Mangroves and desalination of sea water
There has been a lot of research in this field which asserts that mangroves desalinate sea water.
Scholander (1968) concludes that this process in mangroves use an ultrafiltration mechanism in the roots of the plant where membranes extract freshwater which is taken up the plant.

 Scholander, P.F., 1968. How mangroves desalinate seawater. Physiologia plantarum, 21(1), pp.251-261.