Comparative Study on Morphological, Biochemical and Distribution Pattern of Villorita Cyprinoides and Meretrix Casta Bivalve Shells in Vembanad Estuary, Kerala, India.

Abstract Estuaries are among the most commercially significant ecosystems on the earth, and they provide different habitats for numerous bivalve species. Clams are one of the most widely distributed and used aquatic bivalves, providing much more protein-rich food than mussels and oysters. Vembanad estuary is one of the richest clam fisheries coastal wetland in Kerala. The current study focused to compare the morphology and biochemistry of Villorita cyprinoides and Meretrix casta shells in Vembanad estuary. It also attempts to understand the variations in clam distribution caused by salinity fluctuations and sediment texture. According to the morphological and morphometric analysis, medium size shells were found in greater abundance in both species. A total of 306 nos of Villorita cyprinoides shells and 169 nos of Meretrix casta shells were obtained from the ten sample locations of Vembanad estuary. The density of Villorita cyprinoides (192 nos) shells is high in the southern part, and Meretrix casta (108 nos) shells are abundant in the northern portion of Vembanad estuary. Villorita cyprinoides has a negative linear correlation with salinity, as indicated by R² of 0.96. Meretrix casta, on the other hand, exhibits a positive correlation with salinity, with 0.94 linear coefficient. Villorita cyprinoides is more prevalent in clayey and silty sediments, while Meretrix casta is more common in sandy sediments. According to XRF analysis, calcium is the major oxide, with 39.47% and 38.72% elemental concentration in both species Villorita cyprinoides and Meretrix casta respectively. All other oxides were found only in trace amount.