An Ecological Study on Diversity and Composition of Macrobenthos at the Mouth of the Panadura Estuary in Sri Lanka with Special Reference to Water Quality

The ecological surveys with special reference to the dynamic of macrobenthos in the estuaries have not been comprehensively studied in Sri Lanka. Hence, this study was conducted to determine the correlation between physicochemical parameters and macrobenthos diversity and evaluate the pollution level in the estuary using macrobenthos diversity. Macrobenthos and bottom water samples were collected from randomly selected 19 sampling locations using a Grab and Ruttner sampler respectively from May to July 2015 every month. The results revealed that the macrobenthos consist of 13 families belonging to the phylum Mollusca and Arthropoda. The most abundant families were Planobidae (12200 individuals/m²), Veneridae (11400 individuals/m²), and Haminoidae (11000 individuals/m²). A total of 21 species belonging to 15 gastropoda; five bivalvia and one crustacea were recorded. The Venerid sp and Muricid sp were the most abundant (7240 individuals/m²) and the least abundant (520 individuals/m²) species, respectively. The highest species richness and diversity were reported at PE7, exposed to the canal which mainly carried hospital wastes. The lowest species richness and diversity were reported at PE6, consisting of an underlying rock layer, making it difficult for sediment collection. Macrobenthos diversity showed that the sampling locations were separated into several clusters. BOD and nitrate-nitrogen were the main physicochemical parameters affecting macrobenthos diversity based on the correlation analysis. CCA showed that macrobenthos assemblage was affected by the convergence of anthropogenic and natural stressors presented at the lower and upper estuary parts, respectively. Furthermore, H’ index and Pollution Tolerance Index in the estuary were between 2 and 3 and ≤ 20, respectively. Both indices confirmed that the water quality of the estuary was in poor condition. This study is important to determine the baseline information of the Panadura estuary’s macrobenthos.