Phone: 00216 22 74 11 55
Fax: 00216 74 27 44 37
Amira REKIK1, Habib AYADI1, Jannet ELLOUMI1*
1University of Sfax, Faculty of Sciences of Sfax, Department of Sciences of life. Research Unity UR/11ES72 Biodiversity and Aquatic Ecosystem. Street Soukra Km 3.5 - BP 1171- CP 3000 Sfax, Tunisia.
A.REKIK,H.AYADI,J.ELLOUMI , The characterisation and seasonal distribution of diatoms along Sfax northern and southern coasts (Gulf of Gabes, Eastern Mediterranean Sea) in relation to environmental conditions(2017)SDRP Journal of Earth Sciences & Environmental Studies 2(3)
The spatial and seasonal variations of the diatoms communities were examined during four marine cruises conducted between years 2011 and 2012 on 12 stations at the north (restored) and south (not yet restored) coasts. Results revealed a striking difference between the two coasts regarding pH, with strong acidification of seawater in the south, likely caused by industrial activity. Suspended matter was higher in the north than in the south may be reasonably attributed to the recently added soil not yet fully stabilised. The low concentrations of orthophosphate as well as their low values relative to total phosphate show that restoration of the northern part of Sfax coast had positive effects on dissolved inorganic phosphate concentrations. Orthophosphate and total phosphate concentrations were still important in the southern coast. Inverted microscopy analysis of diatoms resolved 31 and 29 taxa in the north and south Sfax coasts respectively. Diatoms dominated community composition in the northern coast (65%), contrary to the southern coast, diatoms do not exceed 40%. Diatoms was characterised by the proliferation of pennate diatoms species (Amphiprora sp., Nitschia longissima, Nitschia sp., Nitschia ventricosa, Plagiotropis sp. ..) in northern part contrasting a progressive augment of centric diatoms species (Biddulphia sp., Leptocylindricus danicus, Leptocylindrus sp., Skeletonema costatum, Rhizosolenia stolforthii ..) in the southern part of the coast. The results confirm that restoration had positive effects on the abiotic variables and diatoms assemblage of the north coast. The case for restoration of the city’s south coast is also reinforced.
Diatoms represent a major part of the eukaryotic primary production in marine ecosystems (Drira et al., 2009). The seasonal succession of diatoms communities were governed by a combination of physical, chemical and biological variables in marine ecosystems (Meiners et al., 2003). Diatoms tend to have considerably higher maximum uptake rates of nutrients than any other group (Litchman et al., 2006). Indeed, diatoms are the preferred food of many grazers in the upper trophic levels and thus form the basis for many of the productive fisheries (Ben Brahim et al., 2015).
The Eastern Mediterranean Sea is eutrophic to oligotrophic, depending on location and season. The Gulf of Gabes in the Eastern Mediterranean Sea is one of the main harbours and is a highly productive ecosystem (Hamdi et al., 2015). The Gulf of Gabes, situated in the south-east of Tunisia, is delimited by arid to semi-arid continental shelves and it is surrounded by the Kerkennah Islands in the north-east, Kneiss islands in the southeast, Djerba Island in the south-east, the lagoons of Boughrara and El Bibane (Hattour et al. 2010). Water area is about 100 km long and 100 km wide with depths varying from 20 to 50 m (Sammari et al., 2006).
Sfax coast, a part of the Gulf of Gabes, are surely associated to the two industrial regions of Madagascar and Sidi Salem, the sewage treatment station ONAS (National Sanitation Office). These regions are recognized for generating contaminants released from commercial, agricultural and domestic effluents (Ben Salem et al., 2015). The residue of phosphate treatment, phosphogypsum, has been stocked along the coast at an abandoned dumpsite from the plant which fabricates phosphoric acid (SIAPE) (Rekik et al., 2012). Over years, due to enlarged pressure from industrial activities and fisheries, there has been a reduction in the biodiversity in the Sfax coast (Rekik et al., 2012). Recently, the north coast of Sfax is subject to restoration from pollution by Taparura project (Rekik et al., 2013ab; 2014; 2015ab); on the other side the Sfax south coast is not yet restored (Rekik et al., 2015c; 2016ab).
