*2.1. Study Area*

The study site is on the Gulf of Mexico in the state of Veracruz, between the coordinates 19◦33 and 19◦36 N and 96◦22 and 96◦24 W (Figure 1). Geologically, this area is a cumulative plain, formed by lacustrine, fluvial and biogenic sediments, occasionally combined with marine deposits [12]. The geomorphological evolution of the site is marked by long-term minimal marine sediment input and intense aeolian transport [15], which are both recorded during storm conditions related to northerly winds. Up until the 1970s, the aeolian transport had favored the formation of significant coastal dunes and active and fully mobile transverse dune fields. From the 1980s onwards, these dunes, particularly extensive on the north side of the rocky ledges (Figure 1), have stabilized naturally [16].

The lagoon of La Mancha is a brackish coastal lagoon, liable to siltation, with a surface of 126 ha, an average depth of 1.4 m and a maximum depth of3m[12,17]. The tides are mixed diurnal with a range of 0.69 m [18], and the lagoon is fed by two permanent river tributaries in the dry season (see Figure 1) and intermittently communicates with the sea [18]. The balance among sea water, rain and groundwater discharges regulates the hydrological variability of the lagoon [12]. The beach communicates with the lagoon in the lagoon inlet, and its natural opening and closing lead to modifications in the environment that alter the dynamics of the lagoon and cause changes in other surrounding ecosystems. The hydrodynamics of the inlet are very dynamic; in winter, a sandbar is formed, which naturally disappears again during the rainy season [9] (see Figure 2). The opening and closing of the lagoon inlet determine the migration of sediments, fish species and nutrients into the lagoon body [18]: when the inlet of the lagoon is closed, the water level of the lagoon rises and the salinity decreases; when it is open, the water level decreases and there is greater salinity and sediment accumulation [15] (see Figure 2). The lagoon inlet is also opened by local fishermen about three times per year in the dry season, in order to increase their catch by altering the normal flooding regime [12].

**Figure 2.** La Mancha: (**a**) beach; (**b**) the lagoon inlet closed by the sandbar in the dry season; (**c**) the open lagoon inlet in the wet season.

The climate of the study area has three pronounced seasons: the rainy season, from June to October; a period of "Nortes", winter storms that occur in the western Gulf of Mexico, from November to March; and a dry season, in April and May [12].

There is a wide variety of natural ecosystems in the study area, including mangroves around the lagoon (Figure 3a,b), coastal dune vegetation (Figure 3c), rainforest, tropical grassland, swamps, secondary vegetation, crop pasture and fruit trees. Mobile dune fields

were reported to be mostly vegetated with *C. punctatus* and *Palafoxia lindenii* in 2008 [16], but recently, *Schizachyrium scoparium* became dominant and replaced those species (Figure 3d).

**Figure 3.** La Mancha: red mangrove in the (**a**) lagoon and (**b**) lagoon margins (*Rhizophora mangle*); (**c**) beach and coastal dunes; (**d**) vegetated dune field.

As the study area forms part of one of the world's largest migratory corridors for birds of prey, La Mancha receives many visiting birds of prey, shorebirds and waterfowl species, as well as marine and terrestrial fauna [11]. The coastal wetlands of the study area provide ecosystem services, such as water filtration, temperature regulation and storm protection, and goods such as fish, as well [19].

Other ecosystem services provided are shelter for animal species in their youth, scenic value for ecotourism and serving as a carbon dioxide sink [12]. The productivity of the mangrove ecosystem can be measured in terms of its primary components, i.e., litter production [20], which is a source of nutrients for the species inhabiting this ecosystem. Utrera-López et al. [20] stated that the mangrove in the area of La Mancha has medium-high litter production, with annual values of 6.92–13.50 t/ha/year.
