Eastern Mediterranean Sea, Tunisia
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Estuarine, Coastal and Shelf Science 219 (2019) 395–408 Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss Synthesis review of the Gulf of Gabes (eastern Mediterranean Sea, Tunisia): T Morphological, climatic, physical oceanographic, biogeochemical and fisheries features ∗ Béchir Béjaouia, , Sana Ben Ismaila, Achref Othmania,b, Olfa Ben Abdallah-Ben Hadj Hamidac, Cristèle Chevalierd, Wafa Feki-Sahnouna, Ali Harzallaha, Nader Ben Hadj Hamidac, Riadh Bouazize, Salem Dahechf, Frédéric Diazd, Khouthir Tounsig, Cherif Sammaria, Marc Paganoa,d, Malika Bel Hassena a Laboratoire Milieu Marin, Institut National des Sciences et Technologies de la Mer, Tunisie b Unité du rayonnement thermique, Faculté des Sciences de Tunis, 2092, Tunis, Tunisie c Laboratoire des Sciences Halieutiques, Institut National des Sciences et Technologies de la Mer, Tunisie d Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, France e Département de Géographie, Faculté des Lettres et Sciences Humaines de Sfax, Laboratoire SYFACTE, Tunisie f Université Paris Diderot, UMR PRODIG, France g Institut National de la Météorologie, Subdivision Météorologique de Sousse, Tunisie 1. Introduction are mostly semidiurnal (Gasparini et al., 2004; Sammari et al., 2006). In addition to tides, anticyclonic winds also drive water circulation Several oceanographic surveys have been done in the Gulf of Gabes (Hattour et al., 2010), bed sediment texture and seagrass density (Ben since the beginning of the twentieth century. The aim of the study by Brahim et al., 2010). the “Pourquoi Pas”? in 1923 was to investigate sea bottom features The Gulf of Gabes is considered highly productive (D'Ortenzio and (Dangeard, 1924). The benthos research began with Le Danois (1925) d’Alcalà, 2009; Ben Brahim et al., 2010), contributing approximately and Seurat (1924, 1929, 1934), who studied the habitats on the inter- 40% of the national fish production in Tunisia (DGPA, 2015) and thus tidal floor. Later, De Gaillande (1970a, b) and Poizat (1970a, b) studied constituting an anomaly in the eastern Mediterranean Basin, which is the benthic sands, the hydrodynamics and sediments of the Gulf, while known to be oligotrophic, as it is governed by the inflow of usually Ktari-Chakroun and Azouz (1971) focused on the bottom typography to nutrient-poor Atlantic surface waters coming from Gibraltar (Berman identify areas suitable for trawling. During the same period, Ben et al., 1984; Krom et al., 2010). The Gulf was recently identified as one Othman (1971) published hydrobiological observations on the south- of the eleven consensus ecoregions of the Mediterranean and is con- east Tunisian coast. The potential of pelagic fish exploitation was in- sidered, together with the Venetian shelf region, as a shallow and vestigated in the frame of the research and development project of phytoplankton bloom region (Ayata et al., 2017). Additionally, this area fisheries during three combined hydroacoustic and oceanographic is usually considered an important nursery for several fish species cruises (June–July and September–October 1972 and April–May 1973) (Hattour et al., 1995; Derbel et al., 2012; Enajjar et al., 2015). that enabled a detailed description of oceanographic properties Since the industrialization in 1970, which involves discharge from (Brandhorst and Messaoud, 1977). The latter study could be considered large-scale phosphate production plants in Sfax and Gabes (Béjaoui the first of its kind, given the investigated geographical space andthe et al., 2004; Ghannem et al., 2010), the phosphogypsum discharge subject matter addressed. (∼12000 ton per day) has become the main cause of the disequilibrium Water circulation highly influences the biological, chemical and of this ecosystem. Recent studies has shown a decrease in fish resources sedimentological features in the Gulf of Gabes. Previous studies showed (Zairi and Rouis, 1999; Hamza-Chaffai and Pellerin, 2003); a loss of that water circulation in the Gulf is closely associated with the Atlantic marine biodiversity (Drira et al., 2008; Barhoumi et al., 2009; Rabaoui waters circulating through the Strait of Gibraltar (Béranger et al., 2004; et al., 2013) and a degradation of water quality (Bel Hassen et al., 2008; Ben Ismail et al., 2012, 2014) and with tidal effects (Tsimplis et al., Drira et al., 2014a, b; Ben Salem et al., 2015). The discharges of 1995; Gasparini et al., 2004). Tides observed in the Gulf of Gabes are phosphogypsum led to a drastic decrease in the seagrass areas, as ob- among the highest in the Mediterranean Sea (up to 2 m in height) and served for Posidonia oceanica assemblages, which were shown to be ∗ Corresponding author. Institut National des Sciences et Technologies de la Mer, 28 rue 2 Mars 1934 Carthage Salammbô, 2025, Tunis, Tunisie. E-mail addresses: [email protected], [email protected] (B. Béjaoui). https://doi.org/10.1016/j.ecss.2019.01.006 Received 6 July 2018; Received in revised form 27 September 