COPEPOD COMMUNITY OF ORHIONMWON AND IKHIOGBE RIVERS, IKPE, EDO STATE, NIGERIA

ABSTRACT

Zooplankton communities are very sensitive to environmental modifications and important indicators for evaluating the ecological status of aquatic ecosystems. This study was carried out from August to January 2021 to determine the community structure of the copepod zooplankton of Orhionmwon and Ikhiogbe Rivers, Edo State, Nigeria. Four stations were studied from upstream to downstream, with a distance of 2 kilometers between each station. Copepod zooplankton and water samples were collected monthly and analysed using standard methods. A total of 125 individuals comprising 8 species, 2 family were found during the study period. Mesocyclops ogunnus and Mesocyclops aspericornis represented the predominant species (24% each) followed by Thermocyclops decipiens (16%), Mesocyclops aquatorialis, Mesocyclops neglectus, Mesocyclops salinus and Bryocamptus birsteini (8% each), and copepodite with 4%. The calculated diversity indices indicated that station 4 was more diverse followed by station 3, while copepod zooplankton species in station 1 were least diverse, and no species of copepods was found in station 2. Community composition varied among the species at the different stations but seasonally was similar in station 1 of both the wet and dry seasons. Higher species number and density was found during the wet season with a trend of declining proportion towards dry months. Monthly variation shows that the highest abundance and copepod zooplankton was recorded in the month of August. There exists a relationship between environmental parameters namely, water level, pH, electrical conductivity, total dissolved solids, turbidity, phosphate, sulphate and zinc and copepod species. Poor water quality seem to be one of the factors responsible for the observed copepod community structure in the Orhionmwon and Ikhiogbe River.