## 1 Introduction  
Estuarine and coastal transitional systems are key environments for ecosystem functions. While only occupying about 4% of total land area and 11% of oceans, they are some of the planet's most productive ecosystems [1]. These systems have attracted human population due to their easy access to natural resources, water-promoted trade, commerce, and waste disposal [2]. This inevitably led to anthropogenic impacts in these sensitive ecosystems. Among the most significant anthropogenic impacts to these ecosystems are land reclamation, dredging, pollution (sediment discharges, hazardous substances, litter, oil spills, eutrophication), unsustainable exploitation of marine resources (sand extraction, oil and gas exploitation, fishing), unmanaged tourism, introduction of alien species, and climate change [3]. Salt marshes are some of the most important ecosystems located in these coastal areas. Worldwide, marine angiosperms such as salt marsh communities and seagrasses are of ecological value in coastal environments, forming extensive intertidal or shallow water habitats, providing food, shelter, and important nursery areas for fish and macroinvertebrates [4]. Due to these important ecological services provided by salt marsh ecosystems to coastal zones, these systems rank among the most productive and valuable ecosystems on Earth [5]. This interest in ecosystem services and its valuation in both the research and policy communities has grown rapidly [6,7]. A previous study pointed out a global value for ecosystem services of about 33 trillion USD per year (in 1995 USD), a significantly larger value than the global gross domestic product (GDP) at the time [5]. This value was later admitted to being largely underestimated and thus increased the attention on the topic [5]. From this, the total value calculated for the ecosystem services provided by coastal ecosystems of the world, including natural (terrestrial and aquatic) and human-transformed ecosystems added 25,782.53 \(\times\) 10\({}^{9}\) USD per year [8], highlighting the important contribution of these ecosystems to the world budget. Salt marshes provide numerous ecosystem services, from coastal protection, flood and storm protection, water purification and flow regulation, air quality, maintenance of fisheries, seafood harvest, habitat/refugia, biological and pest control, carbon and nitrogen sequestration, and nutrient cycling, to recreational, educational, aesthetic, cultural activity, and ornamental setting values [9]. As noted, aside from pollution, eutrophication, and land claim [10], one of the major threats to salt marsh ecosystems is climate change-driven impacts, such as sea level rise, global warming, and atmospheric CO\({}_{2}\) increase [11]. These impacts are not only stressor specific, but also have very different effects on the different halophyte species that compose salt marshes, e.g., [10, 11, 12, 13, 14]. Additionally, Atlantic and Mediterranean ecosystems present a highly variable floristic composition in terms of both species number and abundance [15], conferring even more diverse feedback to any stressor affecting these systems. Several past studies have focused on the physiological response of Atlantic and Mediterranean haplotypes towards several climate change-driven stressors (such as osmotic stress to increased seawater intrusion and evaporation, warming stress, and increased atmospheric CO\({}_{2}\)), providing important insights on how each species will cope with the predicted and ongoing climatic changes, e.g., [12, 16, 17, 18, 19, 20, 21, 22]. Similarly, salt marsh ecosystem services estimation will also depend on the species composition and diversity. Nevertheless, the majority of studies have focused on an area-based salt marsh valuation, disregarding the different services provided by different floristic inventories [9]. One of the most investigated ecosystem services provided by salt marshes is its carbon sequestration ability, commonly referred to as blue carbon sequestration [23, 24, 25, 26].