The intertidal crabs Neohelice granulata and Cyrtograpsus angulatus are common on the south-west Atlantic coast but they rarely share the same microhabitat. They are similar in size and in several life history traits which promote competition. Neohelice granulata is the dominant species in intertidal soft-sediment and salt-marsh areas from southern Brazil to northern Patagonia Argentina, where it forms extensive burrowing beds. Its burrowing activity affects sediment characteristics as well as the infaunal community. When both species coexist N. granulata constrains the distribution and modifies some population characteristics and burrowing behaviour of C. angulatus. However, C. angulatus live in burrows forming dense burrowing beds in soft-bottom intertidal areas where N. granulata is absent. Where both species coexist, C. angulatus rarely constructs burrows and N. granulata clearly dominate soft-sediment areas forming conspicuous burrowing beds. This suggests that these crab species could have similar ecological roles in some effects on sediments related to burrowing activities. In this study, we experimentally compare their effects on sediment characteristics and infaunal community. The results of the experiment showed that C. angulatus modify sediment water and organic matter contents and grain size–frequency distributions similarly to N. granulata. Neither N. granulata nor C. angulatus affected the mean abundance of infaunal organisms during the experiment but their variances showed the same patterns in many cases, indicating similar effects. These results indicate that C. angulatus can modify sediment characteristics similarly to N. granulata, and has similar interactions with infaunal species.

In this note, we registered the occurrence of shell diseases and carapace abnormalities in a natural population of Neohelice granulata from a tropical mangrove forest, in South America, as a part of a wide ecological study. The occurrence of 32 adult crabs (1.77%) with black or brown spotted shells, or deformities on the carapace was registered, collected in the autumn and winter seasons. The low prevalence of shell diseases and abnormalities in this natural population is considered normal and probably caused by injuries occurring during the moult period of crabs.

Neohelice granulata is a crab found in salt marshes and mangroves of the south and south-eastern Atlantic coast of South America. Reproductive biology was studied by taking samples for two years at two salt marshes—‘Prainha’ and ‘Ilha’—in the estuarine region of Patos Lagoon (southern Brazil). Ovigerous females were found most of the year in both salt marshes with average CW ranging from 18.5 (Prainha) to 22.8 mm (Ilha). A significant linear relationship was found between log(CW) and log(number of eggs). Average size at the onset of maturation was 14.9 and 14 mm at Prainha, for males and females, respectively, while at Ilha it was 18.2 and 16.8 mm, for males and females, respectively. Results provided evidence of significant differences in reproductive traits between populations of the two salt marshes. Differences are likely related to the higher organic matter content found in the sediment from Ilha.

Large parts of the south-western Atlantic soft bottom intertidals are inhabited by the burrowing crab Neohelice granulata (previously known as Chasmagnathus granulatus) and the mud crab Cyrtograpsus angulatus, but adults rarely coexist in the same microhabitat. We describe the influence of burrows of N. granulata on the recruitment dynamic of C. angulatus and the effects of different ontogenetic stages of N. granulata on survival of recruits of C. angulatus. A two summer sampling shows that N. granulata burrows facilitate settlement of both species. To evaluate the mortality of recruits inside burrows, we performed a field experiment with juvenile and adult crab exclusion cages and inclusion of juveniles or adults of N. granulata. The results showed differences in crab sizes between treatments, due to predatory interactions that depended on prey size. When only juveniles of N. granulata were present, the higher mortality of C. angulatus was observed in smaller crabs. However when adults of N. granulata were present, larger juvenile crabs are the ones that suffered the highest mortality. These results show that adults are preying upon larger juveniles (of both species) reducing the mortality of the smaller ones that are preyed by the larger ones. We also measured emigration from these burrowing assemblages using bidirectional pitfall traps which showed that C. angulatus juveniles are leaving the burrows towards the subtidal. Here we demonstrate that N. granulata have positive and negative effects on the settlement of C. angulatus. These results highlight the importance of including stage-dependence relationships to analyse species interaction in marine ecology field works.