The lagoon of El Bibane (Tunisia) is a Mediterranean coastal area that is affected by an increasing human impact. Thus, an estimation of its biodiversity and an ecological quality assessment are very urgent. This study investigates the meiofaunal and nematode communities of the El Bibane lagoon both from a taxonomic and a functional point of view. Nematodes were the dominant group as is common in brackish water systems. The nematode community was made up of 62 genera in 22 families. Xyalidae, Chromadoridae and Cyatholaimidae were the richest and most abundant families. The taxonomic composition and biodiversity of nematodes were comparable to those found in other European and Mediterranean transitional areas. Both meiofauna and nematodes showed a clear subdivision between marginal and central areas. The central stations, represented by fine sediments and higher amounts of organic carbon, seemed to be characterized by low meiofaunal densities, nematode diversity and a strong dominance of 1B and 2B trophic guilds. These trends could be related not only to the grain size and organic load, but also to a possible influence of tidal currents that can transport pollutants in the central area of the lagoon coming from the adjacent coastal areas. Shannon diversity and life strategies are not always in agreement in defining the ecological quality, but an overall worse ecological quality was detected especially at S6. The results of this study are an important starting point for the future monitoring of the potential and actual human impact on the El Bibane area over time.

Organochlorines (including organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs)) were analysed in 10 surface sediment samples collected from the Bahiret el Bibane lagoon, which is one of the most productive lagoons and one of the most important active commercial fish traps in the southern Tunisia.The aim was to obtain information concerning the recent deposition of these compounds in this area, together with the levels, the distribution and any potential biological risk. Total concentrations of OCPs and PCBs in the sediments ranged from below the limit of detection (

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Trophic structure of free living nematode from Bizerte lagoon was tested by a microcosmic study after 30 days of exposure with 5 increasing doses of pharmaceutical penicillin G (D1: 3 mg L(-1), D2: 30 mg L(-1), D3: 300 mg L(-1), D4: 600 mg L(-1), D5: 700 mg L(-1)). Results showed significant differences between nematode assemblages from undisturbed controls and those from penicillin G treatments. Selective deposit-feeders (1A) or nonselective deposit-feeders (1B), very abundant in the control microcosm, were significantly affected and their dominance declined significantly. Epistrate feeders (2A) were significantly gradual increase for all microcosms treated with penicillin G, appeared to be more tolerant to the antibiotic and to take advantage of the growing scarcity of other trophic groups. Compared to the control microcosms, omnivorous-carnivorous (2B) was found to be higher in all treated microcosms, with the exception of those treated with D5. Trophic index (Σθ(2)) was significantly reduced in all microcosms treated whereas trophic ratio 1B/2A appears to be insignificant.

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