3.2.2. Problems Affecting the Vegetation and Fauna

The structure and composition of the mangroves depend on a variety of factors, i.e., oceanographic, climatic, geomorphological, edaphic conditions, level and duration of flooding and sediment load [41]. According to several studies, the location of the mangrove forest affects the diameter and height of some specimens: they grow the most in areas protected from wave action. Moreno-Casasola et al. [42] also listed other variables relevant for mangroves in freshwater wetlands: salinity, water regime, conductivity and redox potential.

The dynamics of the vegetation around La Mancha are also clearly related to the opening of the inlet. When the inlet is closed and the water depth of the lagoon reaches <120 cm near the sandbar, the inlet opens naturally, discharging the supratidal accumulation through it. This ebb and flood exchange of water causes variations in parameters such as salinity and sediment distribution. The inlet dynamics are essential for the mangroves: if the inlet is permanently closed, there will be excessive flooding, and the mangroves will die due to a lack of oxygen in the stagnant water; if the inlet is permanently open, salinity will increase, also causing mortality [15].

Animal species are also affected by fluctuations in the water level and the salinity of the lagoon. For instance, oysters, and some other species, have high mortality rates when the water level increases and the oxygen in the water decreases, leading the fishermen to open the inlet, which causes imbalances in the lagoon dynamics [15]. Other environmental factors, such as evaporation and insolation, are <1% significant for mangrove development here [43].

Regarding the vegetation that develops on the coastal dunes surrounding the lagoon, there has been a decrease in the species which were previously most abundant. Previous studies indicated that although trampling on the dunes is infrequent, it is a relevant factor in the area, resulting in vegetation loss and compaction of the sand [31]. The seedlings are totally destroyed by crushing and flattening, leaving only bare soil in some cases [31]. The intensity of trampling is best seen on the steeper slopes, where the vegetation is detached and crushed [44]. The occurrence of this activity is not widespread, and trampling has a low impact; however, it may induce local extinction of some plant species [31].
