Changes in a macrozoobenthic assemblage after beach nourishment based on local knowledge in a brackish lagoon

Coastal habitat restoration is an essential component of conservation management, given the dramatic coastal wetland loss on a global scale. In the Five Lakes of Mikata-goko (western Japan), creation and restoration projects for nature-based coastal protection (semi-natural coastal habitats) have recently been implemented and initiated by the Nature Restoration Committee; however, their outcomes in terms of biodiversity have yet to be evaluated. In this study, spatiotemporal changes in macrozoobenthic assemblages were examined to provide insights into coastal habitat restoration using local knowledge (LK). Natural forces (winds and waves) were used to replenish sand along a sand-starved shoreline in the LK-based practice. The restored shallow-water habitat realized seasonally stable species richness and higher annual richness of brackish-water macrozoobenthic assemblages dominated by previously prevalent species, the Shijimi clam (Corbicula japonica) and the nereid polychaeta (Hediste atoka) compared with adjacent deep, unrestored sites. The changes in assemblage structure were likely due to seasonally stable low-salinity (mesohaline) and oxygen-rich conditions (dissolved oxygen concentration >5 mg L⁻¹), owing to the shallow water depth in the restored habitat. The results suggest that the beach nourishment practice partially and successfully mitigated historical habitat loss in the lakes and, hence, can provide suggestions for future mitigation practices of coastal habitat loss in estuaries.