To determine the impact of restoration work on water quality and biodiversity, the seasonal variation of the diatoms community was studied in a restored ecosystem (north Sfax coast) and a not restored ecosystem (south Sfax coast) at 12 stations (6 stations on each coast). Thus, we studied the diatoms species abundance and diversity together with physical and chemical processes and biological factors along Sfax’s coasts. We hypothesized that the diatoms would change from the northern to the southern Sfax coast according to, (i) abiotic proprieties and (ii) the effect of the restoration and pollution.
2.1. Study site
This research was conducted in Sfax (34°43'N – 10°46'E, Central Eastern Coast of Tunisia), a town with a littoral extends 50 km from the site of Sidi Mansour in the north to Chaffar in the south (Rekik et al., 2012). The north Sfax coast, restored by Taparura project, is described with its geomorphologic polygon. This region includes the phosphate treatment plant (NPK) and the commercial harbour (Rekik et al., 2014). The south Sfax coast, directly exposed to phosphate reject, is a closed ecosystem. This area contains the fishing port, the solar saltern, the SIAPE, the industrial region of Madagascar and Sidi Salem, and commerce locale of Thyna (Rekik et al., 2015c).
2.2. Field sampling
Abiotic and biological samples were collected in 2010 and 2011 on 12 stations at the north (1, 2, 3, 4, 5 and 6) and south (A, B, C, D, E and F) coasts of Sfax (Fig. 1). Physico-chemical and phytoplankton samples determination were collected with a Van Dorn-type closing bottle. Nutriment samples (120 ml) were stored directly at 20 °C in the dark. Phytoplankton samples (1 l) were conserved for enumeration with Lugol iodine solution (4%) (Bourrelly, 1985). Chlorophyll-a samples (1 l) were filtered onto Whatman GF/F glass fiber filters via vacuum filtration which were after that directly preserved at −20°C.
2.3. Physico-chemical variables
Physical factors were determined instantly after sampling using a multi-parameter kit (Multi 340 i/SET). Suspended matter concentrations were determined using the dry weight of the residue after filtration of 0.5 L of seawater onto Whatman GF/C membrane filters. Chemical factors were determined with a Bran and Luebbe type 3 autoanalyzer.
2.4. Phytoplankton enumeration
Phytoplankton samples (50 mL) were identified under an inverted microscope using the Utermöhl method (Utermöhl, 1958). Phytoplankton species determination was made according to different books (Rekik et al., 2012; 2013ab; 2015abc).
Chlorophyll-a was measured with spectrometry, after extraction of the pigments in acetone (90 %). The concentrations were then determined using the SCOR-UNESCO equations (SCOR-UNESCO, 1966).
2.5. Statistical analysis
The abiotic and biological variables analysed in our research were presented to a normalised principal component analysis (Doledec and Chessel 1989). Simple log(x + 1) conversion was executed to variables in order to exactly normalize difference (Frontier, 1973). Means and standard variations were recorded when appropriate. The relationships potential among data were experienced by Pearson’s correlation coefficient. One-way ANOVA employing XLstat software followed by a post hoc evaluation using Tukey’s analysis was used to recognize major variations among north and south coasts.
3.1. Abiotic variables
3.1.1. North coast of Sfax
The mean temperature values fluctuated between 13.65 ± 0.42 and 32.89 ± 2.21 °C. The seasonal distribution of temperature illustrated higher values from winter to summer. The water temperature varied between 13.00 and 36.00 °C with the lowest temperature detected in winter and the highest in summer at station 1 (Table 1). The highest and lowest salinity were recorded during winter (37.34 psu) and summer (39.17 psu) respectively at station 2 (Table 1). The pH mean values were typically alkaline varied between 8.16 ± 0.30 to 8.60 ± 0.13 during autumn and spring respectively. Suspended matter concentrations were more varied in winter than in spring where the average value was about 58.63 ± 3.88 mg l-1, whereas in the winter the highest value of suspended matter was 201.56 mg l-1 (station 6) and the lowest was 85.78 mg l-1 (station 3).
