Short-term effects of bank-stabilising restoration works on macroinvertebrate and meiofaunal communities in the Kalang estuary, NSW

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 stock exclusion and riparian revegetation. The construction of fillets using rock and timber is an increasingly common restoration technique used in estuaries to stabilise banks and promote mangrove growth to reduce wave energy. 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. Rock fillets and rock revetment 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 restoration works and compared with nearby control (actively eroding), reference (mangrove forest), and remnant Swamp Oak Floodplain Forest Endangered Ecological Community (EEC) sites. We found that the macroinvertebrate diversity and meiofaunal abundance 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 may miss important ecosystem services and biodiversity improvements provided by these structures.