Spatial and seasonal variation of the zooplankton in the coastal zone and main khors of Lake Nasser (Egypt)

• Published in: Hydrobiologia 2003-01, Vol.491 (1-3), p.119-132
• Main Authors: EL-SHABRAWY, Gamal M, DUMONT, Henri J
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Coastal zone; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Lakes; Plankton; Seasonal variations; Species diversity; Standing crops; Summer; Synecology; Trophic levels; Zooplankton
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1024466216214

Issue Title: Recent Developments in Fundamental and Applied Plankton Research A prominent feature of Lake Nasser is the presence of khors (dendritic side extensions). We studied the zooplankton of the larger khors and coastal zone of the main lake in 1996 and 1997, and found an assemblage of rotifers, cladocerans and copepods that was partly tropical, partly temperate, at relatively high biomasses. Spatial differences were weak, but the upstream khors (Toushka and Korosko) were consistently richer than the downstream khors (El-Ramla and Kalabsha), with a rather sudden transition around km 150 at El Madiq. Summer standing crops were higher than those in winter by a factor 2-3. The zooplankton of the littoral of the main channel showed the same spatial pattern as that in the khors, being more abundant in spring (average 82300 ind m^sup -3^) than in autumn (average 72700 ind m^sup -3^). Zooplankton dry weight increased from 4 g m^sup -2^ at khor El-Ramla to 7 g m^sup -2^ at khor Toushka. These rather high values had low variation. The number of species, diversity and evenness all showed a high degree of similarity among the khors and in the littoral of the main lake. The lake fish fauna is poor, lacking a pelagic planktivore. The predominance of medium-sized Copepoda (one calanoid, two cyclopoids) in the zooplankton suggests that fish predation is moderate. This is confirmed by the persistence of two Daphnia species at low abundance, although rather strong variations in time suggest that Cladocera suffer from summer predation by invertebrates (copepods) as well as vertebrates (mostly larval fish). Because the zooplankton is underutilised by higher trophic levels, we suggest to assess the benefits of introducing a pelagic zooplanktivorous fish.[PUBLICATION ABSTRACT]