The taxonomic composition, distribution and abundance of the phytoplankton flora of the Obafemi Awolowo University Teaching and Research Farm Lake, Ile-Ife, Osun State, Nigeria

Abstract

The study determined the abundance and distribution of phytoplankton flora of an impoundment in the Agricultural Teaching and Research Farm of ObafemiAwolowo University (O.A.U), Ile-Ife, Osun State, Nigeria. The study was carried out over an annual cycle from September 2006- August 2007, Phytoplankton and water samples were collected monthly from three sampling stations by filtering 50 litres of water through a phytoplankton net of 45μm mesh size to a concentrate volume of about 30ml preserved in 5% formalin solution. The phytoplankton were viewed under a compound light microscope at both scanning power (x40) and low power (x100), measured with an ocular micrometer drawn to scale, counted and later identified using various phytoplankton identification keys on Nigerian freshwaters.

The results showed that one hundred and fifteen species of phytoplankton belonging to five divisions, seven classes, nineteen orders, forty seven families and eighty three genera were recorded. The predominant genera in terms of occurrence and abundance were members of the green algae (Division Chlorophyta) and included Tetradesmus, Ulotrix, Tetraspora, Protosiphon, Chlorella, Closteriopsis and Pediastrum. Phytoplankton occurrence and abundance were slightly higher in the rainy season (600±350) than in the dry season (533±186) (f= 0.918, p= 0.05). The highest values were recorded at the surface stations of the lake.

It was concluded that the water body was comparatively rich in phytoplankton flora. Also the occurrence of some species in the water body such as scenedesmus, stauraastum, Tetradesmus, Ulotrix, Tetraspora and Pediastrum species suggested a high level of primary productivity and a non-polluted lake that was oligotrophic to moderately eutrophic.

Keywords: Phytoplankton, composition, distribution, abundance