Assessment of the ecological status of benthic macroinvertebrate communities in the intertidal flats of Lake Shihwa following tidal power plant operation

Evaluating ecosystem restoration success is essential for understanding recovery processes and informing management strategies. This study assessed the ecological status of benthic macroinvertebrate communities in Lake Shihwa's intertidal flats using monitoring data, before and after the tidal power plant (TPP) commenced operations in December 2011 on the lake's enclosing embankment. Successional community dynamics were examined using taxonomic diversity indices, functional diversity indices, the inverse Shannon–Wiener evenness proportion (ISEP) index, and multivariate community analyses. Following TPP operation, species richness and biomass exhibited a gradual increase, ultimately rising threefold (from 7 to 23 species per 0.05 m²) and nearly doubling (from 110.5 to 241.6 g/m²) by 2023. By May 2015, functional richness in Lake Shihwa had reached levels typical of outer tidal flats. Post-operation benthic macroinvertebrate communities began to resemble those of the outer tidal flats, leading to their classification into two distinct clusters: Cluster A (pre-operation) and cluster B (post-operation). Notably, cluster B was further subdivided into early (B1) and late (B2) phases, indicating a gradual recovery process. The ISEP index indicated a marked improvement in the ecological health of Lake Shihwa since August 2012. Recovery was initially evident in lower intertidal zones with prolonged submergence and near the TPP, reflecting the impact of enhanced seawater exchange. These findings provide empirical evidence that tidal power-induced seawater exchange fosters biodiversity and ecosystem functioning, underscoring the importance of integrating taxonomic and functional indicators with long-term monitoring to ensure effective coastal ecosystem management.