## 4 Discussion  
### N\({}_{2}\)O Emissions from Mangrove Soils are Controlled by Crab Activity and Seasonal Variation  
Our major finding was the decrease of N\({}_{2}\)O fluxes in the bioturbated plots compared to the crab-exclusion plots, as well as the enhancement of N\({}_{2}\)O emissions from dry to rainy seasons at both sites. In the crab-exclusion areas, the suboxic to anoxic soil microsites were preserved (because of the  
Figure 5: Principal component analysis (PCA) for the studied parameters N\({}_{2}\)O, Eh, pH, TOC, TN, and TS, and the effects of the factors Seasonality and Bioturbation. absence of crab bioturbation), stimulating higher N\({}_{2}\)O emissions. Similarly, during the rainy season, large amounts of water were drained to the estuary, reducing redox potential (Eh) and, thus, inducing higher N\({}_{2}\)O emissions. In addition, the absence or presence of bioturbation was driving the SOM dynamics in these mangrove soils. For instance, the bioturbated sites in the rainy season had lower SOM contents and a lower C:N ratio, probably driven by greater soil aeration and oxidation of organic compounds, leading to SOM consumption (Figures 3 and 5). Therefore, bioturbation is significantly important for keeping lower N\({}_{2}\)O emissions (compared to crab-exclusion areas), but seasonality has a key role in the dynamics of nitrogen and N\({}_{2}\)O emissions from mangrove soils in semiarid regions. Denitrification can be one of the major contributors for N\({}_{2}\)O production in mangrove soils [56]. In our study, the Eh values over the rainy season were mostly within the range associated to denitrification, whereas over the dry season, when N\({}_{2}\)O emissions decreased significantly, the Eh values were mostly within the range of nitrification (Figure 6). Mechanistically, comparing the presence or exclusion of crabs, the crab-exclusion treatment led to less soil aeration/oxidation (i.e., more reducing soil condition), which favored denitrification and higher N\({}_{2}\)O emissions, while the presence of crab bioturbation led to greater soil aeration/oxidation (i.e., less reducing conditions) and lower N\({}_{2}\)O emissions. Furthermore, the burrow densities measured during the study (mean: 3.3 \(\pm\) 1.2 and 2.3 \(\pm\) 0.6 during the dry and rainy seasons, respectively) were significantly lower than the densities measured for the same estuary by other studies carried out before 2012 (crab burrow density in the rainy season: 12 \(\pm\) 3 burrows m\({}^{-2}\); dry season: 38 \(\pm\) 12 burrows m\({}^{-2}\); [40]). Additionally, the densities were also lower than those obtained in other parts of the world, where authors have observed clear seasonal differences (Southern Brazil: 30-210 m\({}^{-2}\), [57]; Tanzania: 68 \(\pm\) 17 to 626 \(\pm\) 65 m\({}^{-2}\), [58]), indicating that a decrease in crab populations may affect N\({}_{2}\)O emissions. Crab burrowing activity allows oxidizing compounds (mainly O\({}_{2}\)) to enter throughout wet soils, aerating and oxidizing mangrove soils [40; 57]. Consequently, N\({}_{2}\)O emissions demonstrated a remarkable seasonal influence at both crab-bioturbated and crab-exclusion sites, with significantly higher N\({}_{2}\)O emissions during the rainy season compared to the dry season (Figure 4). These results are similar to N\({}_{2}\)O emissions from subtropical mangroves in India [59; 60; 61], but contrast with other studies that reported higher N\({}_{2}\)O emissions over the dry season [26; 62; 63], although some other studies in the pristine mangroves of India found no significant seasonal differences for N\({}_{2}\)O and CH\({}_{4}\) emissions [64; 65]. Therefore, mangrove ecosystems are mostly encountered in tropical and subtropical climate zones, occupying approximately 140,000 km\({}^{2}\)[66; 67; 68], so that mangroves are widely variable because of alterations in some of the key environmental parameters, including temperature, precipitation, seasonality, tidal regimes, and substrate composition and properties [26; 27].