الفهرس 
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Abstract
Understanding the structure, complexity and dynamics of an
ecosystem is a major issue in ecological research (Frost et aI., 1995). The
study of complex aquatic ecosystems requires detailed information about its
biotic and abiotic parameters. A good characterization of the community
structure is required to solve more applied problems in conservation biology
and resource management. In general a biological community consists of a
collection of species-specific populations underlying a food web, .i.e. the
network of interactions by which consumers exploit and compete for
available resources. The abundance of individual species, and in extreme
cases their disappearance is determined by the balance between their birth-
and death rates. Reproduction involves the conversion of energy gathered by
feeding into offspring, while mortality usually implies falling victim to a
predator. Individual feeding, reproduction and dying determine the dynamics
of the population which in turn determine the dynamics of the community.
The state of the community in terms of the abundance of its member species,
being stable or fluctuating, is hence the overall outcome of the trophic
interaction that constitutes the food web (Oksanen et aI., 19& 1).
In aquatic ecosystems the two major ecological subdivisions are the
pelagic life and the benthic life. In pelagic life organisms that passively drift
and which are maintained in suspension by water current, or float or swim
weakly comprise the plankton. They include heterotrophic bacterioplankton,
the photosynthetic-phytoplankton and the zooplankton which comprise the
animal part of the plankton. The larger strongly swimming animals, such as
fish, are called the nekton (Moss, 1998). The plankton can be categorized by
size into ultraplankton ( <5 um), nanoplankton (5-20 urn), micro plankton
.