The nitrogen form mean concentrations were more important in spring than in autumn. The dissolved inorganic nitrogen concentrations illustrated a general decrease during autumn. The nitrate, nitrite and ammonium concentrations showed a considerable increase during spring, summer and winter respectively. Overall, total nitrogen concentrations increased significantly from autumn to spring in the coast. The concentration of total nitrogen ranged from 13.26 µM at station 6 to 15.51 µM at station 1 during autumn (Table 1). Total nitrogen concentration was about 20.19 ± 1.84 µM in spring. The mean value of orthophosphate concentration was 1.83 ± 0.48 µM in winter whereas in the autumn it was only 0.16 ± 0.02 µM (Table 1). When considering total phosphate concentrations, values were three times that of orthophosphate concentration in winter and spring and up to twelve times in autumn. The N/P: DIN to DIP ratio varied between 1.95 and 15.76 in winter and autumn respectively at station 2. This average was less than the Redfield ratio (16), indicating a probable nitrogen control. On the contrary, the N/P ratio was more important in summer principally at stations 1 (30.15) and 2 (32.88). Silica concentration was considerably more important in winter (22.76 ± 11.09 µM) than in autumn (2.21 ± 0.50 µM) (Table 1). The maximum concentration of silica was registered at station 4 (40.09 µM), and the minimum (1.41 µM) at station 1 (Table 1).
3.1.2. South coast of Sfax
Water temperature ranged from 14.97 to 32.33 °C (23.99 ± 6.31 °C) (Table 1), tending to augment from winter to summer over the study site. Salinity, which ranged from 34.53 to 40.00 psu (37.82 ± 1.36 psu) (Table 1), was instable through the whole study period fluctuated between 36.51 ± 1.10 psu (winter) and 39.44 ± 0.29 psu (autumn). The pH values ranged from 7.08 to 8.45 (7.76 ± 0.39) (Table 1) augmenting considerably in the coastal site: station B in autumn showed the lowest transparency, stations D and E in spring the highest. Suspended matter values varied significantly during winter and summer, while in autumn and spring suspended matter concentrations were relatively invariable. Suspended matter concentrations ranged from 23.87 mg l-1 (station A, winter) to 61.44 mg l-1 (station E, spring) (38.09 ± 10.08 mg l-1) (Table 1).
Nutrient concentrations were irregularly distributed. The dissolved inorganic nitrogen values were more concentrated in autumn. Nitrate concentrations varied from 2.05 to 19.67 μM, with a mean of 7.31 ± 3.93 μM (table 1), the maximum being observed at station E in autumn. Nitrite concentration was in the range 0.17- 6.56 μM with its maximum value at station E in autumn (table 1). Ammonium concentration ranged from 2.01 µm to 11.33 μM, the peak value being observed at station A in autumn. Total nitrogen concentration ranged from 13.83 μM (station C, summer) to 45.43 μM (station E, autumn) (Table 1). The mean value of orthophosphate concentration was 2.51 ± 1.04 µM and 11.42 ± 1.94 µM during winter and spring respectively. When regarding total phosphate concentrations, values were up to three times that of orthophosphate concentration. The average value of the N/P ratio was less than the Redfield ratio (16) in the four studied periods, but its range of fluctuation (0.75 – 34.12) was important (Table 1). The highest concentration of silica was recorded in autumn (61.51 μM) and the lowest (4.18 μM) in winter at station E (Table 1).
