Seascape connectivity with mangroves positively influences tropical saltmarsh blue carbon stocks

Despite exponential increase in global blue carbon studies over the last decade, critical knowledge gaps remain regarding the role of drivers such as seascape connectivity that mediate the carbon storage in tropical saltmarsh ecosystems. The present study addresses this knowledge gap by investigating how seascape-level drivers, specifically connectivity between ecosystems, sediment traits and plant biomass, influence carbon stocks, in connected versus individual tropical saltmarsh (Porteresia coarctata and Myrostachia wightiana) meadows. This study compared the influence of connected saltmarsh meadows (adjacent to mangroves) with individual saltmarsh meadows across four tropical locations and assessed their carbon (C) and nitrogen (N) content in sediment, biomass, various plant traits and C stocks. Stable isotopes tracers (¹³C and ¹⁵N) were used to determine the C contribution from autochthonous and allochthonous carbon sources. Connectivity resulted in increased of plant shoot density, and biomass by 1.7-fold and 1.5-fold respectively than individual saltmarsh meadows. Connectivity resulted in 2.3-fold higher C_org stocks (sediment + biomass) than individual meadows. Connectivity increased the below -ground biomass contribution to sediment C pool by 2 to 10 %, whereas the combined contribution of mangrove leaf biomass was between 7.8 and 26.8 % in both saltmarsh species probably depending on the mangrove density, leaf litterfall and organic matter trapping efficiency of these saltmarsh species. The study underscores the positive role of seascape connectivity with mangroves in enhancing the carbon stocks in tropical saltmarsh ecosystems.