These hydrological and sedimentological phenomena contributed
to the mangrove dynamics, through two opposite processes:
- They facilitated the spread of mangrove seeds and seedlings,
allowingmangrove regrowth on the sides of the river (SW andNW
Ambohibe, Beresaka, Andranopasy and Ankilifaly (Figs. 2 and 4).
- They contributed to the decay and to the death of mangrove
stands in some inland zones by the obstruction of channels.
Massive deposition of sediments led to branches or main courses
of rivers shifting. Between 1979 and 2000, the number of main
river branches fell from three to one, the two northern Mangoky
tributaries disappearing when they were filled with alluvium
(Figs. 2 and 5).