Study area

Sundarbans (21 320 and 22 400
N; 88 050 and 89 E), a natural mangrove forest, which is part of the
estuary associated with the river Ganges, on the northeast coast of
the Bay of Bengal, covering a total area of 9630 km2 out of which
4264 km2 comprising intertidal habitat. The area is covered with
thick mangroves, which can be treated as forest and aquatic sub
ecosystems (1781 km2). In 1985, the Indian Sundarban was
included in UNESCO’s list of world heritage site and in 1989; India
designated 9360 km2 of Sundarban as a law protected forest. In
1985 the area of Sundarban forestwas about 20,000 km2 but now is
only 9630 km2, out of which about 4200 km2 is mangrove forest. It
is the last frontier of Bengal flood plains, sprawling archipelago of
102 islands out of which 54 are impacted.
The tidal Islands at the central positions show elevations of the
order of 3e8mfrom mean sea level. The Ganges drains much of the
Sundarban slopes of the Himalayan and delivers an enormous
amount of sediment (324 x106 t annually) to the Bengal fan. The
Hooghly estuary, a tributary of the river Ganges, is a main artery of
the Sundarban mangrove ecosystem and is dominated by fresh
water discharge from Farrakka dam, which is located 285 km
upstream from the mouth of the river. Tide in the study area is
semidiurnal with tidal amplitude, i.e., 2.5e7 m. Mean current
velocities ranges between 117 and 108 cm s 1 during low tide and
high tide, respectively (Mukhopadhyay et al., 2006).