Macrozoobenthic species composition and distribution in the Northern lagoon of Tunis

Abstract

1 - The macrobenthic community and abiotic parameters of a Mediterranean lagoon (Norhern lagoon of Tunis) was studied on automnal season during 1995, 1996 and 1997. 2 - Analysis of abiotic parametters revealed significant differences between stations. Variations of temperaturs and salinity reported in this studie show a gradient increasing in the direction circulating currents. Tidally driven marine waters cause a contnuous refreshment of lagoon waters, thus promoting oxygenation and nutrient loading. 3 - In total, 61 species were recognized, divided into seven zoo-goups with Molluscs always dominant. A noticeable increase in specific richness occured due to hydrologic and environmental improvement after sanitation in 1984-1988. 4 - Comparison of ecological indexes (specific richness, abundances, density, Shannon- Weaver indexes and evenesses) indicate significant variations in the spatial distribution and structure of benthic community, area A subjected to marine refreshment having a more deversified benthic fauna. In contrast, stations (B and C) remote from the sea display a neat faunal disturbance. 5 - Multivariate analysis help characterize hetergeneity in the benthic community structure of stations; thus, Echinodermata and Porifera phyla represent a great heterogeneity in species abundances. 6 - Physico-chemical properties of lagoon waters and macrobenthic faunal characters help identify three main sectors: i) a northeastern sector near the lagoon entrance, with newly introduced marine species (as Pinctada radiata); ii) a transitional sector which suffered pollution earlier to lagoon sanitation; iii) a sector with confinement and typically lagoonal, eurythermal and euryhaline species