2018; Accepted 10 January 2019 Available online 13 February 2019 0272-7714/ © 2019 Elsevier Ltd. All rights reserved. B. Béjaoui, et al. Estuarine, Coastal and Shelf Science 219 (2019) 395–408 Fig. 1. Localization of the gulf of Gabes. strongly reduced in the more polluted areas (Béjaoui et al., 2004; Ben (Langar et al., 2002), the pearl oyster Pinctada radiata (Tlig-Zouari Brahim et al., 2010). et al., 2009), blue portunid crabs Portunus segnis (Rabaoui et al., 2015) Exploitation of marine resources has been a significant component and Callinectes sapidus (Mancinelli et al., 2017) and the tropical scy- in this historical relationship, and overuse has occurred at different phozoan Rhopilema nomadica (Daly Yahia et al., 2013) (see Fig. 6.) times (Tudela, 2004). Indeed, overfishing caused reductions in fish The purpose of this paper is to provide an in-depth review on the abundance, biomass and species richness and can disrupt ecosystem climatic, geomorphologic, physical, biogeochemical, planktonic and functioning, leading to changes in biological assemblages and the de- fisheries features of the Gulf of Gabes. It is intended to beusedas gradation of marine ecosystem services (Worm et al., 2006). Medi- support for stockholders interested in the Gulf ecosystem. terranean fisheries are typically multi-species and multi-gear, particu- larly the demersal fisheries which consist of numerous small to 2. Field location medium-sized boats (Farrugio et al., 1993). This diversity brings addi- tional difficulties to the task of managing fisheries (Papaconstantinou The Gulf of Gabes, named “Petite Syrte”, is located in the south- and Farrugio, 2000). Coastal fisheries are particularly important in the eastern part of Tunisia with the town of Chebba in the north and the southern region of Tunisia, and almost 53% of the national fishing units Tunisian-Libyan border in the south (Fig. 1). It occupies a wide con- (which represents approximately 13 000 units, including approximately tinental shelf area (Morzadec-Kerfourn, 2002) and represents approxi- 400 trawlers) operate in the Gulf of Gabes. Most fishermen along the mately 33% of the Tunisian coastal waters and more than 50% of the Gulf coastline are small-scale coastal fishermen (63%). They compete 700 km long Tunisian coastline (APAL, 2011). It shelters various islands vigorously with large trawlers and sardine boats based out of the Gulf's (Kerkennah, Kneiss and Jerba) and lagoons (Boughrara and El Bibane) main port cities, especially as fish stocks continue to decline from and several towns, such as Gabes, Sfax, Jerzis and Jerba. overfishing. In the Gulf stocks are already overfished by more than30% (LRMV, 2011) and biodiversity is declining, coinciding with the re- 3. Climate characteristics duction in submerged aquatic vegetation. Invasive species represent an added pressure on ecosystem func- The Gulf of Gabes is characterized by a semi-arid Mediterranean tioning and fisheries. Among the exotic invasive species recorded inthe climate influenced by both a wet temperate component coming from Mediterranean Sea (Galil, 2000; Zenetos et al., 2005), several have been the north and east and a dry and hot subtropical Saharan component recorded in Tunisian coastal ecosystems and specifically in the Gulf of including sand storms coming from the south (Dahech and Beltrando, Gabes; for example, the green algae Caulerpa taxifolia and C. racemosa 2012a). Two main seasons are observed: the summer (June to 396 B. Béjaoui, et al. Estuarine, Coastal and Shelf Science 219 (2019) 395–408 Fig. 2. Mean monthly values of precipitation and temperature for the stations of Sfax (A), Gabes (B) and Jerba (C) (data from National Institute of Meteorology for 1970–2015 period). The total annual precipitations reach 236 mm in Sfax and 234 in Jerba with 110 mm in autumn. September), which is dry and hot, and the winter (January to March), with annual flow estimated to 80 million3 m year−1 (APAL, 2012). The which is wet and cool (Fig. 2). The hot season extends beyond the only continuous inputs in the gulf of Gabes is that of the industrial summer, and the number of sunny days may reach 64.4% (Amari, waste of about 410 million m3 year−1 (Béjaoui et al., 2004). 1984). Two intermediate seasons, spring and autumn, may be observed, The annual evaporation varies from 1600 to 2000 mm (Atlas but the duration depends on the year. The latter is the rainiest season Climatique, 1999) with high temporal and spatial variability; for in- (El Melki, 1996). stance, the monthly evaporation varies from 110 mm during winter to The mean temperature is approximately 11 °C in the winter and 210 mm during summer at Sfax and from 145 to 184 mm at Gabes. approximately 23 °C during the summer (Atlas Climatique, 1999). Globally, evaporation (approximately 1790 mm a year) is not balanced Furthermore, the mitigating effect of the sea can be observed onex- by precipitation (approximately 230 mm a year) and river inputs (80 treme values and their spatial repartition. In fact, the minimum tem- million m3 a year).