Assessment of benthic ecological quality status of small estuaries using multiple biotic indices in East China Sea

With the progress of industrialization and urbanization, human activities are exerting increasing pressure on estuarine ecosystems. Accurately assessing the of benthic ecological quality status (EcoQs) has become increasingly critical for the management and restoration of estuarine systems. This study investigates the community structure and spatiotemporal patterns of macrobenthos in two small estuaries (Oujiang estuary and Aojiang estuary). We use five macrobenthos-based biotic indices (Shannon-Wiener diversity index (H'), the AZTI marine biotic index (AMBI), multivariate AZTI marine biotic index (M-AMBI), benthic index (BENTIX), Benthic Opportunistic Polychaete Amphipoda index (BOPA)) to assess the EcoQs. and examine the consistency among indices. A total of 148 macrobenthic species were recorded in the two estuaries. Mollusks and polychaetes dominated in the intertidal and subtidal zones, respectively, with pollution-tolerant and opportunistic species prevailing across both estuaries. The five benthic indices exhibited low consistency in their ecological assessments. EcoQs were inconsistent at over 50 % of the stations. Among the stations with relatively consistent ratings, the majority reflected acceptable EcoQs. Both AMBI and BENTIX tended to overestimate EcoQs, whereas the H' significantly underestimated it. The discriminative capacity of BENTIX was notably limited in areas subjected to mild pollution or low disturbance. M-AMBI showed correlations with multiple environmental factors and effectively reflected gradients of environmental change within the estuaries. Compared to the other biotic indices, M-AMBI appears to be more suitable for evaluating benthic EcoQs in the study area.