Shipra Yadav1, Disha Yadav2 and Vipin Vyas3
Abstract
Freshwater molluscs serve as critical bioindicators of river health in tropical systems, yet comprehensive assessments linking their spatio-temporal diversity to hydrochemical gradients remain limited in Central Indiaâs Tapti River basin. This study investigates molluscan community structure across 12 sites (T1-T12) spanning 3,698 km², evaluating seasonal responses to water quality parameters amid monsoon-driven hydrology and anthropogenic pressures. Sampling occurred quarterly (post-monsoon, pre-monsoon, summer, winter) following Rapid Bio assessment Protocol (RBP) for wadeable streams using multi-habitat proportional kick-net surveys (D-frame net, 500 ?m mesh). Molluscan abundances were quantified, identifying 10 taxa through standard taxonomic keys. Hydro-chemical profiles (air/water temperature, pH, TDS, EC, DO, chloride, total/calcium/magnesium hardness) were measured in situ and via standard titration (APHA). Alpha diversity indices assessed community structure. Non-parametric Kruskal-Wallis tests evaluated spatial/seasonal variability (?=0.05), while PCA explored unconstrained gradients and CCA constrained species-environment relationships using Python 3.14.0. Diversity indices revealed pronounced seasonal structuring, with pre-monsoon peaks dominated by Tarebia granifera (36.59%), Filopaludina bengalensis (22.76%), and Radix auricularia (21.14%), contrasting post-monsoon mono specificity under stressed conditions. Kruskal-Wallis confirmed significant variability in abundances and parameters. PCA captured mineralization gradients, while CCA pinpointed TDS/EC and chloride/magnesium as dominant filters, explaining 100% constrained variance. Rare Angulyagra microchaetophora favored lowionic sites, tolerant Corbicula fluminea endured high hardness. These convergent analyses establish hydrochemical ions over thermal/DO factors as primary ecological filters driving beta diversity shifts. Prior Tapti studies offered macrobenthic inventories but lacked multivariate integration of seasonal patterns with ionic gradients. This work addresses that gap, positioning molluscs as precise biomonitors for pollution in monsoon influenced rivers and informing conservation of unionids and rare taxa.