Assessment of diversity indices and ecological quality status using multiple biotic indices in the subtidal zone of Cheonsu Bay, Korea.

This study assessed the biodiversity and ecological quality status of Cheonsu Bay in 1993, 2010, and 2020 to evaluate the ecological impacts of dike construction and identify the most suitable biotic indices. Although various biotic indices have been developed to evaluate ecological quality, each reflects a limited aspect of ecosystem status. Hence, utilizing multiple indices is likely to provide a more comprehensive understanding of overall environmental conditions. To achieve this, we applied multiple indices such as BPI, AMBI, BENTIX, BOPA, Simpson diversity index, and taxonomic diversity indices. Most indices, except for taxonomic distinctness, indicated higher pollution levels in 1993 and 2020 compared to 2010. Spearman rank correlation analyses revealed that taxonomic diversity (Δ) reflected short-term environmental shifts, while taxonomic distinctness revealed long-term changes. This suggests biodiversity became richer after 1993 but declined sharply before 2020, coinciding with degraded water quality near the dike, especially since 2017 due to worsening conditions in artificial lakes such as Ganwol and Bunam. Among the indices, BOPA showed strong correlations with abiotic factors and was less sensitive to sampling size and taxonomic expertise, making it a practical and robust tool for ecological assessment in regions with fluctuating sampling conditions or limited taxonomic resources. In contrast, BENTIX showed weaker correlations, rendering it less appropriated for assessing the EcoQs in Cheonsu Bay. These findings highlight the need to manage freshwater quality in dike-formed lakes and support the use of multiple indices as a useful tool for evaluating ecological quality in coastal areas.