3.2. Diatoms community
3.2.1. North coast of Sfax
Chlorophyll-a concentrations were small during the four seasons, with values being inferior to 10 mg l-1. The spatial and seasonal differences in pigment concentrations were not significant in autumn with the exception of station 1 (9.84 mg l-1). Yet, an important augment of Chlorophyll-a concentrations was registered during spring (3.10 ± 1.32 mg l-1) (Fig. 2). Abundance of phytoplankton community fluctuated from 16.42 × 102 cells l-1 to 260.41 × 102 cells l-1 at station 5 and 6 during spring and summer respectively (Fig. 2), with the important mean abundance being registered in winter (135.46 ± 80.73 × 102 cells l-1). The total phytoplankton abundance peaked at the same time, at stations 4, 5 and 6 in winter, however, abundance was low in spring (Fig. 2). Diatoms abundance changed significantly over the study period, with a maximum of 235.71 × 102 cells l-1 in winter and a minimum of 4.34 × 102 cells l-1 in spring (Fig. 2). The maximum individuals number was registered at station 6 bloom of diatoms species such as Navicula sp. (145 × 102 cells l-1), Grammatophora sp. (43.67 × 102 cells l-1), Licmophora sp. (24.67 × 102 cells l-1) and Pleurosigma sp. (13 × 102 cells l-1) (Table 2). Diatoms species composition varied considerably throughout our research (Table 2), with a particularly predominance of Navicula sp. fluctuated from 37% and 63% of total abundance of diatoms during summer and autumn respectively (Fig. 2). The sampled diatoms cells were identified into 31 taxa, belonging to 28 taxonomic genuses, and 20% of which were classified at species level (Table 2). The species richness of diatoms community was more marked in spring, this was particularly clear with 21 species reflecting probably favourable development conditions (Table 2). Among diatoms, there are taxa which are exclusively observed in the north Sfax coast like Chaetoceros sp., Guinardia sp., Hemiaulus sinensis, Hermesinum sp., Leptocylindricus mediterranus, Licmosphenia sp., Melosira italica, Nitschia sp., Plagiotropis sp. and Surirella sp. (Table 2).
3.2.1. South coast of Sfax
Chlorophyll-a concentrations varied from 0 to 25.89 mg l-1 (4.95 ± 6.60 mg l-1) and have a tendency to augment in autumn and spring (Figure 2). Phytoplankton abundance fluctuated from 8.00 × 102 cells l-1 (station B, autumn) to 205.00 × 102 cells l-1 (station F, summer) (Fig. 2). Total phytoplankton were abundant in summer (105.00 ± 64.46 × 102 cells l-1) whereas they were poorly represented in winter (32.00 ± 10.54 × 102 cells l-1) (Fig. 2). Abundance of total phytoplankton peaked during summer at station A (151 × 102 cells l-1), station B (90 × 102 cells l-1), station C (73 × 102 cells l-1) and station F (205 × 102 cells l-1) (Fig. 2). The highest diatoms abundance was recorded in spring at station D (45 × 102 cells l-1) (Fig. 2), associated with an important proliferation of Navicula sp. (24 × 102 cells l-1). Navicula sp., considered as a whole, were more abundant in spring than in autumn, with average abundance values , 12.90 × 102 and 3.00 × 102 cells l-1 in spring and autumn respectively (Fig. 2). Average diatoms abundance was low during autumn, with mean values being lower than 18.00 × 102 cells l-1. Among the species collected, Bellarochea sp., Diploneis sp., Epithemia sp., Leptocylindricus danicus, Leptocylindrus sp., Lithodesmium sp., Lithodesmium undulatum, Rhizosolenia stolforthii and Skeletonema costatum were found only in the south Sfax coast (Table 2). A number of species were particularly prominent at specific seasons, and among these diatoms, Amphiprora sp., Epithemia sp., Leptocylindricus danicus, Leptocylindrus sp., Lithodesmium sp., Skeletonema costatum and Skeletonema sp. were found in spring and Rhizosolenia stolforthii, Synedra sp. and Synedra ulna were collected in autumn (Table 2).
3.3. Statistical analysis
3.3.1. North coast of Sfax
PCA distinguished between four groups surrounding the F1 and F2 component axes thus explaining 56.66% of the variance in the Sfax north coast. The axes selected a group G1 comprising total phytoplankton and diatoms linked to salinity, suspended matter, NH4+ and NO2- concentrations, at stations 5 and 6. F1 component axis which extracted 29.07% of the variability, selected negatively the group G2, with temperature and pH at station 4. G3 formed by chlorophyll-a concentrations, witch were mostly influenced by silica content in station 1. G4 selected, NO3-, T-N, PO43-, T-P and N/P ratio (stations 2 and 3) (Fig. 3).
3.3.2. South coast of Sfax
PCA allowed discrimination of four groups around the components of the F1 and F2 axes explaining 69.23% of the variance in the Sfax south coast. These axes positively selected group G1, formed by diatoms correlated to salinity, NO3-, NH4+ and T-N (station A). The F1 component axis, which extracted 43.59% of the variability, positively selected group G2, a group selected in station D and comprised of pH, NO2-, PO43-, T-P and Si(OH)4. The PCA plots illustrate that, in G3 selected in stations B, C and F, temperature and suspended matter concentrations. The last group, G4, was mainly related to N/P ratio and correlated to total phytoplankton and chlorophyll-a concentrations (Fig. 3).
