Effectiveness of novel hybrid mangrove living shorelines is context dependent

Novel designs of hard structures can address challenges to mangrove survival and serve as effective hybrid nature-based coastal protection. However, a limited understanding of how structures affect mangrove survival may lead to ineffective applications of techniques across diverse environments, potentially resulting in mangrove planting failures. To test how ecologically engineered planting pods may enhance mangrove survival and facilitate natural recruitment, we deployed them at three sites experiencing erosion in Victoria, Australia. We then planted propagules and seedlings inside the pods and on the onshore side and monitored their survival and growth over time. Mangrove pods were effective in Altona (bare mudflats with sparse mangroves naturally present) when Avicennia marina seedlings were planted inside the pods and on the onshore side of pods and in the short term for those planted inside the pods at Lang Lang (bare mudflats without historical mangrove presence). However, they were ineffective for A. marina planted at Grantville (bare mudflats that previously supported mangroves), although they may facilitate natural propagule accumulation. Synthesis and applications. Our study highlights that the effectiveness of hybrid planting techniques is highly context dependent. The loss or absence of mangroves and other vegetative species may result in processes that challenge mangrove survival, in which the planting pods may not be able to overcome. These findings underscore the need for a better understanding of mangrove survival thresholds at different life stages and the ecological factors that influence them, such as historical mangrove presence. Refining the design of hybrid structures to account for site-specific factors will be key to improving their effectiveness. Rather than a stand-alone solution, these techniques should be considered as part of a broader range of interventions, integrated alongside other restoration and coastal protection strategies to maximise ecological and protective benefits across diverse coastal settings.