Zooplankton

Expansion of the water column provides changes in chemical characteristics that favor establishment of invertebrates. As reservoirs mature, there is generally an increase in the biomass of larval forms of terrestrial insects like Mansonia, mayfly nymphs, dragonfly, caddisfly, and truly aquatic insects like hemiptera and colleoptera, and mollusks. Crustacean zooplanktons colonize reservoirs according to feeding behavior; filter feeders being first and predators are last. There are differences between upper and lower sections of the reservoir with copepods being dominant in the former. As the dam fills, there is a succession of crustacean zooplankton from rotifers (Brachionus, Keratella, Filinia, Polyartha) followed by daphnids (Bosmina, Diaphanosoma, Ceriodaph-nia, Daphnia) and lastly copepods (Mesocyclops leurkarti). Due to predation pressure, a shift might occur in community structure affecting diversity.

For example, the introduction of Limnothrissa miodon into Lake Kariba in 1967-1968 led to the decline of large zooplankton by 1968-1974, notably Cerio-daphnia, Diaphanosoma and Diaptomus. Fish tend to select Cladocera, so copepods are more cosmopolitan.

In Lake Kariba, the benthos fauna was studied during a complete flood regime. Recruitment of organic and allochthonous matter from the terrestrial zone during high floods enhanced production of invertebrate biomass. The biomass of fish follows a prey-predatory relationship.

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