Population Dynamics of Fiddler Crabs (Uca spp.) in the Mangrove Creeks of Ondo State

Fiddler crabs of the genus Uca are ecologically significant intertidal crustaceans that contribute to sediment bioturbation, nutrient cycling, and trophic dynamics in mangrove ecosystems. This study examined the population dynamics, species composition, and habitat associations of Uca spp. in the mangrove creeks of Ondo State, South West Nigeria. Surveys were conducted at four sites in the Ilaje mangrove system during wet and dry seasons using timed observation counts within permanently marked 5 by 5 metre plots. Burrow density was counted as an indirect measure of population density, and specimens were captured for morphometric measurements. Habitat parameters including sediment type, organic content, canopy cover, and tidal inundation frequency were measured. Three Uca species were identified: Uca tangeri, Uca inversa, and Uca vocans. Uca tangeri dominated all sites, comprising 67 percent of total individuals. Population density was significantly higher at sites with high organic sediment content and intact mangrove canopy cover. Sex ratio across all sites showed male dominance, consistent with territorial behaviour associated with major claw display. Carapace width distribution indicated a bimodal size structure, suggesting two age cohorts recruiting from the previous two breeding seasons. Dry season surveys yielded higher surface activity and burrow density compared to the wet season, likely reflecting seasonal inundation patterns. The study recommends the use of Uca population metrics as a rapid biodiversity assessment tool in mangrove habitat evaluations in Ondo State. Keywords: Uca, fiddler crabs, mangrove, population dynamics, Ondo State.