Response patterns of benthic functioning in tropical estuaries under varying scales of anthropogenic perturbations

Multifarious human pressures can adversely impact estuaries' benthic functioning, yet this is less understood in tropical regions. This study examined the macrobenthic functional patterns of three differentially impacted tropical estuaries to elucidate the response of traits to stress, link taxonomical and functional structures and metrics and identify influential environmental factors of benthic functioning. Taxonomic and functional indices were positively correlated, suggesting that estuaries were vulnerable to functional shifts following species extinction due to environmental changes. Traits like 'feeding behavior', 'position in sediment', 'lifespan' and 'ecological sensitivity' were found effective markers of stressed zones, where resistant modalities predominated in response to disturbances. Rao's Quadratic entropy (RaoQ) successfully distinguished estuarine zones based on pollution levels, while other functional metrics (richness, evenness, divergence) exhibited anomalous trends. The complementary RLQ and Fourth-corner analyses could effectively discriminate disturbed zones in Ulhas, the estuary with a strong pollution gradient. Specific bivariate functional trait-environmental factor relationships were stronger in more impacted estuaries, while they were less so in the less impacted estuary. Environmental filtering facilitated trait clustering in polluted zones and trait divergence in less polluted estuaries. Salinity, pollutants and granulometry were the major influential factors of functional metrics. The Pressure Index was negatively correlated with RaoQ index only in Ulhas indicating that the discriminatory abilities of functional traits and indices were most effective in highly polluted estuaries. These results provide valuable insights to support sustainable management practices for these critical coastal ecosystems.