Les fonds chalutables de la region nord de la Tunisie. 1.Cadre physique et biocoenoses benthiques

Abstract

The main characteristic of submarine morphology of the region North of Tunisia is its irregularity. The continental shelf often remains narrow, uneven and extended by a steep slope. Hydrological studies of the area reveal complex phenomena. This zone is essentially exposed to 2 opposite influences, one from surface Atlantic water which has its maximum extension during the winter and one from the eastern basin of the Mediterranean which seems to rise to the surface from spring to the summer. The contact of the 'Atlantic' and eastern Mediterranean waters forms an important area of mixed water dominant in the sector of the northern region. The heterogeneous nature of the sea bottom of this region explains the diversity of biocoenoses and their interpretation. Due to this particular type of morphology and the heterogeneous nature of the bottom of this region, the biocoenoses are numerous and broken into fragments with coral organisms being dominant. The light soil of the bottom is generally intercalated with substratum. The following areas are characterized by rich benthic population: corals on 'La Galite' sheld; algal development, northeast of Cap Zebib; abundance of Echinodermata (Antedon mediterranea) in the center of the Gulf.