The present study is the first attempt to investigate the distribution of diatoms assemblage through high spatial resolution sampling in the shallow coastal waters of Sfax during four seasons. Our results demonstrated distinct spatial and seasonal contrasts. The north coast of Sfax is subject to restoration from pollution. The Taparura Project is part of an environmental policy and management program aimed at tackling the pollution threatening the north Sfax beaches and coastal waters. The south coast of Sfax is subject to degradation of water quality. The expansion of industrial and commercial activities in the south Sfax coastal area has become an issue of increasing environmental concern. In order to distinguish between variations provoked by the coast restoration and those of other origin, it was also important to compare the north coast situation to that of the south which is still subject to the same industrial pollution linked to the phosphate and fertilizer industry.
Our results agree with and complement other research performed in arid to semi-arid Mediterranean ecosystems, which illustrated important values for both temperature and salinity starting in spring and arriving at its maximum in summer, followed by a cooling trend with its minimum in winter (Rekik et al., 2013a; 2014; 2015ab). The mean water temperature and salinity registered at the 6 sampling north stations (from station 1 to 6) were significantly higher than those registered at the southern stations (from station A to F). Significant differences were observed in water temperature (r = 3.24 × 10-19, p<0.001, n = 15) and salinity (r = 2.58 × 10-8, p<0.001, n = 15) between northern and southern stations. Results revealed a striking difference between the two coasts about pH, with high acidification of seawater in the south, probably generated by industrial activity (Rekik et al., 2013b). Suspended matter was more important in the north (48.20 – 201.56 mg l-1) than in the south (23.87 – 61.44 mg l-1). The high suspended matter values may be attributed to the shallowness of the sampled north stations, the spatial distribution of tiny particles and tidal action and to the recently added soil, not yet fully stabilised (Rekik et al., 2013b). The low concentrations of orthophosphate as well as their low magnitude relative to total phosphate show that restoration of the northern part of Sfax coast had positive effects on dissolved inorganic phosphate concentrations. Orthophosphate and total phosphate concentrations were still prevalent in the south. Accordingly, the N/P–DIN to DIP ratio (12.63 ± 8.82) was close to the Redfield ratio (16) in the north coast of Sfax. This result clearly shows that the phosphogypsum restoration had been indispensable with, however, phosphate values still elevated enough to quality an oligotrophic status to the north Sfax coast. A major difference with respect to the not restored south coast concerns the high phosphate concentration and which was 6 times higher compared to the north coast. It is noteworthy that phosphogypsum was dumped only on the north coast. Analysis of nutrient concentrations indicates that south coast was not nutrient limited during the four seasons.
Our study explained two key results: (i) phytoplankton was strongly abundant in the north part compared to the south part of our site, indicating favorable growing conditions after the restoration work on the north coast of Sfax, and (ii) diatoms generally dominated community composition in the northern coast (65%) and particularly during winter (94%) and autumn (80%), contrary to the south coast, diatoms do not exceed 40%. Diatoms are important indicators of ecological quality as they react quickly to several physical, chemical and biological factors in marine environment (Davies and Ugwumba 2013). The physicochemical variables such as temperature, pH, suspended matter and ammonium concentrations were found to control the occurrence of diatoms. Our results showed an increase of diatoms in the north Sfax coast correlated with ammonium concentrations (r = 0.66, p<0.05, n = 15). In particular, suspended matter concentrations seemed to be the most important parameter in the north coastal site which may affect the abundance and distribution of diatoms (r = 0.89, p<0.05, n = 15). Lauria et al. indicated that diatoms reacted positively to turbulence, showing enhanced development rates with increased stirring and aeration in laboratory experiment, probably due to the increase of suspended matter during water movement (Amari, 1984). Water temperature seems also to be an important factor that explains the abundance of diatoms in the south coast of Sfax (r = 0.66, p<0.05, n = 15). The low pH values are likely the most important predictor among the physical factors and its negative influence on diatoms abundance (r = -0.64, p<0.05, n = 15) in southern part of the coast. The low pH values can reasonably be attributed to the industrial activity still in function in the south coast while it has been finished in the north Sfax coast (Rekik et al., 2013b). The seasonal variability shows that the littoral of Sfax is subjected to a clear seasonal cycle deference north coast species to south coast species. This was related to the increase of pennate diatoms species (Amphiprora sp., Nitschia longissima, Nitschia sp., Nitschia ventricosa, Plagiotropis sp. ..) abundance in northern part contrasting a progressive augment of centric diatoms species (Biddulphia sp., Leptocylindricus danicus, Leptocylindrus sp., Skeletonema costatum, Rhizosolenia stolforthii ..) in the southern part of the coast. Nygaard (1949) showed that centric diatoms are usually found in eutrophic conditions, whereas pennate diatoms are usually found in non-polluted conditions. Several species of Navicula were dominant taxa strongly growing in that coast and belonging to diatoms. They are conventionally considered as benthic (Welker et al., 2002) and euryhaline species (Mikhail, 2008). Dominance of Navicula species has been previously recorded in many studies in the coastal Sfax water, although they did not reported their dominance over the seasons (Rekik et al., 2013a; 2015ac). This could be explained by the adaptability of this taxonomic group to different nutrition regimes and environmental conditions.
The results confirm that restoration had positive effects on the abiotic factors and diatoms assemblage of the north coast; they also highlight the strong acidification still prevalent in the south that may be responsible for the lower development and occurrence of phytoplankton. The case for restoration of the city’s south coast is also reinforced.
Amira REKIK is grateful to the Society of Studies and Development of the North Coast of the city of Sfax (SEACNVS) for providing access to the sampling site. This work was conducted in the Biodiversity and Aquatic Ecosystems UR/11ES72 research unit at the University of Sfax.
Amari A (1984). "Contribution to the hydrological and sedimentological knowledge of the platform of the Kerkennah Islands [dissertation]." Faculty of Sciences of Tunis.
Ben Salem Z, Drira Z, Ayadi H (2015). "What factors drive the variations of phytoplankton, ciliate and mesozooplankton communities in the polluted southern coast of Sfax, Tunisia?" Environmental Science and Pollution Research: DOI: 10.1007/s11356-015-4416-8.View Article
Ben brahim M, Feki-Sahnouna W, Feki M, Mahfoudi M, Hamza A (2015). "Seasonal and daily fluctuation of diatoms during spring tide periods in Kerkennah Islands." Journal of Coastal Life Medicine 3: 446-452.
Bourrelly P (1985). "Introduction to systematic. Volume II. The blue and red algae." Paris: Edit? par Soci?t? Nouvelle des Editions Boub?e; pp. 450.
Davies OA, Ugwumba OA (2013). "Tidal influence on nutrients status and phytoplankton population of Okpoka Creek, upper Bonny Estuary, Nigeria." Journal of Marine Biology : DOI: 10.1155/2013/684739.View Article
Dol?dec S, Chessel D (1989). "Rythmes saisonniers et composantes stationnelles en milieu aquatiqueII. Prise en compte et ?limination d'effets dans un tableau faunistique." Acta Oecologica Oecologia Generalis 10: 207?332.
Drira Z, Hamza A, Bel hassen M, Ayadi H, Bouain A, Aleya L (2009). "Coupling of phytoplankton community structure to nutrients, ciliates and copepods in the Gulf of Gab?s (south Ionian Sea, Tunisia)." Journal of the Marine Biological Association of the United Kingdom: DOI: 10.1017/S0025315409990774.View Article
Frontier S (1973). "Etude statistique de la dispersion du zooplancton." Journal of Experimental Marine Biology and Ecology 12: 229?262. 90056-7View Article
Hamdi I, Denis M, Bellaaj-Zouari A, Khemakhem H, BelHassen M, Hamza A, Barani A, Bezac C, Maalej S (2015). "The characterisation and summer distribution of ultraphytoplankton in the Gulf of Gab?s (Eastern Mediterranean Sea, Tunisia) by using flow cytometry." Continental Shelf Research 93: 27?38.View Article
Hattour MJ, Sammari C, Ben Nassralli S (2010). "Hydrodynamics of the Gulf of Gabes deduced from observations of currents and levels." Revue Paralia 3: 31-45.View Article
Litchman E, Klausmeier CA, Miller JR, Schofield OM, Falkowski PG (2006). "Multi-nutrient, multi-group model of present and future oceanic phytoplankton communities." Biogeosciences 3: 585-606.View Article
Meiners K, Gradinger R, Fehling J, Civitarese G, Spindler M (2003). "Vertical distribution of exopolymer particles in sea ice of the Fram Strait (Arctic) during autumn." Marine Ecology Progress Series 248: 1?13.View Article
Mikhail S (2008). "Dynamics of estuarine phytoplankton assemblages in Mex Bay, Alexandria (Egypt): Influence of salinity gradients." Egyptian Journal of Aquatic Research 12(4):231?251.
