10.3 Living resources

The Tunisian lagoons host about 1 000 living species with 200 micro flora, 245 micro fauna, 142 macro flora, 45 fish species, two turtle species, one aquatic mammal species and 220 bird species.
No conservation-oriented studies were specifically realized on the issue. However, some research on the impacts of pollutants and other anthropogenic releases were implemented in certain lagoon areas such as those executed in the framework of the water management in the Ichkeul lake, the eutrophication of the lagoon environment of the Bizerte, Tunis and Ghar el Melh and multidisciplinary studies related to biology, ecology and physico-chemistry.

10.3.1 Flora and fauna

The main outputs reflect the interrelation between the flora and fauna composition and distribution and the changes of the water quality. For example, the Ichkeul lagoon is highly influenced by the salinity caused by the freshwater flowing through the water shed around the lake, leading to an important vegetal development at the west subzone of the lake and near the communication with the Bizerte lagoon (where Ruppia cirrhosa substitutes Potamogeton pectinatus with a strong development of the green algae Cheatomorpha linum, Chlorophycea, in the Rupia surrounding zones whereas seeds and bulbs of Potamogeton still exist in the sediment, Potamogeton being the main feed provider for the fowl population). Due to salinity increase in the lake, Scirpus maritimus is being invaded by Salicornia arabica, which was never reported until 1967. The global trend of the marshes ranges from marsh vegetation to a sebkha one, a situation that highly influences the ornithological richness of the area (the last observation reported a net decrease in the avifauna of the lake). Such a trend could be balanced towards the original vegetation by a suitable management of the water level in the lake by means of a lock gate installed a few years ago (Romdhane, 2002).

Thus far, 17 fish species were reported compared with 22 in 1993/1994, including 10 of commercial importance such as: Anguilla anguilla, Barbus callensis, Belone belone, Dicentrarchus labrax, Engraulis encrasicolus, Liza aurata, Liza ramada, Mugil cephalus, Solea vulgaris, Sparus aurata and seven migratory and sedentary species like Aphanius fasciatus, Atherina boyeri, Gambusia affinis, Hyporhamphus picarti.
As far as landscape is concerned, the Ichkeul site is of exceptional beauty with its set of marshes, the mountain, the loamy waters that reinforce the forestry relief and the contrast with the surrounding region (the Djebel raising allows a panorama of the Bizerte lagoon and the Mediterranean coast).
The other lagoons are marine predominant media, where the salinity is close to the Mediterranean surrounding areas. As a result, the flora and fauna are similar to those characterizing the marine environment. For example, in the Ghar el Melh lagoon, the benthic fauna encompasses three biotopes, according to the distance of the area from the sea. Eighteen species belonging to three phyla are reported (Gnassingbe-Maisbe, 2008). The macro fauna is subject to the negative effects of shallow water and to the limited water exchanges with the sea. The capture fish species belong to three groups, which are of sedentary, migratory and casual species nature (SCET-ERI, 2000).
The Bizerte lagoon is influenced, on one part by the seawater that enters into it through an artificial channel and on another part by the high amount of sewage that is discharging organic
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matter, source of severe eutrophication. Several toxic phytoplankton species are reported to be causing shellfish contamination by biotoxin. Phytoplankton blooms with toxic species such as Gymnodinium sanguineum, Alexandrium spp, Prorocentrum lima, Pseudo-nitschia delicatissima and Peridinium quiquecorne were also reported (Bellakhal-Fortuna, 2004). In 1966, 23 dinoflagellate species and 33 diatoms were reported (Azzouz, 1996); since that time diatoms are decreasing. In 1985, 33 species were reported, with 11 Ulvophycae of which Codium fragile, 18 Rodophycae and 4 Phaeophycae (Djellouli, 1985). Fifty per cent of the lagoon sediment is covered by Caulerpa prolifera.
The El Bibane lagoon hosts the longest algal reef of Neogoniolithion notarsii in the Mediterranean. Eighty percent of its sediments are covered by Cymodoce nodosa. The lagoon is directly influenced by the nearby gulf of Gabes, which is considered among the rare areas with significant continental shelves in the Mediterranean.
The Tunis lagoon has undergone big changes after the restoration works, which were implemented in the early 1980s, leading to the improvement of the water circulation inside the lagoon, the rectification of its borders and the decrease of its surface (from 3 000 to 2 500 ha): 38 macrophytes species were identified compared with 10 before the restoration works (Ben Maiz, 1993, Shili 1995 and Trabelsi 1995). It is important to note that Ulva rigida highly decreased when phanerogams appeared (Rupia cirrhosa, Zostera noltii and Cymodocea nodosa). Ben Maiz reported in 2008, 36 dinoflagellates, 33 diatoms, two euglenophycae and one
cyanophycae.
The lagoon aquatic fauna diversity has improved after the restoration works due to the entrance of typically marine species: 39 fish species were identified (M’timet, 1995; Ben Hamouda, 1998) compared with 24 before the restoration works (Chauvet, 1986), Sparus aurata and Dicentrarchus labrax becoming abundant species. In 2004, 118 invertebrate species (of which 69 shellfish with 45 Gasteropods and 17 bivalves) and 57 species (identified for the first time) were reported, Mytilus galloprovincialis and Tapes decussatus being the most important shellfish species (Ben Maiz, 2008).

10.3.2 Wildlife

As far as ornithological richness is concerned, Tunisia is considered as an important ornithological country with 395 bird species, fowls being the most important migratory species observed. Around the Gulf of Gabes, the El Bibane lagoon is hosting a large part of those fowls (79 species belonging to 35 families). The global number of fowls that winter in the lagoon is up to 20,000 individuals, among them the big size cormorant, Phacrocorax carbo, the pink flamingo, Phoenicopterus roseus and Platalea leucorodia.
In Tunisia, three marine protected areas were established: the Galite/Galiton archipelagos, the Zembra/Zembretta Island and the ornithological zone of Kneis. Other marine areas of environmental interest are going to be established within the framework of the MAP (Mediterranean Action Plan) protocol on marine specially protected areas.