Spatial Gradients of Dry-Season Water Physico-chemical Parameters and Seasonal Dynamics of Fish Community Across Mangrove-Agricultural Landscapes in the Irrawaddy Delta, Myanmar

Increasing agriculture in the Irrawaddy Delta of Myanmar is associated with a substantial loss of mangrove cover and fragmentation, with potential consequences for estuarine fish species richness and abundance. To assess these relationships, we surveyed 24 sites across a gradient of mangrove loss, mapping mangrove canopy cover within a 500-meter analytical window around each site. Dry-season water profiles revealed that sites with higher mangrove cover exhibited substantially higher salinity and dissolved oxygen (DO) levels, alongside lower water temperatures, compared to agricultural sites. Fish species richness and abundance (Catch Per Unit Effort, CPUE) were consistently higher in mangrove-dominated sites across seasons, closely reflecting these localized environmental patterns. Non-metric Multidimensional Scaling (NMDS) ordination (Stress = 0.135) and Redundancy Analysis (RDA) revealed highly distinct, habitat-specific spatial segregation in species composition, with the 500 m mangrove cover acting as the strongest predictor among tested environmental variables structuring the fish community (F = 2.892, p = 0.002). These findings suggest that localized mangrove retention is associated with stabilized water physico-chemical conditions, which correlate with higher fish species richness and abundance. Consequently, protecting localized mangrove zones around estuarine networks represents a pragmatic, operationally realistic target for sustaining regional fisheries in data-limited deltaic landscapes.