Evidence of Seagrass-Saltmarsh Connectivity, and their Role in Coastal Seascapes – a Review

Abstract Seagrass beds and saltmarshes are two of the most ecologically valuable coastal habitats globally, providing a wide range of ecosystem services including carbon sequestration, coastal flood defence, and habitat provision for fauna. While both systems can co-occur within the same intertidal zone, they have often been studied in isolation, with less consideration given to how their functional connectivity may influence the continued ecological and geomorphological development of either system. This review collates evidence of the interactions and exchanges which establish functional connectivity between seagrass and saltmarsh habitats as part of a connected seascape. Following a semi-systematic literature review of 492 papers across two major databases, 31 papers were identified as providing evidence of functional connectivity between the two systems. Ten key interactions and exchanges were identified across six broad categories: blue carbon storage, habitat provision, hydrodynamic interaction, nutrient exchange, sediment exchange, and pollutant exchange. These connections were found to exert both positive and negative influences on the continued functioning of each habitat type, with their impacts varying considerably across spatial and temporal scales, from instantaneous local scale bed-marsh processes to long-term larger seascape-scale geomorphological change. These findings highlight the importance of considering seagrass beds and saltmarshes not as isolated systems but as connected components of a wider coastal seascape.