Genesis of islets in Bizerte Lagoon (Tunisia) : settlement of pioneer species

Abstract

This work aims to provide preliminary results on the formation of a new ecosystem incorporating a sebkha and sand islets (lido) along the shores of Bizerte Lagoon (North-eastern Tunisia). This neo-ecosystem is the result of hydrodynamic and geomorphological modification of the lagoon coastline in its North-Eastern part near Menzel Jemil city. This last modification on the lagoon coast confirms the increasing anthropogenic activities, especially with the enlargement of the industrial zone in the area. This latter factor, coupled with the modification of the main river that feeds the lagoon (Oued Jedera river), have a direct consequence on the modification of the coastal drift (in terms of direction, amplitude and periodicity) in the North-Eastern part of the lagoon, which resulted in the formation of littoral cords parallel to the lagoon shore. This new formation of a "lagoonar islet" has resulted into a whole coastal ecosystem, always dynamic and still in formation. This has allowed the settlement of new submarine biodiversity, and a noticeable terrestrial biodiversity of both flora and fauna. Among this, ornithological diversity was prominent. Thus, this work proposes to follow the genesis of this biodiversity new area, parallel to the process of the ecosystem dynamics in progress. Indeed, the consecutive two years of monitoring on fauna and flora, particularly the pioneer species dwelling on it, pointed out the regular presence of 17 bird species, among which Sternula albifrons. This bird species is using the islet as a nesting site. Studies are already underway to confirm the nesting of some others among these avifauna species. The preliminary list of plant species dwelling on the islet extends to 18 species. Among these species, five Chenopodiaceae, five Asteraceae, two Brassicaceae, two Fabaceae, two Poaceae, one Caryophyllaceae (Rhodalsine geniculata) and one Juncaceae (Juncus maritimus). The thanatocenosis seen on the sandy coast shows a large presence of Tellina planata, Ruditapes decussatus, Pinna nobilis and the invasive species Pinctada radiata, which biomass became increasingly important in the Bizerte Lagoon.