ENVIRONMENTAL FACTORS AFFECTING ABUNDANCEAND DISTRIBUTION OF MACROBENTHIC ORGANISMS IN LAKE MANZALAH, EGYPT.

ENVIRONMENTAL FACTORS AFFECTING

ABUNDANCEAND DISTRIBUTION OF MACROBENTHIC

ORGANISMS IN LAKE MANZALAH, EGYPT.

By
MOHAMED A. IBRAHIM*; ATEF A. MOUSA

AND EL-AZAB E. EL-BOKHTY.

* Nationallnstitwe ofOceanogr. & Fisheries, Anfoushy – Alexandria, Egypt.
Key Words: Benthos, Lake Manzalalz. Nile Delta lakes, Egypt.
ABSTRACT
The overall sediment distribution pattern indicates that the bottom
of lake Marz=alah is covered by a predominant type of sediments
composed of 38%, .:/0% and 22% for the sand, silt and clay
respectively. The monthly and seasonal abundance (no. ofori,.lm2
) of
bottom fauna in Lake Manzalah show pronounced changes with no
distinct pattern of variations. Abundance during Spring season was
much higher than other seasons. The average number oforganisms
per square meier ofthe bottom is 1397,3141. 799 and 654 organi m
during Winter, Spring, Summer and Autumn respectively. Tendipes
tentans larva and the Oligochaera Chaetogaster limnaei were found in
all stations forming an overall average of42%for the former and
20.3% for the latter relative to the total abundance. rVhen the
distribution of benthic organisms in lake Manzalah was correlated
with the prevailing environmental conditions, it became evident that
both salinity and the sediment type are the main factors controlling
the distribution ofmacrobenthos in the lake.