Catchment wide disturbances and local land use pressures often result in upper estuaries being a focal point for the degradation of physical habitats, reduced biodiversity and poor water quality. Many environmental restoration projects in estuaries focus on improving the physical structure of estuaries. This often comprises bank stabilisation works to control erosion, in conjunction with bank exclusion and riparian revegetation. The construction of fillets using rock and timber are common restoration techniques in estuaries to stabilise banks and reduce wave energy that aim to promote mangrove growth. Restoration success usually focuses on riparian measures such as the reduction of bank erosion and survival of seedlings. However, rock fillets can also improve intertidal habitat for estuarine fauna by reducing fine sediment loads and promoting the creation of intertidal habitat.
Rock fillets were installed in the Kalang estuary on the NSW mid north coast in mid-2017. We sampled benthic macroinvertebrate and meiofaunal communities before and after restoration works using a BACI design (Before, After, Control, Impact). Benthic invertebrates were assessed six months before and six months after the construction of rock fillets and compared with nearby control (actively eroding), reference (mangrove forest), and remnant EEC (coastal floodplain) sites. We found that the diversity and abundance of macroinvertebrates and meiofauna communities significantly increased at the treatment site. This suggests that bank stabilisation structures can significantly improve instream habitats and assessments that focus on riparian variables alone miss important ecosystem services and biodiversity improvements provided by these structures.