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Egypt. J. Exp. Biol. (Zoo.). 2007; 3(0): 113-126


Hanan M. Mitwally, Rehab A. El-Shanawany, Mohamed I. A.Ibrahim, Omran E. Frihy.


The current work aimed to evaluate the impact of environmental factors (temperature, salinity and pH), sedimentological (grain size, sorting and %organic matter) and hydrodynamic processes (erosion and accretion) on the benthic communities. The study area covers the eastern and western sides off Rosetta estuary. Four seasonal surveys were carried out from April 2000 to August 2001. A total of 25 stations were chosen each survey that was resulted from five profiles and five stations. Samples covered different depths (beach, 1m, 2m, 3m and 4meters). Duplicate cores were taken. The average vertical rate of accretion was 0.057±0.05m/yr whereas that of erosion was -0.035 ± 0.03m/y. The total meiofauna varied from 120 ± 0.565 individulas10cm-2 in winter to 14874 ± 131.84 individulas10cm-2 in summer. Univariate analysis indicated significant variations in abundance of the total meiofauna over dates and within stations. The highest and the lowest abundances were recorded at station 1 and 5, respectively. Results from statistical analysis revealed that Rosetta estuary is highly variable ecosystem. Temporal variation was due to the significant variation in water temperature over dates. Spatial variations were higher at the station scales rather than profile scales. Fine and very fine sand covered the estuary and fluctuated between well and poorly sorted sediment. Salinity affected diversity over dates and among profiles. The higher the salinity, the higher the abundance was. Erosion/ accretion reduced the total number of taxa and total abundance of metazoans taxa. Eight taxa were recorded as dominante ones, these are: Ciliophora, Nematoda, Harpacticoida, Ostracoda, Foraminifera, Gastroricha, Turbellaria, Polychaeta. Meiofauna taxa may respond differently to the hydrodynamic processes. Nematoda had higher abundance in accretion than in erosion sites. The contribution of meiofauna taxa other than Ciliophora and Nematoda was >0.1% and ≤10 %, by an order of magnitude, at accretion and erosion sites.

Key words: Rosetta estuary, environmental factors, hydrodynamic processes, Nematoda, Harpacticoida, Foraminifera, Turbellaria, diversity, factor analysis

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