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Detailed Ecological Assessment Report 2008 – Keenjhar Lake
zooplankton but can also change the composition and size spectrum of
zooplankton community.
Zooplankton density and the gill infection of fish are inversely proportional to each
other. At a low zooplankton density the fish fingerlings change their feeding
behaviour and due to the insufficient zooplankton, they ingest a larger number of
fish parasites from the detritus. It is possible that the lower intensity of gill infection
at a high zooplankton density could also be explained by the more intensive fish
parasite consumption by the copepods.
Dodson and Frey (1991) and Williamson (1991) also include keys to identification.
The keys for the copepods and cladocerans go only as far as the genus level.
Since taxonomy is a dynamic science, names of some groups have changed with
time; thus professionals also use a widely scattered primary literature. In Pakistan,
however, no profound work has been done regarding the identification and keymaking
of the zooplankton and there is dearth of literature which adds to the
complications related to the identification of the rich and diverse zooplankton fauna
of Pakistan up to the species and, in many cases, even up to the genus level.
Zooplanktons are common in the pelagic and littoral regions of ponds, lakes, large
rivers, and oceans. In freshwater, these assemblages are dominated by the rotifers
and two groups of micro-crustaceans—the four orders of cladocerans and the class
Copepoda. The copepods are also dominant in marine environments. The littoral
and benthic regions of freshwater and marine environments characteristically hold
large numbers of the diverse and ancient micro crustacean class Ostracoda. Most
species of these four groups make their living grazing algae from the water column
or off surfaces and are, in turn, a vital link for passing energy up the food chain to
fish.
Zooplanktons occupy an important position in the trophic structure and play a major
role in the energy transfer of an aquatic ecosystem. An inadequate knowledge of
the zooplankton and their dynamics is a major handicap for better understanding of
life processes of fresh water bodies. Such studies have extreme significance and
ecological value since eutrophication is bound with the components and production
of zooplankton.
Among zooplankton, the relative abundance of copepods was dominant in the Keti
Bunder. The abundance of crustaceans collected by the plankton net method was
found healthier than their usual abundance in polluted areas of the oceans.
Detectable changes in the abundance or species composition of zooplankton may
reflect fundamental changes in the aquatic environment affecting phytoplankton. In
turn, because zooplankton are eaten by larger animals, some of which are of
commercial importance, changes in zooplankton communities can provide early
indications of forthcoming changes in the food conditions for fish, birds and
mammals. As most of the zooplankton are relatively short-lived and have
enormously high growth rates, they respond quickly to the environmental
perturbations that influence diversity, such as any localized or broad-spectrum
pollution, degradation and predation pressure. Crustacean zooplankton growth and
development rates are well known to depend strongly on water temperature. The
diversity in the stages of life history of the copepods may also be a sensitive early
warning of temperature increases in the aquatic ecosystems in response to global
atmospheric warming.
WWF Pakistan – Indus for All Programme Page 108 of 188