Zaher Drira

Impacts of an uncontrolled phosphogypsum dumpsite on summer distribution of phytoplankton, copepods and ciliates in relation to abiotic variables along the near-shore of the southwestern Mediterranean coast

In connection with the Taparura Project, studies of spatial distribution of the crustacean zooplankton community, nutrients, phytoplankton and ciliates were conducted in July 2007 at 45 stations spread over fifteen transects along the coast north of Sfax. The results showed that the N/P ratio was lower than the Redfield ratio, suggesting potential N limitation. Phytoplankton was characterised by the proliferation of several diatoms, while ciliates were largely dominated by spirotrichs. Copepods were the most abundant zooplankton present during the entire study period, comprising 61% of the total zooplankton community. Twelve copepod families were identified at every station, with a high percentage of Oithonidae (77% of copepods) dominated by Oithona nana. The abundance of this species was correlated with that of diatoms, Cocoolithophorideae and ciliated Colpodea, suggesting that O. nana may feed on a wide range of prey. Despite human pressure and industrial activities, the coastal waters north of Sfax showed a wide diversity of phytoplankton, ciliates and zooplankton.

Copepod community structure related to environmental factors from a summer cruise in the Gulf of Gabès (Tunisia, eastern Mediterranean Sea)

We studied the summer spatial distribution of the copepod community in both the neritic and oceanic areas of the Gulf of Gabes (Tunisia, eastern Mediterranean Sea) coupled with environmental factors. Copepods were the most abundant zooplankton throughout the sampling period, contributing 7 8% of the total zooplankton. A total of 14 copepod families were identified in all stations, with an overwhelming abundance of Acartiidae and Oithonidae ( 39 .0 5 and 39 . 09 % of total abundance, respectively). Abundance of Acartia clausi and chlorophyll-a concentrations were negatively correlated with salinity, suggesting that this species probably escaped the high coastal salinity ( 3 8 psu). Significant correlation determined between A. clausi and tintinnids at 5 0 m isobaths indicates that these planktonic ciliates probably served as a substantial food link towards higher trophic levels of this area. Conversely, Oithona nana which was well adapted to high chlorophyll-a concentrations and high salinity along the coast, showed significant correlations with Dictyochophyceae, Dinophyceae, Bacillariophyceae and Euglenophyceae, suggesting that this small copepod was capable of feeding on a wide selection of phytoplankton preys.

Assessment of anthropogenic inputs in the surface waters of the southern coastal area of Sfax during spring (Tunisia, Southern Mediterranean Sea)

The coastal marine area of Sfax (Tunisia), which is well-known for its high productivity and fisheries, is also subjected to anthropogenic inputs from diverse industrial, urban and agriculture activities. We investigated the spatial distribution of physical, chemical and biogeochemical parameters in the surface waters of the southern coastal area of Sfax. Pertinent tracers of anthropogenic inputs were identified. Twenty stations were sampled during March 2013 in the vicinity of the coastal areas reserved for waste discharge. Phosphogypsum wastes dumped close to the beaches were the main source of PO4(3-), Cl(-) and SO4(2-) in seawater. The high content in total polyphenolic compounds was due to the olive oil treatment waste water released from margins. These inorganic and organic inputs in the surface waters were associated with elevated COD. The BOD5/COD (<0.5) and COD/BOD5 (>3) ratios highlighted a chemical pollution with organic load of a low biodegradability.

How could thermal stratification affect horizontal distribution of depth-integrated metazooplankton communities in the Gulf of Gabes (Tunisia)?

ABSTRACT The spatial and temporal variability of metazooplankton communities in relation to environmental and trophic factors were studied in the Gulf of Gabes during three periods of increasing thermal stratification in June, July and September. Non-metric multi-dimensional scaling (NMDS) revealed the time and space succession of three zooplankton communities in relation to the degree of thermal stratification. A co-inertia analysis showed the association between these communities and the trophic conditions (abundance and composition of microplankton) driven by stratification. Three divergent communities were evident. The first, characterized by annelid larvae and coastal copepods, was associated with shallow mixed and microplankton-rich water (June, coastal). The second, characterized by euphausiids, amphipods, doliolids and several deep-water copepods, corresponded to highly stratified microplankton-poor water (September). The third, characterized by the most ubiquitous and abundant species, was linked to intermediate water (June deep and July). Temperature and salinity conditions also explained the distribution of key species. Clausocalanus furcatus, Oithona plumifera and Triconia conifera were clearly associated with warm and highly stratified water (September). Enhanced thermal stratification led to higher surface salinity, explaining the emergence of euryhaline taxa such as Oithona plumifera.

Coupling of phytoplankton and ciliate biomasses to environmental factors along the north coast of Sfax (Tunisia, Eastern Mediterranean Sea)

The phytoplankton and ciliate biomasses coupled with environmental factors were investigated in 15 transects in north coasts of Sfax (Tunisia, Eastern Mediterranean Sea) in July 2007. The phytoplankton biomass was dominated by Bacillariophyceae (89.66%), followed by Dinophyceae (10.07%), Coccolithophorideae (0.96%), Cyanobacteriae (0.21%), Chlorophyceae (0.03%) and Euglenophyceae (0.01%). Coscinodiscus sp. (93.26%) was the most abundant species of Bacillariophyceae group and associated with a high nutrient availability. Ciliate biomass was highly variable, with a large dominance of Spirotrichea, up to 96.2%. Biomass followed distinct patterns because of differences in the observed organism biovolumes. The spatial distribution of the ciliates biomass seems to be dependent on environmental factors and probably on their capacity to exploit a wide range of food resources including phytoplankton. The pollution generated by the phosphate-treating manufactory influenced the spatial phytoplankton and ciliate community’s distribution and their diversity along the north coast of Sfax.

Water quality affects the structure of copepod assemblages along the Sfax southern coast (Tunisia, southern Mediterranean Sea)

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.

Copepod assemblages as a bioindicator of environmental quality in three coastal areas under contrasted anthropogenic inputs (Gulf of Gabes, Tunisia)

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 × 10 3 ind m −3 ) followed by Ghannouch area (H′ = 1.74 ± 0.28 bits ind −1 ; 15 species; density = 11.979 ± 5.651 × 10 3 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 × 10 3 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.

Chemical Composition and Some Trace Element Levels in the Surface Waters of Three Coastal Marine Areas Under Contrasted Pollution Influences in the Gulf of Gabes, Tunisia

The Gulf of Gabes (southeastern - Tunisia), characterized by the abundance of halieutic resources, is nowadays facing strong anthropogenic pressures. This paper aimed to assess and compare the anthropogenic inputs of 30 stations belonging to three coastal areas of the Gulf of Gabes (Gulf of Gabes) i.e. the Southern and the Northern coastal areas of Sfax and the Ghannouch area during October and November 2014.