TEMPORAL VARIABILITY OF BENTHIC MACROFAUNA OF THE LOWER LAKE AT WADI EL-RAYAN, EL-FAYOUM, EGYPT

From June 2003 to May 2004 temporal changes of macrobenthic communities were studied in the fish farm-influenced area of lower lake Wadi El-Rayan, El-Fayom, Egypt. Community structure consisted of thirteen species (plus family Naididae-Annelida- which was not further classified) belonging to four major groups: Crustacea (Corophium volutator, Gammarus lacustris, Orchestia gammarella), Annelida (Lumbriculus sp., Tubifex sp.), Insecta (Isotoma sp., Rhyacophila sp., Chironomus sp., Hydroporid larvae, Tipula sp.), and Mollusca (Hydrobia sp, Theodoxus niloticus, Melanoides tuberculata). The monthly species number did not change dramatically during the year. The lowest species richness score was 0.506 in June and the highest was 0.813 in December. Total individual abundances varied from 3.309 to 28.382 ind/m 2 in February and April, respectively. Concentrations of cations and anions significantly varied among the twelve months of the year. Sediment grain size showed no influential effect on the community structure. The temporal macrobenthos variability was influenced primarily by the combined effect of the temperature and the Ca. The difference between the current study and previous similar studies may be due to the current study site being located in a protectorate area under regular surveilance which prevents uncontrolled harmful discharges from the fish farm. Moreover, there are some new recorded macrobenthos taxa which were not recorded in the previous studies. These macrobenthos are Hydrobia sp. (belonging to Mollusca), Isotomus sp. (belonging to Collembola–Hexapoda), and Orchestia gammarella (belonging to Gammaridae–Crustacea).