I think it will depend on what you are looking for. If it is for a number of years, you will need to collect data from the field and analyze it then mapping it. Other ways of looking at it would be the use of satellite imagery of the coastal area in a target timescale.
Time series image analysis (Remote sensing) may helpful for you. For satellite image, you can use Landsat image. And for Software, you can use ArcGIS, ERDAS Imaging or QGIS etc.
I'd recommend doing some research first on what is available (for example start with online search 'mangrove mapping using remote sensing') as a lot of work has already been done & you'll need to select a method that suits your project requirements.
One of the key issues with time series mapping using remote sensing is making sure that the baseline mapping is consistent so you are mapping change in the feature of interest and not changes in the way the data is captured.
http://www.eumetrain.org/data/3/36/print.htm
http://gisgeography.com/spectral-signature/
Depending on what you need (content, scale, extent) here may already be some data to start work with..
If you can see this document Comisión Nacional Forestal. (2016). Inventario Nacional Forestal y de Suelos. Procedimientos de muestreo. Zapopan, Jal., México: CONAFOR. pgs 210-2017, and National Inventory of Mangroves: coverage and distribution CONABIO