Zooplankton-based assessment of the trophic state of a tropical forest river

Abstract

In this study, we explored the usefulness of zooplankton as a tool for assessing the trophic status of a Nigerian 
forest river. The river was sampled monthly and investigated for water physico-chemistry and zooplankton 
community structure using basic statistical measurement of diversity indices to characterize the zooplankton fauna. 
The trophic status of the river evaluated from the physico-chemical parameters indicates that the river is 
oligotrophic. The zooplankton composition was typical of a tropical freshwater river, with a total of 40 species made 
up of 16 rotifers, 12 cladocerans and 12 copepods and their developing stages in the following order of dominance; 
Rotifera > Cladocera > Cylopoida > Calanoida. The zooplankton community was dominated by numerous species of 
rotifers and crustaceans, which are typical of oligotrophic to mesotrophic systems, amongst these includes 
Conochilus dossuarius and Synchaeta longipes. However, the most dominant zooplankton species in West Africa 
freshwater ecosystems namely, Keratella tropica, Keratella quadrata, Brachionus angularis, Trichocerca pusilla, 
Filinia longiseta, Pompholyx sulcata, and Proales sp. amongst others which are indicator species of high trophic 
levels were not recorded in the river. We therefore, conclude based on these facts that the river is clear, oligotrophic 
and it can be used for all manner of recreational activities.