Nygaard G (1949). "Hydrobiological studies on some Danish ponds and lakes. II. ? Det Kong. Danske Vidensk. Selskab." Biology Skrifter 7: 1?294.
Rekik A, Drira Z, Guermazi W, Elloumi J, Maalej S, Aleya L, Ayadi H (2012). "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." Marine Pollution Bulletin 64: 336?346. PMid:22154276View Article PubMed/NCBI
Rekik A, Denis M, Aleya L, Maalej S, Ayadi H (2013a). "Spring plankton community structure and distribution in the north and south coasts of Sfax (Tunisia) after north coast restoration." Marine Pollution Bulletin 67: 82?93. PMid:23260651View Article PubMed/NCBI
Rekik A, Maalej S, Ayadi H, Aleya L (2013b). "Restoration impact of an uncontrolled phosphogypsum dump site on the seasonal distribution of abiotic variables, phytoplankton and zooplankton along the near shore of the south-western Mediterranean coast." Environmental Science and Pollution Research: DOI: org/ 10.1007/s11356-012-1297-y.
Rekik A, Elloumi J, Chaari D, Ayadi H (2015a). "Microphytoplankton and ciliate communities' structure and distribution in a stressed area of the south coast of Sfax, Tunisia (eastern Mediterranean Sea)." Marine and Freshwater Research: DOI: 10.1071/MF15057.View Article
Rekik A, Denis M, Maalej S, Ayadi H (2015b). "Spatial and seasonal variability of pico-, nano- and microphytoplankton at the water-sediment interface in the north coast of Sfax, Eastern Mediterranean Sea." Environmental Science and Pollution Research: DOI: 10.1007/s11356-015-4811-1.View Article
Rekik A, Denis M, Maalej S, Ayadi H (2015c). "Planktonic ciliates in relation to abiotic variables on the north coast of Sfax after environmental restoration: species composition, and abundance-biomass seasonal variation." Journal of Oceanography, Research and Data 8: 1?16.
Rekik A, Ben Salem Z, Ayadi H, Elloumi J (2016). "Spring phytoplankton variability along a south coast of Sfax at the water-sediment interface (Tunisia, Eastern Mediterranean Sea)." Journal of Coastal Life Medicine 4: 121-127.View Article
Rekik A, Ben Salem Z, Ayadi H, Elloumi J (2016b). "Species composition and spring ciliates variability on the south coast of Sfax (Eastern Mediterranean Sea)." Journal of Applied Environmental and Biological Sciences 6: 57-71.
Sammari C, Koutitonsky VG, Moussa M (2006). "Sea level variability and tidal resonance in the Gulf of Gabes, Tunisia." Continental Shelf Research 26: 338- 50.View Article
SCOR-UNESCO (1966). "Determination of photosynthetic pigments in sea water." UNESCO, Paris.
Uterm?hl H (1958). "Zurvervolkommungder quantitativen phytoplankton Methodik. Mitteilungen Internationale Vereinigung fur Theoretische und Angewandte." Limnology 9: 1?38.
Welker C, Sdrigotti E, Covelli S, Faganeli J (2002). "Microphytobenthos in the Gulf of Trieste (Northern Adriatic Sea): relationship with labile sedimentary organic matter and nutrients." Estuarine, Coastal and Shelf Science 55: 259?273.View Article