Living (stained) foraminifera in the Lesser Syrtis (Tunisia): influence of pollution and substratum.

Foraminifera are protozoans with biomineralized tests that can be successfully used as a low cost monitoring tool to assess the health status of marine environments. Living benthic foraminiferal assemblages can provide essential information on natural and/or anthropogenic stresses and provide baseline conditions for studies on fossil material. Several studies have highlighted the negative impact of phosphate treatment industries along the Gulf of Gabes (Lesser Syrtis, Tunisia) on the marine environment. However, only a few studies, based on living (stained) benthic foraminifera, are presently available to assess environmental and/or ecological conditions in this Gulf. Thirty-eight surface sediment samples were quantitatively investigated to identify the dominant living benthic foraminiferal species and potential pollution-sensitive and stress-tolerant species. One-hundred and sixty-one species were identified, and grouped into seven clusters representing different environments within the Gulf. These groups represent polluted settings (Cluster A and B), polluted environments characterized by physicochemical variability (Cluster C), seagrass meadows and "pristine" sites (Cluster D and E) and the region subjected to major industrial impact (Cluster F). The final outlier Cluster, identified the foraminifera barren and all shallow coastal stations. A SIMPER analysis helped identify species with clear and fast responses to environmental perturbations (Ammonia tepida, Amphistegina lessonii, Brizalina striatula, Bulimina marginata, Buliminella elegantissima, Eggereloides scaber, Peneroplis perutusus, Rosalina macropora, Rosalina villardeboana, Trochammina inflata). A comparison with the measured geochemical parameters (TOC, phosphorus in the sediments and heavy metal concentrations in the seawater) has shown that the benthic foraminiferal assemblages are mainly linked to phosphorus, TOC, As and Cd pollution. We also provide here the first compilation of the identified living species in the Lesser Syrtis, their synonyms and digital images of important species.

Impact of industrial phosphate waste discharge on the marine environment in the Gulf of Gabes (Tunisia).

The marine environment in the Gulf of Gabes (southern Tunisia) is severely impacted by phosphate industries. Nowadays, three localities, Sfax, Skhira and Gabes produce phosphoric acid along the coasts of this Gulf and generate a large amount of phosphogypsum as a waste product. The Gabes phosphate industry is the major cause of pollution in the Gulf because most of the waste is directly discharged into the sea without preliminary treatment. This study investigates the marine environment in the proximity of the phosphate industries of Gabes and the coastal marine environment on the eastern coast of Djerba, without phosphate industry. This site can be considered as "pristine" and enables a direct comparison between polluted and "clean" adjacent areas. Phosphorous, by sequential extractions (SEDEX), Rock-Eval, C, H, N elemental analysis, and stable carbon isotope composition of sedimentary organic matter, X-ray diffraction (qualitative and quantitative analysis) were measured on sediments. Temperature, pH and dissolved oxygen were measured on the water close to the sea floor of each station to estimate environmental conditions. These analyses are coupled with video surveys of the sea floor. This study reveals clear differentiations in pollution and eutrophication in the investigated areas.

Correlation between pollution and decline of Scleractinian Cladocora caespitosa (Linnaeus, 1758) in the Gulf of Gabes.

During an expedition in 2014 in the Gulf of Gabes that aimed to evaluate the impact of the pollution of the phosphate industry on the marine environment, numerous dead coral fragments were retrieved from several stations along a 18 km long transect in front of the industry complex of Gabes. Detailed taxonomy of these coral fragments shows clearly that all fragments belong to the species Cladocora caespitosa (Linnaeus, 1758). Quantitative analysis of the coral fragments indicates a positive correlation with stations characterized by positive bathymetric anomalies. We suggest the presence of probable small-scaled (up to 4 m high) biogenic (palaeo-) build-ups composed mainly of coral colonies and bryozoans. Radiocarbon dating of three coral fragments show ages as old as 1897, 1985 and 1986 AD and suggests the presence of living C. caespitosa as close as 6 km to the phosphate treatment industry of Gabes at least until 1986 AD. This latter age coincides with the construction of the ammonium phosphate production plant, in 1979, in the Gulf of Gabes with an increase of the natural phosphate production. The higher impact of pollution on the marine environment in the inner part of the Gulf of Gabes likely induced the decline of C. caespitosa. This is well in agreement with enhanced siltation processes suggested by the sedimentary facies and grain-size analyses presently characterizing the Gulf of Gabes nowadays.