Abstract
This study presents a first compilation of phytoplankton species composition of a stretch of fresh and brackish water ecosystem in Southern Nigeria. Samples collection spanned a period of sixteen months (January 2003 to April 2004). Phytoplankton samples were collected monthly in the open water using plankton net of 55 &mum mesh size towed horizontally for about five minutes. The net hauls were transferred into 200 mL properly labelled plastic containers and immediately preserved with 4% formation solution. Samples were examined and illustrations made with a Leitz Orthoplan Research Microscope equipped with a tracing and measuring devices at the phycology laboratory in University of Benin, Benin City. A seasonal pattern of phytoplankton variation was observed with a hundred and 154 phytoplankton species recorded. The taxa recorded belong to four divisions namely: Bacillariophyceae (diatoms), Cyanophyceae (blue-green algae), Euglenophyceae (euglenoids) and Chlorophyceae (green algae). The Diatoms were the predominant group and account for 79% of total species composition. Others are Chlorophyceae 19.77%; Cyanophyceae 1% and Euglenophyceae, 0.23%. The brackish water stations recorded relatively higher number of species and number of individuals of each species than the freshwater stations. An array of floristically diverse phytoplankton was observed with notable common and cosmopolitan diatom species like <em>Coscinodiscus</em> and <em>Nitschia</em> spp in abundance.
Highlights
The term plankton refers to any small biota living in the water adrift in the water column and incapable of maintaining its position and at the mercy of currents
The amount of phytoplankton in the water column reflects the influence of a number of environmental factors and processes (Suthers and Rissik, 2009)
Some phytoplankton species may be considered as villainsproducing red tides or toxic algae-but there are only a few species responsible
Summary
The term plankton refers to any small biota (usually microscopic) living in the water adrift in the water column and incapable of maintaining its position and at the mercy of currents. Phytoplankton (algae) such as diatoms, grow in the presence of sunlight and nutrients such as nitrogen and phosphorus They are mostly unicellular, filamentous or aggregate of cells and form the base of the trophic structure in the aquatic food chain. Study area: The Osse River takes its source from the Akpata hills in Ekiti State, Nigeria (Fig. 1). The river is characterized by IN OSSE RIVER increased flow rate, high turbidity and muddy water especially after heavy rainfall while dry season is. In this list, algal species are arranged according to characterized by moderate or slow flow rate and clearer their divisions, classes, orders and families.
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