Abundance, Distribution and Diversity of Macrobenthos in Chittagong Coast, Bangladesh

Macrobenthos are an essential element of marine and coastal ecosystems. This study intends to examine the seasonal taxonomic structure of macrobenthic species and determine the physicochemical properties of sediments to understand their role in influencing macrobenthic communities along the coast of Chittagong, Bangladesh. A total of 66 species belonging to 30 families and ten classes were recorded in the study areas. Their density was remarkably higher in the dry season, with a major representation of polychaetes, especially Capitellidae and Nereididae. Capitellidae showed maximum densities at Salimpur Mudflat (787.04 ind. m⁻²) and Salimpur Salt-marsh (625.00 ind. m⁻²) during the dry season, while an exceptionally high peak was recorded at Salimpur Salt-marsh in the wet season (1180.55 ind. m⁻²). Capitellidae remained dominant during the wet season. The values of the biodiversity indices were higher in the dry season compared to the wet season in most of the sampling stations during the study period. According to the habitat, the density of capitellidae was found to be higher in mudflat areas, especially in Salimpur, than in salt-marsh areas. Sediment properties showed noticeable seasonal variations. Electric conductivity, organic matter, and grain sizes were higher in the dry season sediments of mudflat areas, whereas sediments of salt-marsh areas were dominated by sands. Macrobenthos density was positively correlated with electric conductivity (r = 0.77), silt (r = 0.62), and clay (r = 0.45) contents and strongly negatively correlated with sand contents (r = −0.79). Regression analysis also confirmed that sand percentage (R² = 0.56) with p = 0.048 and electric conductivity (R² = 0.49) with p = 0.053 are potential governing factors of macrobenthos density. This study highlights the ecological significance of sediment characteristics in shaping macrobenthic communities and provides a scientific foundation for coastal biodiversity conservation and management policies in Bangladesh.