BENTHIC COMMUNITIES IN THE RIVER NILE, EGYPT III- MEIOFAUNA AT HELWAN REGION

Abstract

The present work is the third in a series titled Benthic communities in the River Nile, Egypt. The first dealt with aquatic stages of Insecta (Ramadan et al, 1998) and the second dealt with Mollusca (Ramadan et ai, 2000). The present work is the first to deal quantitatively with the ecology of the Egyptian Nile Meiofauna. It is hoped to be a contribution to the data base necessary for the development of the resources of the River-Nile. Monthly samples were collected from the eastern and western sides of five stations in the Nile at Helwan region (Industrial area, 30 km. South Cairo) from June 1997 to May 1998. The average standing crop of meiofauna in the whole investigated area during the period of study was 27.3 organisms/10 cm weighing 5.06 mg. fresh weight/10 cm . Nematoda was the dominant group, contributing about 66.3% of the total population density (P. D.) followed by Ostracoda (32.1%). Regarding biomass, Ostracoda occupied the first position contributing 55.5 % of the total biomass of Meiofauna, followed by Nematoda (42.9%). Summer and autumn represented the most productive seasons. The temporal average biomass followed the same trend of population density (P. D.)with some deviation. Nature of the sediment was the primary factor affecting the meiofaunal abundance. A highly significant negative correlation was revealed between the total number of macrobenthos and meiobenthos in (he sampled area. Similarity, a negative correlation was observed between the ostracod Chlamydotheca unispinosa Baird, 1862 and the macrobenthic gastropod Valvata nilotka Jickeli, 1874. The scarce occurence of harpacticoid copepods makes the Nematoda/Copepoda ratio reaches its maximum value indicateing heavy polluted area.