Optimising ecological and engineering outcomes of hybrid mangrove living shorelines using life-cycle informed restoration

Living shorelines recover coastal ecosystems, provide coastal protection, and offer co-benefits that include biodiversity enhancement, carbon sequestration, water purification, as well as supporting cultural and social values. Due to this, there is increasing interest in the uptake of living shorelines over conventional engineered structures (e.g. seawalls, breakwaters) that face growing economic and environmental pressures. Although complex coastal ecosystems (e.g., mangroves, biogenic reefs) can affect hydrodynamic processes and sediment transport once established, natural recovery in areas where these habitats have been lost is challenging due to environmental changes and lack of self-facilitation processes. Living shorelines characterised by mangroves can include a structural component known as a hybrid approach that facilitates the environmental conditions required for mangrove establishment and/or persistence. In this study, we synthesised existing hybrid techniques extracted through a systematic literature review on global mangrove restoration into a morphological matrix based on their expected functions to support mangrove establishment. Second, we tested whether application of a subset of hybrid mangrove living shoreline techniques had been applied based on their expected function using a case study on Australia's east coast. By embedding ecological knowledge into the structural design of hybrid living shorelines, our findings highlight an opportunity to improve habitat establishment, optimise design outcomes, and reduce the risk of over-engineering. We present a decision tool to inform where scientific inquiry is important in the decision-making process. By considering a life-cycle informed approach, techniques can be selected that are more economical, garner stronger community support, and better achieve engineering and ecological objectives.