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2.1. Oceanic Habitat in the TerritorialWater
The Exclusive Economic Zone (EEZ) of Sierra Leone covers
about 160,000 km
2
(Fig. 2.1, Tab. 2.1). The continental
shelf of the coast of Sierra Leone is about 100 km wide in
the north and tapers to about 13 km in the south towards
Liberia. The total continental shelf area covers about 30,000
km
2
and it is perennially enriched by nutrients from the
river networks, rendering the coastal environment a unique
ecosystem, which serves not only as an important habitat for
assemblages of marine organisms but also as a feeding and
breeding ground for most economically targeted species.
The Sierra Leone continental shelf can be divided into four
zones: the inner shelf, the middle shelf, the outer shelf and
the shelf edge. The shelf is characterized by relatively plain
surfaces inclined at angles of a few minutes and with an
average width of about 62 km. The outer shelf limit lies at
an average depth of 160 m. Each shelf zone is characterized
by different angles of inclination of the bottom and they lie
parallel to the coast in extensive strips. The inner shelf zone
could be traced up to depths of about 20–30 meter, and is
the zone of active wave activity. The geomorphology of this
zone is closely related to that of the adjacent coast.
2. Major marine ecosystems
Major relief features include the coastal valleys of the Futa-
Jallon highlands composed mainly of Paleozoic sands. The
coastal valleys are covered with weathered and erosion
products of the Futa-Jallon highlands. High temperature
and moisture enhance intensive chemical weathering.
The weathered material finds its way into rivers and is
carried to the coast, where it is transported alongshore.
The relief of the rivers catchments enables the movement
of large quantities of terrigenous material (mainly quartz)
into the ocean with waters of the surface flow. Other
sediment sources including biogenic sediment sources
are of secondary importance to the region. The chemical
composition of the sedimentary material has a wide range
and various types can be identified.
The middle shelf zone lies at depths between 20–30 meter
and 60–70 meter and is usually the widest part of the shelf
with a comparatively smooth surface. The bottom slopes
at an angle of some few minutes and at some locations
it is less than a minute. The outer shelf lies below 60–70
meter depth and is smaller in width with greater angles
of inclination of the bottom. In some parts bed rock is
common. This part of the shelf is commonly incised by the
heads of canyons.
Figure 2.1:
Maritime boundaries of Sierra Leone
(GRID-Arendal)