Abstract
The present study on the effects of high tide on zooplankton population was systematically carried out at the Cross River Estuary for a period of six months (January 2017 – June 2017). Zooplankton in the aquatic food web play an important role and their distribution is influenced by latitudinal temperature gradients. Samples were collected at high tide from three (3) stations within the Cross River Estuary. A total of 17 species belonging to 3 families were identified. Copepod was the most abundant group constituting 82.09% of the total density, followed by Rotifera (Rotifer) with 10.01% and Cilliophora (Ciliate) recording 7.90%. Zooplankton densities ranged from 1 – 2,506 cells/ml in the rainy season and 1 – 418 cells/ml in the dry season. ANOVA showed no significant spatial and temporal variations in zooplankton composition (P>0.05). The dearth of zooplankton species and groups during this present study could be due to high tide and the closeness of the Cross River system to various sources of pollution particularly from anthropogenic and industrial sources.

Key words: Zooplankton, Population, High tide, Cross River Estuary