SPECIES COMPOSITION AND SEASONAL POPULATION DYNAMICS OF THE BENHIC FAUNA IN KHOR KALABSHA, LAKE NASSER, EGYPT

Abstract

Seasonal population dynamics of the benthic fauna and nature of sediment at Khor Kalabsha, Lake Nasser, have been investigated between October 1989 and September 1990. The benthic fauna in Khor Kalabsha was rich in density and biomass. They were dominated by aquatic insects followed by gastropod molluscs and oligochaete annelids. The khor sediments are sandy or silty sand at littoral localities (sand content 87.37%), forming sandy silt at the offshores (53.58% silt and 25.92% clay). The average annual density of benthic fauna at the 1 ittoral stations amounted to 10.292 organisms/m2, with 33.9 gm wet wt./ nr. The offshore stations harboured lower densities of benthic organisms that averaged 908 organisms/m2, with 4.0 gm wet wt./ m2. Aquatic insects constituted 85.1% by number (8757 insects/m2) at the littoral stations. These values declined to 63.0% (average = 574 insects/m2)-at the offshore stations. Benthic fauna attained their maximum persistence in winter while the spring and summer sustained lowest densities. Gastropod molluscs constituted 11.1% by number (1138 organisms/m2) at the littoral stations. Their occurrence at the offshore stations was very rare and constituted 6.6% by number (60 organisms/m2). Oligochaetes constituted 3.8% at the littoral stations. At the offshore stations, they formed numerically 30.4% of the total benthos. Spearman Correlation Coefficient revealed negative relationship between the density or biomass of benthic fauna at littoral stations and organic carbon, inorganic phosphorus and total carbonate. In contrast, a positive correlation was recorded for organic phosphorus. At the offshore stations, Spearman Correlation Coefficient indicated