Seasonality and crab activity affects the nutrients and physicochemical parameters in mangrove soils, thus, affecting the emissions of greenhouse gases, such as nitrous oxide (N₂O). Climate change may intensify rainfall and/or enhance droughts, affecting mangroves and associated biota. Crabs are natural soil bioturbators responsible for soil aeration and turnover. We evaluated the effect of Ucides cordatus crab on N₂O emissions from mangrove soils under a semiarid climate in Northeastern Brazil. Soil and gas samples were collected over the rainy and dry seasons in crab-naturally-bioturbated and crab-exclusion mangrove plots. We measured the soil’s pH, redox potential, and the total contents of carbon, nitrogen, and sulfur. We found higher N₂O emissions in the crab-exclusion sites compared to the bioturbated sites, as well as higher N₂O emissions in the rainy season compared to the dry season. The fluxes of N₂O (µg m⁻² h⁻¹) were 47.3 ± 9.7 and 8.9 ± 0.5 for the crab-exclusion sites, and 36.5 ± 7.8 and 4.5 ± 2.1 for the bioturbated sites (wet and dry seasons, respectively). The soil turning over by macrofauna led to lower N₂O fluxes in natural crab-bioturbated areas, and seasonality was the environmental factor that contributed the most to the changes in N₂O emissions. Broadly, anthropic activities and seasonality influence nitrogen fate, N₂O emissions, and ecological services in coastal ecosystems.