STRUCTURE AND ORGANIZATION OF THAU LAGOON IN TERMS OF BENTHIC FAUNA (MACROFAUNA-MEIOFAUNE) - RELATIONS WITH CONFINEMENT

The biogeological organization of Thau lagoon was investigated through the granulometric analysis of surficial sediments and study of the qu alitative and the quantitative distribution of benthic macrofauna and meiofauna. These show clearly that the lagoonal system is organized ac cording to confinement as conceived by Guelorget and Perthuisot (1983 a; 1992), which depends upon the rate of exchanges with the open sea a nd the hydrodynamic pattern of the basin. The latter appears to be com posed of a pair of lagoonal subsystems separated by a hydrodynamically unstable barrier. The northern subsystem displays the classical conce ntric organization of Mediterranean lagoons with a clearly defined hyd raulic umbilicus. The southern subsystem displays a transverse origina l organization due to a large zone of exchanges with the sea through t he sand bar.The basin is globally subject to only slight confinement, but displays signs of organic matter accumulation due to the intensifi cation of shellfish culture.