Variability in the structure of epiphytic assemblages of Posidonia oceanica in relation to human interferences in the Gulf of Gabes, Tunisia.

In this study we evaluate whether the pattern of spatial variability of the macro-epiphyte assemblages of leaves of Posidonia oceanica differed in relation to anthropogenic interference in the Gulf of Gabes (southern coast of Tunisia). A hierarchical sampling design was used to compare epiphytic assemblages at 5 m depth in terms of abundance and spatial variability at disturbed and control locations. The results indicate that the biomass and mean percentage cover decreased at locations near the point of sewage outlet in comparison to control locations. These losses were related to the distance from the source of disturbance. This study revealed that the diversity is reduced in disturbed locations by the loss of biomass and the mean percentage cover, explained by means of a multiple-stressor model which plays an important role in the macro-epiphytes' setting. It is urgent to propose the best management plans to save the remaining P. oceanica meadow in the Gulf of Gabes and its associated epiphytes.