## 3 Results and Discussion
### Climate Change Impact on Salt Marsh Composition and Ecosystem Services  
Considering the data available in the literature regarding the impacts of climate change on the primary production, and thus biomass and coverage area, it becomes evident that different climate change scenarios will have different impacts on the different salt marshes depending on the species abundance (Figure 6, Table 5). _Halimione portulacoides_ appears as the species more affected by the climate change scenarios considered, with an average reduction of 37% of its primary productivity. Thus, systems with a lower presence of this species (such as the Ria Formosa coastal lagoon), will be less impacted in the future by the climate change scenarios considered. As most of the system is dominated by plant species with a C\({}_{3}\) photosynthetic metabolism, there is an apparent increase in salt marsh coverage under a CO\({}_{2}\) rise scenario. Underlying this fact is the physiological characteristics of C\({}_{3}\) metabolism, which under present-day atmospheric CO\({}_{2}\) concentration is not completely saturated and can thus still be improved under higher atmospheric CO\({}_{2}\) concentrations [14,16]. On the other hand, systems dominated by C\({}_{4}\) haplotypes (such as _S. maritima_) will have a minor increase in its coverage, as C\({}_{4}\) photosynthesis evolved to be at its maximum saturation rates under present-day atmospheric CO\({}_{2}\) conditions and thus no primary production improvement will result from rising atmospheric CO\({}_{2}\) and, in fact, can result in a stress condition for these C\({}_{4}\) haplotypes [14,16]. This is observed in the Ria Formosa coastal lagoon salt marsh abundance (Table 5) and species coverage change (Figure 6). Nevertheless, it is important to notice that all of the scenarios considered were applied individually and, e.g., the expected atmospheric CO\({}_{2}\) rise is known to be accompanied by an increase in atmospheric temperature, which might balance this apparent increase in salt marsh area due to increased atmospheric CO\({}_{2}\). On the other hand, salt marshes dominated by low marsh species, such as _S. maritima_ and _S. perennial_, are expected to have lower impacts from prolonged submersion driven from the expected sea level rise. This is the case of the Sado estuary and Ria Formosa coastal lagoon (Table 5, Figure 6), due to the natural adaptation of these low marsh species to tidal submersion and its physiological mechanisms to overcome this potentially stressful condition [12,53]. Regarding thermal stress driven from increased global warming, it is expected to have similar effects in all systems as the species more affected by this condition (_A. tripolium_ and _Salicornia_ sp. ), although among the most abundant species in the Portuguese estuarine systems, have a comparatively reduced coverage when compared to the remaining high-coverage species (Figure 6). Osmotic stress resulting from increased saltwater intrusion, soil salinization, and increased evapotranspiration due to global warming has a more pronounced effect in the middle and upper marsh species [49,52]. Thus, except for the Ria Formosa coastal lagoon, the majority of the transitional systems evaluated are dominated by woody succulent chemopods (Figure 6) that naturally inhabit the upper areas of the marsh that are less prone to submersion, but more affected by sediment evapotranspiration. These floristic inventories make these systems more prone to reductions of the primary productivity driven from increased osmotic stress driven from salinization and reduced water availability [48,51].