Summary
The present study was made to provide information about some biological components of the ecosystem in Damietta Branch, specially the free living protozoa which have been neglected for thus far. So this work is an attempt to address this group in our knowledge of the protozooplankton community in the Damietta Branch of the Nile.
The present study deals with protozooplankton, ones of the most important groups of organisms that must be well studied in large river system. These organisms reflect the status of the river, since any environmental term easily affects them.
Results can be summarized as follows:
•• Values of pH lied at the alkaline side with range 7.6 at Talkha and 7.8 at El-Kanater.
• Average values of D.O ranged between 6.2 mg/L at Faraskour and 8.4 mg/L at El-Kanater.
• Generally for all the nutrients, the highest average concentrations were recorded at the northern stations especially El-Serw and Faraskour.
• During the present study, four main group of protozooplankton were recorded, forming 74.9%, 13.8%m 8.9% and 2% of the total protozooplankton. Insect larvae, Free living Nematoda and Polycheate larvae were gathered into one group termed other organisms, forming 0.4% of total protozooplankton.
• The average protozooplankton density showed a decrease from El-Kanater north to Talkha, where a remarkable drop in the density was recorded during all months of the study, due to thermal pollution resulted from electrical power station and the high current discharge of the coaling water used by this electricity generating station. The population density increased again at El-Serw and reaches the maximum at Faraskour, due to stagnation of the water at this station due to the nearly complete closing of the Nile branch by Faraskour Impoundment.
• The seasonal variation of the total zooplankton showed two peaks during the period of study one in May and other in February.
• Rotifera was the most abundant group during the study with 57 species belonging to 33 genera were recorded.
• During the present study Rotifera was dominated by 5 genera, Keratella, Brachionus, Conchilus, Polyarthra and Asplanchna.
• The second most abundant group was Copepoda with 5 species belonging to 5 genera from 3 main sub-orders Cyclopoida, Calanoida, Harparticoida were identified in the area investigated.
• A gradual decrease in density of Copepoda was observed northwards with a maximum average at Faraskour and a minimum at Talkha.
• Protozoa occupied the third dominant position in protozooplankton community. Three major phyla of protozoa were present; Ciliophora, Rhizopoda and Heliozoa, 31 genera containing 39 species were recorded.
• The average density of Protozoa was highest at Banha and Faraskour. The least occurrence was at El-Serw, Two peaks were observed, the first one was in March, which the second one was in October.
• Protozoa was dominated by Arcella, Carchesium, Epistylis, Centropyxis and Difflugia. 12 Protozoan species were recorded for the first time in the Nile in Egypt during the present study.
• Cladocera were the fourth abundant group in the protozooplankton community with 17 species belonging to 14 genera. Standing crop of Cladocera showed a gradual decrease northwards from El-Kanater to Zefta where the minimum value was recorded, then gradual increase was observed from Talkha to Faraskour where the maximum density was recorded. Cladocera was dominated by Bosmina, Ceriodaphnia, Diphanosoma, Moina and Chydorus.