Benthic community resilience in two differently impacted tropical estuaries: Taxonomic vs functional approaches

Abstract

Estuaries experience incessant modifications due to various stressors causing shifts in the benthic species community structure and ecosystem functioning. Two tropical estuaries along Northwest India, exposed to varied intensities of anthropogenic perturbations, were sampled seasonally for two consecutive years. Specific aims were to assess, compare and link the macroinvertebrate taxonomic and functional structures, to evaluate the resilience of estuarine benthic ecosystems by employing the multiple-trait approach and to identify major influencing environmental drivers for patterns discerned. Taxonomic and functional compositions in both the estuaries produced varied segregations along the estuarine zones, driven primarily by natural estuarine gradients like salinity and sediment grain size, despite extant anthropogenic stressors. Multiple traits contributed to the variance in benthic functioning. The Biological Trait Analysis (BTA) revealed that both the estuaries had similar trait compositions in the lower zones, while the middle and upper zones of each estuary presented different permutations of traits. The functional complexity at different estuarine sections was influenced by the variability in taxonomic composition and species dominance. However, relationships between Functional Diversity (FD) and species diversity were equivocal, signifying that taxonomic diversity may not be an efficient proxy for benthic functioning. As the zones had differential stressors and disturbance acts as a filter, discrete functional trait profiles of opportunistic traits were visualized along the potentially impacted zones. Thus, the less impacted lower zones had multiple traits, while the mid-upper zones that were subject to both anthropogenic and natural stressors had fewer traits. A more consistent functional structure, higher functional redundancy and substantial proportion of recolonisation traits (small-sized, short-lived, motile forms) suggested better resilience in one study estuary than the other one. Our study advocates that the inclusion of both taxonomical and functional metrics can provide in-depth inferences related to the macrobenthic community resilience and this coupled approach is imperative for effective future management programs.