Phytoplankton diversity indices of Osse river, Edo state, Nigeria.
The phytoplankton diversity indices of Osse River, Edo State, Nigeria, were investigated monthly from January 2003 to April 2004. The plankton samples were collected from five sampling stations in the open water of the river using a plankton net of 55μm mesh net tied to a motorized boat and towed at low speed for five minutes at each station. The samples were transferred into 200ml capacity properly labeled plastic containers and immediately preserved with 4% formalin solution. Each sample was concentrated to 10ml volume in the laboratory by centrifugation and two drops from this 10ml were used for slide mount for microscopic examination using a Leitz Orthoplan Research Microscope at the phycology laboratory, Department of Plant Biology and Biotechnology, University of Benin, Benin City. Ten slide mounts were examined and phytoplankton organisms recorded in each mount. Identification of phytoplankton organisms was done by reference to standard texts and monographs in the phycology laboratory, University of Benin. A total of 154 species belonging to 4 divisions of algae (Bacillariophyta, Chlorophyta, Euglenophyta and Cyanophyta) were recorded. In terms of abundance, Bacillariophyceae had the highest distribution of phytoplankton (79.00%), Chlorophyceae, Cyanophyceae and Euglenophyceae presented 19.77%, 1.00% and 0.23% respectively. Species richness was highest in station 1 (11.43) and lowest in station 5 (6.25). Species diversity was lowest in station 5 (1.83) and highest in station 1 (3.43), while Simpson index and evenness were low in all the five sampling stations studied. The heterogeneity and abundance of phytoplankton observed in this study shows the river to be eutrophic and can support fish production. This is the first documented report on the phytoplankton community structure of Osse River.
Key words: Phytoplankton, species and diversity