The fate of the San Blas mangroves is sealed. They will age and disappear. The dynamism of the Rio Santiago drainage system that has nurtured and replenished them for centuries is inconvenient to the goals of humans, and has been largely eliminated. Humans do not want rivers to flood, so they have lined the channel with flood control levees. Humans want to use the river water to grow tobacco, beans, tomatoes, and chilis, and build vast complexes of irrigation canals to divert it before it reaches the sea. Humans want electricity, and construct huge reservoirs that trap the sediment that would otherwise create new shallows along the coast. As long as there humans inhabiting the area at their current density these "wants" are unlikely to change in any significant degree.
The mangrove ecosystem is a transitional phenomenon. It can only exist on the fringe of a dynamic coastal morphology. The natural process is that forest increases on the ocean side, consolidating the sediments carried down by the river into the delta, and shrinks on the land side as sedimentation fills in the water channels allowing it to be colonized by dryland vegetation. In this manner the mangrove forest makes a slow, stately progress across the landscape.
Human activity has removed the rejuvenating supply of water and sediment, so the growth rate of the mangrove toward the sea has diminished. Indeed, there are significant areas that are experiencing coastal erosion that is eating into the mangrove front. Meanwhile, the tidal flux continues carrying sediment into the mangrove water channels, albeit at a reduced rate, thereby slowly, but inexorably filling them up. The inevitable result is a decrease in the surface area of the mangrove forest, even without any direct interventions on the mangroves themselves. If this situation continues long enough the mangroves will disappear entirely. There is no indication that there will be any alteration of this human behavior in the short term. From the point of view of the mangroves and the multitude of species that are dependant upon them there is a ray of hope. Every indication is that humanity is so quickly destroying the environmental systems upon which its survival depends that it will soon vanish, leaving what remains to get on with the great experiment. Species homo sapiens will likely go down as another Darwinian dead end that created a brief flash in the pan of the geologic record.
Given the bleak long term outlook, why should one be concerned about the state of the mangroves and the human activities that are taking place in them? Is it not as futile as rearranging the Titanic's deck chairs? There are at least two reasons. First, the rate of the mangrove forest's demise can be changed. There is a choice. We can either ignore it's plight and allow the fulfillment of human "wants" to quickly eradicate the existing remnants, or we can work to minimize further human impacts on the system, thereby prolonging the benefit stream for all mangrove users, both human and non-human, for many decades into the future.
The second reason lies in the optimism found at the core of human nature. No matter how bleak the outlook there is always hope. Who can say that humanity will not experience an epiphany that will change the present headlong rush to disaster? Preserving the mangroves for as long as possible will maximize the opportunity for such an unlikely event to occur. Clearly, if we don't try, it won't happen.
The first step is to learn more.