Macrobenthic assemblages and its relationship with water and sediment quality in estuarine ecosystem of Sandwip Island, Bangladesh

Macrobenthic organisms are critical components of estuarine ecosystems, playing essential roles in sediment stabilization, nutrient cycling, and serving as bioindicators of environmental quality. The present study assessed the macrobenthic assemblages at Sandwip west beach and Banglabazar ghat, Sandwip Island, Bangladesh. Sampling was carried out in winter 2026 during low tide, and sediment samples were systematically collected, sieved, preserved, and examined in the laboratory for taxonomic identification. A total of 42 macrobenthic species were recorded, and total abundance was higher at Sandwip west beach than Banglabazar ghat. Arthropoda was the dominant macrobenthic group (47.2%) at Sandwip west beach, followed by polychaete (36.4%), crustaceans (7.4%) and gastropods (3.9%). Consistently, arthropoda (53.9%) also formed the dominant group at Banglabazar ghat, followed by polychaete (23.0%) and bivalves (15.7%). Ecological indices revealed higher community complexity at Sandwip west beach, with Shannon–Wiener diversity (H′, 1.22), Margalef richness (D′, 0.73), and Pielou’s evenness (J′, 0.74). Banglabazar ghat exhibited comparatively lower diversity (H′, 0.78, D′, 0.55, J′, 0.55), dominated by a few tolerant taxa. The higher nutrient content at Banglabazar likely supported fast-growing and tolerant taxa such as arthropoda and bivalves. These results underscore the ecological significance of Sandwip Island estuarine habitats and demonstrate the influence of sediment and water quality on macrobenthic diversity, abundance, and community structure. The findings provide baseline data for macrobenthic species compositions in the coastal areas of Bangladesh.