Application of functional diversity and hierarchical modelling to evaluate the macrobenthic community dynamics from river Thakuran, Sundarbans estuarine system

Abstract

This study investigates the impact of season-driven environmental shifts on macrobenthic assemblages from Sundarbans estuarine system using a combination of ordination and hierarchical modelling approaches. Hierarchical Modelling of Species Communities (HMSC) was applied to decipher species-environment and trait-environment relationships, assess functional traits, and species associations across pre-monsoon (PreM), monsoon (Mon), and post-monsoon (PM). Between class analysis depicted significant difference (p = 0.0001) in environmental parameters between seasons. A total of 119 macrobenthic species belonging to 6 phyla and 73 families were recorded during the faunistic survey. Polychaetes were observed as the most dominant taxa, comprising more than 50 % of the total species documented. Maximum macrobenthic species abundance of 21953 ind.m⁻² was observed during PreM that drastically reduced to 7948 ind.m⁻² and 7928 ind.m⁻² in Mon and PM respectively. Functional diversity indices displayed distinct spatio-temporal patterns, with higher values recorded in downstream stations (T7 and T8) during Mon. Furthermore, 20 functional traits in 5 categories were used to identify the prevalence of macrobenthic functional groups. Eight functional groups were identified, and mode of reproduction forming the node of divergence. Functional traits like large body size and deposit-feeder were prevalent during Mon, while suspension feeders and carnivores dominated during PreM and PM. According to HMSC results, fixed effects explained 96.7 % variance of species occurrence with percentage of clay and silt explaining most variance of 21.5 % and 12.2 % respectively. Furthermore, phosphate concentrations support species with asexual reproductive strategies and detritivorous feeding habits, at 0.80 support value. These findings highlight the importance of trait-based ecological modelling for understanding estuarine macrobenthic assemblages in response to seasonal dynamics.