~ 398 ~ International Journal of Fisheries and Aquatic Studies 2019; 7(4): 398-405 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2019; 7(4): 398-405 © 2019 IJFAS www.fisheriesjournal.com Received: 11-05-2019 Accepted: 15-06-2019 Job Bassey Etim Department of Biological Oceanography, Faculty of Oceanography, University of Calabar, Calabar, Nigeria Correspondence Job Bassey Etim Department of Biological Oceanography, Faculty of Oceanography, University of Calabar, Calabar, Nigeria Assessment of phytoplankton species composition, abundance and diversity within the itu bridge-end area of the lower cross river system, Nigeria Job Bassey Etim Abstract This paper reports on the phytoplankton species composition, abundance and diversity within the Itu bridge-end area of the lower Cross River system, Nigeria, which was undertaken for nine months (February- October, 2018). Surface water samples were collected for phytoplankton studies by filtration method, using a-20L plastic bucket and a-55μm standard plankton net. Samples were concentrated to 10ml, stored in well-labeled plastic bottles and preserved in 4% buffered formaldehyde solution prior to laboratory analysis. Samples were analyzed by addition of 1-2 mls of Lugol’s iodine solution which enhanced phytoplankton cell identification under an inverted microscope of x 10 and x 40 magnification using standard texts and atlases. Total of 57 phytoplankton species spread into 5 taxonomic families (Bacillariophyceae, Chlorophyceae, Cyanophyceae, Euglenophyceae and Chrysophyceae) were identified. All identified species of the phytoplankton were those common in the tropical river system. A total of 36.34% of the phytoplankton were Bacillariophyceae, with 20.54% of Euglenophyceae, 20.38% of Cyanophyceae, 16.47% of Chlorophyceae and 6.27% of Chrysophyceae. There was a predominance of Melosira variance in the Bacillariophyceae, Anaena spiroides in the Cyanophyceae, Euglena gracilis in Euglenophyceae and Ceratium hirudinea in the Chrysophyceae. The complete absence of the genus Coscinodiscus in the Bacillariophyceae interplayed by the low ranges of the Margalef’s index of (2.58 – 3.09) for Bacillariophyceae, (2.11 – 2.62) for Chlorophyceae, (1.44 – 1.86) for Cyanophyceae, (1.24 – 1.90) for Euglenophyceae and (0.79 – 1.18) for Chrysophyceae, and the high values (>1) of the Shannon- Wiener indices which ranged between 1.96 – 2.36 for Bacillariophyceae, 1.63 – 1.95 for Chlorophyceae, 1.73 – 2.05 for Cyanophyceae, 1.92 – 2.05 for Euglenophyceae and 1.34 – 1.60 for Chlorophyceae connote the Itu bridge-end area of the lower Cross River system to be under the threat of pollution. There was a significant relationship (p<0.05) between phytoplankton abundance and month of sampling. Based on the results of the study, proper management strategies of this area of the river system are outlined and recommended. Keywords: Assessment, phytoplankton, species composition, abundance, diversity, ITU bridge-end area 1. Introduction The productivity of any aquatic ecosystem depends on the amount of plankton present in the said water body (Davies et al, [16] . Prasad [48] is of the view that plankton is all organisms (Plants and animals) which live in water that have limited power of locomotion, largely move by means of flagella or other various mechanisms which alter their distribution by changes in buoyancy and are more or less passively drifted by waves and water currents. Odiete [40] and Davies et al [16] is of the view that plankton, typically phytoplankton growth and distribution depend on the carrying capacity of the environment and on the concentration of nutrients at both intracellular and extracellular levels Phytoplankton constitutes the most important components of the food chain in every water body Ajuonu et al, [4] ; Job et al, [28] ; Ekanem et al, [21] ; Ada and Job, [1] . All other living organisms in water depend directly or indirectly on them for food Ajuonu et al, [4] . More than 95% of the photosynthetic activities in the world oceans are as a result of phytoplankton and nearly ¾ of the world’s primary production and nearly of the oxygen in our environment is released by phytoplankton Ekanem et al, [21] ; Ada and Job, [1] . The distribution, abundance and diversity of phytoplankton have been reported to be influenced, to a large extent, by human activities particularly the building of barriers, bridges and dams across river systems Job et al [54] ; Haslam [27] ; Fenchel [26] ; Ada and Job [1] .