos decápodos en el Atlántico sudoccidental, entre los 25º y los 55°S, pertenecientes a 49 familias. El suborden Dendrobranchiata incluye 6 familias con 23 especies. El suborden Pleocyemata consta de 10 familias con 35 especies de Caridea, 1 familia con 2 especies de Astacidea, 1 familia con 1 especie de Palinura, 2 familias con 7 especies de Thalassinidea, 8 familias con 44 especies de Anomura y 21 familias con 131 especies de Brachyura. En la región templado cálida del Atlántico sudoccidental se han registrado 200 especies; el 73% de las mismas se extienden hacia el norte de la región en estudio ("especies tropicales"), el 27% habitan entre las latitudes de Rio de Janeiro y Tierra del Fuego. De éstas, 44 son endémicas. El número de especies tropicales disminuye con el aumento de la latitud, aunque con diferentes patrones en distintas familias; la expansión hacia el sur parece estar limitada por cambios ambientales entre los 29°-35°S, principalmente el descenso de la temperatura invernal y el efecto del Río de la Plata. La región templado-fría incluye 39 especies, 24 de las cuales habitan también el Pacífico sur. Muchas especies templado-frías (50%) alcanzan latitudes menores a 42°S en aguas profundas del Atlántico. Se resumen los datos referidos a la distribución geográfica, ciclos de vida e importancia económica de las especies de la región. El número de especies y familias es similar al que se encuentra en las costas del Pacífico, entre las mismas latitudes, pero existen diferencias en la composición faunística