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The study of copepod assemblages indicated the presence of 22 species and 12 families in the southern coast of Sfax, 20 species and 13 families in the northern coast and 14 species and 8 families in the Ghannouch area, with a dominance of Oithonidae (79, 51 and 43% in the southern, northern and Ghannouch coasts, respectively). The relative abundance and the richness diversity of Oithonidae were found to be the most relevant indicators of anthropogenic pollution. Oithona nana, Euterpina acutifrons and Acartia clausi differed significantly in abundance between these three areas under differing degrees of pollution. The study of the structure, composition and density of the copepod fauna showed that the southern coast was a pollution-resistant ecosystem (H′ = 1.49 ± 0.33 bits ind−1; 22 species; density = 51.375 ± 4.340 × 103 ind m−3) followed by Ghannouch area (H′ = 1.74 ± 0.28 bits ind−1; 15 species; density = 11.979 ± 5.651 × 103 ind m−3) and the northern coast, considered as a restored area (H′ = 1.95 ± 0.26 bits ind−1; 21 species; density = 6.516 ± 4.304 × 103 ind m−3). The three ecosystems can thus be classified according to their degree of resistance to the anthropogenic inputs based on the results of the physico-chemical parameters and the species diversity as follows: southern coast > Ghannouch area > northern coast.

The concentrations of selected dissolved trace elements (Ni 446-919 µg L -1 , Pb 383-1015, Fe 195-739, Cu 217-318, Cr 156-336, Zn 9-236, Mn 0-187, Co 0-310, and Cd 26-77) were assessed in the surface water of 30 stations belonging to three coastal areas along the Gulf of Gabes, i.e., the southern (stations 1-10) and northern (stations 11-20) coastal areas of Sfax and the Ghannouch area (stations 21-30) during October and November 2014. Results showed that dissolved metals in surface waters, which were analyzed by means of flame atomic absorption spectrophotometry, followed the concentration levels (Pb>Ni>Fe>Cu>Cr>Co>Mn>Cd>Zn) on the southern and (Ni>Pb>Fe>Cu>Cr>Zn>Mn>Co>Cd) on the northern coasts of Sfax, and (Ni> Fe>Pb>Cu>Cr>Zn>Co>Cd>Mn) in the Ghannouch area. In the southern and the northern coasts of Sfax, all analyzed metals were detected in 100% of sampled stations except Co, which was revealed in 90 and 80% of stations, respectively. However, in the Ghannouch area all analyzed metals were detected in 100% of sampled stations except Mn, which was revealed in 70% of stations. These trace elements, except for Fe and Mn, exceeded the safety limit of the USEPA water quality criteria for the protection of aquatic fauna and flora survival and their uses. The Sfax and Ghannouch coastal areas should be considered relatively polluted with metals (Zn, Ni, Pb, Co, Cr, Cd, and Cu). The elevated metal contents were attributed to anthropogenic waste inputs around the study area. The main sources of Ni and Co loading in the seawater were the SIAPE phosphoric acid and fertilizer plant and a waste water treatment plant located close to station 1. Whereas the fishing harbor of Sfax, which is situated on the southern coast (station 9), is the second source of high amounts of Cd, Mn, Cr, and Pb. This situation has led to serious human health risks and chronic toxicity caused by their potential bioaccumulation in some aquatic fauna such as shrimp, fish, crab, shellfish, mollusk, and cephalopoda.

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The Sfax southern coast (Gulf of Gabes, Mediterranean Sea) has been under increased anthropogenic pressure for many years. In the present study we investigated the effects of this anthropisation on the spatial distribution of copepod assemblages in relation to the physicochemical features of seawater at 20 stations sampled on 19 March 2013. Copepods represented 73% of total zooplankton abundance. Small planktonic copepods (<1.45mm), including pollution-tolerant species (e.g. Oithona nana, Paracalanus parvus, Harpacticus littoralis and Tisbe battagliai), proliferated exclusively in stations of ~0.5-m depth characterised by high coastal anthropogenic inputs. The largest copepod species were dominated by Calanus helgolandicus (1.45–2.5mm) in the offshore zone in depths of ~3m. Substantial numbers of Oithona plumifera (7.5%) were found at depths between 0.5 and 3m. Copepod diversity was significantly higher in the southern zone, which is less affected by sewage, than in the northern zone, which was subjected to higher pressure (Shannon–Wiener index H′=1.5–2.5 and ≤1.5 bits individual–1). A shift in the planktonic copepod community between the two zones was linked to deterioration of water quality, with higher phosphorus levels, turbidity and chemical oxygen demand (COD) in the northern zone.

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