biological diversity and tropical forests in tunisia - PART

3.1.4. Culf of Cabes: Rass Kaboudia to the Libyan border
The majority of the coastline south of Rass Kaboudia forms the Culf of
Cabes. The coastline of the gulf consists of narrow, shallow, muddy
intertidal flats or sandy beaches. From Ras Kaboudia to approximately
5 km south, near Amra (~riba), the shoreline is steep enough to prevent
large areas from being exposed durkng low tides. The shoreline soon
levels 'out and most of the rest of the coastline to Jerba (except 25 km
near Cabes, parts of Caraet bou Crara, El Kantra to Zareis and Rass ~djkr)
is typified 'by intertidal flats. Large expanses occupy more than 25,000
ha, of which c.14,600 ha is situated at Kneiss (van Dijk 1986).
Dunes cover much of the shore inland of the intertidal flats and
beaches, except at the gypsous cliffs of Tar-el-Jorf and Bou Crara and the
calcareous cliffs of Ras Maamour to Zarzis en-0thman 1973). Inside the
littoral dunes, long narrow aebkhets often form, such as sebkhet Dreiaa,
south of Skhira.
Flat coastal plains subside very gradually into the sea. At some
points the water is less than 50 m deep for more than 100 km from shore,
and at no point is the water over 100 m deep within 100 km from shore.
The flat shelf is so extensive that the -200 m isobathe is 250 km from
shore en-0thman 1973). The shallow water amplifies the weak tidal
influences of the Atlantic ocean and results in tidal amplitudes of up to
2 m in the Gulf of Gabes (Van Dijk 1986). Surface currents consist of
water with a constant temperature (14 - 15' C) and relatively low salinity
(37.3 - 37.9 ppm) throughout the year (Van Dijk 1986). Near the shore,
the shallower waters are usually warmer (c.19.5' C) and saltier (38 ppm).
The sabtropical Saharan influence is much stronger at the Culf of
Gabes thac along the coast to the north. Temperatures remain mostly
betweec 20 - 30 C from May to August and the average yearly precipitation
is less thac 200 mm, most of which falls between September and March.
Sirocco wicds occur aboat 35 days per summer, and rapidly dessicates the
vegetatioc. Bioclimates range from Semi-arid Inferior by Rass Kaboudia,
to Arid Superior by Sfax and Arid Inferior south of Sfax. Due to the sea,
bioclimates are all of the mild winter variant.
A. Vegetation
Lowland halophile vegetation and vegetation found on littoral sands
are similar to that of corresponding areas north of Rass Kaboudia (see
Section 3.1.3~). However, the vegetation found on higher, less saline
ground differs significantly from that on the coast to the north. There
are essentially no forest or maquis associations along this section of
coast, but there are some oasis (see Section 3.7). Climax vegetation
types are those characteristic of secondary steppes of low plains and
Subdesertic Littoral Steppes. The actual associations present are those
typical of degraded lands (Le Houerou and Fromect 1969).