Trophic analysis of female mangrove crabs at two sites from Southeastern Brazil (Rio de Janeiro)

The mangrove crab Ucides cordatus (Linnaeus, 1763) is a burrowing crab with an important role in mangrove nutrient cycling. The species holds major socioeconomic importance, generating yield for traditional and low-income populations. Despite its ecological and economic importance, there are few experiments in Brazil applying stable isotope tools to trophic crab classification, and even fewer considering females in the reproductive period. Females have different energy demands than males; studies examining C and N can reveal details regarding the differences. Hence, the present study is the first analysis of the delta C-13, delta N-15, and the C/N ratio in ovigerous females of two populations from Southeastern Brazil (Caceribu River - Guanabara Bay and Gargau mangrove - Paraiba do Sul River secondary estuary). The Caceribu mangrove is larger and is located in one of the most impacted bays in the world. In the Paraiba do Sul River region, the mangrove swamp is about ten times smaller, has a substantially lower population in the surrounding area, and is more influenced by agricultural activities. The delta C-13 analysis confirmed mangrove leaves as their main food source. The significant delta C-13 variation between the Guanabara and Paraiba do Sul estuary populations can be related to differences in food availability and nutritional value. However, the delta N-15 values can be related to the ingestion of other food items during the breeding season as well as the influence of anthropogenic mangrove degradation. At both study sites, the delta 15N values were higher than those observed in other mangrove crab populations and other herbivorous species. Significant (p < 0.05) isotopic differences were found among populations, suggesting variations in biogeochemical cycles that may be related to different environmental conditions between the sites.