Australian tidal wetlands and their response to sea-level rise

Abstract

This thesis examines the dynamics, trophic relationships, and climate change responses of mangrove and saltmarsh ecosystems through five interconnected themes, spanning over two decades of research from local to global scales. The work provides the first comprehensive treatment of Australian saltmarsh biogeography and demonstrates regional-scale mangrove encroachment into saltmarsh areas across four continents, linking this phenomenon to global climate change drivers. The research establishes that mangrove expansion in temperate regions is limited by dispersal barriers rather than physiological constraints. Through innovative use of stable isotopes and detailed surveys, the research reveals crucial trophic dynamics, demonstrating the importance of saltmarsh in supporting estuarine food webs. Key findings include the synchronization of crustacean and mollusc spawning with spring tides, creating unique feeding opportunities for commercially important fish species. This work provides the first detailed assessment of fish utilization patterns in temperate Australian saltmarshes. Analysis of the first Australian network of Surface Elevation Table-Marker Horizon stations, expanded to 289 installations, reveals critical thresholds in mangrove response to sea-level rise. Global synthesis of 478 monitoring stations demonstrates that while sediment accretion often keeps pace with sea-level rise, subsidence prevents surface elevation from maintaining equilibrium. The research pioneers the application of stable isotopes to determine carbon provenance in tidal wetlands, demonstrating the influence of geomorphic setting on carbon accumulation and revealing that moderate sea-level rise can enhance carbon sequestration. Novel long-term studies of biomass change provide some of the highest estimates of carbon accumulation in the literature. These scientific insights inform new management frameworks, demonstrating vulnerability thresholds under warming scenarios and developing predictive models for vegetation dynamics and carbon accumulation. The work has directly influenced policy developments, including the listing of coastal saltmarsh as an endangered ecological community and the development of emission abatement frameworks.