biological diversity and tropical forests in tunisia - PART

the number of species (zouali 1975) is highest at the east end (20) and
lowest at the west end (5). The medtolittoral eone contains dense
Potamogeton beds that have abundant invertebrate populations and are
important feeding areas for fish and waterfowl. Dominant species include:
Hydrobia ventrosa
Sphaeroma hookeri
Nere5s diversf color
Idothea vkridks
In the waters of the infralittoral eone (marsh edge), fluctuations in
water level, temperature and salimity are unfavorable for &vertebrate
populations (zouali 1975). However, the Djoumine marsh has freshwater
channels that contain the richest and most diverse aquatic fauna b the
area (UCL 1977). Characteristic species knclude dragonflies, alderflies
Sialis sp., Corixid water bugs, water scorpions Nepa sp., Dytiscid water
beetles, crustaceans (~ssellus) , freshwater molluscs Limnea sp., flatworms
Turbellaria sp. and other freshwater species not found in the lake or
acywhere else in the area in such abundance.
- Fish. Several species of fish are exploited by commercial fishermen
at Ousd Tinja (zoaali 1975); these include:
Anguilla anguilla Mugil cephalus
Dicentrarchus labrax M. ramada
Barbas barbus Solea solea
Alosa fallax Aphanhs fasciatus
Syngnathus abaster Engraulis encrasicholus
Herpitofauna. The distribution of reptiles and amphibians is
influenced by ths water level and salinsty in the lakes and marshes.
Dominant species and their habitat types are:
C. Influences
5 Rana ridibunda 1 Malpolon monspessalanus
1.2 Bafo viridis 1,3,4 Natrix maura
4 B. bufo 2,4 Discoglossus p2ctus
2,4 B. maaritan2cus 2,3,4 Clemmys leprosa
1 Lacerta ocellata 4 Emys orbicularis
1 = upper marsh 3 = brackish water 5 = A l l 4 habitats
2 = lower marsh 4 = fresh water
Although Lake Ichkeul is included En Ichkeul National Park, human
influences are still affecting the the environment. The marshes are
overgrazeed by cattle to the point that the buffalo become malnourished
(IUCN 1987); fishing is still done at Oued Tinja and sometimes in the
lake; aod occasional poaching occurs. Non-marsh areas around the lake are
cultivated and runoff water from the fields contain sediments and possibly
chemical pollutants.
A cacal was dag through the Djoumine marsh by the Rural Works
department. The Rural works department does not consider the canal
necessary, but so far no action has been taken to fill the canal. As
water drains from the marsh into the canal, the vegetation composition
changes acd the habitat value for waterfowl decreases.