Impacts of Coastal Infrastructure Upgrades on the Endangered Marine Alga Nereia lophocladia

Coastal protection infrastructure is routinely upgraded to address structural degradation and rising sea levels. Such work can have unintended ecological impacts depending on the habitats and species involved, as well as the environmental mitigations undertaken. Here, we completed an 8‐year assessment of the impact of a breakwater upgrade at Coffs Harbour (Australia) on the abundance and size of the endangered marine brown alga Nereia lophocladia . Divers completed targeted surveys of N. lophocladia sporophytes at two breakwater and five adjacent natural reef sites before and after the construction work. Prior to the breakwater upgrade, N. lophocladia sporophytes were observed in each breakwater and natural reef site. Following the construction works, N. lophocladia sporophytes were rarely found on the breakwater and only on old rocks that existed prior to the upgrade. However, N. lophocladia continued to be found on natural reefs throughout the entire study. This environmental impact on N. lophocladia abundance was supported by a significant BA × CI interaction. The impact on N. lophocladia abundance did not, however, extend to differences in the size of sporophytes. As upgrades to coastal protection infrastructure will become increasingly common in coming decades and can impact threatened species, environmental regulations should be improved to ensure these upgrade works comply with the principles of ecological sustainable development.